UNIVERSITY OF CALIFORNIA COLLEGE OF AGRICULTURE AGRICULTURAL EXPERIMENT STATION BERKELEY, CALIFORNIA THE BIOLOGICAL CONTROL OF MEALYBUGS ATTACKING CITRUS HARRY S. SMITH AND H. M. ARMITAGE BULLETIN 509 March, 1931 UNIVERSITY OF CALIFORNIA PRINTING OFFICE BERKELEY, CALIFORNIA CONTENTS PAGE Introduction 3 The mealybugs 5 The citrophilus mealybug, Pseudococcus gahani Green 5 The common mealybug, Pseudococcus citri (Risso) 11 The Baker mealybug, Pseudococcus maritimus (Ehrh.) 13 The Japanese mealybug, Pseudococcus krauhniae (Kuwana) 14 The long-tailed mealybug, Pseudococcus longispinus (Targ.) 16 The Mexican mealybug, Phenacoccus gossypii Towns, and Ckll 16 The insect enemies of mealybugs 18 The mealybug destroyer, Cryptolaemus montrousieri Muls 18 The Sicilian mealybug parasite, Leptomastidea abnormis (Gir.) 20 The brown lacewings, Sympherobiidae 21 The green lacewing, Chrysopa californica Coq 21 Leucopis bella Loew 22 History of development of biological control 22 Mass production of Cryptolaemus 28 Planting and developing the host plant 29 Growing the host insect 37 Growing the Cryptolaemus 40 Method of handling beetles 43 Collecting in insectary 44 Liberating in field 44 Liberation of larvae not satisfactory..., 45 Number of Cryptolaemus liberated per tree 46 Timing field liberations 48 Determining the sequence of liberations 49 Trunk banding as an aid to control 51 Relation of ants to mealybug control 55 Effect of spraying and fumigation on biological control 57 Buildings and equipment 59 Size of rooms > 60 Floor plans of building 63 Building construction 63 Room construction 64 Ventilation 64 Room equipment 65 Floor racks 67 Insect-proofing the room 68 Operating equipment 68 Heating 68 Economics of problem 70 Appendix 72 Local insectaries 72 Labor and materials tables 72 Government Argentine ant syrup 73 Literature cited 74 THE BIOLOGICAL CONTROL OF MEALYBUGS ATTACKING CITRUS 1 HARRY S. SMITH 2 and H. M. ARMITAGE3 INTRODUCTION During the past ten years the mealybugs have come to be regarded as pests of major importance by citrus growers and horticultural officials. These insects are more resistant to fumigation or spraying than any of the other scale pests of citrus ; it is this resistance which has been responsible for their bad repute. The damage by mealybugs is caused by the extraction of sap from the trees and the excretion of honeydew upon which the sooty mold fungus grows, as in the case of the black, citricola, and cottony cushion scales. The deposit of black smut which appears on the leaves, together with the feeding of the insects, particularly around the buttons of the fruit, in time causes a heavy drop, while the deposit on the fruit itself makes the process of washing difficult and expensive. Reduc- tion in grades of fruit because of the feeding of the insects results in serious losses to the grower. Frequently early picking of the fruit is necessitated, which forces it onto unfavorable markets. After a severe, uncontrolled infestation, orchards generally fail to set a good crop for the coming season. It is the belief of the writers that the mealybugs, if uncontrolled, are capable of causing greater damag-e to the citrus industry than any other pest occurring in California, Citrus-feeding mealybugs have existed in California for many years. The exact time that they appeared as pests of citrus in the open is not known, but it was probably in the eighties. About 1904 they began to attract attention in San Diego County and from that time to the present these insects have, in one part or another of Cali- fornia, been sufficiently numerous to cause serious losses to the growers who were so unfortunate as to have their trees infested. 1 Paper No. 223, Graduate School of Tropical Agriculture and Citrus Experi- ment Station, University of California, Riverside, California. 2 Associate Professor of Entomology, and Entomologist in Experiment Station, Riverside. 3 Entomologist and Deputy Agricultural Commissioner of Los Angeles County in charge of Insectaries, Los Angeles. 4 University of California — Experiment Station These earlier records refer, of course, to the common mealybug, Pseudococcus citri (Risso). The attack by this insect was very spo- radic and, while it was rather generally distributed, serious damage occurred only in relatively small districts, particularly in parts of San Diego, Ventura, Santa Barbara, and Los Angeles counties. In 1913 the situation became greatly complicated by the appearance in Cali- fornia of another species, the citrophilus mealybug, P. gahani Green. This species has spread with such rapidity and is so much more diffi- cult to control than the so-called common mealybug that the latter nowadays attracts comparatively little attention. Fig. 1. — The Orange County Insectary, at Anaheim, California. (Courtesy U. S. Army Air Service.) Great difficulty has always been experienced in the attempt to control these insects on citrus trees. The ordinary methods of control for scale insects, i.e., spraying and fumigation, have uniformly failed to bring relief, even when applied at much greater strength than has been necessary to handle satisfactorily such pests as the black, red, and purple scales. Much experimental work has been carried out by the United States Department of Agriculture, the Citrus Experiment Station, and the County Agricultural Commissioners, in the hope of discovering improved methods or more satisfactory insecticides for the purpose, but the resistance of these insects has been so great that it has seemed practically impossible to destroy them without seriously damaging the tree and fruit. The situation led entomologists to give consideration to radically different methods for the suppression of mealybugs, and out of this has come the biological method, the discussion of which is the pri- mary object of this bulletin. Bul. 509] Control of Mealybugs Attacking Citrus THE MEALYBUGS The mealybugs are members of the scale-insect family, or Coccidae. They differ from the armored scales, such as the red scale and purple scale, in that they have no separate, hard, shell-like covering. Other groups of scales also are without this covering, such as the black and citricola scales. From these the mealybugs differ in certain structural characteristics, and in the fact that they retain their power of loco- motion throughout life. Mealybugs have received their common name because of the white, mealy, or cottony covering of wax which they support in greater or lesser degree throughout life. Generally their eggs are deposited in a loose cottony sac secreted by the females in the form of waxy threads, although one species is viviparous. The early stages of the two sexes are practically indistinguishable. After a few days, how- ever, the time depending largely upon the temperature, the male insect crawls off into a protected place and forms a small white cocoon, in which it spends the pupal period of 9 or 10 days. At the end of this time the adult male emerges, a tiny two-winged insect having two long, white anal filaments. The adult male does not feed, its only function in life being to fertilize the females. The Citrophilus Mealybug, Pseudococcus gahani Green. — The females of this species, when mature, are regularly oval, flattened, soft-bodied insects. They are covered with a coarse, granular, white wax, which is much thinner in the folds of the segments and in the four more or less confluent longitudinal series of impressed dots. The darker body color shows through the folds, and gives the impression of a symmetrical pattern not easily confused with that of other species. The waxy covering extends along the margins in a series of short stout filaments with an anterior pair of slightly greater length and a posterior pair one-fourth to one-third the length of the body, flanked on each side by a filament approximately one-half that length. The adult females differ little from the immature forms of the same sex except in size and in the distinctness of the waxy pattern. A slight pressure or irritation of the body results in exudation of claret- colored bead-like drops of liquid from dorsal glandular pits, two of which are close to the anterior and two close to the posterior end. This claret-colored exudation is sometimes very pronounced even in the immature forms, materially aiding in determining the species in life. The species is oviparous, the adult females congregating on the University of California — Experiment Station Fig. 2. — The citrophilus mealybug, Pseudococcus galiani Green. (After Essig.) Bul. 509] Control of Mealybugs Attacking Citrus 7 trunks of infested trees in large masses and depositing- their eggs in irregular cottony sacs. The males in the adult form are minute, deli- cate, reddish-colored two-winged individuals bearing two long, white, waxy anal filaments. They are seldom observed in the field except as pupae, but are seen commonly in the insectary. The observations of Clausen (1915) 4 have been corroborated by the more recent investigations of Basinger ; 5 they note that there are apparently four definite generations of this species in the field annually, though the occurrence of intermediate overlapping genera- tions is indicated by the finding of limited numbers of all stages at all seasons of the year. The length of these definite generations as worked out by Basinger varies from 57 days in midsummer to 168 days during the winter and early spring months. Overwintering is carried out largely in the intermediate stages. The majority of the overwintering mealybugs reach maturity in March and early April. The progeny from these adults are commonly referred to as the 'peak generation'; they mature during June and July. In the interior, drier citrus areas there is a marked decline in numbers due to summer heat, while in the milder coast areas further increase in numbers is checked by the increasingly active natural enemies, particularly by Cryptolaemus. There is later a slight increase in the fall in the interior areas as the temperatures decrease. This is also the case in the coast areas in some infested properties in which mechanical treatment for other insect pests interferes with the com- pletion of control by natural enemies. The critical period in the season's infestation occurs at the time of the presence of the peak generation in May. While there is undoubt- edly a high natural mortality at this time among the young migrating from the trunk back to the fruit and foliage, countless numbers reach the newly setting fruits where their extensive feeding around the stems has a tendency to exaggerate a condition locally known as 'June drop.' When abundant, the maturing individuals are respon- sible for the killing of considerable inside wood, the softening of the stem-end of maturing fruits, and the excessive smutting of the fruit and foliage by the sooty-mold fungus developing in the copiously excreted honeydew. It has been obvious ever since Clausen determined this insect as a new species, that it was of foreign origin. Until recently it had 4 See "Literature Cited" at the end of the bulletin, for complete data on citations, which are referred to in the text by author and date of publication. 5 A. J. Basinger, Citrus Experiment Station, Riverside (unpublished notes). 8 University of California — Experiment Station been recorded only from the British Isles in addition to the California records. Recently Ferris (1927) has recorded it from South Africa, but it has undoubtedly been introduced there, as it has been in Cali- fornia. The history and method of its dispersal here led to the assump- tion that it originated in some country in the Pacific maintaining direct steamship communication with San Francisco. Consequently, foreign collectors of the State Department of Agriculture and the University of California, while not searching specifically for the citro- philus mealybug, have always been on the lookout for it, especially when working in the various countries of the Pacific. Clausen knew the species intimately and searched for it in China, Japan, the Philip- pines, and Formosa. Silvestri was supplied with both dry and slide mounts and covered the same territory and in addition Indo-China. Failure to find the species in the Orient led to the conclusion that it may have originated in Australia, New Zealand, or some of the South Pacific islands. Accordingly, an agent of the University, Harold Compere, was sent to Australia in August, 1927, in an effort to dis- cover the country of its origin. As has been previously reported (Smith and Compere, 1928) he found the species at Sydney, New South Wales, under conditions which indicate that to be its native home. He also found it in New Zealand, where it evidently had been introduced from Australia. In California it was first found at Upland, San Bernardino County, over an area of 3 acres of citrus in 1913 and a rapid natural spread was recorded over adjacent acreage until in 1919 over 1000 acres were included in the infested area. In the meantime infestations had been discovered in 1916 in 100 acres of citrus in and around the city of Riverside, Riverside County, 20 miles south and east of the initial infested area, and in a very limited area at Pasadena and Altadena in Los Angeles County, 35 miles to the west. In 1918 it spread to the east in San Bernardino County to Cucamonga and Alta Loma and in 1919 south in Los Angeles County to Alhambra. Evidence has since brought to light the fact that infestations of this species had unquestionably occurred in the San Francisco Bay region and in the cities of Los Angeles and Long Beach as early as 1913 on ornamental street trees, particularly the grevillea (Grevillea rohwsta). Up to 1921 all of the commercial-citrus infestations had been recorded from the warmer, drier interior areas of the citrus belt. With the exception of the initial outbreak at Upland, which reached a serious peak during 1917 to 1919, it has been found that the summer heat under interior conditions normally restricts the Bul. 509] Control of Mealybugs Attacking Citrus 9 degree of infestation to a very low point and that the seasonal changes, permitting a lesser number of generations and a greatly retarded development during the winter months, has a tendency materially to decrease the rate of natural spread. It was not until this insect invaded the citrus plantings of the coast area with its mild, warm, humid climate, permitting a less interrupted development, that it assumed the rank of a major pest. It first appeared in Orange County at Anaheim in 1921 on a few trees in the heart of an extensive coast citrus acreage. It has spread in that county with amazing rapidity, until in 1929 over 45,000 acres, representing more than 75 per cent of the total citrus acreage of the county, were recorded as being infested. Similarly in the coast area of Los Angeles county in 1922 several citrus properties were recorded as infested and the same rapid spread has occurred. In 1929, 17,000 acres were infested, rep- resenting 32 per cent of the total citrus acreage of the county. The restricting influence of interior climatic conditions is definitely shown by the fact that in Los Angeles County only 14 per cent of the 43,000 acres of citrus lying in the interior areas is infested, while practically 100 per cent of the 13,000 acres in the coast areas is infested. In the coast areas many serious infestations occurred before steps were taken to make available the necessary number of Cryptolaemus for control purposes. In spite of the stringent quarantine measures restricting the movement of any fruit, plants, orchard equipment, or other mate- rials from infested to clean areas, infestations of this species were recorded in relatively rapid succession from Hollywood and Beverly Hills in Los Angeles County and Anaheim in Orange County in 1921 ; from Covina, Rivera and San Fernando in Los Angeles County, Ful- lerton in Orange County, and Oxnard in Ventura County in 1922 ; from Glendora and Whittier in Los Angeles County, Santa Ana and Garden Grove in Orange County, and Montecito and Carpinteria in Santa Barbara County in 1923 ; from North Whittier Heights in Los Angeles County in 1924 ; from Santa Paula and Fillmore in Ventura County in 1925 ; from Ventura in Ventura County, and Olive, Tustin, and Yorba Linda in Orange County in 1926 ; and from San Diego and La Jolla in San Diego County, Pomona in Los Angeles County, and Corona in Riverside County in 1927. Since that time new infes- tations have been found in all areas as a result of natural spread, rapidly linking up these earlier centers of infestation. A study of the infested citrus acreage shows that this species is now well dis- tributed throughout the entire group of southern coast citrus-produc- ing counties and is present in all of the interior citrus-producing 10 University of California — Experiment Station counties with the exception of Imperial. It will undoubtedly be only a very few years until it will have spread by natural means to all of the intervening acreage. Of the native insect enemies of the citrophilus mealybug the green lacewing, Chrysopa calif omica Banks, is probably the most important. Both the larva and adult feed on all stages of the mealybug and were it not for the fact that it is severely attacked by secondary parasites as it approaches possible controlling numbers, it might alone be a con- trolling factor in many districts. Next in importance is the dipterous predator Leucopis "bella Loew, the larvae of which do effective work in the mealybug egg masses. The small ladybird, Scymmis sordidus Horn, is often abundant, and attacks particularly the egg masses and immature individuals. The black ladybird beetle, Rhizobius veniralis (Er.), is an occasional feeder. The hymenopterous parasite Pseiida- phycits ang elicits (Howard) occasionally attacks the immature stages. The introduced species are represented by the ladybird beetles, Cryp- tolaemus montrousieri Muls. from Australia and Scymmis binaevatus Muls., from Cape Town, South Africa. Recently (Smith and Com- pere, 1928) a ladybird beetle, Midas pygmaeus Blaekb., a dipterous predator, Diplosis sp., and two hymenopterous parasites, Tetracnemus pretiosus Timb. and Coccophagus gunieyi Compere, have been intro- duced from Australia. These recent introductions are now develop- ing in a very encouraging way in the citrus groves and are already of great value in the control of the citrophilus mealybug. The citrophilus mealybug has proved to be such a general feeder that it seems unwise to attempt to give a complete list of host plants. It is of economic importance on citrus, pears, apples, grapes, and a large number of ornamentals. The principal effect of attack by this mealybug is a decided fruit drop, not only of the young fruit, but of the mature fruit as well when it is held on the trees late in the season. These insects have a habit of feeding beneath the button or sepals of the young fruit. This is particularly conducive to premature drop. A severe attack of this pest in the orchard causes a pronounced dropping of the leaves and very greatly reduces the set of fruit for the following season. The copious secretion of honeydew, which makes it possible for the sooty-mold fungus to thrive, is also an important source of injury to trees and fruit. Aside from the possible bad effect of this dense black coating on the physiology of the tree, the sooty mold is extremely difficult to remove from the fruit and increases the expense of washing. Bul. 509] Control of Mealybugs Attacking Citrus 11 In addition to the actual loss of the fruit through dropping, another important result of mealybug" attack is the lowering of the grade of fruit which does reach maturity. Woglum and Borden (1922) state, "One packing-house manager reported a lowering of the grades from one severely infested orchard of from 30 to 40 per cent of the highest-classed fruit. The lower grades are also seriously affected and frequently fall to culls, or unmarketable fruit. Serious infestations on lemons have been know to result in an almost complete loss of the crop, the fruit grading as culls. ' ' Several cases of complete loss on oranges have come under our observation. When this happens in groves which may yield from $1,000 to $1,500 worth of fruit per acre, further exposition of the capabilities of this insect for serious damage seems unnecessary. The Common Mealybug, Pseudococcus citri (Risso). — The females of this species when mature are somewhat similar to the preceding species; regularly oval, flattened, soft-bodied insects. They are inclined to be broader in proportion to their length and more flattened than the citrophilus species. Moreover, the white waxy covering is less granular and more smoothly arranged and thus gives no dis- tinctive body pattern, although its thinness along a more or less broad mid-dorsal longitudinal band is emphasized by the brownish-gray appearance given that area by the body color showing through. The true body color varies from light-yellow to brownish-orange, often appearing gray through the waxy covering in the adult females. The waxy covering extends along the sides of the body in a series of short, stout, lateral filaments, which gradually lengthen as they approach the anal end and terminate in an elongated anal pair often one-quarter the length of the body. As in the other species the adult females differ very little from the immature forms of the same sex, except in size and the abundance of waxy covering. When irritated or slightly pressed the adult females exude a yellowish to orange liquid, in con- trast to the claret color of that from the citrophilus species. This species is also oviparous; the eggs are deposited in irregular loose cottony sacs, usually at the point where the maturing adult completes feeding. The sexes differ very little in the immature forms. As they develop the males pass through a complete metamorphosis. They spin a loose white cottony cocoon from which they later emerge as minute, delicate, amber-brown, two-winged individuals, bearing the custom- ary two long, white, waxy anal filaments. The citrus mealybug in the coast citrus area appears to have three or more generations a year. It shows a tendency to reach injurious 12 University of California — Experiment Station numbers both in the early spring, from eggs deposited by females which have overwintered principally in the intermediate stages, and in late fall, the latter being more severe. Summer heat seems to play an important part in checking the spring generation, while native natural enemies are extremely active in checking the fall outbreak. The young mealybugs have a marked tendency to cluster on new growth. This insect seems to have first appeared in California as an orchard pest about 1885. Although it was known as the ' harmless greenhouse mealybug' in the early eighties, it later became a recognized pest of a wide range of ornamentals in greenhouses throughout the entire United States. Once established in the field it spread rapidly through San Diego, Orange, Los Angeles, Ventura, and Santa Barbara coun- ties. From 1904 to 1910, infestations on citrus reached a serious degree in many localities in those counties, particularly in Ventura. As late as 1918, there were scattered outbreaks in both the coast and interior areas of the southern part of the state, though particularly along the coast. Since that time, however, there has been a rapid decrease in the number and severity of infestations and during the past six or eight years field infestations have been practically unknown, excepting in San Diego County. The almost complete disappearance of this species as an economic pest of citrus may be directly attributed to two factors: first, the wide-spread liberations of Crypt olaemus in the control of the citro- philus species ; and second, the introduction of a small hymenopterous parasite of this species known as Leptomastidea abnormis (Girault) from Sicily in 1914 by the California State Department of Agricul- ture. This parasite was subsequently propagated in large quantities by the State Department of Agriculture and widely distributed throughout the infested areas of the state. Such light infestations as have been observed recently have always shown extensive evidence of its work. In addition to these introduced natural enemies, the citrus mealybug is particularly susceptible to the attack of numerous native predators which are listed here in the order of their importance. The brown lacewings, Sympherobius barberi Banks and S. calif ornicus Coq. ; the green lacewing, Chrysopa calif omica Banks ; the ladybird beetles, Hyperaspis lateralis Muls., Scymnus sordidus Horn, 8. guttu- latus Lee, and S. nebulosus Lee. ; and the dipterous predator, Leu- copis bella Loew. The host plants of the common mealybug cover a relatively wide range of greenhouse and field plants in addition to citrus. Bul. 509] Control of Mealybugs Attacking Citrus 13 The effect of an attack by this mealybug- is very similar to that of the preceding- species although it is more inclined to remain in the outside of the tree. A heavy infestation weakens the fruit so that there is considerable drop. Fruits that remain on the tree are fre- quently so affected that they fall into a lower grade, and the set for the following year is greatly reduced. The honey dew secreted by the insects is conducive to the development of sooty mold, necessitating the thorough washing of the fruit, and the black deposit is frequently difficult to remove. Often defoliation occurs, resulting in serious physiological disturbances in the tree. Only a few years ago, this mealybug was by far the most important species as far as the citrus grower was concerned. As before mentioned, it is now greatly sur- passed in economic importance by the citrophilus mealybug. It seems unlikely that it will ever again be of much economic importance in orchards where the citrophilus mealybug is found, because the con- trol measures required by the latter seem sufficient to keep the less prolific species in check. The Baker Mealybug, Pseudococcus mai^itimus (Ehrh.). — Although the adult females resemble the citrophilus species in size, they differ somewhat from them in shape, being more elongated in proportion to their width. Their waxy covering consists of a very fine powder, which because of its thinness often appears to be wholly lacking. The lateral waxy filaments are almost hair like, with the anal pair half the length of the body. The body color is more often pink- ish though sometimes shading into gray. The exudations of the adult females when irritated are lemon-yellow to orange. The males of this species differ little from those of the other species considered except in the body color, which is slightly pinkish as compared with the red of citrophilus and the amber of citri. The species is oviparous, the adult females depositing their eggs in loose cottony sacs, usually at the point where feeding is completed, but often exhibiting a tendency to migrate to the trunk trap bands as does the citrophilus, or to curled dried leaves which have lodged in the tree, for the purpose of oviposition. This is the same species as that known as the grape mealybug in northern California. It is apparently native to the United States. It seems to be the hardiest and most adaptable of any of the species attacking citrus, since it attacks grapes as far north as Michigan. This insect is distributed generally throughout the state and occurs commonly on grapes and pears in the San Joaquin, Sacramento, and Santa Clara valleys in northern California, and over a wide range of 14 University of California — Experiment Station hosts in the coast belt in southern California. It occurs commonly on ornamentals in greenhouses throughout the state and it is not uncom- mon on citrus in the southern part. Early spring infestations in citrus orchards are exceedingly light and it is not until midsummer or early fall that they become suffi- ciently numerous to be noticeable. The native insect enemies of Pseudococcus maritimus in the order of their importance in southern California are as follows: the two brown laeewings, Sympherobius barberi Banks and S. calif ornicus Banks, the former being the more abundant; the dipterous predator Leucopis bella Loew; the hymenopterous parasite, Chrysoplatycerus splendens (How.), of which this species seems the preferred host; the green lacewing, Chrysopa calif ornica Coq. ; and the two small lady- bird beetles, Scymnus nebulosus Lee. and 8. sordidus Horn. In cen- tral California, where P. maritimus is a pest of grapes and pears, Timberlake and Clausen (1924) record the following internal para- sites: Acerophagus notativentris (Girault), Anagyrus clauseni Tim- berlake, A. subalbicornis (Girault), Chrysoplatycerus splendens (Howard), Pseudaphycus ang elicits (Howard), Pseudleptomastix squammulata Girault, and Zarhopalus corvinus (Girault). Z. shel- doni Ashmead is recorded from southern California. Of the intro- duced forms the Cryptolaemus (C. montrousieri Muls.) is probably the most important in southern California, and owing to its extensive distribution for the control of the citrophilus mealybug, should pos- sibly receive more credit for assisting in its control than it does. Another introduced ladybird beetle, Scymnus binaevatus Muls., from South Africa, so far has not been observed to be particulary attracted to it in California. The Baker mealybug attacks a wide range of ornamentals, both in the greenhouse and in the field, in addition to citrus, walnuts, grapes, pears, and apples. The injury caused by this species does not differ in any important way from that inflicted by the two species previously discussed. On rare occasions only has this species become sufficiently abun- dant in citrus orchards to warrant control measures, and even then it is usually cleaned up by native natural enemies. Its presence on citrus trees, however, is often a source of alarm for the grower, who mistakes it for the citrophilus mealybug. The Japanese Mealybug, Pseudococcus krauhniae (Kuwana). — The adult females resemble Pseudococcus citri in form, waxy covering, short stubby lateral filaments, and other superficial characters, but Bul. 509] Control of Mealybugs Attacking Citrus 15 when fully matured differ noticeably in that they are much larger. However, when irritated they exude the claret-colored liquid similar to that of P. gahani. Moreover, they migrate to the trunk of the tree for the purpose of ovipositing as does P. gahani, the eggs being depos- ited in loose irregular cottony sacs. During the summer of 1918 the attention of Armitage was called to an infestation of mealybug on oranges at Ojai, in Ventura County. This infestation had been present for several years and was thought to be the common mealybug. Because of certain differences, however, specimens were sent to G. F. Ferris, specialist on this group of insects, who found them to be Pseudococcus krauhniae (Kuwana), a species theretofore known only from Japan. This discovery of an additional species of citrus-feeding mealybug in California caused some alarm, but the valley in which it occurs is isolated from the other citrus districts of Ventura County, and so far as known there has been no spread. As a matter of fact, during the eight years since its discovery this insect has not given any indication that it is more to be feared than the common mealybug. In the short time during which it was under general observation in the field it exhibited a seasonal life history similar to that of the citrophilus mealybug in the interior area at Uplands. Aside from the attack by native natural enemies, the hot, dry summers of the infested area no doubt had a distinctly restrictive effect on its develop- ment. The infestation reached a peak in late spring, rapidly lessen- ing during the summer months, with only a slight increase during the following fall. The native brown lacewings, Sympherobius barberi Banks and 8. californicus Banks, more particularly the latter, were observed as being the most important enemies of this species and were believed responsible for the ultimate control of this infestation. The green lacewing, Chrysopa calif ornica Coq., was also observed feeding on this species to a limited extent. Efforts to establish the Crypt olaemus on this species resulted in failure, though carried out on an extensive scale, under what were considered favorable field conditions. This is the only species of citrus-feeding mealybug in California for which the Crypt olaemus have apparently shown an aversion. The only host plants recorded in California are persimmon (Diospyros sp.), orange {Citrus sinensis), and wisteria (Wisteria floribunda) . The type host is Wisteria (Krauhnia) floribunda in Yokohama, Japan. 16 University of California — Experiment Station Long-tailed Mealybug, Pseudococcus longispinus (Targ.). — The adult females of this species somewhat resemble Pseudococcus mari- timus in body size and form but are much less robust. In addition they are easily distinguished from the latter by their much longer fine hair-like marginal filaments and by the extremely long one or two pairs of anal filaments, which are often as long as the body itself. The adults appear whitish owing to the heavy coating of granular wax, but not uncommonly the intermediate stages have a slight greenish- gray cast along a mid-dorsal longitudinal area. The exudation caused by irritation is almost colorless, being slightly yellow. The species is viviparous, the young being born alive under a thinly woven cottony web which the female secretes about her body, and under which they remain sheltered for a time before beginning to feed. So far as observed the seasonal life history of this species differs little from that of the other species described in this bulletin, with the exception that in the field on citrus it has never increased to any serious degree. It is often found, particularly in the coast areas, scattered among the clusters of other species. It does, however, reach a severe peak in late fall on dracaenas, its preferred host, in the field. The presence of this species on citrus in California so far as known is confined to the coast areas of Santa Barbara, Ventura, Los Angeles, Orange, and San Diego counties. It is, however, of common occur- rence on ornamentals in the greenhouses of the state and in the open in the nurseries of the coast area in the southern part. Little attention has been given to the natural enemies of this spe- cies, principally because its occurrence is only occasional and on a limited number of hosts. It has been observed, however, that the Crypt olaemus will attack it. The Mexican Mealybug, Phenacoccus gossypii Towns, and CklL — The mature females differ very little in size or form from the several species previously described in this paper. However, the covering of coarse white granular wax, which takes the form of a pronounced mid-dorsal longitudinal ridge, together with its grayish body color, make it difficult to confuse with any other species on citrus. The species is oviparous, the eggs being deposited in elongated compact cottony sacs. Oviposition usually takes place on the under- side of the foliage of the infested plant or tree, and frequently in curled dried foliage lodged in the plant. Irritation produces a practically colorless exudation of liquid from the four dorsal glandular pits, and is entirely unlike the exudates Bul. 509] Control of Mealybugs Attacking Citrus 17 from other described species. When crushed the body contents pre- sent a distinctive dirty greenish color. The seasonal life history seems to conform in general to that of the common mealybug' (Pseudococcus citri) and the Baker mealybug (P. maritimus). Infestations, however, often reach a serious stage in midsummer on certain preferred truck crops such as the eggplant, tomato, pepper, and okra, as well as on a few native weed hosts, par- ticularly sunflower and cocklebur. This pest has been incorrectly known as the Coleman mealybug (Phenacoccus colemani Ehrh.) since 1917 when it was first reported on geranium from Glendale, Los Angeles County. It has recently been determined by Ferris (1927) as the Mexican mealybug, P. gossypii. Each year it has been found to occur on an increasing number of host plants, particularly herbaceous perennials, and over an increasing area until it is considered to occur in the San Joaquin Valley and throughout the entire southern part of the state, with the possible exception of Imperial Valley. Citrus has appeared to be only an occasional and perhaps accidental host. Early attempts to grow it on lemons at the State Insectary in Alhambra for use in producing Cryp- tolaemus were unsuccessful. Armitage, however, has observed indi- viduals to mature and oviposit on lemon foliage in a houseyard at Claremont, and on orange foliage in the San Fernando Valley, both in Los Angeles County. D. W. Tubbs has observed a similar case on orange trees at Anaheim in 1925-26. The native dipterous predator Lewcopis bella Loew, is important in the natural control of this species. The larvae feed extensively on the egg masses. The brown lacewing, Sympherobius barberi Banks, and the small ladybird beetle, Scymnus sordidus Horn, have also been observed to feed on it in some abundance. Cryptolaemus has been used successfully to control it on ornamentals. The sunflower and cocklebur, the geranium, hollyhock, lantana, and certain truck crops such as tomato, pepper, eggplant and okra, are severely attacked, in addition to large numbers of other wild and cultivated plants. 18 University of California — Experiment Station THE INSECT ENEMIES OF MEALYBUGS Mealybugs as a group seem to be especially susceptible to attack by insect enemies of various kinds. Their habit of feeding in clus- ters in unprotected situations renders them easily accessible to para- sites and predatory insects, and their great reproductive capacity makes it possible for them to support a large number of these enemies without danger of extinction. Many of the parasites are specific in their attack; that is to say, they are limited, or largely so, to a single species of mealybug. The predators, on the other hand, are more general in their feeding habits, their activities being limited by the conditions of the environment under which the mealybugs exist, rather than by the specific identity of the host insect. In California the insect enemies of mealybugs consist of both native and introduced species. Only the more impor- tant ones will be discussed here, the others having been mentioned in the treatment of the individual species of mealybugs. The Mealybug Destroyer, Cryptolaemus montrousieri Muls. — This ladybird beetle is a native of Australia, where it feeds on the golden mealybug, Pseudococcus aurilanatus (Mask.), as well as on other species. It was successfully introduced into California in 1892 by Albert Koebele, who visited Australia in search of beneficial insects, under the joint auspices of the United States Department of Agricul- ture and the old State Board of Horticulture in California. From the importations made at that time the insect was firmly established in the orchards and was thoroughly distributed to all parts of the state where mealybugs were known to exist. It did not, at that time, seem to be able to adapt itself to the varied climatic conditions in southern California, and very largely disappeared excepting in San Diego and Santa Barbara counties, where it has persisted ever since the original introduction. In these counties, according to reports, it has often without artificial aid increased to such numbers as to clean up the mealybug infestation. At the time of the severe outbreak of the common mealybug in Ventura County in 1909 it was reintroduced in considerable numbers and did excellent work in the control of the pest. In general, however, where it occurred at all in infested orchards outside of San Diego and Santa Barbara counties, it was relatively unimportant so far as mealy- bug control was concerned, and it failed entirely to persist in the interior sections where there is a relatively low humidity and greater extremes of temperature. Bul. 509] Control of Mealybugs Attacking Citrus 19 These facts are of great interest since, compared to the present position of Cryptolaemus in the control of mealybugs, they indicate very clearly what has been accomplished by the propagation and distribution of the beneficial insects in large numbers. At the present time, although the mealybugs occur over a far greater area than formerly, and under even more varied conditions as regards tempera- ture and humidity, biological control is almost the sole method in use, and has given excellent results in the interior as well as along the coast. ... * 4(£ &r J "ft. d > * /'" J L>? '"•■-•- ■ Pt Fig. 3. — Larvae of Cryptolaemus montrousieri Mulsant, greatly enlarged. Cryptolaemiis montrousieri is a black ladybird with the head, prothorax, tips of the wing-covers and abdomen reddish. It is about one-eighth to one-sixth of an inch long. . The larvae are longer, sometimes attaining a length of one-third to nearly one-half inch (fig. 3). They are covered with a white, cot- tony secretion of wax, which gives them an appearance very similar to that of mealybugs, particularly before they reach their full size. Growers and others often mistake these beneficial larvae for mealy- bugs and destroy them. With a little experience, however, they may be distinguished at a glance, since the arrangement of the wax or cottony covering is different, as is also the method of locomotion. 20 University of California — Experiment Station The eggs are small, oval in shape, and of a lemon-yellow color. They are laid usually in the cottony egg-sac of the mealybug, or in the vicinity of clusters of the host insects. Although the adult beetles feed upon mealybugs almost exclu- sively, it is the larvae which are depended upon for the major part of the control work. Cryptolaemus is ideal for this purpose, since it has no known parasites, does not tend to disperse widely when colonized, is easily propagated under insectary conditions, and feeds on all the important citrus-feeding mealybugs. The Sicilian Mealybug Parasite, Leptomastidea abnormis (Gir.). — This valuable internal parasite of the common mealybug was success- fully introduced from Sicily and established in California by the State Department of Agriculture in 1914 (Smith, 1917). It at once demon- strated its adaptability to the California environment and spread with great rapidity until within two or three years it apparently occupied all the territory infested by its host. This dissemination was, of course, greatly aided by continued propagation and distribution of the para- site by the State Insectary. At the present time it is practically impossible to find a colony of the common mealybug which is free from attack by this parasite. Unquestionably it has been an important factor in the practical dis- appearance of its host. In the insectaries when the common mealybug is used as food for Cryptolaemus, this parasite presents something of a problem, since it destroys large quantities of mealybugs and is practically impossible to keep out. In the field it is not as effective as some of the predators when the infestation is heavy, but where the mealybugs are scattering it is undoubtedly of great value. This parasite can readily be distinguished from other known mealybug parasites occurring in California by its striking appear- ance, which is due to its peculiar habit of holding its wings aloft. One wing is held in such a manner as to appear broken at the base. These peculiar wings, with their characteristic banding, serve to identify it. Oviposition takes place soon after the adult parasite has emerged. It prefers the first and second stages of the mealybug in which to deposit its eggs. In nature, as a general rule, but a single egg is placed in a mealybug. In confinement it will deposit as many as 100 eggs in a single host insect. The time of development from egg to adult ranges from 25 to 45 days, depending upon the temperature. As intimated before, the principal host of this parasite is the com- mon mealybug, Pseudococcus citri. Colonies were sent to Hawaii, where it is reported to breed on the sugar cane mealybug (P. sac- Bul. 509] Control of Mealybugs Attacking Citrus 21 chrari (Ckll.) ) but is said not to thrive on that species. It is reported also to breed on P. Jcrauhniae (Kuwana) and P. vir gains Ckll. there. In spite of its widespread abundance, we have been unable to rear it from the citrophilus mealybug, and evidently it is unadapted to that species. The Brown Lacewings, Sympherobiidae. — These insects are among" the most important enemies of the mealybugs in California excepting the citrophilus species, particularly during the cooler portions of the year when other enemies are less active. They are generally dis- tributed throughout the infested area and by some writers are cred- ited with being the most effective of any of the predatory insects attacking particularly the common mealybug. While this was undoubtedly true formerly, the general propagation and distribution of Cryptolaemus on a large scale during more recent years has natur- ally altered the situation, and the brown lacewings cannot now be so ranked. They seem to be easily raised in quantity in confinement but the common mealybug is now of so little importance that there is little need for such activities. There are three species which commonly feed upon mealybugs in California. These are Sympherobius calif ornicus Banks, 8. barberi Banks, and S. angustus (Banks). The adult lacewings are small, about % inch in length, and light brown in color, with the netted wing-veins showing rather conspicuously. The eggs are deposited singly within the egg masses of the mealybugs or nearby, and are pearly white in color. The larvae are a dull gray, and are rather active in habit. Pupation takes place in a delicate transparent oval cocoon. There are several generations annually, the number being dependent upon temperature and abundance of food. Breeding occurs throughout the year, there being no true hibernation. The larvae, within the cocoons, are destroyed by several species of parasites. This greatly reduces their effectiveness. The Green Lacewing, Chrysopa calif ornica Coq. — This insect would be one of the most important enemies of mealybugs, particularly the citrophilus species, if it were not destroyed in large numbers by para- sites. It is, nevertheless, of considerable value as a predator, par- ticularly in the interior sections. However, it does not take readily to propagation in confinement and the attack by parasites makes it poorly adapted to use as an agency for biological control. It is an omnivorous feeder and has been definitely credited with destroying Cryptolaemus larvae in the case of a light infestation of mealybug and a consequent food shortage. 22 University of California — Experiment Station The adult lacewing is from % to % inch in length and is of a bright green color with beautiful gauzy wings carried arched over the back when not in use. The body has a yellowish stripe down the back. The eggs are generally deposited singly on long stalks. The eggs themselves are light green in color, but the eggshells, after hatching, are white. The function of the long stalk seems to be to prevent can- nibalism, since the larvae are extremely voracious and, upon hatching, will destroy the remaining eggs if within reach. The larvae are provided with long, sickle-shaped jaws which are constructed like a hypodermic needle, in that they are hollow. After piercing an insect the juices are drawn through these hollow jaws, which enable the larvae to feed with great rapidity. On reaching maturity the larva spins a dense, spherical, white cocoon, usually attached to the bark or some other rough surface, on the tree. In this cocoon the insect undergoes its transformation to the adult stage. Leucopis bell a Loew. — This dipterous predator is one of the most important enemies of the mealybugs in southern California, Where the infestation is severe and of long standing it becomes very abun- dant, but it does not get into action promptly enough to reduce an infestation before serious damage results. It is a small silvery-gray fly with indications of longitudinal stripes on the thorax and faint dark spots on the abdominal segments. The eggs are small and white and deposited in the mealybug clusters or in the egg-masses. The larvae are yellowish white, and the pupa- rium is dark brown, pupation taking place in the old mealybug masses. There are several generations a year. It is attacked by several hymen- opterous parasites. HISTORY OF DEVELOPMENT OF BIOLOGICAL CONTROL The biological method of control, as applied to mealybugs, has received more or less attention in California for more than thirty years, dating back to the introduction of the ladybird beetle Crypto- laemus montrowsieri from Australia in 1892. Mealybugs were con- sidered to be pests of minor importance at that time and for a period of about fifteen years after its introduction biological control received practically no further attention. The increase of the common mealybug in 1908 or 1909 brought about a renewed interest in this subject and finally resulted in the sending of an entomologist to Sicily in 1914, from which place the internal parasite Leptomastidea abnormis was imported. Prior to Bul. 509] Control of Mealybugs Attacking Citrus 23 this time, in 1910, George Compere had made a trip to the Orient for the State Commission of Horticulture and had sent in several enemies of mealybugs, but only one of these, Scymnus bipunctatus Kugelann, became established and that only temporarily. This ladybird was again introduced from the Philippines in 1913, but apparently it has now disappeared. In 1915 and 1916, work carried on by the United States Depart- ment of Agriculture demonstrated conclusively that the Argentine ant had an unfavorable effect on the efficiency of the natural enemies of the common mealybug. A series of experiments indicated that under certain conditions the eradication of the Argentine ant from infested trees resulted in the disappearance of the citrus mealybug within a period of six weeks to three months, through attack by para- sitic and predatory enemies; it then remained under control through- out the year. Untreated trees a few feet away remained severely infested. Further observations, however, indicated that the requisite natural enemies were often not present in the orchard, or if present occurred in insufficient numbers to bring about prompt suppression of the pest. Concurrently with these investigations there was being developed at the State Insectary at Sacramento a method of growing mealybugs on potato sprouts in order to make possible the mass production of natural enemies for orchard use. This method appeared to be of practical value, and the State Department of Agriculture authorized the establishment of a branch laboratory in southern California for the purpose of determining whether or not the citrus mealybug could be kept in control by the mass production and liberation of parasites and predatory insects through the use of laboratory-grown food. This insectary was established at Alhambra, Los Angeles County, in July, 1916. The efforts of this laboratory were first largely directed toward the production and colonization of the newly introduced Sicilian mealybug parasite, Leptomastidea abnormis (Gir.), but during the same period investigations were carried on to determine the applica- bility of the potato-sprout method to the production of Cryptolaemus montroiisieri. This method seemed to give promise of success and a field demonstration was accordingly arranged, in cooperation with A. A. Brock, then Horticultural Commissioner of Ventura County. The first Cryptolaemus produced at the Alhambra laboratory were colonized in what is known as the Culp orchard, at Santa Paula, This orchard had a mealybug record of long standing, having been more 24 University of California — Experiment Station or less heavily infested by the common mealybug' for several consecu- tive years immediately preceding' the trial. The infestation proper covered 2 acres in one part of a 5-acre tract of very large, bearing lemon trees. The trees had suffered considerably during these years from the attack of the mealybug, the yield was very light and the fruit was so covered with sooty-mold fungus that it was necessary to hand-wash it at the packing-house. This condition existed in spite of many attempts to control the mealybug by spraying and fumigation. Light liberations of Cryptolaemus were made over the infested area in April and May, the production of the laboratory not being very great at that time. During June it was possible to increase the size of the liberated colonies greatly, and by the middle of June a total of 6,900 beetles had been generally distributed over the area. Larvae of Cryptolaemus from the earlier liberations were already making their appearance. The second generation of larvae appeared during the latter part of July and reached its height during the first week in August. They were so abundant at that time as apparently to out-number the mealybugs. By the first of September the Crypto- laemus were still very plentiful and it was necessary to search dili- gently to find a single mealybug. An examination of the burlap band traps, placed around the trees, showed them to be filled to overflowing with pupae of the Crypto- laemus while thousands of larvae had sought every conceivable pro- tected place in which to pupate, including the oil-filled heaters which were stored under the trees. Summing up the work, the liberation of 6,900 beetles over a period of two months during the early stages of infestation was sufficient during the succeeding two months to bring about a complete clean-up of the infestation. During August, September, and October of the year of this demonstration over 21,000 beetles were collected from the orchard without reducing the orchard population appreciably; these were distributed to other infested orchards in that district. Another orchard near Santa Paula was so heavily infested with mealybugs that the owner attempted double fumigation as a control measure. The result of the first night 's work was so disastrous to the trees that the owner appealed to the Horticultural Commissioner for advice. On September 9, 6,800 beetles, collected from the Culp orchard, were liberated over the infested area. Observations during the next two months revealed a repetition of the conditions which prevailed in the Culp grove during the clean-up period. By Novem- ber 13 the infested area was commercially clean and the beetles had Bul. 509] Control of Mealybugs Attacking Citrus 25 gone into hibernation in the burlap bands. The following" spring the remaining beetles completed the clean-up almost to the point of eradi- cation. The results of this work were so encouraging that Ventura County, upon the recommendation of Commissioner Brock, estab- lished an insectary for the propagation of Crypt olaemus. This insec- tary has been kept in operation to the present time. During this same period a demonstration was staged in the Scho- field orchard at Pasadena in which the citrophilus mealybug occurred, in company with the common species. In this orchard it was first necessary to control an infestation of the Argentine ant. This was done in the course of experimental work by the Federal Bureau of Fig. 4. — The first commercial insectary established in California. Limoneira Rancho, Santa Paula. Entomology. The results with Cryptolaemus were similar to those secured in the Culp grove at Santa Paula. These successful demonstrations of the value of artificially propa- gating and distributing the Cryptolaemus for mealybug control, aroused much interest in this method in other districts infested with the pest. The first insectary to be built and operated aside from the State Insectary was that of the Limoneira Company at Santa Paula in 1916 (fig. 4). This was originally designed for the propagation of the Sicilian mealybug parasite. It was at once remodeled, after the demonstrations with Cryptolaemus, and by gradually increasing the size it has been able to care for the mealybug infestation on the large Limoneira Ranch, with entire satisfaction. This was followed by the erection of the Ventura County Insec- tary, the establishment of which has already been recorded. In 1919 an insectary was established by the Horticultural Commissioner of 26 University of California — Experiment Station San Bernardino County, to care for the infestation of the citrophilus mealybug in the vicinity of Upland. During the same year an insec- tary was built by the San Diego Land Corporation at Chula Vista to care for the common mealybug infestation on their own properties and also to produce CryptoJaemus for outside growers, which they supplied at cost of production. Later this insectary was enlarged and taken over by the County Horticultural Commissioner, by whom it is being operated at the present time. In 1919, following the successful introduction of Aphycus lonns- buryi How., a black-scale parasite, into California, a group of growers Fig. 5. — Part of insectary of the San Gabriel Valley Pest Control Association, Pasadena, California. in Los Angeles County formed an organization known as the San Gabriel Valley Pest Control Association, for the purpose of propa- gating and distributing this parasite for black-scale control. An excellent insectary was built and equipped at Pasadena (fig. 5). The citrophilus mealybug having increased and spread to such an extent as to cause the growers serious losses, this insectary and personnel later undertook the propagation of CryptoJaemus and other insect enemies of the mealybug. In 1919 the Santa Paula Citrus Association of Ventura County decided to undertake biological control work and erected an insectary for carrying out this project on a large scale. Somewhat later, when the citrophilus mealybug had broken out in the Oxnard district of Ventura County, the Oxnard Citrus Association attacked the problem Bul. 509] Control of Mealybugs Attacking Citrus 27 vigorously by erecting a large group of insectary buildings which are being used for the production of natural enemies of mealybugs. The citrophilus mealybug seems to find conditions in this district especially favorable, but in spite of this, the organization has been able to keep it under commercial control by the use of the biological method. The citrophilus mealybug appeared in Orange County in 1921 and gave ample evidence of its ability to do extensive damage in that section. The growers were organized by the Horticultural Commis- sioner and raised funds to build and equip an insectary at Anaheim, which has since developed into one of the largest and best-equipped plants for the production of Cryptolaerrms in the state (fig. 1). Insectary of the Fillmore Citrus Protective District, Fillmore, California. With the continued spread and increasing damage of citrophilus in Los Angeles County, the Horticultural Commissioner, with the support of many of the citrus growers' associations, undertook the production of Cryptolaemus on a large scale, and insectaries were established at Rivera and in the City of Los Angeles in 1923 and at Downey in 1926 for this purpose, which have since been under the supervision of Armitage. Santa Barbara and Riverside counties soon followed with county insectaries, the insectary at Riverside being built from funds raised by the growers themselves. Both insectaries are operated under the direction of the County Agricultural Commissioners. The latest insectaries to be established are those at Fillmore, Ven- tura County, by the Fillmore Citrus Protective District (fig. 6), the Chapman Ranch at Fullerton, Bastanchury Ranch at Fullerton, and Powers Ranch at Ventura. Thus it will be seen that there are in operation in southern Cali- fornia at the present time, fourteen insectaries devoted almost exclu- 28 University of California — Experiment Station sively to the production of Crypt olaemm for use in the control of mealybugs attacking citrus. As the work has expanded, cost of production has gradually decreased and will perhaps continue to do so as experience and inves- tigation increase our understanding of the many problems involved. A more detailed discussion of the economics of the situation will appear on a later page. MASS PRODUCTION OF CRYPTOLAEMUS It is not practical to attempt to collect sufficient mealybugs in the field to propagate Cryptolaemus extensively, though in the late part of the season production may sometimes be profitably increased through the use, as extra food, of field-collected material. The citro- philus mealybug is sometimes available from infested trunk trap- bands. Insectary operations, therefore, as applied to Cryptolaemus pro- duction, or to the production of almost any other insect predator or parasite, naturally fall into three distinct operations : first, the grow- ing of a suitable host plant on which the insect pest under considera- tion may be reared in quantity ; second, the production of the insect pest on the host plant material thus grown ; and third, the propagation of the beneficial insect itself on the food thus provided. While methods in the mass production of Cryptolaemus are still in the developmental stage, there has been much definite improvement in the mechanics of the work during the past few years, and present operations are following rather well-defined lines. The unit of production continues to be a small redwood tray, specifications for which are given later on in this bulletin. In these trays the potatoes used in developing the potato sprouts are planted. The unit of operation was formerly a small cloth-covered cage containing a maximum of three trays. Now, as a result of the inves- tigations conducted by Armitage in 1924, under the office of the Los Angeles County Horticultural Commissioner, this has been changed to a room of variable size holding from 100 to 1,000 or more trays. Whereas the trays were formerly transferred from one location to another during the process of growing, infesting, stinging, 6 and finally production, they are now placed directly in the rooms at the time of 6 'Stinging' is used to denote the introduction of the adult Cryptolaemus in the rooms for oviposition. While the expression is not strictly correct, it has been generally adopted by insectary workers. Bul. 509] Control of Mealybugs Attacking Citrus 29 planting" and remain there throughout the entire process. This method of operation is now in general use in all Cryptolaemus- producing insectaries in California. In these rooms the temperature, humidity, and aeration are care- fully controlled throughout the various stages of the work. When the Cryptolaemus larvae become full grown, suitable material, usually burlap tacked to the face of the trays, is provided as an aid to pupa- tion of the Cryptolaemus. Later, the emerging adults, being strongly phototropic, are collected from cloth-covered windows into containers for field liberation. This, in brief, describes the method of operation. More detailed consideration of the various phases of the work follow in their proper sequence. Planting and Developing the Host Plant. — Early investigations by Smith in connection with the study of the life history of certain parasites of the Baker mealybug indicated that the potato sprout was the most suitable host plant for the latter. In fact, it was this develop- ment that made the operation of the present large-sized insectaries for the propagation of Cryptolaemus at all practical. While numerous other host plants have been and are still being tried, none has yet been found which has the year-round availability of seed potatoes, the adaptability to simple laboratory methods, and the ability to stand the continued abuse of laboratory practices. While the propagation of the potato sprouts is a comparatively simple problem, success is dependent upon close attention to several details, the neglect of any one of which may result in failure. Naturally the first and a very important point to be considered is the selection of the seed tubers. In this respect many varieties which possess a reputation for heavy top growth have been tried and their merits carefully considered. The variety known as British Queen produces an excellent long, succulent, sturdy sprout but seems to retard the development of the mealybugs with which it is infested. California Burbank also produces an excellent sprout, but the mealy- bug will not feed on it satisfactorily. Red Rivers and Bliss Triumphs, the former not readily available on the California market, both red- skinned varieties, have recently been tried by several insectary oper- ators. While both varieties produce an abnormally rapid growth of numerous, large, succulent sprouts, they have exhibited at times a tendency to break down very rapidly under heavy infestation and the necessarily high temperatures required. Their suitability will require more careful investigation. Idaho Rurals produce very usable sprouts but have too few eyes. 30 University of California — Experiment Station The Idaho Russet has met best all of the requirements of laboratory use up to the present time. It is readily available on the open market during the critical nine months' operation period from October 1 to July 1. It comes from a tuber-moth-free area, which is very impor- tant, because this potato pest develops rapidly under insectary con- ditions, often destroying- valuable host material before it can be put to its proper use. The Idaho Russet variety produces an abundance of long, slender, succulent sprouts which are susceptible to easy infes- tation, and it withstands to a marked degree heavy infestation and other necessary insectary abuses. Well-matured, small to medium-sized tubers, averaging 4 to 8 ounces in weight, possessing an abundance of well-formed eyes, are selected for planting. Freedom from cuts and bruises is desirable, since the conditions under which the tubers are placed in the insec- tary make them very susceptible to destructive rots and molds which gain entrance through such injuries. Lots of tubers which show any appreciable percentage of Fusarium wilt are rejected, and as far as possible those affected with scab and particularly Rhizoctonia are avoided. The application of standard treatments for the control of both scab and Rhizoctonia have been carried out with fair success, but generally speaking appear not to justify the labor and expense involved in their use. Some insectary operators dust their tubers with copper-carbonate before planting to prevent the spread of rots in the tray. Though small seed pieces, split tubers, and seed end pieces have all been tried repeatedly in the interest of economy, careful experimen- tation has demonstrated that whole tubers produce better and more hardy sprouts under insectary conditions. Sprouts developed from whole tubers seem less dependent on the medium in which they are being grown and consequently are less seriously affected by the fluc- tuating moisture content of the trays, which may occur under the most careful handling. The whole tubers are planted in a prepared soil medium composed of four parts of light sandy loam to one part of screened dairy manure (fig. 7). The top is then covered with V2 inch of coarse plaster sand, which serves as a mulch, minimizing the danger of drying out and baking under the heated room conditions. Fifteen to eighteen tubers, depending on size, weighing approximately 6 pounds, are required to plant one tray. One thousand trays require 6.2 cubic y'ards of soil, 1.55 cubic yards of dairy manure and 1.55 cubic yards of plaster sand. When operating under average planting conditions, one man Bul. 509] Control of Mealybugs Attacking Citrus 31 can plant 10 trays an hour, including the placing of the trays in the rooms. When planted the trays are placed in the production rooms, usually on well-constructed racks (fig. 8). These racks should be in the form of evenly spaced shelves not less than 12 inches apart. The weight of each filled tray is approximately 38 pounds, and vertical Fig. 7. — Method of planting potatoes in trays. supports must be placed between the shelves for every 3 trays, allow- ance being made for sufficient side clearance between trays so that they may easily be installed or removed. The first tier of trays is never placed directly on the floor but is supported on 1-inch floor strips. Armitag'e has been operating 25,000 trays over a five-year period without the use of racks, by stacking the trays checker-board fashion, 32 University of California — Experiment Station beginning with the floor strips and providing permanent cleat sup- ports on the walls at both ends of the room (fig. 9). A specially con- structed tray is used for this purpose. It has a depth of 6 inches on the ends while the sides are the standard 4 inches in depth. By stacking the trays on the wider ends a 2-inch opening is provided laterally between trays, permitting cross ventilation throughout the entire stack and continued lateral growth of the sprouts from one Fig. 8. — The use of racks for supporting trays. tray to another. The trays are usually staggered 12 high, leaving 2 feet between the top trays and the 8-foot ceiling. Each method of handling has its advantages and either may be used with satisfaction. Where racks are used the trays are more easily placed in position ; poor trays may be easily removed and new ones added ■ and less labor is required to keep the sprouts out of the aisles and within the confines of the racks. Where the stacking method is used all of the host plant or host insect material in the entire lot of trays is directly accessible to the mealybugs or to the feeding Crypt olaemus larvae. This minimizes the danger of cannibalism, which may result from overinfesting individual trays or concentrating Bul. 509] Control of Mealybugs Attacking Citrus 33 Cryptolaemus larvae at points of egress from one shelf to another. Moreover, the cost of constructing- and installing racks is avoided, more trays are handled in the same amount of room space with no loss in production per tray, and at the close of the production period the entire room is emptied, thus greatly facilitating cleaning. Fig. 9. — The checkerboard method of supporting trays. As the detailed construction and arrangement of the rooms will be considered later, it need not be discussed here other than to men- tion that all of the trays in the rooms are directly accessible for such individual care as may be required throughout the various stages of the work. The average period required for developing the potato sprouts to the point where they are ready for infesting with the mealybug is 60 34 University of California — Experiment Station days, or 40 per cent of the total 150-day cycle of operation. However, this period is considerably lengthened during the winter months when the new crop seed tubers are more or less immature, and reduced almost to 30 days in midsummer when fully matured seed from cold storage is used. As the bulk of the planting for early spring production takes place in November and December when only new-crop seed tubers are available, many methods of eliminating or reducing the rest period Fig. 10. — Tray of sprouts ready f( iting. were tried out. Using cut seed pieces, cutting around the eyes, peel- ing between the eyes, dipping in nitrate of soda, solution, injecting ether, dipping in ethylene-chlorhydrin solution, exposure to ethylene gas and many other methods have been tried, but from the commercial standpoint no uniformly beneficial results have been secured. This problem, however, is in need of further study. The sprouts are allowed to develop in subdued light in order to promote longitudinal growth and to limit the formation of chlorophyl, which tends to inhibit the settling down of the mealybugs during the period of infestation (fig. 10). A temperature averaging 65° F and a humidity of approximately 70 per cent is maintained during the growing period. The moisture requirements of the growing sprouts necessitate that the trays be watered at 10-day intervals. Top trays Bul. 509] Control of Mealybugs Attacking Citrus 35 and others directly exposed to ventilators dry out rapidly, and must be watered every 5 days. For this purpose, water is made available in each room and the operation is carried out by the use of an ordinary i^-inch garden hose fitted with a radiator faucet for control at the nozzle end. The nozzle used during- this phase of the work has a fan- shaped, finely perforated outlet. Later this is exchanged for a simple piece of %-inch pipe 12 inches long by which the water may be dis- tributed around the base of the sprouts without disturbing the host insect material with which they are infested (fig. 11). Fig. 11. — Nozzle used for watering sprouts. Fertilizers in many forms have been tried on the growing sprouts and in some cases are being used regularly. Liquid manure is the one most favored, but there seems to be some question as to the value of fertilizers because of the subdued light in the rooms. Considerable labor is saved by incorporating dairy manure in the soil medium several weeks before planting, with benefits equal to the other methods. Other materials, such as sphagnum moss, wood shavings, sawdust, and coarse sand have been used as growing media but with less satis- factory results than with prepared soil mixtures. Tule dirt, a black flocculent material composed of decayed organic matter similar to peat, which produces enormous crops of potatoes in the Sacramento and San Joaquin valleys of California, is being used with excellent results in the insectary at Lodi in San Joaquin County. Should its 36 University of California — Experiment Station general use seem desirable it is readily available in large quantities for the cost of transportation and handling 1 . Armitage has successfully operated rooms using whole tubers in open trays with no growing medium. Twice the number of tubers was required, but a proportionate increase in production was secured, without any increase in equipment or room space. Other advantages of this method of operation were a material decrease in the amount of labor involved in the initial planting and in the subsequent care of the room and the elimination of the frequent waterings with their attendant troubles from overwatering or drying out. In addition, the tuber itself serves as a host of the more mature mealybugs, with the interstices favoring collective oviposition and offering an acceptable place for pupation by the Cryptolaemus. This method, so far as now understood, is limited, however, to late-season use when completely mature seed tubers are available, as otherwise the prolonged period of sprout development makes it unpractical. The development of more effective methods of accelerating sprout growth in new tubers would give this method of host plant culture preference over any other. There are several attendant troubles in the growing of the host- plant material, the more important of which are 'tip-burn' or 'tip- dieback'; damping-off due to Rhizoctonia; aphis, and potato tuber moth. 'Tip-burn,' which affects the sprouts soon after they are out of the ground, produces numerous weak laterals, which in turn are themselves often affected. Its cause has not been determined. It is, however, believed to be entirely physiological and due to a combina- tion of conditions in the rooms, particularly relating to ventilation and humidity. Damping-off is induced by overwatering and slow evaporation, in spite of the fact that each tray is drained through a ^-inch crack through the entire length of its bottom and that care is taken to avoid saturating the soil. Some insectary operators report successful control of damping-off by spraying with Semesan, but in general it may be prevented by avoiding the humid conditions which favor it. This disease usually gains access because of nonelimination of Rhizoctowia- infected seed when planting. It girdles the sprouts at the surface of the soil and if it does not kill them immediately, it so weakens them that they soon succumb to the attack of the mealybug. Aphis sometimes find their way into the rooms on the clothing of the laborers and unless checked in time, serious damage to the sprouts results. Nicotine paper, nicotine dust, and light dosages of hydro- Bul. 509] Control of Mealybugs Attacking Citrus 37 cyanic acid gas give satisfactory control with little or no injury to the sprouts. In fact, the latter treatment has been successfully used with little material injury to the mealybugs on infested sprouts. The potato tuber moth, once established, offers the most serious problem and sometimes causes the total loss of sprouts. Repeated treatments with hydrocyanic acid gas at dosages which will not injure the sprouts may be successfully given during the growing period of the host plant, while later, trapping of the adults is all that can be done without injury to the host-insect material. The best policy is to attempt to prevent their establishment in the rooms. Fig. 12. — Sprouts infested with mealybugs. Growing the Host Insect. — This phase of the work probably requires more individual labor and care than any other operation in the entire process. The species of mealybug to be used is an important consideration. Only two kinds, the common mealybug (Pseudococcus citri) and the citrophilus (P. gahani) are now in use. While the common mealybug has many advantages over the citrophilus in producing host food for the Cryptolaemus in the laboratory, the species used has in some instances obviously been restricted by the absence of one or the other in the locality in which the insectary was established, regardless of its particular adaptability to the work. 38 University op California — Experiment Station The advantages of the common mealybug are its restricted migra- tory habits, it being more inclined to remain on the host even under overinfested conditions; its shorter life cycle under laboratory tem- peratures — two weeks less than that of the citrophilus ; and a possible higher degree of infestation and a consequent increase in available food with less injury to the potato sprouts. Its particular disad- vantage is its susceptibility to attack by the internal parasite, Lepto- mastidea abnormis, which occurs everywhere in the field and is difficult to keep out of the production rooms. This condition is somewhat offset by rapid operation of the room before the parasite can increase greatly. Delay usually results in a serious loss of valuable food material. The citrophilus mealybug is successfully used through necessity in several insectaries. More care to avoid overinfesting is necessary, the sprouts being more adversely and more rapidly affected by the maxi- mum infestation required ; the development to a usable stage is less rapid ; and the mature females have the undesirable trait of migrat- ing away from the host plant for oviposition, which is carried out collectively on the tray edges or corners and in the corners of the rooms. However, it has no important insect enemies in the laboratory to restrict its development. As laboratory production of the beetles must anticipate by several weeks the active period of the mealybug in the field, it is obvious that little host material would be obtainable in the field for laboratory use. An ample supply of mealybugs therefore must be made available in the insectary for evenly infesting the host plant material as it matures. This is a simple matter in those insectaries which operate continuously, for once under way, hatching mealybugs may be removed in sufficient quantities from one room, even though that room is considerably advanced in its production of the Cryptolaemus itself, and transferred to the next room requiring infesting. Where an insectary is being operated on a seasonal basis, as will be discussed later, and the peak production is desired over a short period in the spring, infesting requires the advance preparation of a sufficient number of trays of mealybug-infested host-plant material to meet the insectary needs. In either case infestation of the sprouts is accomplished through the use of temporary host material in small units. For this purpose wild sunflower, cocklebur, Australian pepper, wild tobacco, or mallow are most commonly used in the order of their availability. Up to the present time dependence has been placed on native or wild growth of the plants mentioned, but as the work has increased in scope it has Bul. 509] Control of Mealybugs Attacking Citrus 39 become imperative that a controlled source of supply be developed. Plots of sunflower and a special variety of mallow are being grown for this purpose. In practice the stems or leaves of the selected host material are distributed over the trays of hatching mealybugs, where they are left 6 to 12 hours, depending on the length of time required to infest them completely. These pieces are then collected, and distributed accord- ing to the operator's judgment, over the new trays of sprouts, and the mealybugs allowed to trasfer to the new host as the temporary host dries. The proper degree of infestation for an average tray can be determined only by experience. During this period a constant room temperature of 80° F, or slightly less, and a relative humidity of approximately 70 per cent, is maintained. The requirements of the temporary host material aside from its availability are that it shall retain its moisture a sufficient length of time to permit handling and still be attractive to the mealybug. It is also necessary that it dry rapidly without breaking down, permit- ting the mealybug to transfer to the new host. Some plants such as the wild tobacco, Australian pepper, and mallow must be removed as soon as the mealybugs have left, because these plants tend to develop molds and rots, which are later transmitted to the sprouts. Care must be exercised to avoid bringing aphis into the rooms on the field-collected material, for they easily transfer to the sprouts. Egg masses of the citrophilus mealybug are sometimes available in the orchard later in the season, for use in infesting the sprouts. Masses may be scraped from the trunks of infested trees or they may be secured from the trunk trap bands. Such material is always placed in closed cloth or perforated paper sacks which will permit the egress of the hatching mealybugs and not the insect enemies present. If the latter are permitted to escape into the room they will prac- tically destroy the host insect material before it is ready for use. In an effort to reduce the labor involved in the preceding method of infesting, which requires the use of five to ten pieces of host mate- rial per tray, handled three or four times, Armitage attempted during the past season to develop the necessary mealybug on the host-plant material during the latter 's growing period, using the citrophilus species. It was estimated that the progeny of 1,000 adult mealybugs were required to infest an average tray of potato sprouts to the desired degree. The labor of infesting was then reduced to placing the equiva- lent of 1,000 adult mealybugs, in this case approximately 2,000 newly hatched mealybugs, on each tray as soon as the average length of 40 University of California — Experiment Station sprouts had reached one inch. These mealybugs were allowed to pass through one generation without perceptible injury to the host while the latter was developing. The progeny of this generation automat- ically infested the maturing sprouts to the desired degree. Some difficulty was experienced because of a variation of several degrees in temperature between the top and bottom of the room. This condition permitted a more rapid development of the mealybugs in the top trays and created an undesirable off-stage development throughout the room. In spite of the extra labor necessary to correct this con- dition, the 3,000 labor-hours required to infest an equal number of trays in the old manner was reduced to less than 500 hours. A method of heating the rooms more uniformly than those now in use would make this process entirely practical. Estimation of the amount of infested material necessary to infest completely a given number of trays is a difficult matter. When spe- cially prepared for that purpose, one tray will, within the margin of safety, produce sufficient material to infest 25 trays. Under the newly suggested method of preinfesting the sprouts one tray will take care of approximately 100 to 125 trays. When infesting is accomplished by transferring from one room to the next, labor is the only item requiring consideration. Approximately 100 labor hours per 1,000 trays are required to carry out the necessary operations connected with completely infesting mature sprouts by the method now in general use. The elapsed time between date of infestation with newly hatched mealybugs and the introduction of the Cryptolaemus adults to start production varies with the species of mealybug used. Those operators who use the common mealybug have found the development of this species so rapid that the Cryptolaemus must be introduced not later than two weeks after date of infestation, otherwise the mealybug will pass through to the egg stage, hatch, and the young succumb from a lack of food and thus be lost before the Cryptolaemus larvae have completed their feeding. A premature hatch and migrating indi- viduals are held temporarily by introducing quantities of fresh sun- flower, cocklebur, rhubarb, or other suitable plant material. When the citrophilus mealybug is used, the appearance of the males in quantity in the room, which occurs approximately 30 days after infesting, is an index of the time for introducing the Cryptolaemus. Growing the Cryptolaemus. — In addition to producing the mealy- bug in the insectary for infesting purposes and for food, it is neces- sary to arrange for a pre-production of Cryptolaemus adults so timed Bul. 509] Control of Mealybugs Attacking Citrus 41 as to be available for use in propagation. Twenty-five adult beetles are required to 'sting"' each tray of infested sprouts. It has been determined that the food available in one tray will mature the progeny of that many adults. A standard room of 360 trays therefore requires 9,000 beetles. These beetles are allowed to remain in the production rooms an average of 18 trays, after which the living beetles remaining, about 50 per cent of the total, are removed, mixed with other stock, and used in a second room for the same purpose. According to Brani- gan 7 the full oviposition period of Crypt olaemus is six weeks, with the majority of the eggs being deposited during the third and fourth weeks. Inability to determine the age of the stock used and the fact that the beetles have not completed their oviposition during the 18 days warrants their reuse. The use of a large number of beetles over a short oviposition period is desirable in order that the larvae may be of relatively uniform age. Otherwise, under the crowded condition in the rooms, cannibalism is stimulated, the older larvae feeding on the younger and later the larvae feeding on the pupating individuals. In introducing the beetles the required number are placed directly in each tray. Subdued light tends to maintain this even distribution and experience has shown that under a constant temperature of 80° F and a relative humidity of approximately 70 per cent, oviposition will occur uniformly throughout the rooms. There is, however, an advanced development of the larvae in the upper trays where the temperature is several degrees higher than at the floor, particularly when an individual room heater is used. This condition is being successfully offset by introducing the heat into the rooms through a series of floor radiators where heat under forced draft is used, or through a net-work of pipes distributed over the floor where hot water is used. Burlap strips 5 inches wide are provided along the face of the trays and on the wall back of the trays (fig. 13), either laterally or vertically, to which the maturing larvae crawl and attach themselves for pupation. Freshly oiled surfaces have also been found attractive to pupating larvae, particularly where boiled linseed oil has been used as a tray preservative. 8 Its general use for that purpose is however not recommended at this time, as there has been some evidence of mortality of pupae because of it. The larval feeding period under laboratory conditions is 12 to 20 days and the pupation period is 8 to 12 days. The emerging adults 7 Unpublished notes. 8 Howard B. Sheldon. Unpublished notes. 42 University of California — Experiment Station are attracted by light to a cloth-covered window at one end of the room from which they are collected by hand in containers of 10 adults each, ready for liberation in the field. Production starts approximately two weeks after the parent stock has been removed and reaches a peak in about 25 days. The collections Fig. 13. — The placing of burlap strips for pupation of Cryptolaemus. are largely completed in 45 days. If the room is not needed for replanting it will continue to produce a few hundred beetles a day for some time, but generally the rooms are cleaned out as soon as the greater part of the expected production has been secured. Each tray planted will produce an average minimum of 400 adult beetles, though production not uncommonly reaches from 700 to 1,000 adults per tray. Bul. 509] Control of Mealybugs Attacking Citrus 43 METHOD OF HANDLING BEETLES The enormously increased production of the present-day insec- taries has made imperative the selection of an inexpensive nonbreak- able container, for use in transporting" the adult beetles from the insectary to the field. As a result, the gelatine capsule has replaced the glass vial of earlier days, eliminating breakage, bulk, necessity of washing after use, cloth caps, rubber bands, shredded paper, etc., and supplying a container much more easily handled at a fraction of the cost of the vial. The general practice of liberating the beetles in colonies of ten adults each has determined the size of the container and a 'OOO' standard, medicinal gelatine capsule, % inch in diameter and 1 inch in length is most commonly used for this purpose. Such containers can be purchased through any wholesale drug house as low as $2.25 per 1,000 in lots of 100,000 or $1.25 per 1,000 in lots of 1,000,000. Where liberating practices make it possible these containers may be used five or six times. In fact they are more easily handled after becoming glazed and hardened from use. They become brittle, how- ever, and are gradually discarded. It has been found that under cool conditions the adult Cryptolae- rrms can be kept in these containers without food and without other air than that admitted through the joint in the capsule for 5 to 7 days with little or no mortality. Perforated capsules show no extension of the 'no-mortality' period. Some beetles have been kept experi- mentally for 14 days with only 10 per cent mortality. In general practice, however, the beetles are liberated within 48 hours after col- lecting, or 72 hours at the most, so that there is no loss in handling. The small size of these containers makes it possible to handle con- veniently many thousands of insects at one time. In both collecting and liberating, a small apron made of strong serviceable cloth and divided into two conveniently deep pockets is used. In collecting, the empty capsules are carried in the left-hand pocket and when filled are returned to the right hand pocket. When liberating, the filled capsules are carried on the left and the empty container either dis- carded, if badly worn, or recapped and returned to the right-hand pocket for reuse. For convenience in determining the number of beetles liberated in an individual property, the capsules are put up in perforated paper sacks, in multiples of one hundred. A 1-pound sack will con- 44 University of California — Experiment Station veniently hold 100 capsules, slightly more than sufficient for one acre of citrus trees. Collecting in the Insectary. — Collecting the adult beetles, 10 to a container, from the cloth-covered windows of the production rooms at a temperature of 80° F presents probably the biggest labor problem in connection with the work, and there is opportunity for the develop- ment of methods or machinery which will speed up this phase of the operation without sacrificing accuracy of count. Several methods are being experimented with at the present time but none has been developed to a practical stage. At present, collecting is being carried out by hand. There is one authentic record of a collector at the Orange County insectary who collected 48,000 beetles in 8 hours or 6,000 an hour. This record was made under ideal conditions with the collecting screens well covered with insects at all times. There are a few records above 30,000 for 8 hours under similar conditions and many over 20,000. However, the season average on which the necessary labor for collecting is estimated and which includes collecting from both lightly and heavily pro- ducing rooms, is 2,000 an hour. Liberating in the Field. — In some counties the beetles are turned over to the growers by the insectary operator on presentation of a written recommendation from the District Agricultural Inspector as to the number necessary, and the grower is permitted to make the liberation on his own property. In other cases where liberations are at a distance and for use on infested ornamentals in house yards the capsules are placed in pasteboard mailing tubes with screw tops and mailed special delivery, bearing a prominent label advising the carrier that the contents of the package are live beneficial insects and should be kept from extreme heat or cold. Such material has usually gone through with no mortality among the beetles. Liberations are also made direct by insectary employees in many of the infested districts. The systematic liberation of a fixed number of beetles on each tree in the infested orchard makes possible the use of a liberation crew of ordinary laborers under competent supervision. In practice, each member of the crew carries from 3,000 to 5,000 beetles, depending on the size of the property. Each man covers two rows of trees on each trip across the property. Citrus trees as a whole are usually rather heavily foliated but it is always possible to find an opening leading into the center of the tree. In liberating, each tree is approached and the contents of a single capsule, 10 beetles, thrown through such an opening into the center Bul. 509] Control of Mealybugs Attacking Citrus 45 of the tree. The beetles leave the capsules like so much shot but within 12 to 18 inches suddenly take wing, striking- and lighting on the inside branches of the trees. In this way it is possible to main- tain equal distribution, at least until the liberation is completed. If liberated in the open row, many beetles fly straight up for 10 or 15 feet and then scatter out over several rows or even further to adja- cent properties, with the result that distribution bears no direct relation to the area being covered. Under average field conditions, allowing for transportation of the crew and including the necessary time used in advising the grower, liberations average 4,000 beetles per man-hour. From the figures given in the preceding paragraph it will be seen that for each two men used in the laboratory in collecting one man is required in the field in making liberations. Liberation of Crypt olaemiis Larvae Not Satisfactory. — Early in the work the question of liberating Crypt olaemus in the larval stage rather than in the adult came under careful consideration. It was thought that by so doing, time might be saved in the production of the insects and that the necessity of producing sufficient food in the insectary to mature such larvae might be eliminated. However, the experimental liberation of 200,000 insect ary-gr own larvae over a 40-acre block of infested citrus trees, using varying numbers up to 200 per tree, but mostly 50 per tree, indicated such a practice to be inadvisable. The immediate mortality of the larvae was high, owing partly to handling and partly to cannibalism in the containers while transporting them to the field. There was also evi- dence that the cool temperatures in the field at the time of this experi- ment retarded considerably the activity of the larvae. While the cost of producing larvae is much less than that of adults, the cost of libera- tions, if properly made, combined with the apparently increased num- ber required per tree and the high mortality, more than offset any advantage gained in handling that stage. Larvae are necessarily one-third to half grown before they can be successfully collected in the laboratory, thus materially limiting their short feeding period in that stage in the field. It has been contended that in the case of light infestation, the placing of the Crypt olaemus on the tree in the larval stage would force them to hunt out the mealy- bugs. While it is true that they would be forced to remain on the tree on which they were placed, the chance of their finding the scat- tered mealybugs would be small owing to the enormous amount of twig and foliage area to be covered in their search. Liberated adults 46 University of California — Experiment Station will place their eggs in close proximity to the mealybugs so that the newly hatched larvae can easily find them. It would not be practical to place the individual larvae in similar positions. Therefore, with our present understanding of larval liberations, they have not been continued. Number of Crypiolaemus Liberated Per Tree. — Prior to the recent development of improved methods, permitting mass production of Cryptolaemics at low cost, it was felt that the activities of an insec- tary were necessarily limited to the placing of a colony of Crypto- laemus on each tree throughout the various infested properties and that further than that, provided such liberations were favorably made in relation to seasonal and mealybug conditions, laboratory production could not economically compete with natural reproduction in the field. At that time the immediate demands of a large infested acreage required that some minimum number of beetles per tree be decided upon in order to permit the equitable distribution of the material available. This number was therefore arbitrarily set at 10 adults per tree. While some insectary operators attempted to place the beetles only on trees which actual inspection showed to be infested and to vary the number liberated according to their idea of the severity of the infestation, it has been general practice to use the number stated. It was also felt that under this plan, while beetles might often be placed on trees on which there were no mealybugs, their instinct would lead them to redistribute themselves over adja- cent trees much more efficiently than could the operator. It was obvious that control in any except possibly the extremely light infestations would not result from the direct feeding of the liberated adults or even from their immediate progeny. Field experi- ence has since indicated that under this method, increase to controlling numbers is reached in the larvae of the second generation, which in early spring requires a minimum of 90 days and during the warmer summer months a minimum of 60 days. In light and medium infestations, which normally represent 90 per cent of the total infestations, this method has permitted satisfac- tory control before serious injury to the host plant has resulted. In the other 10 per cent representing heavy infestation, reaching a peak in the middle of May, with the period of activity of the Cryptolaemus starting about April 1, serious losses have sometimes occurred. This is apparently because there was insufficient time for the liberated beetles to increase to controlling numbers before the peak infestation was reached. Bul. 509] Control of Mealybugs Attacking Citrus 47 In order to offset this condition, and with present laboratory pro- duction making much heavier liberations possible, experiments are being conducted by the Citrus Experiment Station and by several insectary operators to determine just what number of adults per tree is required to secure control from the feeding" of their immediate progeny. It is assumed that a definite number of Crypiolaemus larvae are necessary to clean up a heavy infestation. This number is not attained until the second generation larvae are produced, when the liberations are limited to 10 adults per tree and there is no appreciable winter carryover of Crypiolaemus. As previously stated, this takes a period of 90 days in the spring, but where the infestation is very heavy to start with, serious damage has occasionally resulted before this 90-day period has elapsed. It seems logical, therefore, that this condition might be remedied by stocking such groves with considerably larger Crypiolaemus populations in the spring, so that this controlling num- ber, whatever it is, would be reached earlier in the season. If these assumptions are correct it would be necessary to liberate in the groves in the spring a number of adult Crypiolaemus equal to the adults which produce in one generation the controlling number of larvae. Just what this number is will have to be determined by grove experiments on a considerable scale. It may be estimated by assuming that the actual rate of increase in the field is the same as that in the insectary. Since the minimum increase in a well-operated insectary is approximately sixteen fold, a liberation of 10 adults per tree would result in the production of 160 adults per tree in the next generation; therefore 160 would theoretically be the number necessary to produce in one generation the number of larvae required to reduce the infesta- tion before damage occurs. It would be entirely practical to colonize this number of Crypiolaemus in the heavily infested orchards if injury can be avoided by this procedure, since usually less than 10 per cent of the infestations grade heavy. Liberations of 30, 50, and 100 adults per tree have been made experimentally by some insectary operators without appreciably advancing the date of control. During the 1928 season Armitage followed a liberation program using 30 beetles per tree liberated in lots of 10 adults each at 10-day intervals, on all heavy infestations, 20 per tree in a similar manner on all medium infestations and 10 per tree on all light infestations. No difference in the date of control was observed over previous years' liberations of 10 adults per tree regard- less of degree of infestation. 48 University of California — Experiment Station While it has been generaly recognized that there is often a winter carryover of adult Cryptolaemus, no effort has been made to deter- mine the extent of this in the individual property, as it was thought advisable, unless the carryover was obviously very heavy, to disregard this point. Unquestionably any appreciable winter carryover mate- rially assists in early control. It may be that this carryover is of more importance than has been generally assumed, and work is now in progress to determine exactly what relation it has to the total num- ber of Cryptolaemus required for satisfactory control. Timing Field Liberations. — Whether field liberations of Crypto- laemus should be carried out continuously throughout the year or whether they should be confined to an optimum period based on sea- sonal development is open to more detailed investigation. The limiting of liberations to the optimum period requires comparatively greater insectary space and production equipment for a given acreage, and the expense and labor per insect are somewhat higher. Under this plan, however, the liberations are made at a season when all conditions are at an optimum for the work of the beetles, resulting in greater efficiency per beetle produced. The system of confining the liberations largely to an optimum period in the spring seems best adapted, in general, to those districts in which the Cryptolaemus are paid for directly by the grower in whose orchard they are used. The system of continual liberations throughout the year, however, has been successfully carried out, par- ticularly under county government support, where the expense is pooled so as not to be a burden for any individual. Under either method, both of which are being successfully prac- ticed, it is generally agreed among insectary operators that a peak production of Cryptolaemus available for field liberations during the spring months is desirable, with a second lighter peak production in late summer to permit the re-covering of infested properties in which necessary mechanical treatment for other pests may have interfered with the completion of control. The time of making the initial liberations is correlated with the seasonal development of the mealybug, the earliest date at which minimum daily temperatures permitting Cryptolaemus activity occur, and the avoidance of any conditions such as heavy rainfall, which might restrict their continuous activity during the control period. For later liberations the proximity to the period of control measures for other pests should be kept in mind ; it is necessary that there should be sufficient time after such liberations to permit unrestricted Bul. 509] Control of Mealybugs Attacking Citrus 49 natural increase through one or more generations, depending on the severity of the infestation. The citrophilus mealybug normally reaches a seasonal peak, in the heavier infestations, in May. Average weather records, and minimum activity temperature (70° F) for the Cryptolaemus as determined from experience in the insectary, indicate April 1 as the beginning of an uninterrupted period for their field activity. April 1 also marks the beginning of a period of several months of decreasing to minimum rainfall, favoring the undisturbed activity of the Cryptolaemus. Certain mechanical control measures for other pests may seriously interfere with the work of the beetles, and where the time of appli- cation of these is known beforehand, liberations should be made suffi- ciently in advance to permit the beetles to reach controlling numbers before other treatment is applied, or they may be withheld until after such treatment. Cryptolaemus have been recorded as being reproductively active as late as September 1, though generally speaking very few larvae are observed in the field after that time. Therefore, that date would mark the close of the liberation season insofar as immediate control through field increase can be expected. Where the operations of an insectary make such a procedure permissible, liberations may be continued until December 1 for the purpose of establishing a field population which, owing to the ability of the adult Cryptolaemus to carry over several weeks of cool weather, might assist in early-season control before the spring laboratory production is available for distribution. Inasmuch as it takes three to five months to bring an insectary to peak production, it is impossible to take advantage of any unexpected early favorable field conditions; therefore, the production should be arranged for the time when average records indicate that such field conditions will be favorable. The period for liberations, therefore, lies between April 1 and Sep- tember 1 with pre- and post-season liberations permissible, where laboratory operations make it possible, either to take advantage of unexpected early favorable field temperatures or to build up an over- wintering population which in itself might take advantage of such conditions. Determining the Sequence of Liberations. — Obviously it would not be practical to attempt to cover all infestations of mealybug with Cryptolaemus anywhere near simultaneously where large acreages are involved. The optimum period for making liberations is April, May, and June, and the bulk of the laboratory production can be 50 University of California — Experiment Station arranged to occur during those three months. In order to allocate the beetles to the best advantage it therefore becomes advisable to grade all infestations immediately before the liberation period. With this in mind it has become an established practice in all dis- tricts to carry out an annual spring survey, giving to each infested property a grading designating the degree of infestation. The desig- nations in most common use are 'T' or trace, No. 1 or light, No. 2 or medium, and No. 3 or heavy. Where a more detailed definition of the condition in the orchard is desired the additional symbols of 'H' for heavy and 'L' for light are used to indicate the variation within each grading. In defining these grades experienced inspectors versed in the seasonal relationship between the host plant, the insect pest, and its enemies would class as a No. 1 or light infestation one which would not become an economic problem during the season, one which would in fact require little additional attention during that period ; as a No. 2 or medium infestation, one which would require the liberation of Cryptolaemus not later than June in order to check its increase to damaging numbers during the season; and as a No. 3 or heavy infes- tation, one which would unquestionably require early an,d careful attention in order to prevent serious loss. In some of the larger districts where inexperienced inspectors are used and inspections are carried out during the period of oviposition by the citrophilus mealybug, the trunk trap band is used as an indi- cator of the degree of infestation. Roughly 1 to 50 adult mealybugs or egg masses in the band is considered a ' light ' infestation ; 50 to 100 a * medium infestation and over 100 a 'heavy' infestation. It will be readily seen that there may be a wide range in degree in the * heavy ' infestations ; for the adult mealybugs or egg masses may number from 100 to several thousands, as they not uncommonly do. Other methods of grading are under consideration but have not as yet reached a stage to justify their general use. After the determination of the degree of infestation, liberations are carried out in the order of their severity, the 'heavy' infestations being covered first, the 'medium' infestations next, and lastly such of those 'light' infestations as may on second inspection show such liberations to be advisable. Records of annual inspections covering several thousand acres of citrus in Los Angeles County over a five-year period show that an average of 8 per cent of the recorded infested acreage will grade 'heavy' each year, 14 per cent 'medium' and the balance or 78 per Bul. 509] Control of Mealybugs Attacking Citrus 51 cent 'light.' All 'heavy' and 'medium' infestations must be covered with Cryptolaemus each season, and having* determined by experience that 60 per cent of the 'light' infestations can be covered to advan- tage, it is not a difficult matter to estimate in advance the seasonal Cryptolaemus requirements. To this estimate must be added the average annual increase in infested acreage which may occur through natural spread. This is a variable factor having a direct relation to the area concerned. It has been found that the movements of the Cryptolaemus adults away from the areas of liberation will normally take care of the uncovered balance of the light infestations each season. TRUNK BANDING AS AN AID TO CONTROL The adult female citrophilus mealybug has a characteristic habit of migrating to the tree trunks for the purpose of oviposition and in so doing seeks out crevices, old wounds, scaly bark, and other pro- tected places. This led to the early practice 9 of installing trap bands on or near the trunk with the original intention of using them as part of the program of mechanical control. It was thought that satisfac- tory control might be secured by removing and destroying these bands together with their contents at a certain stage in the development of the peak spring generation, at the same time washing or spraying the trunk and main branches of the trees from which they were removed with a heavy stream under pressure. It soon developed, however, that sufficient mealybugs remained in the fruit clusters and bark crevices in the upper and outer parts of the tree to reinfest the tree to a serious degree. It was also later found that while this practice might have had some value in reducing the degree of infestation in the interior areas where a single, short period of migration of females occurred, in the coast areas an almost continuous migration throughout the greater part of the spring and summer months, requiring repeated trunk treatments, made this work unpractical. In this connection an unforeseen value of trap bands appeared which has since played an important part in the successful applica- tion of the biological method of mealybug control. It was observed that the larvae of Cryptolaemus as well as many of the native natural enemies of the mealybug, such as the lacewings and native ladybird beetles, showed a marked preference for the underside of such bands as a protected place in which to pass through their transformation E. J. Branigan, unpublished notes, 1916. 52 University of California — Experiment Station periods. In the absence of such trap bands the larger percentage of the larvae were forced to pupate either in the open on the trunk, in the few curled dried leaves which might lodge in the trees, or, in the main, in the dried leaves on the ground. In the latter case they were subjected to the attack of many omnivorous species of predaceous ground beetles or to the injurious effects of cultural operations. These conditions naturally produced a rather high mortality. Under the trap bands they are well protected and it has been proved that when the bands are properly installed and properly cared for, an extremely high percentage of emergence results, to the immediate benefit of the control work. Other benefits derived from the use of these bands were also noted. They were found to have a tendency to concentrate the mealybug, particularly in light infestations, where they were attractive to their natural enemies. This greatly facilitated the establishment of the latter. An equal number of mealybugs distributed over the tree is not, in many cases, attractive to Cryptolaemiis and the adult beetles will fly away from the trees on which they are placed, in search of more abundant food. Bands have also been found to serve as an excellent guide in determining the degree of infestation prior to mak- ing Cryptolaemiis liberations and to serve as an index of the progress being made in the control. The evidence so far indicates that some type of trunk band is of value in the Cryptolaemiis work. Therefore, their use has been recommended and in general their installation and subsequent care has been carried out by practically all owners of infested citrus orchards in southern California. Several methods of installing traps have been put into effect by the growers. Old newspapers crushed together and loosely crowded into the crown branches have been used in many cases. Some growers have been unable to resist the temptation to burn the accumulated mealybugs, in the hope of hastening control. Experience has shown that these mealybugs will ultimately serve as the necessary food to hasten the increase of the natural enemies to controlling numbers. Similarly a cheap grade of wrapping burlap, cut into strips 4 or 5 inches wide and 36 inches long, pushed together accordion fashion and crowded loosely into the crown branches of infested trees is in use in many districts. In either of the preceding methods, however, careless crowding of the material produces many crevices into which the mealybug may crawl, but which the larger natural enemies cannot penetrate. If the larvae of the latter do enter, it may restrict their Bul. 509] Control of Mealybugs Attacking Citrus 53 feeding and eventually prevent the escape of emerging- adults from the pupal cases of trapped insects. In the case of the burlap the adult Crypt olaemus may also deposit eggs through the material into the crevices from which the larvae may never escape. Under such conditions the trap material might do more harm than good. Wadded material in the crowns when it becomes wet from rain or heavy fogs Fig. 14. — Citrophilus mealybug congregating under burlap trap band for oviposition. is many days drying out, sometimes becoming moldy and repellent to both the mealybug and the natural enemies. The method preferred by us at present, and one which has been in general practice over a large acreage since the inception of the work, consists of a single wrap of a cheap grade of wrapping burlap, cut into narrow bands, placed around the main trunk well up under the main branches. It should be sufficiently loose so that the four fingers of the hand may be inserted between the band and the trunk. While clean burlap sacks may be cut into the proper width bands 54 University of California — Experiment Station and used satisfactorily, the purchase of 7-ounce wrapping- burlap 42 inches wide in 100-yard bolts, cut with a power cutter into 5-inch widths is recommended. The present market price of such material is 10 cents a yard in the bolt with 50 cents a bolt additional for cut- ting ; a 100-yard bolt 42 inches wide will make eight skeins 100 yards long and 5 inches wide or 800 yards of banding material sufficient to band 1,000 average-sized trees at a cost slightly over 1 cent a tree for material. In installing" bands the skein is carried into the orchard entire. It should never be cut to length in advance because of a general tendency to underestimate the circumference of the tree trunks, thus wasting considerable material. A 6-d finishing nail is first driven slightly downward into the trunk and well up under the main branches. The banding material is hooked over the nail approximately 1 inch from the upper edge of the band, leaving 6 inches of surplus material to allow for later shrinkage, passed loosely around the trunk once, again hooked over the nail, and cut approximately 1 inch beyond. The surplus material should always be against the tree for if on the outer end of the band, it will act as a flag, allowing- a heavy breeze to unfasten the band from the nail. Tacks should never be used in installing bands, nor should the nails be folded over or driven into the trunk farther than sufficient to hold them firmly. The bands should be so installed as to permit easy removal for loosening, replac- ing, or frequent inspection, The driving of nails into citrus trees has never been known to cause any injury. An average laborer should install 50 bands an hour at a cost of 50 cents an hour or 1 cent per band, making the total cost of installation for materials and labor approximately 2 cents a tree. The bands may be subsequently cared for in the course of general orchard opera- tions and at a nominal expense for labor. Installed in the described manner, bands are always accessible for the necessary inspections. Once installed, bands should be considered as permanent equipment in the orchard. The material shrinks rapidly and care should be taken to see that they are loosened at least once in the spring- and again in the fall. New material will last two years, preferably being- replaced in the spring of the second year. The old band should be hung over a limb to permit the escape of overwinter- ing natural enemies. Dirty bands containing the remains of a heavy infestation of mealybugs may be profitably reversed the second year, for both the mealybug and the Cryptolaemus seem to prefer a clean band. Bul. 509] Control of Mealybugs Attacking Citrus 55 The advantages of the band as recommended lie in the following facts : The band is installed at the one point on the tree where it is in the path of all migrating 1 mealybugs and Cryptolaemus larvae ; the single loose wrap dries within a very few hours after becoming wet, and is never moldy. It offers few crevices in which the mealybugs may be protected from the Cryptolaemus or in which the latter may become trapped during its immature stages. Recently a promising new banding material, in the form of a corrugated paper for which the Cryptolaemus larvae have indicated an exceptional preference, has been tried out by Armitage. These paper bands are cut and installed much the same as the burlap, the material being cut so that the corrugations are vertical when the band is applied to the tree. While paper bands are more bulky to handle, last only one season, and cost slightly more, their apparent greater efficiency in maturing larger numbers of Cryptolaemus larvae makes their use worthy of further investigation. Properly installed and properly cared for, any type of trap band is of value, but otherwise may actually retard control and favor the infestation by protecting the mealybug from its natural enemies, or by permanently trapping the latter. RELATION OF ANTS TO MEALYBUG CONTROL The relation of ants, particularly of honey-feeding ants, to bio- logical control has been discussed so often that it needs no more than a brief mention here. Ants seem immediately to sense the presence of any insect, either parasite or predator, which is inimical to their interests. When an adult Cryptolaemus alights on an infested tree, its wings are frequently seized by ants before they can be withdrawn under the protective elytra. The beetles are then destroyed by the ants, or if released, they immediately seek safety in flight from the infested area where they are needed. In a like manner parasites are not allowed to rest long enough to search for a suitable host, but are kept continuously on the move. The ants are more aggressive in pro- tecting a light infestation than a heavy one where an abundance of natural food seems to give them a sense of security. While it is not impossible to establish Cryptolaemus or to secure ultimate control of the mealybug by using Cryptolaemus where ants are active, establishment and control are often delayed to such an extent that serious damage to the host plant results. 56 University of California — Experiment Station The Argentine ant (Iridomyrmex humilis Mayr) is without ques- tion the most aggressive and widely distributed ant in the citrus areas of California. Anticipating later trouble from ants when using Cryptolaemus in mealybug control, intensive eradication campaigns are being conducted (Ryan, 1928) over large areas. This work is conducted cooperatively by the citrus growers or under the direct supervision of the county agricultural officials, the cost being borne by the growers through their district organizations. Detailed surveys are made each spring and fall and freshly prepared arsenical syrup is maintained on all infested trees in the control area over the period necessary to secure eradication, sometimes three years. In a similar manner intervening cities have cooperated by instituting city-wide control at city cost. Present application of the poison syrup is by means of either leak-proof paraffin paper cups or pressed aluminum cups, holding 2 ounces of syrup when about two-thirds filled. They are attached to the tree trunks by means of a specially designed bracket, or by hang- ing on a finishing nail driven into the tree. The paper cups offer an inexpensive method of applying the poison and when empty may be replaced with new containers. The aluminum cups cost a little more but may be washed and refilled at an appreciable saving over the paper cups. Care must be taken with any container to prevent leak- age, because severe cases of gumming have been caused by the syrup coming into contact with the bark. This intensive ant-control work is definitely favoring the biological control of the mealybug and is an important factor in its application. Species of native ants, particularly the large gray ant, (Formica cinerea Mayr), the small black ant (Prenolepis imparls Say), and the bicolor ant (Dorymyrmex pyramiciis var. bicolor Wheeler), also require attention and in some cases have been successfully controlled by increasing the arsenical content in the government formula for the poison syrup. There remains some work to be done, however, in developing a more satisfactory method of controlling these species, and this is now being undertaken by the Citrus Experiment Station. Bul. 509] Control of Mealybugs Attacking Citrus 57 EFFECT OF SPRAYING AND FUMIGATION ON BIOLOGICAL CONTROL It is unfortunate from the standpoint of the biological control of mealybugs that it is often necessary to resort to fumigation or spray- ing for the control of other serious insect pests in the orchard, for without question such measures seriously disturb the activities of Cryptolaemus. This is particularly true of the annual late summer and fall treatments for black scale, which in many instances must be applied at a time when the Cryptolaemus are reaching controlling numbers. In all cases, however, it is recommended that such treat- ments should never be omitted in order to protect the Cryptolaemus; for it is much easier to reintroduce the latter than to recondition a grove which has been allowed to suffer from the attack of some other uncontrolled pest. Fumigation probably results in more direct killing of the Crypto- laemus than do sprays. When oil or sulfur sprays are applied they seem to have a repellent effect against the adult. The larvae, having the same waxy covering as the mealybugs, seem in part to be able to throw off the materials without permitting a killing penetration. But the adults, having the power of flight, seem to leave the orchard imme- diately after treatment is applied. In fact, experience has indicated that it is inadvisable to attempt to establish the Cryptolaemus sooner than two weeks after such materials have been applied, as the adult beetles apparently refuse to remain on the trees if liberated at an earlier date. Incidentally, by temporarily reducing the mealybugs by spraying, a general exodus of adult Cryptolaemus in search of heavier infestations takes place. As a consequence, the few remaining mealy- bugs are permitted to build up again undisturbed, and the infesta- tion sometimes reaches a serious degree before the Cryptolaemus become reestablished. Where the insectary operator is informed by the grower of such necessary interference with the work of the beetles, he can usually check any serious increase in the mealybug by releasing additional beetles as soon as the fumes from the material have dissipated. As previously stated, fumigation seems to give a more direct kill of the Cryptolaemus, though it is by no means complete. While mak- ing field checks during fumigation operations, it was observed by Armitage that many adult beetles were apparently dropped to the 58 University of California — Experiment Station ground by the first shock of the gas, where they were exposed to a lower concentration, and as a consequence many escaped death. So far as observed, those adults which happened to lodge in the tree where they were exposed to the full concentration of gas over the entire period were all killed. In the case of the larvae, their usual position of feeding in the clusters of mealybugs was such that the greater portion of them remained in the tree where they were sub- jected to the full exposure of gas, which accounts in part for the rela- tively high mortality in this stage as compared with adults. Later it was found that many of the live larvae, which at first were thought to have escaped the gas through some inherent resistance, had, instead, migrated up into the tree from the dried curled leaves on the ground underneath, where they had been feeding on eggs deposited in a similar position by the mealybugs. Definite checks of the actual mortality among adults during fumi- gation were made by spreading" a canvas sheet under a tree prior to treatment and immediately collecting and counting- all beetles which were dropped by the gas. The beetles collected from under each tree were then spread out on a paper plate in such a manner that no later mortality would result from the absorbed gas of the mass and left under the tree on the ground, carefully protected from any outward disturbance. Twelve and 24 hours later they were carefully rechecked to determine the number recovering from the effects of the gas. In general they were observed to leave the plates as soon as they had fully recovered. In making these checks it was revealed that careful collecting with a hand screen (fig. 15) within the limits of reach on the tree would account for about one-fourth to one-sixth of the total Crypt olaemus adult population present. For example, the screen check of 97 per tree, with an average collection after fumigation of 414, would indi- cate a one to four ratio. This factor may be used to advantage in checking Crypt olaemus populations to determine the winter carry- over of adults, for any other purpose. The following is representative of several mortality checks made. Large Valencia orange trees at Rivera, California, were fumigated for purple scale, using- an 88 per cent schedule liquid HCN for one hour. Mealybug control had been completed. A hand-screen check ahead of fumigation indicated an average total of 388 adult Crypto- laemus per tree using the 1 to 4 ratio. A similar screen check on the following day, of trees treated the preceding night, indicated an average total of 100 live adult beetles per tree. Bul. 509] Control of Mealybugs Attacking Citrus 59 After the fumigation, which took place on September 26 and 27, the Cryptolaemus were collected under eleven trees. A total of 4,558 beetles was obtained. Of these 63.1 per cent were dead, and 36.9 per cent recovered. The average number of Cryptolaemus per tree was 414. Fig. 15. — Method of collecting Cryptolaemus for population data. It is evident from the figures that mortality is far from complete, though sufficient to interfere seriously with control if not completed prior to treatment. As this grove consisted of 10 acres averaging 80 trees per acre or 800 trees, the average population per tree of 414 adults indicated a total population of 331,200 adult Cryptolaemus in the orchard. BUILDINGS AND EQUIPMENT Almost any building which can be divided into rooms, each having an outside window or windows exposed to direct light, can be success- fully operated as an insectary for the production of Cryptolaemus. However, economy of labor in handling the thousands of trays neces- 60 University of California — Experiment Station sary to operate the larger insectaries suggests the desirability of a definite floor plan. Size of Rooms. — The first consideration is the size of room to be used. Rooms varying in tray capacity from 120 to 1,000 trays have been operated successfully. However, experience has shown that a small room is desirable for the reason thai it is much easier to infest Fig. 16. — Plan A, small production room, 8 by 12 by 7 feet. a small number of trays to an even degree, both from the standpoint of available infesting material, and from the standpoint of the amount of labor required to complete properly this part of the work. Also, should any phase of the work fail from some uncontrollable cause, as sometimes happens, less material would be lost in the smaller unit. Two suggested floor plans of rooms are offered here, either one of which, with slight variation, should meet average Crypt olaemus- production requirements. Bul. 509] Control of Mealybugs Attacking Citrus 61 For the smaller insectary, plan A (fig. 16) is suggested. This plan permits a larger number of rooms which may be operated in rotation, thus insuring continuous production, if desired. Under this plan is incorporated a room 8 by 12 feet with a 7-foot ceiling ; the trays are Fig. 17.— Plan B, standard production room, 12 by 18 by 8 feet. 62 University of California — Experiment Station racked or stacked along the side walls on both sides of a central aisle. At one end of the aisle is a door which may open directly outdoors or into an inside hallway. At the opposite end is a 3 by 5 foot cloth- covered window reaching- to the ceiling, from which the beetles are collected. The room capacity under this plan is 120 standard trays, which should with reasonable care give a production of 48,000 adult beetles for each cycle of operation. Fig. 18. — View of interior hall of Los Angeles County Insectary, Rivera, California. For the larger insectary a room 12 by 18 feet with an 8-foot ceiling as shown in plan B (fig. 17) is recommended as being the most easily handled and the most economical to operate. In this case two aisles are permitted with a double row of trays in the center of the room, accessible from either aisle, in addition to the trays along the two side walls. A room this size has a capacity of 360 trays and a mini- mum production capacity of 144,000 beetles per cycle of operation. The size of the cloth-covered collecting window in the center of the outside wall is increased to 4 by 5 feet, extending from a point 30 inches above the floor to within 6 inches of the ceiling. A door gives entrance to the room at the hall end of one aisle while the heating unit is installed at the hall end of the other aisle. Bul. 509] Control of Mealybugs Attacking Citrus 63 Plan B may be extended indefinitely, in multiples of two tiers of trays, as the particular operator may desire. But for the reasons previously stated, the smaller rooms are considered preferable. Floor Plans of Buildings. — Figure 18 shows the position of the described rooms on both sides of a central hallway, permitting- a col- lecting window on the outside wall of each room. While economy in handling suggests the use of a single building, one of the largest insectaries in operation in southern California, that of Orange County at Anaheim, is satisfactorily operating a group of 28 buildings. Each building is made up of six rooms, with the col- lecting window at one end and a door leading directly outside to a covered walk at the other. Each unit of two buildings is heated - . JUL..* Fig. 19 -Los Angeles County Insectary, Rivera, California. through the use of hot-water radiators supplied by a separate outside heating plant located between the buildings. The excessive wall exposure naturally is conducive to greater fluctuation in tempera- tures, increasing the control problem. One of the advantages of this arrangement, however, is the decreased danger of total destruction of the plant by fire, as recently occurred in Los Angeles County. Figure 19 shows the new Los Angeles County insectary designed to house 10,000 trays, having a minimum productive capacity of 4,000,000 beetles for each cycle of operation of approximately five months. The cost of this building including thermostatically con- trolled hot-water heating units and mechanical ventilation was $20,000. Building Construction. — Unless constructed along the lines used in the Orange County insectary, as described, a warehouse type of structure is suggested, providing a central hallway for access to the rooms. By warehouse type of structure is meant permanent outer walls and flooring and trussed self-supporting roof. It is recom- mended that the outer walls be constructed 10 feet above the floor line 64 University of California — Experiment Station or 2 feet higher than the ceiling of the contemplated production rooms. The production rooms may be built in later of such construction and material as would permit removal or change to meet new develop- ments or requirements in insect production. While wood or stucco may be satisfactorily used, hollow tile or hollow cement brick are suggested as offering an excellent type of material for wall construction. In the proper-sized window opening, centered for each proposed room, metal sash and glass may be used, incorporating an adjustable ventilation panel. In many insectaries the floor is either of dirt or of concrete laid directly on the ground. Such floors, however, are difficult to heat, and have a retarding influ- ence on the insect development in the lower part of the room. A double wood floor, interlined with one of the standard insulating fiber wall- boards which has a very high resistance to heat radiation, at least 12 inches above the ground, is recommended. The top floor should be of tongue and groove material, leaded-in so as to prevent any later damage from watering the host plant material. Louvre ventilation along the peak of the roof has been found of considerable assistance in controlling room temperatures. The roof may be covered with any practical economical material. A lining of insulating wallboard is desirable, though it is not abso- lutely necessary, provided the structure is properly ventilated. Boom Construction. — The rooms may be built into the structure, using 2 by 3 inch studding and fiber-board walls and ceiling. The opening left opposite the window in the outer wall should be covered first with 14-mesh window screen (copper preferred) and then white cloth sheeting (fig. 20). It is to this cloth-covered window that the beetles are attracted by light, where they are later collected for field distribution. Ventilation. — The entrance door should be fully screened and may be covered with black cloth of open weave, if necessary for correct ventilation. In the ceiling should be at least four ventilators 12 by 14 inches equally spaced, covered with 14-mesh window screen. The installation of adjustable louvres in these ventilators is advantageous. Where an individual heating plant is used in the room, there should be a vent below or directly back of the heating unit and below the point of heat generation to permit an intake of cold air as an aid to circulation. In some instances, particularly near the coast, it has apparently been necessary to operate an electric fan continuously in such a position as to force the heat from the unit to the floor and create circulation. Otherwise excessive condensation of moisture has Bul. 509] Control of Mealybugs Attacking Citrus 65 occurred. Of course where a mechanical ventilation system is installed, the number, size, and placement of the suggested vents is subject to complete revision. Room Equipment. — Each room should have ceiling electric out- lets centrally located over the aisle, or aisles, with a control switch Fig. 20. — Proper placing of collecting window in rearing room. outside the room near the door. An electric convenience outlet under the collecting window will be found useful for connecting up an extension cord and light for use in examining closely the host-insect material in the rooms. Water outlets may be installed at convenient points in the outside hallway to provide a means of watering the host- plant material with a %-inch garden hose. However, such an outlet in each room under the collecting window would be more convenient. 66 University of California — Experiment Station Where a thermostat is used in the fuel line it may be most effect- ively installed 18 inches from the ceiling at the end of the center rack directly across from the collecting- window. A standard maximum- minimum thermometer placed head high on the wall at one side of the collecting window is useful to check against the thermostat (fig. 21). Fig. 21. — Position of thermostat and thermometer in rearing room. Where tray-supporting racks are used they should be constructed of 1 by 2 inch pine, with the shelves placed not less than 12 inches apart from floor to ceiling and with vertical supports of 2 by 2 inch pine for each three trays, allowing % i ncn clearance between trays. The wall racks may extend the full length of the room, and because of wall support at the ends do not necessarily need to be cross-braced. Bul. 509] Control of Mealybugs Attacking Citrus 67 The center racks, however, which may extend from the inside end wall to within 30 inches of the collecting window or outside end wall will need to be carefully cross-braced because of lack of end support. The wall racks should be constructed to a depth equal to the length of a single tray, while the center racks should be slightly more than the depth of two trays. Each shelf should be constructed of three longitudinal strips of 1 by 2 inch material, one in the center and one at each end of the supported tray. In-setting the outside supporting strips in the vertical supports will materially strengthen the rack. The rooms should be of such size, and the supporting racks so placed, that not less than 30 inches of aisle space is permitted. An aisle of 36 inches is preferred and is shown in the floor plans suggested. Where the staggered method of stacking the trays is used, floor strips 1 by 2 inches, net, should be properly spaced and permanently installed, including leveling, which has a definite value in the strength of the stack. Permanent cleats are then installed on the end walls, properly spaced to accommodate alternate trays, and perfectly leveled. The construction of an end support for the center rack opposite the collecting window is necessary (fig. 13). This supporting frame is plumbed and tied permanently to the floor strips with light wooden strips. All of the material used, with the exception of the last- mentioned strips, should be 1 by 2 inches net, so as to have a definite dimension from which to figure proper spacing. When stacking the trays a plumb line is used. Where hot-water pipes are used on the floor it will obviously be necessary to construct the floor strips of material of such dimensions as will clear them. Floor Racks. — Floor racks are provided in all rooms to prevent walking on and killing thousands of Cryptolaemus larvae which find their way to the floor during the operation of the rooms. Such racks may be constructed of 1 by 3 inch surfaced material of the proper length, the four boards used being spaced 1 inch apart and held in position by cross ties of the same material, placed at 4-foot intervals. It was found that the killing of a few larvae under the cross-ties of warped racks attracted others, which, feeding on the crushed bodies, were in turn killed when the walk was used. This fact, together with a desire to prevent pupation on the floor under the cross-ties, where the pupae or emerging adults would certainly be crushed, has led to the use of carriage bolts as legs to raise the racks % i ncn °ff °f the floor. Two 1 by % 6 inch bolts at each end of the cross-ties are satis- factory for this purpose. When these legs are used, the crawling larvae have access to the floor racks only at these few small points of contact with the floor. 68 University of California — Experiment Station Insect-proofing the Room.. — It is important that all cracks and crevices which might permit the movement of insects either from or into the room be effectively closed. It is important to eliminate hiding places for pupating insects, since the debris from these would be difficult to remove when cleaning the room. For this reason all unfin- ished edges where screen and cloth are applied should be covered, but mouldings should be avoided. A 2-inch gummed paper tape has been found to be admirably adapted to closing all such openings, gives a smooth, neat, finished covering, and may be easily removed or replaced where necessary. The door crevices may be effectively guarded by rubber weather stripping and by inexpensive mechanical spring devices which automatically hold the door tightly against the jam. Operating Equipment. — The only operating equipment requiring special mention are the trays in which potato sprouts are grown. As previously stated, the standard dimensions for such trays are 14V2 by I6V2 by 4 inches, though many operators are using trays varying from 16 to 18 inches square. A depth of 4 inches seems to be standard where they are used on racks, the supporting end being increased to 6 inches where the trays are stacked. Because of their continuous association with moisture it is advis- able to construct all trays of redwood. Being subjected to heavy loads and fairly rough handling, they should be of at least i^-inch stock. The tray will be materially strengthened if the ends are made of %-inch material. It is advisable also to use cement-coated box nails in assembling trays, 5-ds being used in the sides and bottoms and 7-ds in the ends. The bottom boards should be separated by not less than Vi inch in order to prevent buckling of the tray when wet and also to provide drainage. When planting, this crack is covered with a piece of light paper. Surfaced material, cut to proper length and width in the mill, may be purchased in quantities sufficient to make 1,000 trays at 14 to 25 cents a tray, depending on the local costs. The labor of making will average 2% cents a tray. Heating. — Insectary operations require a system of heating which will permit maintaining a controllable temperature ranging between 60° and 70° F during the period of host-plant development, and between 80° and 90° F during the period of insect development. Such heating should be thermostatically controlled. Experience makes it seem apparent that with care almost any type of heating equipment can be used satisfactorily. However, of all the types used by the various insectaries in California engaged Bul. 509] Control of Mealybugs Attacking Citrus 69 in the propagation of Cryptolaemus, including electricity, gas, steam, hot water, and hot-air gas radiators and common gas burners, hot- water radiation offers the most satisfactory type and should receive first consideration in any plans for permanent insectary buildings. Application of the heat evenly at the floor is desirable in order to offset an 8° to 10° F variation between ceiling and floor when a centralized heating unit is used in the room. Such a variation in the room temperature tends to create a very uneven development of both host plant and insect material, a condition to be avoided as far as possible. Hot water provides a satisfactory method of floor heating. A system using hot water supplied by radiation units in each room, has been used with a marked degree of success in the Orange County insectary by placing single ordinary radiator sections, in series, flat on the floor in the aisles. Under this plan a central heating unit is caring for twelve rooms, 12 by 10 feet with an 8-foot ceiling, in two unit buildings of six rooms each at a cost, installed, of approximately $500.00. A hot-water system heating through radiation from a series of lateral galvanized iron pipes spaced equally over the floor of the room and supplied from an outside heating unit has been used experi- mentally by Armitage with very good results at a low cost of installa- tion and operation. One of the most economical, though possibly less desirable types of heating equipment is that of an individual hot-air gas radiator in each room with thermostatic control of the gas supply. A 30-inch six-section stove of a type costing approximately $11.00 is being used by the Los Angeles County Insectary to maintain the necessary tem- peratures in the 12 by 18 foot rooms outlined under "Size of Rooms." An ether-diaphragm thermostat, costing $12.50, in the fuel line, per- mitting a bypass of gas sufficient to burn a pilot light at all times, will satisfactorily control the heat within a variation of two degrees either way from point of setting. Electric heating units are being used satisfactorily in some insec- taries where special rates make its use economical. In general how- ever, the cost of operation is prohibitive. 70 University of California — Experiment Station ECONOMICS OF PROBLEM From the time the work ceased to be experimental, the biological control of the citrophilus mealybug' by the use of Cryptolaemus has given practical results comparable with those secured against the other scale pests of citrus by mechanical methods. At first it was felt that a heavy infestation could be more easily brought under control than a light infestation. It is undoubtedly a fact that the effect is more lasting under these conditions, since the enormous production of Cryptolaemus in a heavily infested grove finally reaches a point where starvation takes place, bringing about a frantic search for food on the part of the ladybird beetles which results in near-extermination of the host. Consequently, a longer period is required for the mealybugs to regain their abundance after the Cryptolaemus have disappeared through lack of food. Experience has shown, however, that as a general rule even the lighter infesta- tions can be prevented from becoming serious by proper colonization of Cryptolaemus. This is very important, since to permit an infesta- tion to become heavy always results in serious losses which are not confined to the season's crop, but extend over into the following year. In handling a light infestation greater care is necessary in timing the colonization of the beetles. The cost of biological control as applied to mealybugs is very small compared with the cost of spraying or fumigation. It is diffi- cult to arrive at an exact comparison, but it is probably safe to say that on the average it costs about $40.00 an acre to fumigate an orange grove. In some localities it is necessary to fumigate every year, in others once every 3 or 4 years suffices. Assuming that on the average fumigation is necessary every other year, about $20.00 a year would be the cost of this operation. At the present time it is the practice to colonize 10 adult Cryptolaemus per tree in infested groves. The cost of production and distribution of these insects during the past season was about $2.50 a thousand. Ant control costs about $1.60 and banding about $2.00 an acre. At this rate mealybug control would amount to $5.60 an acre, figuring 80 trees per acre. The cost of production of Cryptolaemus is gradually being lowered and the difference will probably become still greater. These figures are mentioned only to give an idea of the cost of the operation. Fumigation is not satisfactory for mealybug control regardless of the cost, and in our present state of knowledge should Bul. 509] Control of Mealybugs Attacking Citrus 71 not be attempted for this purpose. On the other hand, there may be conditions under which water washing would be justified, but these could arise only as an emergency, when something" has gone wrong with the biological control program. If a situation arises where the only possibility of saving a crop of fruit appears to be a resort to washing this may be undertaken, but it should be done with the knowledge that it is only an emergency measure and its beneficial effects will be short, since it apparently is not possible to remove a sufficient percentage of mealybugs by this method to prevent a prompt return to the previous infested condition. Since the biological method is practically the only method of attack against the citrophilus mealybug, the steady advance of that species into new territory has necessitated a continued expansion of facilities to cope with it. Various agencies have undertaken this work, not only governmental, but private and cooperative. In many of the interior citrus-producing counties of southern California where the citro- philus mealybug is still a minor pest, the county government has established and has maintained insectaries through the agricultural commissioner, distributing the Crypt olaemus wherever necessary at no direct cost to the grower. In Orange County, where, as previously stated, this insect is a major pest over some 45,000 acres of citrus, the growers have assessed themselves on a packed-box basis, creating a fund from which they have built and equipped a $50,000.00 insectary for the production of Crypt olaemus. This plant is operated by the County Agricultural Commissioner out of county funds, the beetles being distributed over the infested acreage on recommendation of the District Agricultural Inspector at no further direct cost to the individual. Under this plan liberations are being made throughout the year. In Los Angeles County, which operates insectaries of capacity equal to Orange County, though partly in leased buildings modified for insectary purposes and serving 20,000 acres of infested citrus, the cost is more of a direct charge against the grower served. The county board of supervisors, through the Agricultural Commissioner, has furnished the necessary buildings and equipment and advanced the operating funds with the agreement that the county will be reim- bursed by the growers at a price per liberated beetle based on the actual cost of production. The insectary organization is given full power to determine the time and extent of liberations and to make its own liberations as conditions may require, billing designated packing associations for the necessary cost. This charge is prorated 72 University of California — Experiment Station from a district exchange through its member packing associations, sometimes directly to the grower, but being more often absorbed by the house to which the grower belongs. Recognizing the fact that the beetles may not all remain in the orchard in which they are lib- erated, and that control is to the benefit of the district as well as the grower concerned, the district properly assumes part of the cost. The fact remains, however, that assessments may be made directly on the grower receiving the insects, limiting the liberations to as near the period of optimum field conditions as possible and thus making the operation of the insectary a seasonal affair. Careful attention to the field conditions favoring biological control is required on the part of the insectary operator. This plan has been operating successfully for five years. APPENDIX Local Insectaries. — The following organizations are operating insectaries in California at the present time for biological control of mealybugs : Limoneira Company, Santa Paula. Ventura County, Santa Paula. Santa Paula Citrus Association, Santa Paula. San Bernardino County, Upland. San Diego County, Chula Vista. San Gabriel Valley Pest Control Association, Pasadena. Orange County, Anaheim. Oxnard Citrus Association, Hueneme. Los Angeles County, Downey and Eivera. Santa Barbara County, Santa Barbara. Eiverside County, Riverside. San Joaquin County, Lodi. Fillmore Citrus Protective District, Fillmore. Chapman Ranch, Fullerton. Powers Lemon Company, Ventura. Bastanchury Ranch, Fullerton. Labor and Materials Tables. — The following table is given for use in estimating the amount of materials and labor required in the opera- tion of an insectary where Cryptolaemus is being used. Bul. 509] Control of Mealybugs Attacking Citrus 73 Labor Insectary : One man per hour will Plant and place in rooms 10 trays Water and care for 100 trays Collect in the laboratory 2,000 Cryptolaemus Liberate in the field including transportation and records 4,000 Cryptolaemus Band trunks with burlap 50 trees Ant Control: One man per hour will Put out new poison containers 60 cups Replace poison containers 70 cups Fill containers with syrup in laboratory 400 cups Reclean old containers (aluminum) 250 cups Materials Insectary : 1 sack potatoes (120 lbs.) will plant 20 trays 1 tray host material will produce (average) 400 Cryptolaemus 2 trays (Cryptolaemus @ 10 per tree) will take care of 1 acre Ant Control: 100 lbs. cane sugar will make 22 gallons syrup 1 gal. syrup will fill 150 cups Government Argentine Ant Syrup: Granulated sugar 12 pounds Water 11 pints Tartaric acid (crystalized) 7 grams Benzoate of soda 9 grams Boil slowly for 30 minutes. Allow to cool. Dissolve sodium arsenite (C.P.) % ounce In hot water y 2 pint Cool. Add poison solution to syrup and stir well. Add to the poisoned syrup: Honey, strained 2 pounds Mix thoroughly. 74 University of California — Experiment Station LITERATURE CITED Abmitage, H. M. 1929. Timing field liberations of Cryptolaemus. Jour. Econ. Ent. 22:910^-915. Bodenheimer, F. S., and M. Gutfield. 1929. tiber die Moglichkeiten einer biologischen Bekampfung von Pseudo- coccus oitri Risso in Palastina. Zeit. Angew. Ent. 25:67-136. Clausen, Curtis P. 1915. Mealybugs of citrus trees. California Agr. Exp. Sta. Bui. 258:19- 48. figs. 1-8. Essig, E. O. 1910-1911. The natural enemies of the citrus mealybug. Pomona College Jour. Ent. 2:143-146, 260-264; 3:390-397; 4:518-522. Ferris, G. F. 1927. Mealybugs. California State Dept. Agr. Mo. Bui. 16:336-342. Gomez Clemente, F. 1929. El Cryptolaemus montrouzieri Muls., parasito del Pseudococcus ctiri Risso. Estacion Regional de Patalogia vegetale, Valencia. 45p. plates 1-11. figs. a-o. Poutiers, R. 1922. L'acclimatation de Cryptolaemus montrouzieri Muls. dans le midi de la France. Annales des Epiphyties, 8:3-18. figs. 1-12. Ryan, H. J. 1928. District Argentine ant control in citrus orchards. Jour. Econ. Ent. 21:682-690. Smith, Harry S. 1917. The life-history and successful introduction into the United States of the Sicilian mealybug parasite. Jour. Econ. Ent. 10:262-268. plates 13-14. figs. 9-13. Smith, Harry S., and H. M. Armitage. 1920. Biological control of mealybugs. California State Dept. Agr. Mo. Bui. 9:103-158. 1 plate, figs. 39-67. Smith, Harry S. 1923. The introduction and establishment of Scymnus oinaevatus Muls. in California. Jour. Econ. Ent. 16:516. Smith, Harry S., and Harold Compere. 1928. The introduction of new insect enemies of the citrophilus mealybug from Australia. Jour. Econ. Ent. 21:664-669. TlMpERLAKE, P. H., and C. P. Clausen. 1924. The parasites of Pseudococcus maritimus (Ehrhorn) in California. Univ. Calif. Publ. Entom. 3:223-292. plates 18-19. figs. 1-8. Woglum, R. S., and J. D. Neuls. 1917. The common mealybug and its control in California. U. S. Dept. Agr. Farmers' Bui. 862:1-16. figs. 1-4. Woglum, R. S., and A. D. Borden. 1922. Control of the citrophilus mealybug. U. S. Dept. Agr. Bui. 1040:1-20. figs. 1-13. STATION PUBLICATIONS AVAILABLE FOR FREE DISTRIBUTION BULLETINS No. 253. 263. 277. 279. 283. 304. 310. 331. 335. 343. 344. 347. 348. 349. 357. 361. 362. 363. 364. 368. 369. 370. 371. 373. 374. 179. 388. 389. 390. 391. 392. 393. 394. 396. 404. 405. 406. 407. 408. 409. 410. 412. Irrigation and Soil Conditions in the Sierra Nevada Foothills, California. Size Grades for Ripe Olives. Sudan Grass. Irrigation of Rice in California. The Olive Insects of California. A Study of the Effects of Freezes on Citrus in California. Plum Pollination. Phylloxera-resistant Stocks. Cocoanut Meal as a Feed for Dairy Cows and Other Livestock. Cheese Pests and Their Control. Cold Storage as an Aid to the Market- ing of Plums, a Progress Report. The Control of Red Spiders in Decid- uous Orchards. Pruning Young Olive Trees. A Study of Sidedraft and Tractor Hitches. A Self-Mixing Dusting Machine for Applying Dry Insecticides and Fun- gicides. Preliminary Yield Tables for Second- Growth Redwood. Dust and the Tractor Engine. The Pruning of Citrus Trees in Cali- fornia. Fungicidal Dusts for the Control of Bunt. Turkish Tobacco Culture, Curing, and Marketing. Bacterial Decomposition of Olives During Pickling. Comparison of Woods for Butter Boxes. Factors Influencing the Development of Internal Browning of the Yellow Newtown Apple. The Relative Cost of Yarding Small and Large Timber. Pear Pollination. A Survey of Orchard Practices in the Citrus Industry of Southern Cali- fornia. Walnut Culture in California. Pruning Bearing Deciduous Fruit Trees. The Principles and Practice of Sun- Drying Fruit. Berseem or Egyptian Clover. Harvesting and Packing Grapes in California. Machines for Coating Seed Wheat with Copper Carbonate Dust. Fruit Juice Concentrates. Crop Sequences at Davis. I. Cereal Hay Production in California. II. Feeding Trials with Cereal Hays. The Mat Bean^ Phaseolus Aconitifolius. The Dehydration of Prunes. Citrus Culture in Central California. Stationary Spray Plants in California. Yield. Stand, and Volume Tables for White Fir in the California Pine Region. Alternaria Rot of Lemons. The Digestibility of Certain Fruit By- products as Determined for Rumi- nants. Part I. Dried Orange Pulp and Raisin Pulp. Factors Influencing the Quality of Fresh Asparagus After it is Harvested. A Study of the Relative Value of Cer- tain Root Crops and Salmon Oil as Sources of Vitamin A for Poultry. Planting and Thinning Distances for Deciduous Fruit Trees. No. 415. 416. 418. 419. 420. 421. 423. 425. 426. 427. 428. 431. 432. 433. 434. 435. 436. 438. 439. 440. 444. 445. 446. 447. 448. 449. 450. 451. 452. 454. 455. 456. 458. 459. 460. 462, 464. 465. The Tractor on California Farms. Culture of the Oriental Persimmon in California. A Study of Various Rations for Fin- ishing Range Calves as Baby Beeves. Economic Aspects of the Cantaloupe Industry. Rice and Rice By-Products as Feeds for Fattening Swine. Beef Cattle Feeding Trials, 1921-24. Apricots (Series on California Crops and Prices). Apple Growing in California. Apple Pollination Studies in California. The Value of Orange Pulp for Milk Production. The Relation of Maturity of California Plums to Shipping and Dessert Quality. Raisin By-Products and Bean Screen- ings as Feeds for Fattening Lambs. Some Economic Problems Involved in the Pooling of Fruit. Power Requirements of Electrically Driven Dairy Manufacturing Equip- ment. Investigations on the Use of Fruits in Ice Cream and Ices. The Problem of Securing Closer Rela- tionship between Agricultural Devel- opment and Irrigation Construction. I. The Kadota Fig. II. The Kadota Fig Products. Grafting Affinities with Special Refer- ence to Plums. The Digestibility of Certain Fruit By- products as Determined for Rumi- nants. Part II. Dried Pineapple Pulp, Dried Lemon Pulp, and Dried Olive Pulp. The Feeding Value of Raisins and Dairy By-Produces for Growing and Fattening Swine. Beans (Series on California Crops and Prices). Economic Aspects of the Apple In- dustry. # The Asparagus Industry in California. A Method of Determining the Clean Weights of Individual Fleeces of Wool. Farmers' Purchase Agreement for Deep Well Pumps. Economic Aspects of the Watermelon Industry. Irrigation Investigations with Field Crops at Davis, and at Delhi, Cali- fornia, 1909-1925. Studies Preliminary to the Establish- ment of a Series of Fertilizer Trials in a Bearing Citrus Grove. Economic Aspects of the Pear Industry. Rice Experiments in Sacramento Val- ley, 1922-1927. Reclamation of the Fresno Type of Black-Alkali Soil. Yield, Stand and Volume Tables for Red Fir in California. Factors Influencing Percentage Calf Crop in Range Herds. Economic Aspects of the Fresh Plum Industry. Lemons (Series on California Crops and Prices). Prune Supply and Price Situation. Drainage in the Sacramento Valley Rice Fields. Curly Top Symptoms of the Sugar Beet. BULLETINS — (Continued) No 466. The Continuous Can Washer for Dairy Plants. 467. Oat Varieties in California. 468. Sterilization of Dairy Utensils witn Humidified Hot Air. 469. The Solar Heater. 470. Maturity Standards for Harvesting Bartlett Pears for Eastern Shipment. 471. The Use of Sulfur Dioxide in Shipping Grapes. 472. Adobe Construction. 473. Economic Aspects of the Sheep in- dustrv 474 Factors Affecting the Cost of Tractor Logging in the California Pine 475 Walnut Supply and Price Situation. 477. Improved Methods of Harvesting Grain 478 Feeding and Management of Dairy Calves in California. 479 I Irrigation Experiments with Peaches in California. II. Canning Quality of Irrigated Peaches. 480. The Use. Value, and Cost of Credit in Agriculture. tt _ . 481. Utilization of Wild Oat Hay for Fat- tening Yearling Steers. . 482. Substitutes for Wooden Breakpins. 483 Utilization of Surplus Prunes. No. 484. 485. 486. 487. 489. 490. 491. 492. 493. 494. 495. 496, 497 498 500 The Effects of Desiccating Winds on Citrus Trees. Drying Cut Fruits. Pullorum Disease (Bacillary White Diarrhea of Chickens). Asparagus (Series on California Crops and Prices). Cherries (Series on California Crops and Prices). Irrigation Water Requirement Studies of Citrus and Avocado Trees in San Diesro County, California, 1926 and 1927. Olive Thinning and Other Means of Increasing Size of Olives. Yield, Stand, and Volume Tables for Douglas Fir in California. Berry Thinning of Grapes. Fruit Markets in Eastern As.ia. Infectious Bronchitis in Fowls. Milk Cooling on California Dairy Farms. _ , , m Precooling of Fresh Fruits and Tem- peratures of Refrigerator Cars and Warehouse Rooms. A Study of the Shipment of Fresh Fruits and Vegetables to the Far East. . Pickling Green Olives. . Dehydration of Grapes. CIRCULARS No. 117. 127. 178. 203. 212. 230. 232. 239. 240. 241. 243^ 244. 245. 248. 249. 250. 253. 255. 257. 258. 259 261 262 263 265 266 The Selection and Cost of a Small Pumping Plant. House Fumigation. The Packing of Apples in California. Peat as a Manure Substitute. Salvaging Rain-Damaged ?™nes. Testing Milk, Cream, and Skim Milk for Butterfat. «,.-_■ Harvesting and Handling California Cherries for Eastern Shipment, Harvesting and Handling Apricots and Plums for Eastern Shipment. Harvesting and Handling California Pears for Eastern Shipment. Harvesting and Handling California Peaches for Eastern Shipment. Marmalade Juice and Jelly Juice from Citrus Fruits. Central Wire Bracing for Fruit Trees. Vine Pruning Systems. Some Common Errors in Vine Pruning and Their Remedies. Replacing Missing Vines. Measurement of Irrigation Water on the Farm. Vineyard Plans. . Leguminous Plants as Organic Ferti- lizers in California Agriculture. _ The Small-Seeded Horse Bean (Vicia faba var. minor). Thinning Deciduous Fruits. . Pear By-Products. . Sewing Grain Sacks. Cabbage Production in California. Tomato Production in California. Plant Disease and Pest Control. Analyzing the Citrus Orchard by Means of "Simple Tree Records. No. 269. 270. 273. 276. 278. 279. 282. 287. 288. 290. 294. 295. 296. 301. 302, 304 307 308 310 311 312 313. 316. 317 318 319 320 An Orchard Brush Burner. A Farm Septic Tank. Saving the Gophered Citrus Tree. Home Canning. Olive Pickling in Mediterranean Countries. . The Preparation and Refining of Olive Oil in Southern Europe. Prevention of Insect Attack on Stored Grain. Potato Production in California. Phylloxera Resistant Vineyards. The Tangier Pea. Propagation of Deciduous Fruits. Growing Head Lettuce in California. Control of the California Ground Squirrel. Buckeye Poisoning of the Honey Bee. The Sugar Beet in California. Drainage on the Farm. American Foulbrood and Its Control. Cantaloupe Production in California. The Operation of the Bacteriological Laboratory for Dairy Plants. The Improvement of Quality in Figs. Principles Governing the Choice, Oper- ation, and Care of Small Irrigation Pumping Plants. , Fruit Juices and Fruit Juice Beverages. . Electrical Statistics for California Farms. , , . . Fertilizer Problems and Analysis of Soils in California. . Termites and Termite Damage. Pasteurizing Milk for Calf Feeding. Preservation of Fruits and Vegetables by Freezing Storage. 13m-3,'31