UNIVERSITY OF CALIFORNIA PUBLICATIONS COLLEGE OF AGRICULTURE AGRICULTURAL EXPERIMENT STATION BERKELEY, CALIFORNIA CITRUS FRUIT INSECTS By H. J. QUAYLE BULLETIN No. 214 (Berkeley, Cal.. May, 1911) W. W. SHANNON - SACRAMENTO - - - SUPERINTENDENT OP STATE PRINTING 1911 EXPERIMENT STATION STAFF. E. J. Wickson, M.A., Director and Horticulturist. E. W. Hilgard, Ph.D., LL.D., Chemist (Emeritus). W. A. Setchell, Ph.D., Botanist. Leroy Anderson, Ph.D., Dairy Industry and Superintendent University Farm Schools. M. E. Jaffa, M.S., Nutrition Expert, in charge of the Poultry Station. R. H. Loughridge, Ph.D., Soil Chemist and Physicist (Emeritus). C. W. Wood worth, M.S., Entomologist. Ralph E. Smith, B.S., Plant Pathologist and Superintendent of Southern California Pathological Laboratory and Experiment Station. G. W. Shaw, M.A., Ph.D., Experimental Agronomist and Agricultural Technologist, in charge of Cereal Stations. E. W. Major, B.Agr., Animal Industry, Farm Manager, University Farm, Davis. F. T. Bioletti, B.S., Viticulturist. B. A. Etcheverry, B.S., Irrigation Expert. George E. Colby, M.S., Chemist (Fruits, Waters, and Insecticides), in charge of Chemical Laboratory. H. J. Quayle, M.S., Assistant Entomologist, Plant Disease Laboratory, Whittier. W. T. Clarke, B.S., Assistant Horticulturist and Superintendent of University Exten- sion in Agriculture. H. M. Hall, Ph.D., Assistant Botanist. C. M. Haring, D.V.M., Assistant Veterinarian and Bacteriologist. John S. Burd, B.S., Chemist, in charge of Fertilizer Control. E. B. Babcock, B.S., Assistant in Agricultural Education. W. B. Herms, M.A., Assistant Entomologist. J. H. Norton, M.S., Assistant Chemist, in charge of Citrus Experiment Station, River- side. W. T. Horne, B.S., Assistant Plant Pathologist. J. E. Coit, Ph.D., Assistant Pomologist, Plant Disease Laboratory, Whittier. C. B. Lipman, Ph.D., Soil Chemist and Bacteriologist. R. E. Mansell, Assistant in Horticulture, m charge of. Central Station grounds. A. J. Gaumnitz, M.S., Assistant in Cereal Investigations, University Farm, Davis. E. H. Hagemann, Assistant in Dairying, Davis. B. S. Brown, B.S.A., Assistant in Horticulture, University Farm, Davis. F. D. Hawk, B.S.A., Assistant in Animal Industry. J. I. Thompson, B.S., Assistant in Animal Industry, Davis. R. M. Roberts, B.S.A., Field Assistant in Viticulture, University Farm, Davis. J. C. Bridwell, B.S., Assistant Entomologist. C. H. McCharles, B.S., Assistant in Agricultural Chemical Laboratory. N. D. Ingham, B.S., Assistant in Sylviculture, Santa Monica. E. H. Smith, M.S., Assistant Plant Pathologist. T. F. Hunt, B.S., Assistant Plant Pathologist. C. O. Smith, M.S., Assistant Plant Pathologist, Plant Disease Laboratory, Whittier. F. L. Yeaw, B.S., Assistant- Plant ^Pathologist, Vacaville. F. E. Johnson, B.L., M.S., Assis'tanVin Soil Laboratory. Charles Fuchs, Curator Entomological Museum. P. L. Hibbard, B.S., Assistant in Fertilizer Control Laboratory. L. M. Davis, B.S., Assistant in Dairy Husbandry, University Farm, Davis. L. Bonnet, LA., Assistant in Viticulture. S. S. Rogers, B.S., Assistant Plant Pathologist, Plant Disease Laboratory, Whittier. B. A. Madson, B.S.A., Assistant in Cereal Laboratory. Walter E. Packard, M.S., Field Assistant, Imperial Valley Investigation, El Centre M. E. Stover, B.S., Assistant in Agricultural Chemical Laboratory. P. L. McCreary, B.S., Laboratory Assistant in Fertilizer Control. E. E. Thomas, B.S., Assistant Chemist, Plant Disease Laboratory, Whittier. Anna Hamilton, Assistant in Entomology. Mrs. D. L. Bunnell, Secretary to Director. W. H. Volck, Field Assistant in Entomology, Watsonville. E. L. Morris, B.S., Field Assistant in Entomology, San Jose. J. S. Hunter, Field Assistant in Entomology, San Mateo. J. C. Roper, Patron, University Forestry Station, Chico. J. T. Bearss, Foreman, Kearney Park Station, Fresno. MILLER, Foreman, Forestry Station, Chico. CONTENTS. INTRODUCTION. Page. THE BLACK SCALE (Saissetia oleae Bern.) 445 Life history 449 Seasonal history 451 Distribution and spread 452 Parasites and predaceous enemies — Scutellista cyanea Motsch 456 Other enemies 459 Control 459 THE RED OR ORANGE SCALE (Chrysomphalus aurantii Mask.) 459 Life history 460 Seasonal history 462 Food plants 463 Distribution and spread .. 463 Parasites — Aphelinus diaspides How 463 Predatory enemies — Rhizobius Lophanthw Blaisd 464 THE YELLOW SCALE (Chrysomphalus aurantii var. citrinus Coq.) 465 Distribution 465 Life history 465 Parasites 465 Control ± 466 THE PURPLE SCALE (Lepidosaphes beckii Newm.) 466 Life history 466 Seasonal history 468 Natural enemies 469 Control 469 THE COTTONY CUSHION SCALE (Icerya purchasi Mask.) 469 Present status in California 470 Life history annd habits 472 Natural enemies . 472 SOFT BROWN SCALE (Coccus hesperidum Linn.) 475 Life history 476 Natural enemies . 476 HEMISPHERICAL SCALE (Saissetia hemisphaerica Targ.) 478 Natural enemies 478 THE GREEDY SCALE (Aspidiotus rapax Comst.) 480 THE OLEANDER SCALE (Aspidiotus hederae Comst.) 481 THE CITRUS MEALY BUG (Pseudococcus citri Risso.) 481 Life history and habits 483 Natural enemies 484 Control 484 CONTENTS— Continued. Page. RED SPIDERS (Tetranychus mytilaspidid Riley) 485 (Tetranychus sexmaculatus Riley )_: 485 Life history and habits 486 Control 487 SILVER MITE .(Phytoptus oleivorus Ash.) 489 Life history and habits 489 Control 490 THRIPS 490 Life history and habits 493 Control 493 APHIS (Aphis gossypii) 493 THE ORANGE TORTRIX (Tortrix citrana Fern.) 494 Life history and habits - 495 FULLER'S ROSE BEETLE (Aramigus fulleri Horn.) 499 Life history, habits and control 499 DIABROTICA SOROR 501 SERIOUS CITRUS FRUIT PESTS NOT YET ESTABLISHED IN CALI- FORNIA 503 The Orange Maggot (Trypeta ludens Loew.) 503 The Citrus White Fly (Alerodes citri R. and H.) 504 SPRAYING FOR CITRUS FRUIT INSECTS 505 FUMIGATION 506 INSPECTION AND QUARANTINE 511 CITRUS FRUIT INSECTS. By H. J. Quayle. INTRODUCTION. That insect pests are one of the important factors in the citrus fruit industry of southern California is shown by the fact that more than half a million dollars are expended annually in their control. This amount includes only what is actually expended in fumigation and spraying, and does not take into consideration the loss of fruit from im- properly treated trees or trees not treated at all. The cost of fumigation in one county alone amounts to $200,000 annually. Furthermore, each county maintains a horticultural commissioner, and many of them a corps of inspectors, primarily on account of insect enemies, who are charged with the quarantine and inspection work, the cost of which in some of the counties may run as high as $25,000 annually. That all of this vigilance is necessary seems to be warranted from the thirty years ' experience of the most important citrus fruit section of the United States. It has been estimated that the average cost of fumigation per tree, taking the whole of the citrus belt, amounts to about 30 or 40 cents, which means an expense of approximately $30 to $40 per acre, and this is done on an average about every other year. This is intensive insect fighting, but w T hen the improved market value of the fruit is considered, it is money judiciously spent with such a valuable crop as the orange or lemon. Commercial citrus culture in California is confined to seven counties south of the Tehachapi mountain range, namely, Santa Barbara, Ven- tura, Los Angeles, Orange, Riverside, San Bernardino, and San Diego ; and the two counties north of this range, namely, Tulare in the upper San Joaquin Valley, and Butte in the upper Sacramento Valley. The southern counties form a section contiguous to the coast line, and which has a coast climate, excepting the Riverside-Redlands district, which approaches the interior conditions on account of its distance from the ocean (60 to 75 miles), without being separated by a w T ell-defined natural barrier. The San Joaquin and Sacramento Valley citrus dis- tricts have the typically interior climate which is characterized by hotter summers than that of the more equable coast counties. These general climatic differences appear to account for the differences in the insect pests, not only of the northern and southern sections, but also within the latter section itself, since even here there is a wide range of variation. However, it is not safe to speak too confidently of the influence of climate on insect distribution. Time has changed a num- 444 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. ber of ideas to correspond with the facts as they exist to-day. It had been asserted that California need have no fear of the citrus white fly, yet this pest got a fairly good foothold in a part of the State least unsuited to it, according to theory. It was also held that the black scale would not exist in the Riverside section, yet it occurs there and attacks citrus trees. Likewise, the purple was supposed not to become a pest in arid California, and, if it did become established, it would be limited to a narrower range than its distribution at the present time indicates. In general, however, it may be said that the black scale thrives best in sections' near the coast, as shown by its prevalence in the citrus belt from Santa Barbara to San Diego, and also on deciduous trees in the coast counties of the north. The interior valley citrus sections are not troubled with the black scale, though it may occur there on such plants as the olive and oleander. The purple scale, thus far, is limited to the coast counties, occurring with the black, but not of such wide distribu- tion. The red and yellow scales occur both near the coast and in the interior, though they are considered the more typical scales of the warmer interior sections. Aside from the scale insects mentioned, the next most general citrus tree pests are to be found among the spiders and mites. The Florida red spider and the six-spotted mite are widely distributed, while the silver mite of the lemon is restricted to a limited section in San Diego County. The mealy bug has become a rather serious pest in certain limited sections in Ventura and San Diego counties, and also smaller infestations in other counties. The soft brown, cottony cushion, and a few other scales sometimes occur in considerable numbers over small areas, but are not usually considered permanent pests. A species of thrips has recently come into prominence as a pest in the San Joaquin section. The orange tortrix is the only insect that burrows into the orange itself to any extent, and this fortunately has not become a very important pest thus far. Other insects which attack the fruit occasion- ally are grasshoppers, katydids and cutworms. Other biting insects attacking the leaves only are .Fuller's rose beetle and the common Diabrotica. A couple of dozen species will thus cover all the insects of economic importance attacking citrus trees in California, and of these, practically all of the control work is directed against but four of the scale insects, the black (Saissetia olece Bern.), the red (Chrysomphalus aurantii Mask.), the yellow (Chrysomphalus aurantii var. citrinis Coq.) and the purple (Lepidosaphes beckii Newm.). The present publication is intended to give a popular account of all those species likely to be considered of economic importance, together with their chief attendant parasites or enemies. This will include a discussion of their life history and habits, mainly, since the principal reliance for control, which is Bulletin 214] CITRUS FRUIT INSECTS. 445 fumigation, is discussed in separate publications from this station and also the Department at Washington. A brief outline of spraying and fumigation is, however, appended at the close of this bulletin which gives the essential facts for these operations. The control of those pests which are not handled by fumigation or spraying is given at the close of the discussion of each species. Most of the photographs were made by Professor R. W. Doane of Stanford University, who assisted in the investigation of citrus fruit insects during the summer of 1910, while the drawings are the work of Miss Anna Hamilton. THE BLACK SCALE. (Saissetia olece Bern.) The Black Scale (Saissetia olece Bern.) ranks first among the citrus pests of southern California. This statement is based upon the amount of control work actually directed against it, and its wide distribution throughout the cit- rus belt. The purple scal,e and the mealy bug may be more diffi- cult insects to control, but their distribution is not so general as that of the black. In the county horticultural commissioners ' re- ports tabulated on next page, the black scale is given first place in three counties, Los Angeles, San- ta Barbara, and Orange. The sec- ond in two others, Ventura and San Diego. While the mealy bug is given first place in Ventura, it will be noticed that most of the control work is against the black. This scale also has a wider dis- tribution in San Diego County than the purple, and should probably be entitled to first place there. Where control work is directed against the purple, and the black is associated with it, the extra dosage used against the former keeps the black well in check, otherwise it would have to be reckoned with separately. The Fig. 1. -Black Scale (Saissetia oleae Bern.) on orange twig. 446 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION. TABULAR STATEMENT CONCERNING CITRUS INSECT PESTS BY COUN Riverside. R. P. Cundiff. Commissioner. San Bernardino. S. A. Pease, Commissioner. Los Angeles. A. R. Meserve, Commissioner. Orange. Roy K. Bishop, Commissioner. I. Most important scale insect pest II. Seond most import- ant III. Third most import- ant rv. Annual cost fumigat- ing V. Annual cost spraying. VI. Annual cost fumigat- ing 10 years ago VII. Annual cost spraying 10 years ago 1_~ VIII. Proportion of fumi- gating and spray- ing for black scale.. IX. Proportion fumigat- ing and spraying for red and yellow. _ X. Proportion fumigat- ing and spraying for purple XI. Acreage in citrus fruits 10 years ago. XII. Present acreage __. XIII. Other control work.. Red. Yellow. Black. $75,000 8,000 20,000 5,000 *30-40% 60-70% No purple in county. 16,000 N. cardinalis for cottony cushion. C. Lecanii for soft brown. Red. Yellow. Black. $200,000 10,000 60,000 25,000 33J% No purple in county. 24,000 57,000 Spraying for red spiders. Black. Red. Purple. $175,000 5,000 Nearly all. 17,800 29,200 Black. Red. Purple. $35,000 1,000 12,500 Mealy bug pest Sulfur for red in certain sec- spider, tions. 75% for black in 1910. Bulletin 214] CITRUS FRUIT INSECTS. 447 TIES GIVEN BY THEIR RESPECTIVE HORTICULTURAL COMMISSIONERS. Ventura. San Diego. Santa Barbara. Butte. Tulare. E. 0. Essig, Commissioner. C. H. Stuart, Commissioner. C. W. Beers. Commissioner. Earle Mills. Commissioner. A. G. Schulz. Commissioner. Citrus mealy bug. Purple. Black. Yellow. Black. Black. Purple. Soft brown. Long-tailed mealy bug. Citrus mealy bug. Yellow. Work just begun. 1908-9, 3,000 1909-10, 10,000 1910-11, 20,000 $10,000 None. $1,500 None of the economic scales yet estab- lished in commer- cial groves. None, except for mealy bug. 1,000 One orchard spray. None. 2,000 acres sprayed for thrips in 1910. No fumigation then. Same as to-day. No records. None. No fumigation then. Same as to-day. No records. None. Practically all. 50% None. None in commer- cial orchards. Only two infesta- None. 100% tions in county. 1-16 50% None. No purple in county. 10,000 7,000 1,400 1,200 1,800 • 12,000 13,000 Lime-sulfur for Scutellista does Parasites control Parasites and red spider. Predaceous ene- mies: cottony cushion and mealy bug. good work some years. Also crypto- laemes on mealy bugs. Black. Para- sites give excel- lent control of purple. predatory ene- mies for cot- tony cushion and soft brown. 448 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. only sections where the black is not considered a serious pest in the south are certain sections of Riverside and San Bernardino counties. The chief injury occasioned by the black scale is not due so much to the loss of sap through feeding, nor is it due to the poisonous effect on the plant tissues through the insertion of its thread-like mouth parts. The black scale excretes large quantities of so-called honey dew which falls upon the upper surface of the leaves and fruit, and this serves as a medium for the growth of a fungus known as the sooty mold fungus. This necessitates the washing of the fruit, which operation alone adds to the cost of the handling, but the chief injury is due to the wash water becoming infected with blue mold and other fungi. Since the fruit comes in contact with the sides of the tank, brushes, elevators, and Fig. 2. — Mature Black Scales. drying racks, it is impossible to escape some abrasion of the fruit, into which the spores of the fungus readily make their way. Regarding the washing of oranges, Powell in Bulletin 123 of the Bureau of Plant Industry, U. S. D. A., says the following: ' ' Oranges are washed primarily to remove the sooty mold fungus that grows in the so-called honey dew exuded by the black scale (Saissetia olece Bern.). The Valencia orange is sometimes washed to raise the grade by making the fruit clean and attractive, and the Washington Navel is occasionally washed with that end in view. "When the present investigation by the Bureau of Plant Industry was undertaken, from one third to one half of the oranges of California were washed, practically all the fruit in some sections being treated in this way, especially where the growers had been over-confident in the parasite Scutellista cyanea Motsch, or in the use of oil sprays as a means of holding the black scale in check." More detailed ;in«l complete publications will follow on the Black, Red and Purple Scales. Bulletin 214] CITRUS FRUIT INSECTS. 449 Aside from the damage to the fruit, this sooty mold fungus often forms a complete coating over the surface of the leaf, which greatly interferes with the natural functions of the leaf by shutting off light. Light is necessary for the formation of starch and sugar, and conse- quently the sugar content of the fruit may be reduced as a result of black scale infestation. The black scale, as already intimated, does not conspicuously interfere with the growth of the tree. There is probably no case where this insect has killed a tree, though some of the smaller twigs may be severely injured. However, the sooty mold fungus may also have its effect on the general growth of the tree, because of its interference with the manufacture of sugar which is necessary for the formation of the living matter (protoplasm) of the tree. LIFE HISTORY OF THE BLACK SCALE. The Egg is almost white in color when first deposited, but later as it approaches the hatching time it becomes distinctly orange. If the eggs of this scale are placed end to end in a single line it will require about 80 to equal one inch in length. The number laid varies from 300 to nearly 3,000, the average being from 1,500 to 2,000. These will be deposited during a period V of two months during which time from 25 to 40 will be laid each day. The time required for the hatching is from fifteen to twenty days during the spring or summer months. Eggs of this insect may be found at any season of the year in some section of the southern California citrus belt, FlG - 3.— Male of Black Scale. though the great bulk of them are to be found in May, June and part of July. The time of maximum egg production in 1910 was about the second week in June. This will vary from year to year, and there appears during some years to be a more uniform hatch than in other years. However, practically all the young appear by the middle of August, or first of September, from that great majority of scales that mature in the spring. The young upon hatching from the egg remain beneath the parent scale for a day or two before emerging. Upon making their way from beneath the old scale they actively crawl about for a time but almost always settle within two or three days. A large majority settle on the leaves or tender twigs. Those settling on the leaves rarely come to maturity there. As they become partly grown they loosen their hold 450 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. and migrate to the twigs and branches. The young scales seem unable to become established, in any large numbers, on the older corky branches. Once becoming fixed on the twigs they remain, in the case of the females, throughout their entire existence. This migration from leaves to stems may occur when the scale is nearly one half grown, but usually takes place prior to that time. Fig. 4. — Leaf on right showing sooty mold fungus as a result of Black Scale infestation. Normal leaf on left. The female black scale undergoes a couple of molts, but the legs are not lost in the .process, as is the case with the red scale. While the legs are retained throughout its life they are functionless after the scale is about one half grown. It is during the growing period, and partic- ularly as they approach maturity, that the honeydew is excreted. It is Bulletin 214] CITRUS FRUIT INSECTS. 451 this honeydew that the ants, which are so frequently seen on black or soft brown scale-infested trees, are after. They do not feed on the scales, as is often supposed, and neither do they attack the tree itself. The rela- tion of the ants, therefore, is largely neutral, though indirectly they may be somewhat detrimental through their protection of the scales from parasites and other enemies. Again, on the other hand, ants have been seen abundant enough, especially in the case of the soft brown scale, to take up all the honeydew as fast as it was excreted so that the fruit and foliage remained clean. The adult female, which becomes full grown in eight to ten months, is hard and leathery in texture, and approximately a solid hemisphere in shape. As the eggs are deposited beneath, the tody itself gradually becomes hollow, so that when all the eggs are deposited the scale becomes simply a hollow hemisphere filled with eggs. On the back of the full- grown scale, and from the time it is half grown as well, there is a distinct letter H, which is one of the best common characters for distinguishing it. The color varies from dark brown to jet black, which is darker than any of the other common scale insects of the orange. The male of this insect in most localities has not been seen, though during some years it does occur in considerable numbers in many sec- tions of southern California. As many as 97 male puparia from which males had emerged, have been seen on a single orange leaf in San Diego County. The males occur commonly, also, in Los Angeles and Orange counties. The puparium in which the later stages of the male insect is passed is glassy white and resembling in shape a partly grown soft brown scale. They are much longer and narrower than the female scale at the same stage. The male which emerged from those transparent glass-like scales are like those of all scale insects in being active winged insects. They are, however, weak fliers, and the wind may be an impor- tant aid in wafting them from one tree to another. SEASONAL HISTORY OF THE BLACK SCALE. There appears to be but one complete generation of the black scale in a year, and the majority of the insects reach maturity in the spring months. The seasonal history of the scale differs in detail, according to locality. On citrus trees in southern California there is more or less overlapping, so that, in some sections, the insects may be found in some of the stages at all times of the year. Likewise, they may be found in most of the coast districts as far north as San Francisco. In the interior valleys, where the seasons are a little more pronounced, more of the scales come to maturity at a definite time. Young will be found during the winter months, but they are very few as compared with the early summer months. Mortality. The black scale suffers its greatest mortality during the 452 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION. period when the young are active, and again at the molting periods. Fully 50 per cent in many cases fail to get settled, and often this runs as high as 95 per cent. They seem unable to become fixed in any large numbers on stems that are old and corky. This can be explained because of their delicate mouth-parts being unable to penetrate, into the harder tissue. But in those cases, where they fail to get a foothold on the leaves, as many do, and where there seems to be something to prevent them from settling, the matter is not so easily accounted for. In addition to this mortality, on account of the insects themselves, they are, of course, during the active period more likely to be attacked by enemies and succumb to other outside agencies. During the molting periods the insects # are undergoing a profound physiological change, and many fail to pass through this critical period. During the younger stages of the insect there are also likely to be hot weather periods that kill them off in large numbers. Young black scales just hatched and placed on soil in the sun, with a temperature of 108° to 110° in the sun, died in 1 to 1J hours. At a temperature of 119° to 122° they died in 15 minutes, and at a temperature of 130°, died in 5 minutes. In all cases those under the same conditions in the shade were not affected. It is not uncommon to find as high as 90 per cent or more of the partly grown young on orange leaves killed by what appears to be heat or other climatic condition. While, therefore, a black scale may lay 2,500 eggs, and that would represent the progeny at the end of the year, this condition never obtains in nature. After the loss of first settling, the loss during the molts, the weather, diseases, parasites, and other enemies, the number coming to maturity is very small as compared with the number of eggs produced. DISTRIBUTION AND SPREAD OF THE BLACK SCALE. The distribution of the black scale over the citrus belt of the State has been given in the introduction. It thrives best in the coast sections, and the reason for this is the cooler summers. Often here, as indicated above, hot weather periods bring about considerable mortality, but not to such an extent as in the interior valleys. The black scale is to be found in greatest numbers on the underside of the smaller twigs and branches of the tree. On young trees, one to three years old, they may occur even down on the trunk, but are very rarely found here in mature trees. The statement has been made that they occur on the roots of certain plants, such as the nightshade. "While they may get a few inches below the surface in loose soil, they are still on the stem of the plant and are not to any extent root-infesting insects. Aside from the citrus trees, the olive is the one worst infested; in fact, it attacks the olive in prefer- ence to the orange. It was on this tree that the black scale was first discovered and named by a Frenchman named Bernard in 1782. The Bulletin 214] CITRUS FRUIT INSECTS. 453 oleander and pepper are also favorite host-plants for this insect in southern California. The total range of plants attacked is large, and includes many of the deciduous fruit trees of the State. Rate of Travel. The spread of this insect, like most other scales, is dependent very largely upon outside agencies rather than on its own powers for traveling. It is only three or four days at most when the scale crawls to any extent, and no very long distances can be covered by such a small insect as the active larva. Over smooth paper they are capable of traveling at a maximum rate of 6 feet in an hour. On the basis of a scale living four days and going at full speed all the time it Fig. 5. — Washing oranges to remove sooty mold fungus which grows in the so-called honeydew from the Black Scale. From Bull. 123, Bur. Plant Industry, U. S. D. A. would cover 720 feet. But no scales under ordinary conditions do this, nor do they have smooth paper to walk upon. Experiments on the rate of travel of these young scales over smooth sand showed that they covered a 10-inch strip in from 1^ to If hours. Several thousand scales were liberated in the center of a 4-foot circle of ordinary orchard soil. The first scales reached the edge in 2 hours. Only a very small per cent of the total number succeeded in getting over the 2-foot radius of soil. Similar tests were made where the width of the soil to be traversed was 4 feet, but none came to the edge during the same day. The finer the mulch the more difficult it is for travel, and in the compacted irrigation furrows they were found to make much more rapid progress. While, therefore, there may be some young black 454 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. scales that will make their way from one tree to another, or possibly to a second or third tree away, by their own powers of locomotion, this means of transfer must be considered a rather small factor in the total spread. The Wind as a Factor. The wind is one other means of spreading scale insects about which considerable has been said with but little actual data presented to support the claims. Wind is an important factor in aiding the flight of small weak flying insects, as winged plant lice and the winged males of scale insects; but it is not an important factor in the spread of the female black scale in any stage. The crawling young are not often dislodged from the tree by the wind. A strong current of the air from a foot-bellows, much stronger than the wind blows in this section, was directed against a twig with numerous active young black scales. None were dislodged until the twig was brought within six inches from the mouth of the bellows and even then only a small proportion were blown off. Once dislodged, they would be carried a short distance as they were falling. From this and other experiments it would seem to indicate that it would be very unusual for a scale to be dislodged from the tree by the wind alone; but once dislodged, they would alight a short distance further in the direction the wind was blowing. If the trees were close together, they might alight on an adjoining tree, but, with the navel orange as ordinarily planted, this would be exceptional. Of course, the wind is an important means of transporting the males and insuring fecundation of the females that might be spread by other means ; but in the case of the black scale, where the male is so rare, this is not of much significance. Other Agencies. The rapid spread, over a considerable area, of such insects as the black scale must, therefore, be accounted for in other ways than their own powers of locomotion, or through the agency of the wind. Active flying or crawling insects are probably the most important, and of these, the ladybird beetles must be considered as the worst offenders. These insects move about among the scales themselves, upon which they feed, and many instances have been observed where there was a young scale insect on the backs of these beetles. About 100 of these beetles were confined for a day in a jar containing black scale infested twigs, and, upon examination, it was found that the young scales were being carried around on the backs of the beetles. About one beetle in every ten or fifteen carried from one to four young scales. These beetles, of course, fly from one tree to another and the rapid spread of the scale is thus effected. Other active insects must also be considered as impor- tant, but less so than the ladybird beetles. Birds, without doubt, also spread scale insects, for these, resting on scale-infested twigs for a time, allow abundant opportunity for the active young to crawl upon them. Bulletin 214] CITRUS FRUIT INSECTS. 455 Because of the long flight of birds they would be specially likely to trans- port them long distances and thus account for isolated scale infestations. The ordinary operations of man must also be considered as a factor in the spread of scale insects. Indeed, it has been through the trans- porting of nursery stock that different species of scale insects have such a wide distribution over the world. Practically all the scales of citrus fruits in this State have thus been imported from other countries. What applies in the exchange of pests between foreign countries, also applies between different states and also different counties in our own State. While nursery stock is the chief means of spreading scale insects long distances, man may again be responsible, through picking boxes, wagons and the like, of spreading scales to adjoining sections and different parts of his own premises. The operations of picking the fruit, through Fig. 6. — Drying racks where fruit is placed after washing as a result of Black Scale infestation. From Bull. 123, Bur. Plant Industry, U. S. D. A. wagons, picking boxes, clippers, gloves, etc., and the movement of teams in cultivation may all aid in the distribution of the scale over the orchard. Different articles, such as sticks, boards, rags, and gloves, were placed in a scale infested tree and allowed to remain for some time, and, upon examination, had scales crawling over them. The young black scale will rarely live more than four or five days without food, so that infested articles, such as picking boxes, if allowed to remain five or six days or a week before carrying into other groves, there will not be much danger of infestation. 2-B214 456 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION. PARASITES AND PREDATORY ENEMIES OF THE BLACK SCALE. (Scutellista cyanea Motsch.) By far the most important enemy of the black scale in California is Scutellista cyanea Motsch, introduced into this State from South Africa by the United States Department of Agriculture through Dr. L. 0. Howard in cooperation with E. M. Ehrhorn and Alex. Craw in 1900. This insect has become well established in most parts of the State where the black scale occurs. Little, if anything, therefore, is gained by distributing a half dozen or a dozen of these parasites in an orchard where they already occur in considerable numbers, aside from a possible moral effect. In isolated places, where it does not now occur, of course, this artificial distribution should be encouraged. There is often a very great difference in the abundance of Scutellista in different sections and also in the same sections at different seasons, it is not uncommon to find as high as 75 to 80 per cent of the scales parasitized in a certain section, and the following year a low percentage of parasitism. There is considerable irregularity, therefore, in its abun- dance, and the black scale still remains the most important citrus fruit pest in the State. Usually where there is a heavy parasitization by the Scutellista, the black scale is very abundant on the tree. Again, there may be few black scales and fewer Scutellista, indicating that other factors are at work aside from the parasite. We are accustomed to judge of the efficiency of Scutellista by the per- centage of exit holes in the scales, but this is not the only criterion. The Scutellista is an egg parasite, almost entirely, so that in no way does it reduce the injury of the generation of scales attacked. The scale has come to maturity, sucked all the sap, and given off all the honeydew it would have given off anyway, whether it was attacked by the Scutel- lista or not. The efficiency of Scutellista, then, must be judged by its power to reduce the progeny of the black scale. It may seem that there ought to be a direct relation between the numbers of exit holes in the scales and the number of young present. But this is not necessarily true, for the reason that the Scutellista does not always consume all the eggs. It is not infrequent to find a very high percentage of exit holes, and, also, a great abundance of young. Cases have been observed where the percentage of exit holes ran as high as 75 or 80 per cent, yet on leaves immediately adjoining this, more than 700 young black scales were counted on each. On healthy trees, and where all conditions are favorable for the growth of the scale, they grow very large, and a large number of eggs are deposited, more than enough to bring the Scutellista larva to maturity. This, together with the fact that the scales left unin- Bulletin 214] CITRUS FRUIT INSECTS. 457 Fig. 7. — Scutellista cyanea Motsch, egg x70 ; larva x25 ; pupse, ventral and dorsal views x20 ; adult xl7 ; inverted Black Scale showing four pupse ; exit holes in scales. 458 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. festedby the parasite will produce 2,000 or more young, it is easy to account for the tree becoming infested again the following year. "Where the scales are small, the Scutellista larva consumes all the eggs and the number of young is greatly lessened. LIFE HISTORY OF SCUTELLISTA. The Egg of the Scutellista is pearly white in color, larger in size than those of the black scale, among which it is found, and has a long taper- ing stalk at one end. They are deposited under the black scale during the egg stage or a little while previous. There may be more than one egg deposited under a single scale though apparently not by the same Scutellista. While there may be several eggs under one scale there are not more than two, sometimes three and very rarely four, Scutellista come to maturity. The total number of eggs laid is diffcult to obtain under field conditions. Judg- ing from experiments in the insect ary on the rate of laying and length of adult life, we are inclined to put the maximum at about 25 or 30. The time required for hatching is from five to six days. The Larva is the familiar white grub-like creature seen upon lifting the black scale. There is considerable difference in size, depending upon the size of the scale and number of eggs. As stated above, eggs may be deposited under scales without eggs, and larva have also been seen attached and feeding on the scale itself. The larval stage lasts from sixteen to twenty-one days. The number of eggs consumed during this period varies greatly. They are able to mature on the smallest number laid, which is 500 or less, or they may consume 2,000 or more. They feed by sucking the contents of the eggs, leaving the shells, or the body juices of the scale itself. Pupa. Upon completing its growth as a larva, the insect changes into the resting or pupal stage, at which time it changes to a black color, and remains in this stage from seventeen to twenty days. Adult. The adult is shown in figure 7, and is the common metallic blue fly -like insect seen walking about on scale-infested twigs. It lives about ten days in this stage. SEASONAL HISTORY OF THE SCUTELLISTA. The life of the Scutellista is, of course, dependent upon the life of the black scale. Just as the black scale may be found somewhere in all stages at all times of the year 2 so will the Scutellista. But, like the scale on which it is dependent, it is to be seen in greatest abundance in the early summer. It has been stated that the maximum egg period of the Bulletin 214] CITRUS FRUIT INSECTS. 459 black scale in 1910 was about the middle of June. This was also the maximum larval period for the Scutellista. And the maximum number of adults appeared about one month later, or the middle of July. The egg stage being five to six days and adult life ten to twelve days, the total life cycle will be from fifty to sixty days. These periods are under summer conditions, and in winter they go through their develop- ment much more slowly. Under favorable conditions there may be as many as four or five generations in a year in southern California. OTHER ENEMIES OP THE BLACK SCALE. Another egg parasite (Tomocera California) was formerly said to occur abundantly on the black scale, but it has been of little significance of late years as compared with the Scutellista. At the present time it is most frequently met with in the citrus groves of Santa Barbara County. Several ladybird beetles feed upon the black scale, among which the most important is probably Rhizobius ventralis, Fig. 25. The steel- blue ladybird beetle (Orcus chalybeus) also occurs abundantly in Santa Barbara County, where it feeds on the black and also the yellow scales, the two commonest scales of that section. THE CONTROL OF THE BLACK SCALE. Aside from the control by natural enemies, which some growers are still inclined to rely upon, fumigation, and in some cases spraying are the standard control measures for this scale. For a brief discussion of these measures see pages 505-511 of this bulletin. THE RED OR ORANGE SCALE. (Chrysomphalus aurantii Mask.) The red scale is the second most important citrus fruit scale in Cali- fornia. It is associated with the black in the coast sections, but also occurs beyond the limits of the black as a pest in the interior. Its man- ner of injury differs from that of the black in the fact that no honeydew is given off. The injury from the red scale is due directly to the feed- ing, whether this is on account of the loss of sap, toxic effect on the tissues of the plant, interference with the functions of the stomata when the scale is abundant, or a combination of these causes. It is usual to speak of the effect in the case of the San Jose scale on apple and pear because of the discoloration it produces in the tissues. But the discol- oration is not evident in the case of the red scale on citrus trees, though this toxic effect may be present without producing a discoloration. Of 460 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. course, there is a discoloration produced on the leaves in the form of yellow spots, but this is due to the loss of chlorophyl, rather than a poisonous substance which reddens the tissue about the point of puncture. At any rate, the red scale which infests leaf, twig, branch and fruit, may seriously injure a tree in a very short time. Fig. 13 shows a large portion of an orange tree killed in two years by infestation with the red scale. In this respect it is much more • virulent than any of the other Fig. 8. — Red Scale (Chrysomphalus aurantii Mask.) on grape fruit. scales of citrus trees. Aside from this serious effect on the tree, the red scale very readily gets on the fruit, thus marring its appearance and market value. LIFE HISTORY OF THE RED SCALE. The Active Young. No eggs are laid by the red scale, so the starting point in the life history is the active young, which are born alive. These are the minute yellowish creatures which may be seen crawling around on fruit and leaves infested with this scale. They appear somewhat like granules of sulfur. After remaining under the parent scale for a Bulletin 214] CITRUS FRUIT INSECTS. 461 day or two they emerge and actively crawl about for a short time, but usually settle within one or two days. The Fixed Young. As soon as they settle they begin the secretion of white cottony fibres with which they cover themselves. This later be- comes more compacted and reddish in color, and also contains parts of two molted skins of the insect. They remain fixed beneath this covering throughout their entire existence. During the summer months they come to maturity in about 2J months and in the winter from 3 to 3^ months. The Adult Female. The red scale is so called because of the reddish appearance of the mature scale, but the reddish color is almost entirely in the scale covering, the insect beneath being yellow usually. The scales are circular and about the size of the head of an ordinary pin. The young are produced at the average rate of 2 or 3 a day for a period of two months in summer. During the winter the production of young is almost at a standstill during the colder or wet weather. But during a spell of warm weather they may appear in considerable numbers. Our records of two or three dozen accurately kept for each day during the production of young, the number varied from 25 to 143 with an average of 55 for each scale. The emergence of young averaged from 2 to 3 per day. During the colder days the young probably remained under the parent scale a little longer, so that the maximum or 8 were probably not born on the same day ; though eight would appear for two or three days in succession. Development of the Male Bed Scale. The red scale undergoes its first molt in from sixteen to twenty days after birth. Up to this time the males and females are exactly alike, but from this stage on they lose all re- semblance to one another and might be taken for different insects. The male, after the first molt, becomes elongate, and it is during this stage that the characteristic elon- gated male scale covering is produced. Under this scale it changes to a pro-pupa, then to a true pupa, and finally to the adult, which is a frail insect with two wings. While the female thus undergoes but two molts and does not change materially, the male passes through four molts and emerges as an active insect from 1J to 2 months from birth. — Male of Red Scale. 462 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. SEASONAL HISTORY OF THE RED SCALE. There may be as many as four generations a year in southern Cali- fornia. While the young from a single scale, which will run from 40 to 80, is not nearly so large as the black, the increased number of genera- tions accounts for them more rapidly in- festing a tree. The first great production of young in the spring occurs in May and June and from that time on to No- vember they are al- ways to be found in Fig. 10. — Red Scale, mature females and young. large numbers. Scales matured in slightly less time in the interior section at Kiverside than nearer the coast at Whittier. Fig. 11. — Red Scale on orange leaf. The greatest mortality occurs during the active period of the young. In all our breeding experiments the per cent would average about 40. Bulletin 214] CITRUS FRUIT INSECTS. 463 FOOD PLANTS. While the red scale is essentially a citrus pest it is known to attack other plants, including some of the deciduous fruit trees; but in Cali- fornia it is of little consequence outside of the citrus fruits. A more or less common weed, in poorly cared for California orchards, is the nightshade, and this plant is readily attacked by this scale. Ivy is another often attacked. DISTRIBUTION AND SPREAD OF THE RED SCALE. The maximum rate of travel of young red scales over smooth surfaces is at the rate of 4^ feet per hour. The rate of travel over orchard soil, where there is a fine mulch, is practically negligible. We have not suc- ceeded thus far in getting them across a 3-inch strip of such soil. If these young scales are watched closely, they will be seen to nearly always fall back in their attempt to ascend a small particle of earth. Thus they are able to make no progress, and one kept under constant observation did not travel half an inch in two hours. If there is a fine mulch in the grove, as most are kept in California, there is little danger of the spread of the red scale as dependent upon their own powers of locomotion. But here again, if the soil is compacted, as in irrigation furrows or after a rain, they can travel very well. Other points taken up under the head of "Distribution and Spread of the Black Scale" also applies for the red. PARASITES OF THE RED SCALE. (Aphelinus diaspidis Howard.) The commonest parasite of the red scale, and the only one of any economic significance, is the little chalcid {Aphelinus diaspidis How- ard). This parasite is well distributed over the citrus belt, but since the highest parasiti- r*t«T-^ r**»£ zation seen during v_ j^/f 3 ^^"^^ the past three years would not exceed 5 or 10 per cent, it is of little consequence as a control factor. The egg of this parasite is deposited beneath the scale, and the grub-like larva upon hatching FlG attaches itself to the scale and sucks the body juices 12.- Aphelinus diaspidis How. Yellow Scales. Parasite on Red and x39. It is not, therefore, an internal para- 464 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION. site, for at no stage is it within the body of the scale insect itself. The eggs hatch in five to seven days ; the larva grows to maturity in twelve to sixteen days ; it is eight to ten days in the pupal stage, and lives as an adult four or five days. The number of eggs deposited is not large, and probably will not exceed 25 or 30. Fig. 13. -Large portion of orange tree killed as result of two years' infestation of Red Scale. There are certain of the ladybird beetles that feed on the red scale, the commonest being a small black species (Bhizobius lophanthce) shown in Fig. 25. The eggs of this beetle may be laid beneath the scales, but the larva upon hatching travels about, attacking many different insects. Bulletin 214] CITRUS FRUIT INSECTS. 465 THE YELLOW SCALE. (Chrysomphalus aurantii var. citrinus.) This scale is very similar in appearance to the red scale, and in the absence of typical specimens, or considerable material, it is impossible to distinguish the two. The structural characters of the insects them- selves are identical. But the scales as seen on the tree are usually not difficult to determine. The yellow is distinctly lighter in color, lies flatter upon the leaf, and is often slightly larger in diameter. When the yellow scale dies, the scale covering becomes darker in color, in which case they are much more difficult to separate. But aside from this difference in general appearance there is a distinct variance in habits. The red scale attacks all parts of the tree, whereas, the yellow is limited almost entirely to the leaves and fruit. Leaves may be very badly infested with the yellow, and but an occa- sional scale on the twigs, while in the case of the red, the twigs and branches really become infested first. Because of the fact that the twigs are not attacked its power to injure the tree is not so great, and it can not be counted as serious a pest as the red. DISTRIBUTION OF THE YELLOW SCALE. The yellow scale occurs scatteringly over practically the whole of the citrus belt in southern California, having much the same distribu- tion as that of the red ; but in the Sacramento Valley citrus section it appears to occur exclusively, there being no red to the writer's knowl- edge thus far seen in that section. LIFE HISTORY. The life history of the yellow scale is the same in all particulars as the red, so that it need not be repeated here. PARASITES AND PREDACEOUS ENEMIES. The parasite discussed in connection with the red scale also attacks the yellow. But there is another common parasite of the yellow, and which, in former years, was said to be a very effective check on this scale. Many people still believe that the disappearance of the yellow scale in places where it was once much more prevalent than now was due to the work of this parasite. There is no doubt that the early reports con- cerning this parasite were, like many others, greatly exaggerated and based upon no careful observations. This parasite of the yellow scale has the scientific name of Aspidiotiphagus citrinus Craw. It is strictly an internal parasite, living with the body of the scale insect itself, and 466 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. emerging when about half- grown. At the present time it is most abun- dant in Santa Barbara County, and counts made show that as high as 25 per cent of the scales may be parasitized. The control of the red and yellow scales is effected by fumigation, for which see the close of this bulletin. THE PURPLE SCALE. (Lepidosaphes beckii Newm.) The purple scale was introduced in California upon cuttings from Florida in 1892. Statements were then made that it would not thrive in the drier California climate, but it has succeeded very well in many of the coast sections from Santa Barbara to San Diego. Its eastern limit at present is in the eastern part of Los Angeles County, and has not yet appeared in Riverside or San Bernardino counties, nor any of the northern citrus sections. The purple scale is the most difficult to handle of the four scales thus Fig. 14. — Purple Scale on orange leaf. far mentioned, because of the resistance of the eggs to fumigation. It attacks leaf, branch, and fruit, often becoming incrusted on but a portion of the tree, usually the lower side. Parts of the tree will thus be badly injured by the dropping of the leaves and the killing of the branches, but it seldom, if ever, destroys the entire tree. The retention of the scales on the fruit after it comes into the packing house is another point against the purple scale. LIFE HISTORY OF THE PURPLE SCALE. The eggs of the purple scale are the pearly white oval-shaped bodies, which are to be seen upon lifting the mature scales. They are almost Bulletin 214] CITRUS FRUIT INSECTS. 467 completely enclosed by the firm scale-covering above and the lighter cotton-layer beneath, forming a sack with the opening at the posterior tip, through which the young make their escape. It is for this reason, largely, that the purple scale eggs are so resistant to hydrocyanic acid gas on account of the difficulty of the gas reaching them. The number of eggs deposited is from 30 to 40 extending over a period of three or four weeks. The eggs hatch in fifteen to twenty days during the summer months. From the time the eggs first appear until the last ones hatch, therefore, is a period of about two months, so that about six weeks or two months ought to be allowed between fumigations, where Fig. 15. — Purple Scale on orange leaf enlarged. two treatments are made, as sometimes is done with this scale. The most eggs are present in the spring or early summer (May and June) though all through the season they may occur in all stages. The Young. The young scales upon hatching remain under the parent but a day or two, and after another day or two of actively moving about over the plant, they settle down and remain stationary, in the case of the female, throughout the rest of their lives. They first secrete a couple of coarse, entangling threads, which serve as protection until they have opportunity to cover themselves with the permanent scale covering. The female undergoes two molts within a period of one to one and a half months. Eggs will be deposited at the end of two months in sum- 468 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION. mer, and during winter it is prolonged to three and over. Young will begin appearing in a little less than three months from the time the parent was an active young scale. The old scale dies soon after the production of eggs. The male purple scale, after molting four times and going through the usual pro-pupal and pupal stages, emerges as a winged insect after a period of approximately two months in summer and three months in the winter season. The scale of the male is long and narrow and easily distinguished from that of the female. Fig. 16. — Orange incrusted with Purple Scale. SEASONAL HISTORY OF THE PURPLE SCALE. Taking the minimum period from young to young in midsummer at 80 days and the maximum in winter at 120 days, there will appear during the season between three and four generations of the purple scale. In the case of warmer dry winters there may be four full genera- tions in the year. There appears to be a maximum period of eggs and young in May and June, and again in August and early September. The season of greatest mortality is here again coincident with the season of greatest production of young ; but a larger portion of the young suc- ceed in getting established than is the case with either the red or the Bulletin 214] CITRUS FRUIT INSECTS. 469 black scales. The provision for mortality, as indicated by the number of eggs produced, is not so great as in the black scale, for the black scale produces fifty times more eggs than the purple. NATURAL ENEMIES OF THE PURPLE SCALE. Aspidiotiphagus citrinus Craw, is the only parasite we have thus far taken from the purple scale. This is strictly an internal parasite, and attacks the scale only between the first and second molts. The egg is deposited within the insect, and there hatches a very minute white larva with a tail-like appendage, which disappears with the later molts. The adult makes its way out through a circular exit hole in the posterior one third of the scale. This parasite is not gen- ^ erally distributed over the localities where the purple scale occurs, and it is only occasionally that the parasite will be met with ; but where it does OCCUr, the amount Of Fl ?; ^ --^pidwUphagus citrinus Craw x40. Parasite on Purple, Yellow, and Red Scales. parasitization may run as high as 30 or 40 per cent. During the winter months it has taken at least five days for the eggs to hatch and nine weeks are necessary for its complete life cycle. In summer it requires much less time. In addition to this internal parasite several kinds of ladybird beetles may be occasionally seen to feed upon the purple scale, and the com- monest of these are Bhizobius lophanthce Blaisd. and Scymnus margi- nicolles. For the control of the purple scale, see discussion on fumigation on page 506. THE COTTONY CUSHION SCALE. {I eery a purchasi Mask.) The cottony cushion scale is a native of Australia and was introduced into California, probably upon an acacia at Menlo Park, in 1868. Twenty years later it was widely spread over the State and considered a very serious menace to the citrus fruit industry. In 1889, the Austra- lian ladybird beetle (Novius cardinalis) was introduced through the efforts of the Division of Entomology of the United States Department of Agriculture. In a short while it was reported to have the scale under subjection, and has usually apparently kept it so ever since. This importation has always been referred to as the most successful case on record of one insect keeping another under control. In fact, it 470 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. has been the stimulus, the support, and the hope for the future, for a large amount of work along the line of importing one insect to prey upon another. This has been espe- cially true in this State, and while much good work may have been done, there has not been approached any such signal success as seemed to be the case with cardinalis. PRESENT STATUS OF THE COT- TONY CUSHION SCALE IN CALIFORNIA. "While the cottony cushion scale is at present a pest of comparatively little conse- quence, it is still one of the commonest insects inquired about throughout the entire length of the State where citrus trees are grown. While the cardinalis is pret- ty well distributed over the State, and often appears un- aided in an infestation of cottony cushion scale, yet in many cases it does not occur, and neither does the scale become very abundant. The checking of the scale in such cases must be accounted for through some other factors. Sometimes, too, the beetle is slow in getting the scale under control. On the sta- tion grounds at Riverside fifty or seventy-five orange trees have been infested with the cottony cushion scale, as bad as occurred when the insect was at its height, for at least four years. During this time also the ladybird beetle has been present. The scale becomes very abundant each spring, when the cardinalis begins Fig. 18 -Cottony Cushion Scale on orange twig. Bulletin 214] CITRUS FRUIT INSECTS. 471 work and effectively checks them. The beetles are present in April, May, and June, and disappear in July. Some young scales are left ..^t^MHHKSSMHPQMto^, •£^sy5w ^igtfjjl jltfvi^tfofr Fig. 19. — Young Cottony Cushion Scales on orange leaf. Larva and adult of the Australian ladybird beetle also shown feeding upon the scales. Fig. 20. — Different stages in the development of the Cottony Cushion Scale. and those have a chance to multiply and severely infest the tree again before the cardinalis appears in the spring. This has been the history of the infestation for the past four years. 3— B214 472 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION. LIFE HISTORY AND HABITS OF THE COTTONY CUSHION SCALE. The large fluted cottony mass that is so characteristic of this scale is secreted only by the female when it is full grown. This is for the protection of the orange yellow eggs that are deposited within the mass and which is enlarged as the 500 to 800 eggs are deposited. These require ten to twelve days to hatch in summer and may be prolonged to three weeks in winter. The larvae settle upon the leaves and twigs, arranging themselves largely along the mid rib and veins of the leaf. In the later stages they prefer the twigs and branches, or even the trunk. Occasionally, they develop on the leaves, but very rarely upon the fruit. Unlike the other scales mentioned, the cottony cushion scale travels throughout the greater part of its life, or until the egg sack is secreted. There is a great variation in the time of development of the different scales, even during the same season. Some will mature in three months, while others will go four months and over. There are about three generations a year in southern California, but on account of the irregularity in development these are not at all distinct. The season of greatest production of young is May and June. The injury from this scale is due to the honeydew given off, and also to the direct attack upon the tree. Fig. 21. — Male of Cottony Cushion Scale. NATURAL ENEMIES OF, THE COTTONY CUSHION SCALE. Novius cardinalis, the Australian ladybird beetle, is the most effective enemy of the cottony cushion scale, and in most cases may be relied upon to control it. The adult beetle lays from 150 to 200 orange red eggs, most usually in the cottony egg sack. These hatch in five or six days and the larvae begin at once to feed upon the eggs. . Later, they feed upon all stages of the scale and their growth as a larva is completed in three weeks. The pupal stage lasts about a week, wljen the adult beetle, with red and black markings, appears. This beetle is known to feed only upon the cottony cushion scale, or their own kind, if food becomes scarce. For this reason, upon the cleaning up of an infestation of scale, the beetles themselves often die, so that there is cause for maintaining a supply and sending them out to new infestations. Another enemy of the scale is the dipterous or two-winged parasite (Cryptochcetum, iceryce Will.). This is said to have occurred quite abundantly in former years, but is no longer considered an important Bulletin 214] CITRUS FRUIT INSECTS. 473 aid in the control of the scale. This is a small black fly with green metallic reflections. The larva lives with the scale and the adult Fig. 22. — Exudation or honeydew from Cottony Cushion Scale crystallized and before growth of fungus has started. V TBI Si J if* ■ l_ 1 Fig. 23. — Pupae of N. cardinalis on orange tree. Fig. 24. — Different stages of the larva of N. cardinalis. emerges through an exit hole, which characterizes those scales parasi- tized. Infestations of this scale very often occur with no evidence of 474 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. the parasite, showing that its distribution is not so general as that of many others. It has been most frequently met with during the past two or three years in Santa Barbara and Orange counties. The main reliance for control, therefore, is the ladybird beetle (Novius cardinalis) and if specimens are not already present among the scales they may usually be obtained from the State Insectary, Sacramento. >, tf""^* I A 1 LO Fig. 25. — Some common ladybird beetles. All enlarged 5 times. 1. Scymnus marginicollis, Mann., feeding on Red and Purple Scales. 2. Rhizobius lophanthae, Blaisd., feeding on Red and Purple Scales. 3. Scymnus nebulosis, Lee., feeding on Red and Yellow Scales. 4. Rhizobius sp. feeding on Purple Scale. 5. Hyperaspis, 8 notata, on Monterey Pine Scale. 6. Novius koebeli, Oliv., feeding on Red Scale. .7. Rhizobius ventralis, Black, feeding on Black Scale. 8. Orcus chalybeus, Boisd., feeding on Black, Red, Yellow, and Purple. 9. Novius cardinalis, Black, feeding on Cottony Cushion. 10. Cryptolsemus montrouzeri, feeding on Mealy Bug. Bulletin 214] CITRUS FRUIT INSECTS. 475 Fig. 26. — Some common ladybird beetles, all enlarged five times. 1. Olla plagiata, Casey, feeding on Aphids. 2. Axion plagiatom, Casey, feeding on Black Scale. 3. Hippodamia convergens, Guer., feeding on Aphids and scale insects. 4. Coccinella calif ornica, Mann, feeding on Aphids and scale insects. 5. Hippodamia ambigua, Lee, feeding on Aphids and scale insects. 6. Hippodamia ambigua, Lee, feeding on Aphids and scale insects. SOFT BROWN SCALE. (Coccus hesperidium Linn.) This scale, while seldom occurring in injurious numbers over an entire orchard, often severely infests an occasional tree or portion of a tree; but the infestation is usually of short duration, due, in most cases to 476 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. the efficient Avork of one or two parasites. This scale is thoroughly distributed over the world, and attacks a large number of widely dif- ferent plants. Its injury is due chiefly to the copious amount of honey- dew given off, and the consequent growth of the sooty mold fungus. It attacks the smaller twigs and the leaves. LIFE HISTORY AND HABITS OF THE SOFT BROWN SCALE. No eggs are deposited by this scale, the young being born alive, as is the case with the red scale. The active young soon settle and remain fixed, though there may be some movement until it is about one half grown. They molt twice and come to maturity, and produce young in sixty-five days during the summer months. The largest number 7 W^^ i ^\^0m .^ Fig. 28. -Aphycus flavus How. parasite or soft brown scale. x40. Fig. 27. — Soft brown scale on orange twig. summer months. and five. of young we obtained from a single scale has not exceeded 30 distributed over a period of thirty to thirty-five days. There may be, thus, several gen- erations in a year, but during the winter their development is very slow. The young usually ap- pear abundantly in May, and again in July, and also in September, but on account of the overlap- ping, many may be present continually during the The total number of generations will be between four NATURAL ENEMIES OF THE SOFT BROWN SCALE. There are two common internal parasites of the scale, Coccophagus lecanii Fitch, and Aphycus flavus How. The former emerges when the scale is nearly grown or of considerable size, while the latter emerges Bulletin 214] CITRUS FRUIT INSECTS. 477 usually while the scale is still small, not more than half grown. Those scales parasitized with lecanii may be known when the parasite is in the pupal stage by the black color which is shown through the scale. The Fig. 29. — Coccophagus lecanii, Fitch, parasite of soft brown and other scales. other parasite is yellowish in color, and does not make the scale appear black. These are strictly internal parasites and the Aphycus is the Fig. 30. — Soft brown scales with exit holes of parasites. Partly grown scale shown at top of figure. more effective when abundant because the scales are checked before they attain any size. The scale is often alive for some time after the parasite has changed to the pupa. Other parasites taken from this scale are Encrytus flavus and Coccophagus lunulatus. 478 TXIVERSITY OF CALIFORNIA EXPERIMENT STATION. HEMSIPHERICAL SCALE. (Saissetia kemisphaerica Targ.) Fig. 31. — Hemispherical scale, Saissetia hemisphaerica, on leaf of Christmas berry. absence of the letter H, its lighter color of brown, and its smooth shiny surface. Full grown scales of this species are commonly found on the leaves as well as the twigs, and some have the habit of settling on the very edge of the leaf. NATURAL ENEMIES OF THE HEMIS- PHERICAL SCALE. Coccophagus lecanii, the same internal parasite that attacks the soft brown scale, also attacks the Hemisphaerica scale and emerges from the scale when about one half grown. Another parasite, This is a scale that is of little con- sequence as a citrus tree pest, though it is commonly found on such trees in certain sections as Santa Barbara and San Diego. It is essentially a green- house scale, but thrives out of doors in mild climates. Here, in California, it more readily at- tacks certain orna- mental plants, as the Christmas ber- ry, oleander, and palm. It is easily distinguished from the black, which is its nearest ally on citrus trees, by the Fig. 32. Hemisphaerica scale on leaf of orange. Bulletin 214] CITRUS FRUIT INSECTS. 479 Comys fusca, is found commonly in this scale, and this one emerges when the scale is nearly or quite full grown. Scutellista cyanea, the T ^'■^S^m 11 ™*aS Fig. 33. — Hemispherical Scale on twig of orange. Fig. 34. — Male puparia of Hemispher- ical Scale. Fig. 35. — Comys fusca How., parasite on Hemispherical, Brown Apricot, and other scales. xl8. egg parasite of the black scale, also occurs occasionally in this scale, as well as some of the other internal parasites. 480 UNIVERSITY OP CALIFORNIA EXPERIMENT STATION. THE GREEDY SCALE. (Aspidiotus rapax Comst.) This scale sometimes infests the twigs of citrus trees and also com- monly occurs on the older fruit that may be still remaining on the tree Fig. 36. — Orange Infested with Greedy Scale (Aspidiotus rapax, Comst.), from the previous year, or the older tree-ripe lemons. It is thus on the older fruit that this insect attracts most attention, and so long as it is confined to such fruit, the injury is of little consequence. But, occa- sionally, it will also be found on marketable fruit and is often associated in scattering numbers with other scales. It may be distinguished from the red or yellow by its lighter gray color and its much greater con- vexity. The greedy scale infests a long list of plants and occurs more abundantly on acacia, laurel, and other shade and ornamental trees than upon citrus trees. The parasite Aphelinus fuscipennis How., has been bred in some numbers from this scale. Bulletin 214] CITRUS FRUIT INSECTS. 481 THE OLEANDER SCALE. (Aspidiotus hederce Comst.) This scale is known as a citrus fruit scale because of its occasional occurrence on lemons, and goes by the common name of Lemon Peel Fig. 37. — Oleander Scale (Aspidiotus hederse). Scale. It does no injury particularly to the tree, and is mentioned here because it is sometimes met with on the fruit. THE CITRUS MEALY BUG. (Pseudococcus citri Risso.) The citrus mealy bug is widely distributed over the citrus trees of the State from Chico to San Diego, but it is considered an important pest only in certain restricted localities, notably in Ventura and San Diego counties. It is also found commonly on the citrus trees of the Sacra- mento and San Joaquin valleys. It has been known to occur in the State for the past fifteen or twenty years, but has never been consid- ered a very serious pest, except recently in San Diego and Ventura and to a less extent in other counties. The mealy bug is an insect that 482 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION approaches the extent of a pest more or less periodically, and in many cases where it is present for a few years will disappear without any well known specific causes. The mealy bug attacks all parts of the tree, leaf, branch, and fruit, Fig. 38. — Citrus mealy bug (Pseudococcus citri Risso). The two figures on the right show the development of the cottony mass in which the eggs are deposited. seeming to delight particularly in the fruit. Masses of the insect with eggs and young may cluster on the fruit, and in the case of the navel Fig. 39. — Mealy bug on oranges. orange, will be sure to be found secreted in the navel end. It also gives off a very sticky sort of honeydew that makes it exceedingly difficult to wash the fruit clean, in addition to getting the insects themselves removed. Hidden in the navel of the orange, they may pass through Bulletin 214] CITRUS FRUIT INSECTS. 483 the washing machine and also the hand cleaning. This also happens on the lemon, and when this fruit is left in the packing house for curing, they may continue to breed undisturbed. On account of its habit of seeking protected places, they congregate at the base of the petiole of the leaf or stem of the fruit causing the leaves and young fruit to drop prematurely. Because of the injury to the fruit, from the attacks of the insects themselves, and also through the vigorous washing and cleaning, the loss through decay in transit is often very heavy. Fig. 40. — Mealy bug on lemons. LIFE HISTORY AND HABITS OF THE MEALY BUG. The eggs of this insect are laid in a cottony mass which is secreted by the mature female as the eggs are deposited. The number laid by a single individual will be from 350 to 400, and they require about eight to ten days to hatch during the warmer months and in winter from fourteen to eighteen days. The young move about more or less throughout their development. They may not, of course, migrate very far, for they are usually busy feeding. The time of development of the mealy bugs varies consid- erably, taking 2\ months from March to May and about 1^ months during the summer. Males have completed their life cycle in two months in winter and only about one month during the warmer weather of summer. The females appear to have the habit of producing eggs 484 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. before they attain full size, in which cases they continue to enlarge as the eggs are deposited. NATURAL ENEMIES OF THE MEALY BUG. The mealy bug being a soft-bodied insect and exposed as it is on the tree, is subject to the attacks of a considerable number of parasites and predaceous insects. Space will not permit of a full discussion of these here. There are several different species of ladybird beetles that prey upon them, and the one that is to us best known, and probably the most important, is Cryptolaemus mon- fig. 4i.-Hemerobius larva. trouzieri. The larvae of this beetle are covered with cottony tufts, and as they occur among the masses of the mealy bug, are not readily distinguished from them. The beetle itself is black in color and tipped with yellowish brown at either end. The under side is light brown, excepting where the legs arise, which is black. Beside the ladybird beetles there are the lacewing Hemerobius and Syrphus fly larvae, and several internal parasites that attack the mealy bug. Professor R. W. Doane, who assisted in this investigation during the summer of 1910, has observed one Hemerobius larva eat 16 partly- grown mealy bugs in an afternoon. CONTROL OF THE MEALY BUG. This insect is one of the most difficult of all the pests to actually kill all of its numbers. It is very or quite resistant to fumigation dosages as ordinarily used on citrus trees, and because of its habit of congregating in masses or hidden away in the navel of the orange or other secluded places, it is impossible to reach or kill them all with a spray. But of the two methods, the experience in San Diego County and also more recently in Ventura, is that the spray is more effective than fumigation. The spray that Mr. Essig, Horticultural Commis- sioner of Ventura County, especially recommends is the carbolic acid emulsion, consisting of 1 gallon of crude carbolic acid and 8 pounds of whale-oil soap to 170 gallons of water. The soap and carbolic acid are dissolved in hot water. Kerosene emulsion, or the kerosene water spray, discussed at the close of this bulletin, will also give fairly satisfactory results. But with bad infestations two or three sprayings should be made at intervals of three or four weeks. Bulletin 214] CITRUS FRUIT INSECTS. 485 RED SPIDERS. {Tetranychus mytilaspidis Riley.) (Tetranychus sexmaculatus Riley.) The species named above are the two common species of red spiders attacking citrus trees in the State. They occur all over the citrus belt and in one place or another do considerable injury each year. In the early spring is when they become most abundant and do most damage. Later in the spring or summer they largely disappear, although they may be found on the trees the year around. The injury caused by the red spiders is due to the consuming of the plant juices, as indicated by the pale spots where their mouth parts are Fig. 42. — The Florida Red Spider. xl40. inserted. This gives a mottled effect to the leaf, and later assumes an ashy gray or yellowish appearance with but little chlorophyll or green matter left. Leaves thus affected later fall from the tree. The same effect is produced on the fruit as regards the grayish or silvery appear- ance of the rind. Another phase of injury that has become important in some packing houses during the past year is the breeding of the spiders and consequent injury to lemons during the curing process. Both species of red spiders have come into the State from Florida. These are commonly distinguished by the differences in color and mark- ings. T. mytilaspidis, or the Florida red spider, is distinctly red in color, while T. sexmaculatus, or the six-spotted mite, is pale gray in color with six dark spots. The former does the more injury of the two, and is more generally distributed. In addition to the differences in the mites themselves, their habits of feeding are different. The Florida red spider feeds generally over the entire surface of the leaf or fruit making a uniform mottled effect, whereas the six-spotted species feeds largely 486 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. on the under side of the leaf and is confined to restricted areas. These are usually along the mid rib, and extend outward and forward in the direction of the cross veins. These spots are pale colored with old cast skins and black specks on the surface, and covered usually with a web. On the upper surface the leaf is swollen upward, corresponding to the depression on the lower surface, and the area is smooth and pale yellow- ish in color. LIFE HISTORY AND HABITS OF THE RED SPIDER. What follows on the life history has been worked out for T. mytilas- pidis, but the other species is probably very similar. The eggs are minute, nearly-spherical, red bodies, occurring singly Fig. 43. — Orange leaf with area in center showing work of the Florida Red Spider. on the leaf and held in place by an upward projecting stalk with radiating guy threads extending down to the leaf. They require ten days to hatch during May, when they are most abundant. From to 6 or 7 eggs will be deposited each day. after egg laying begins. This will continue for about four weeks, and the average number laid each day will be 2 or 3. Many of the spiders do not lay for the full period so that the number of eggs deposited will range from 30 to 75. The young mite at once begins to feed and comes to maturity in twelve days, during which time it has molted three times at intervals of three days each. The young mite as it hatches from the egg has but six legs, but during the first molt it acquires another pair, making eight, which is the usual number for most spiders and mites. In twelve days to two weeks they are depositing eggs, which is continued for a month longer. The entire life cycle, therefore, will be about forty days, allowing ten days for the eggs to hatch, twelve days for the devel- opment of the young and four weeks for adult life. Male spiders, which are smaller in size than the females, are usually present, but we Bulletin 214 J CITRUS FRUIT INSECTS. 487 have determined that eggs may be produced and young hatched without them. Fig. 44. — Orange leaf on right showing characteristic feeding areas of six- spotted mite on lower surface. On left, upper surface of same leaf. CONTROL OF RED SPIDERS. The standard remedy for spiders and mites is sulfur. It is usually applied dry, dusted over the tree. This may be done by hand, but better by a rotary bellows. In procuring the sulfur, fineness is the most important consideration. The vapor of sulfur is effective but for a very short distance, a fraction of an inch, so that evenness of distribu- tion, instead of large amounts here and there, is more efficient and less wasteful of the sulfur. There is no stated time for application. It should be applied just as soon as injury by the spiders is apparent. This will be some time in the early spring. A temperature of about 75° 4— b214 488 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION. is necessary to properly vaporize the sulfur. The higher the temper- ature above this, the more quickly the sulfur acts. Select, therefore, days that will have a bright, warm sun in the middle of the day, but mm/7 / J lH. « 1^ ^» ./' - 1 . -' . ' \ y*^&F Fig. 45. — Tip of orange twig showing work of six-spotted mite on the leaves. apply the sulfur in the early morning while the dew is still on the foliage. If a sulfur spray is desired, use 30 pounds of sulfur and 15 pounds of lime, as milk of lime, to 200 gallons of water, or 1 to 35 or 50 parts of the commercial lime sulfur. Bulletin 214] CITRUS FRUIT INSECTS. 489 THE SILVER MITE. (Eriophyes oleivorus Ash.) The silver mite in California is restricted to a comparatively small section in San Diego County. This, again, is an imported pest, having come into the State from Florida in 1889. The once familiar russet orange of Florida was the result of the work of this mite on the rind. This mite attacks both the foliage and the fruit, but, of course, the most injury is done to the fruit. The green lemon takes on a decidedly Pig. 46. — Lemon on right showing work of silver mite. silvery appearance, which is due to the extraction of the oils and green matter, or chlorophyll. On account of this silvery effect on the lemon, which is the principal variety of citrus grown in the section, it is known here as the silver mite. In Florida it is called the rust mite of the orange. If the lemons are allowed to ripen on the tree they take on this russet effect, but not to such a marked extent as is the case with the orange. LIFE HISTORY AND HABITS OF THE SILVER MITE. The eggs are somewhat like the red spider eggs, excepting that they are pale yellow in color and smaller. They are laid singly or in small clusters on the foliage or fruit, and hatch in four or five days in summer and ten to fourteen days in winter. The young mite soon begins to feed, and after about a week sheds its skin, which brings it to the adult 490 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION. form. A couple of weeks are all that are necessary, therefore, to bring it from the egg to maturity. This will be the period for the warmer y^ nlulW^' weather, and in colder weather this jiff IffijlilUa. will be doubled. The adult mite, Fig. 47, looks very different from its near ally, the red spider. It is FlG - ^.-snver Mite. more worm-like and has but four legs, while the red spider has eight. THE CONTROL OF THE SILVER MITE. Same as for red spiders, page 487. THRIPS. Most orange or lemon growers are familiar with the fact that upon shaking the blossoms into the hand, there will be likely to be seen Fig. 48. — Work of thrips (Euthrips citri) on fruit. small yellowish to black insects running about. These are thrips of which some species are limited almost entirely to the blossoms, while Bulletin 214] CITRUS FRUIT INSECTS. 491 others attack the leaves and fruit and do serious damage. The orange thrips (Euthrips citri Moul.) causes a leathery, distorted growth, and gives a pale silvery color to the leaves. On the fruit they often work around the stem making a very distinct ring, as shown in Fig. 48, some- times also working down in streaks, as in Fig. 48. Later, they attack the blossom end where the line of injury is not so distinctly and abruptly marked off. This injury to the fruit, while not affecting its edible qualities, decidedly lowers its market value, and such fruit must be consigned as an inferior grade. The part of the tree attacked is the tender growth, and, with a severe infestation, the growth of the tree is considerably interfered with. The foregoing account of thrips injury is due to the citri species or regular orange thrips. This species occurs in greatest abundance in Fig. 49. — Characteristic rings at stem end of small oranges made by thrips (Euthrips citri). the San Joaquin citrus section. It also occurs in southern California, and occasionally does some injury in the Redlands district and more rarely in the other parts of the citrus belt. Its occurrence at Redlands may be due to the fact that the climate there is more nearly like that of Tulare County. The same species also occurs in Arizona and does considerable injury there. However, the only place where it is serious enough thus far to warrant inaugurating control measures is in the San Joaquin belt where, during the past year, about 2,000 acres of orange trees were sprayed. Another species (Heliothrips hcemorrhoidalis) has been observed to do even more serious injury than the citri species on a few trees. In Santa Barbara County three or four cases of a few trees each were seen to have practically the entire foliage and also the fruit severely 492 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. affected by this species. The leaves were of a mottled pale color and many had yellowed and dropped off, and the entire surface of the fruit has a pale silvery color, as shown in Fig. 50. This species has also been Fig. 50. — Orange on right showing work of thrips (Heliothrips hsemorrhoidalis). taken on oranges in Kern- County, but we have no report of damage from that section. The species commonly occurring in the blossoms of citrus trees are Fig. 51. — Work of thrips (H. hsemorrhoidalis) on orange leaf. Euthrips tritici Fitch and Euthrips occidentalis. These are common species widely distributed over the State and attacking various kinds of plants. Thus far these have done no very serious injury to the fruit or foliage of the orange tree. They occur in the blossoms for the Bulletin 214] CITRUS FRUIT INSECTS. 493 purpose of feeding on flower parts, and where their numbers are large, as is often the case, they probably do some injury to the flower and consequent setting of the fruit. But this injury may never become serious enough to warrant any attempt at control. The few trees that were attacked so severely by the hcemorrhoidalis in Santa Barbara County would certainly warrant spraying. But the most widespread injury is done by E. citri and the discussion below on control has special reference to this species. A certain brown spot that is commonly found on oranges was sup- posed to be due to thrips, according to a theory that was promulgated several years ago. Just what is the cause of such spots is not yet known, but thus far no evidence has been adduced to prove that it is due to thrips, and it is certainly not characteristic thrips injury. LIFE HISTORY AND HABITS OF THE ORANGE THRIPS. Adults of this species appear in the early spring and there is a suc- cession of broods on to November. In 1910, they first made their appearance in the Lindsay section about April 15th. By April 22d they were found commonly feeding upon the more tender leaves. According to Mr. J. R. Horton of the Bureau of Entomology, Wash- ington, who has been investigating this species, the period of develop- ment is from seventeen to twenty-three days and the average life of the adult about twenty-five days. He has also determined that pupation does not occur in ground, like its ally the pear thrips, but in rubbish, old leaves, blossoms, and under bands, in the case of trees so protected. CONTROL OF THRIPS. Spraying seems to be the most satisfactory means of combating the thrips and the spray that has been recommended by the Bureau of Entomology consists of : Commercial lime sulfur (33°) 2£ gals. Black leaf extract v 2 gals, of 2|%, or 14 fluid oz. of 40%. Water 200 gals. The first spraying was done in 1910 on April 25th, and it is necessary to follow this with a couple more applications at intervals of about ten days. A strong pressure, 175 pounds, is necessary to reach all parts of the tree. APHIS. (Aphis gossypii.) Often in the early spring on the tender shoots of citrus trees Aphids will be found thickly covering the twig and underside of the leaves. The result of their injury is a curling of the leaves and a checking in growth of the shoot. Fortunately, these insects never completely infest a grove, and only rarely an entire tree. Their attack is confined to a few shoots, usually so that the effect on the whole tree is not so 494 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. serious. Again, they disappear very suddenly in the midst of a maxi- mum infestation. Many people attribute this disappearance entirely to a Braconid parasite which attacks them. But this statement is not always based on close observation. When the lice disappear there is nothing left but the mummies of those which have been parasitized. The conclusion is that they have all been thus killed. As a mat- ter of fact, where there is one mummy left, there were often a score or more of lice during the infestation, and, since it is only the mum- mies that remain, it is not surprising that the parasite should have all the credit. Diseases and weather conditions usually must be consid- ered more important factors in the control of the plant lice than both parasites and predaceous enemies. But, how- ever, they disappear, the important thing is that they often do so, and the grower is relieved of the necessity of inaugurating control measures. In those few cases where they are present and do much injury, they may be killed by a nicotine or weak soap or oil spray. In the case of budded trees, where there is much tender growth, this is sometimes advisable. Fig 52. — Coccinella abdom- inalis. Sav, feeding on Aphids. x5. THE ORANGE TORTRIX. (Tortrix citrana Pern.) Orange growers of southern California have been years more or less familiar with the work of a worm burrowing into the fruit. But very little has been known about the insect itself or its habits. This insect was first described in 1889 and has been reported as doing injury at intervals since that time. During the season of 1909-10 it was the cause of considerable concern in cer- tain sections of the south- ern California citrus belt. It was most abundant in Los Angeles County, from fig. 53.— Eggs of orange Glendale to Covina. In some of the packing houses for a great many tortrix. xl4. during the early Bulletin 214] CITRUS FRUIT INSECTS. 495 part of the season the wormy fruit amounted to between 5 and 10 per cent. The injury is due to the burrows made in the fruit, and those usually go no deeper than just through the rind. There is considerable variation in size of the burrows, as shown in Fig. 56. Fruit that is otherwise sound must be classed as culls on account of these burrows, and in the worst infested places a special man was delegated to sort these out in the packing house. Not only do the holes themselves mar the fruit, but these are the source of infection for several kinds of decay, including the blue mold, the navel end rot, and the wither tip fungus. An orange that may show no outward signs other than the worm hole may be badly infected with decay in the interior. Such a case is indicated in figures 57 and 58. The burrows in the fruit also often cause it to drop prematurely, especially if the fruit is still small, so that all the injury by this insect is not accounted for in the packing house alone. This insect attacks a wide range of food plants aside from the orange. Among those may be mentioned the apricot, willow, oak, wild walnut, golden rod, and a large number of greenhouse plants. On these plants the larvae feed upon the leaves mostly, and these are matted together by means of silk threads which it secretes. In the case of Pelargoniums, they also work in the tip and branches similar to a borer. LIFE HISTORY AND HABITS OF THE ORANGE TORTRIX The eggs are laid on the leaves, usually the lower sur- face and also on the orange it- self. These are laid in masses of from 10 to 35, and overlap one another like fish scales. An individual egg is cream color, 3/100 of an inch in di- ameter, disc-shaped, and with distinctly marked hexagonal net work. Two or three of these masses may be laid by a single moth, the total number of eggs varying from 30 to 75. occurs in twelve days. The young larva upon hatching feeds upon the surface of the fruit at first by making small burrows, but later confines its feeding to a single burrow. A thin network of silk is often spun about the entrance. Fig. 54. — Larva and adult of orange tortrix (Tortrix citrana Fern.). Larva enlarged 5 times. Moth about lh times natural size. Hatching 496 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION. Larva in the insectary entered the fruit on the underside, where it was resting on the surface. In the field the most usual place of entry is where two oranges are in contact or where a leaf is resting upon the fruit. The full grown larva is about half an inch long and the color varies from greenish white to dark gray, with irregular stripes, which show more distinctly in the darker specimens. During the growing period the worms remain almost continuous- ly within the fruit, but upon reaching maturity they may emerge and wander about seeking a suitable place for pupa- tion. If such a place is not found they will pu- pate within their burrow, in fact, this a very com- mon place chosen. The total period necessary to bring the larva to Fig. 55. — Orange tortrix. Pupal skin in burrow and moth which emerged from it. Fig. 56. — Squares of orange rind showing the different types of burrows made by the orange tortrix. maturity is from fifty-five to sixty days and the pupal period lasts from nine to twelve days in midsummer. There is considerable overlapping of broods so that the number is Bulletin 214] CITRUS FRUIT INSECTS. 497 not very well defined. But there is a period in the spring, when the moths are abundant, and again in the early fall. Moths were common in May and the first part of June, and practically none seen in July and August. Judging from the appearance of the worms and of the moths there are probably three generations in a year, in the orange groves. It has not been un- common to find the larva of this orange worm parasi- tized. Those species that have been reared are two new species of Braconids, not yet described. These, upon completing their de- velopment, about the time Fig. 57. — Orange showing burrow of orange tortrix. No evidence of decay on outside. the worm is full grown, emerge and pupate in a cylindrical silken cocoon. As for artificial control of this insect, spraying with an arsenical might be feasible if they became very abundant, but it is not likely that this will ever be necessary. With the present status of in- jury the most practical measure is to pick up and destroy all dropped fruit in the field while the larva is still within its burrow, and also the de- struction of the wormy culls as they are sorted in the packing house. This is a case where an insect, that is probably native and accustomed to feed upon other plants, has adjusted itself to new conditions. Fig. 58. — Same orange as shown in figure 57 cut into showing infection as result of the burrow of the orange tortrix. 498 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. Fig. 59. — Oranges showing two stages of decay induced through the burrows of the orange tortrix. Burrows shown in center of areas. Fig. 60. — Burrows in fruit and leaf folded by Amorbia emigratella, Busch, a Central American insect introduced into Hawaii but hitherto not recorded from California. Bulletin 214] CITRUS FRUIT INSECTS. 499 FULLER'S ROSE BEETLE. (Aramigus fulleri Horn.) This is a grayish brown beetle that measures something more than a quarter of an inch long. It tapers toward the head, which ends in a short snout. The grayish-brown coloring is due to scales which cover the body. These beetles may be seen clinging to a twig, the underside of a leaf, or at some fork among the smaller branches. They are nocturnal, and have the habit of feeding at night, while during the day remain quiet and avoid the light as much as possible. The characteristic injury of the beetles on orange leaves is shown in figure 62. On large trees they feed mostly in the lower and interior part of the tree, this being due partly to their light-shunning habits. But it is on newly budded trees that this insect does the severest injury. They especially delight in the tender FiG 61 _ Fuller - s leaves and often destroy most of the foliage. rose *> eetle - x4 - LIFE HISTORY AND HABITS OF THE ROSE BEETLE. The eggs are laid in batches of from 10 to 50, usually in some scar on the bark of the tree. These require three or four w r eeks to hatch. The larva crawls down to the ground and feeds on the roots of the tree. Usually more injury is done, though not often appreciated, to the roots by the larva of this insect than is done by the beetle on the foliage. The fact that the adult beetle is unable to fly and is dependent upon crawling alone for the ascent of the tree, makes it easy to prevent their attack on the foliage. The method most popular with orange growers is to band the tree trunk with cotton. A band of this about 4 inches wide is placed about the tree and tied by means of a string on the lower side of the band. The band is then pulled down over the string so that it extends out a short distance from the trunk. Tree tangle-foot makes another excellent barrier. 500 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. Fig. 62. — Work of Fuller's rose beetle on orange leaves. Fig. 63. — Small orange trees banded with cotton for protection against Fuller's rose beetle. Bulletin 214] CITRUS FRUIT INSECTS. 501 Fig. 64. — Work of white ants in orange wood. DIABROTICA SOROR. This is the familiar green beetle with twelve black spots that is to be seen everywhere and on all sorts of plants. It often does much damage to the tender, growing shoots of the orange. The lemon foliage is but rarely attacked. In a grove where orange and lemon trees were planted alternately, it was ob- served that no noticeable in- jury occurred on the lemon, while all the young growth of the orange was severely at- tacked. In the case of budded trees, they are specially likely to suffer from the attacks of Diabrotica. The larva is sub- «ffi?.y&, terranean and feeds on several * " ? * ^ 7 ^ different kinds of plants. CONTROL OF DIABROTICA. There are two methods of handling diabrotica, namely, jarring and poisoning. If the trees are small the beetles may be jarred off on a tarred or oiled screen in the early morn- ing while they are still slug- gish. Or the tender growth, where the feeding occurs, may be sprayed with arsenate of lead, 8 pounds to 200 gallons of water, or 1J pounds paris green to 200 gallons of water. Diabrotica soror. 502 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. Fig. 66. — Work of Diabrotica soror on orange leaves. Fig. 67. — Paper sacks on recently budded orange trees for protection against Diabrotica. Negative by J. E. Coit. Bulletin 214] CITRUS FRUIT INSECTS. 503 SERIOUS CITRUS FRUIT PESTS NOT YET ESTABLISHED IN CALIFORNIA. The reader will have noticed that in the discussions of the various pests in this bulletin, that all the important ones, without exception, have been imported into this State. We have with us, therefore, prac- tically all the serious citrus fruit pests excepting the orange maggot and the white fly; and even the latter got fairly well established in the upper Sacramento valley a few years ago. A few additional scale insects might still be imported, but it is probable that none of these would rank in importance with those that are already here, and on account of the universal practice of fumigation, these would be con- trolled along with the others. But such insects as the white fly, the orange maggot, and other fruit flies would probably necessitate the inauguration of additional control measures that would greatly increase our already heavy tax for insect protection. Fig. 68. — Larva of orange maggot. x4. THE ORANGE MAGGOT. {Trypeta ludens Loew.) This is an insect that is a serious pest of oranges in Mexico. The larva or maggot develops within the fruit similar to the codling moth within the apple. From 4 or 5 to 15 or 20 of these maggots may occur in a single orange. The eggs from which these maggots hatch are deposited on the fruit. About 70 eggs ^tftyfifffiW^ are laid by a single fly, and these are -^ distributed over from eight to a dozen oranges. When the worm has attained its growth it leaves the fruit, which usually falls. In case it does not fall, the maggots drop to the ground. The complete life cycle requires about three months. APPEARANCE OF THE ORANGE MAGGOT. From our point of view it is most important to know what the insect looks like, especially the maggot so that in case it appears, there will be no delay in reporting its presence. The larva or mag- got is dirty white in color and when ma- Fig. 6 ». — Pupa of orange maggot. x4. 5— b214 Fig. 70. — Fly of orange maggot (Trypeta ludens. x3. 504 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. ture measures slightly less than one half of an inch long. This is the stage of the insect that occurs in the pulp of the orange. The pupa- rium which is the next stage is light brown in color, barrel-shaped and measures about one third of an inch long. The adult fly is straw yellow in general color with brownish markings on the wings, which when spread measure about five sixths of an inch across. THE CITRUS WHITE FLY. (Aleurodes citri R. & H.) The citrus white fly is one of the most important pests of citrus fruits in Florida. There it outranks all the scale insects as a pest and is less amenable to treatment. It was formerly held that an insect that thrives so well in a humid climate like that of Florida would not be likely to become an important pest in our arid Cali- fornia climate. But such a claim can be no longer held, since the white fly got a foothold two or three years ago in certain points in the Sacramento valley. This, too, in a section that has the typical dry, hot, interior climate. Fig. 71. — Larva of white fly. xl8. The nature of injury of the white fly is similar to that of the black, soft brown, and other unarmored scales; that is, it is not so much the life of Fig. 72. — Cast skin of white fly. Fig. 73. — Adult of white fly. xl5. the tree that is threatened, as the injury consequent to the honeydew and sooty mold. Leaves of trees infested with white fly may be com- pletely covered with the insects themselves on the under side, together Bulletin 214] CITRUS FRUIT INSECTS. 505 with the sooty mold on the upper side, and thus the natural functions of the leaves are impaired, and fruit from such trees is tasteless and insipid. The larva of the white fly is shown in figure 71. It is ovel in shape, slightly less than one sixteenth of an inch long, of a pale greenish yellow color and lies very flat upon the leaf. The adult is a small fly measuring about one tenth of an inch long and covered with a fine white powder, hence the name white fly. SPRAYING TOR CITRUS FRUIT INSECTS. Spraying which is the main reliance for the control of most in- sects of deciduous trees has never been quite satisfactory with the citrus tree. On ac- count of the dense foli- age of the citrus tree it is very difficult to reach all its parts, and since there is no dormant period, the application of insecticides suffi- ciently strong to kill . all stages of the insects is not permissible. Formerly, spraying in the citrus belt was more widely practiced than at present. Spray- ing has lost ground Chiefly for the reason FlG - 74.— Leaf infested with white fly. that growers have come to more generally believe in the better efficiency of fumigation. Spraying came into ill-repute also through the injury due to the old distillate spray, which not only spotted the fruit, but dropped the leaves in many cases. 506 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION. In spite of the fact that, as a general practice nnder all conditions, spraying is out of the question, it still has a limited place in the control of citrus scales. Eighteen thousand dollars is expended annually for spraying citrus trees in Riverside and San Bernardino counties. If there is a uniform hatch of black scale, and they are all small, there is no doubt but that a thorough spraying will keep them in check. But in the case of the purple scale, with eggs always likely to be present, very poor results may be expected. The principal field for spraying is in the case of young trees infested with the black scale or a few trees about the dooryard, where it is often difficult to get the work done by fumigation. The objection formerly held in regard to the injury to the tree and fruit no longer occurs with the lighter grade of oil used. The distillate was a 28° gravity oil, and was used at a strength of 2 per cent. The oil that is now in most general use is a cheap grade of ordinary kerosene. This is used at a strength of 10 per cent, the formula being as follows : Kerosene or water white oil 20 gallons Water 200 gallons This is applied only with a power outfit with a good agitator which is necessary to make a mechanical mixture of the oil and water. Where there are but a few small trees, and a hand outfit is to be used, kerosene emulsion may be substituted. The formula is as follows : Kerosene 1 gallon Soap -J pound Water 15- gallons Dissolve soap in a gallon of hot water, add 1 gallon of kerosene, and mix by turning nozzle of spray pump back into mixture, and then dilute to make 15 gallons. FUMIGATION. It is not intended in this general bulletin to discuss all the phases of the subject of fumigation, but simply to give a few of the more impor- tant facts. Those wishing a more detailed treatment of the subject should send to the State Experiment Station for Circulars 11 and 50 by Prof. C. W. Woodworth, and to the Bureau of Entomology, Wash- ington, for Bulletins 79 and 90 by Mr. R. S. Woglum. VARIATION OF DOSAGE. Seven or eight years ago the experiment station had a man in the field for the purpose of determining the actual practice of scheduling dosage. Practically all of the fumigating outfits then operating in the State were visited, and the tented trees accurately measured and the doses given them by the scheduler recorded. Thus, the dosage and measure- Bulletin 214] CITRUS FRUIT INSECTS. 507 ments of over 2,000 trees were made, representing the actual practice of 30 fumigators. From this study it was found that for a 10-foot tree, having the two dimensions approximately equal, the dosage varied from 2 to 7J ounces. And for a 20-foot tree the variation was from 7 to 32 ounces. This is evidence enough, without further comment, in favor of some system of measurement or accurate calculation of dosage as against the old system of guessing. FACTORS IN VARIATION OF DOSAGE. There are three principal factors that account for the great variation in dosage : first, there is the inaccuracy of judging the exact size of the tree, and the consequent dosage ; second, there is the difference of opinion of different fumigators as to the dose a particular sized tree infested with a particular scale should have. For example, a tree infested with red scale that measures 20 feet over the top and 30 feet around the base ; one man will say it should have 4 ounces, another 5, another 6, and another 8. Thus, there may be a variation of 50 per cent for the same tree and infested with the same insect; third, there is the variation in dose as the size of the tree varies. We will assume that all fumigators agree on, say four ounces as the proper dose for a tree 20 by 30 feet. Then, for a tree twice that size, the same people will vary their dose from 10 to 30 ounces. This is a difference in basis of calculation or variation, as the size of the tree increases or diminishes. The first two of these factors are easily remedied. The exact size of the tree can be ascertained by some system of measurement ; and there should be a general agreement as to how much cyanide is necessary to kill the different scales. But the third factor, namely, varying the dosage properly according to the size of the tree, is a more difficult and complicated question. BASIS FOR DOSAGE. The first dosage schedule published was based upon the cubic contents. This, naturally, would be the logical basis for calculation ; but in actual practice it was soon found that a large tree required a dose proportion- ally less than a smaller tree. This is accounted for through the leakage of gas, and a small tree has more tent surface per unit of volume than a larger tree. So many widely different schedules were proposed until finally actual field practice established a more or less elastic schedule with the approximate proper variation in dosage according to the size of the tree. AREA BASIS. This has worked out into practically an area basis rather than a volume basis, that is, trees receive a dose more nearly according to the 508 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION. area of their tent surface than to the cubic contents of the tented tree. This basis of dosing a tree according to the tent surface was proposed by Woodworth of this station in 1903, and it is the one adopted by Mr. Woglum. SCHEDULES AND CALCULATION. The following is a very simple formula by means of which any one can construct his own schedule. This formula is simply to multiply the circumference of the tented tree by the distance over the top and point off two places. The result is the number of ounces of cyanide for the given tree for the purple scale, or the maximum dosage : Examples: A tree 20x30 6 ounces cyanide. 30x40 12 ounces cyanide. This is the schedule for the purple scale and corresponds in general with Mr. "Woglum 's schedule No. 1. For the red and yellow scales, or for the black scale, excepting where it is full grown, reduce this schedule by one quarter. Examples: A tree 20x30 6 ounces for purple. 4.5 for red, yellow and black. 30x40 12 ounces for purple. 9.0 for red, yellow and black. SODIUM CYANIDE. Mr. Woglum has demonstrated that sodium cyanide is equally as satisfactory as the potassium, both in generating properties and efficiency in killing the scale; and since it will be apparently cheaper than the potassium it seems probable that it may sooner or later come into very general use. Heretofore, the experience with sodium cyanide has not been satisfactory for the reason, chiefly, that the product was not pure enough. "What has been passing for 98 to 100 per cent sodium cyanide has been a 98 to 100 per cent purity in terms of potassium cyanide, whereas, if we accept potassium as a basis of purity, the sodium cyanide should be 126 to 133 per cent pure. It is unfortunate that this above-a- hundred per cent purity should have got started, but since we are accustomed to potassium as a standard possibly it is justifiable. Any- way, all we need to know is that a pound of chemically pure sodium cyanide contains about one third more cyanide or cyanogen than the potassium, and will thus produce more gas. FORMULA FOR SODIUM CYANIDE. Since there is more cyanide or cyanogen in a pound of sodium cyanide than in a pound of potassium cyanide, it will require a proportionally greater amount of acid. One of the uses of water in the generation of hydrocyanic acid gas is to dissolve the residual sulphate and thus pre- vent it from coating the cyanide not yet generated or reached by the Bulletin 214] CITRUS FRUIT INSECTS. 509 acid. In the case of sodium cyanide there is approximately one third less of the sulphate formed, and consequently the water may be reduced about one third. Therefore, the proportions of cyanide acid and water will differ in case sodium cyanide is used, and the formula that has been found to be satisfactory is: Sodium cyanide 1 part by weight. Acid 1$ parts by volume. Water 2 parts by volume. It should be noted that in case sodium cyanide is used all dosage tables should be reduced one quarter. ADULTERANTS. The commonest adulterant of cyanides is sodium chloride or common salt, and this is likely to get into sodium cyanide, particularly in large amounts. The presence of this salt produces a reaction in which hydro- chloric acid is formed and this acts in turn directly upon the hydrocyanic acid gas, thus decomposing it. In order to avoid this adulterant a high degree of purity should be insisted upon, and this, stated in terms, of the potassium salt should be 124 to 133 per cent pure. COMPARATIVE COST OF SODIUM AND POTASSIUM CYANIDE. A good sodium cyanide can be bought for 27 or 28 cents per pound as against potassium at about 25 cents. It requires a little more acid for the sodium so that the acid bill is higher and the cost per pound of cyanide is higher. But since one pound of the sodium will generate as much as one and a quarter pounds of the potassium, the cost is really in favor of the sodium cyanide, and this, if calculated out, will be found to amount to from 1J to 3^ cents per pound. FORMULA FOR POTASSIUM CYANIDE. The proportions of cyanide, acid and water that have been found to produce the greatest amount of gas are : Cyanide 1 oz. avoirdupois. Acid 1 fluid oz. Water 1 3 fluid ozs. The water and acid are first placed in an earthenware vessel and the cyanide added. EXPOSURE. The usual exposure is from 45 minutes to 1 hour. 510 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION. SEASON FOR FUMIGATING. The fumigating season extends from August to January. The fruit is more susceptible to injury until it attains about the size of a walnut. Fumigation during extremes of temperature (above 70° and below 35° F.) may injure foliage and fruit, or during a high wind. TENTING MATERIAL. To secure the tightest possible material is good economy. If maxi- mum dosages are used with old leaky tents, it may be necessary to reduce the dosage with the tighter material. And the reduction from the given schedules should not be made the same for all sizes of trees, because, as the tenting material becomes tighter, the schedule should approach more nearly that of the volume basis. MEASUREMENT OF TENTS. The distance over the tented tree may be obtained by having the tents marked according to the Morrill system, or any other, and the distance around secured by a tape or accurate pacing. The following tables are based upon the formula given above. The schedule for the purple scale corresponds in general with that of "Wog- lum's schedule No. 1, and those for the red, yellow and black are on the basis of three quarters of this schedule : SCHEDULE FOR PURPLE SCALE. Circumference trees 16-56 feet. 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 10 H 14 2 2 2 24 24 3 3 (Distance around.) 3 3* 12 2 2 24 3 3 3 34 34 34 4" 4* 14 24 3 3 34 4 4 4 4* 4* 5" 5* 16- H 4 4 44 5 5 5| 6" 6 6j 7 18 | 4 44 4 I 5 54 6 6 6* 7 7 7* 20 I 5 54 6 6 6* 7 7| 8 8 8* 9 22 g 6 64 7 7" n 8" 8 84 9" 94 10 - 24| 7 71 '2 8 8| 9 94 10 10 10*, 11 84 9 9* 10 IO4 11 11} 12 9* 10 10* H llj 12 12" 13 114 26 5 8 12| 13 28 14 141 15 30 " 104 ll" 11* 12 13 13* 14 12 12| 13 14 14j 15 14* 15 154 16 32 15j 16 17 174 SCHEDULE FOR PURPLE SCALE. Circumference trees 40-80 feet. 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80 154 16* 17 17* 184 19 20 " 184 19" 20 204 21| 22 (Distance around.) 20 204 21* 22 23 24 25 20* 21* 22" 23 24 244 25* 26 2l| 22* 23* 24 25 26 26* 27* 284 23 23* 24* 25* 26 27 28" 28j 29£ 30* 46 1 24* 25* 26* 27* 28* 294 30 31 32 33 34 48 1 " 25* 26* 27 J 28* 29* 304 314 32* 334 344 35 50 8 28 29" 30" 31" 32 33 34 35 36 37 38 52 " 30 31 32 33 34 35 36 37 38 394 4 <>4 54 32 33 344 35* 36* 37* 38J 39J 40 41 42 56 34* 354 36| 38| 39" 40 41 42*, 434 44 4 i 7 Bulletin 214] CITRUS FRUIT INSECTS. 511 SCHEDULE FOR RED, YELLOW, AND BLACK SCALES. Circumference trees 16-56 feet. 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54 56 (Distance around. ) io i i i i i 14 n 2 2 2 24 12 1 1 1£ 2 2 2 2i 2* 24 3 3 14 14 2 '2 2| 3 3 3" 3" 3 34 4 16- d 2| 3 3 3 3HM 4 4|4i 54 18 « 3 3 3 3| 4" 4 4 4j 5 5 54 20 ° 34 4 4" 4 44 5 54 6 6 6* 22 § 4 4i 5 5" 54 6" 6 64 64 24 I 5" 54 6 6 64 64 7 7" 74 8 84 26 3 6 6 64 64 7" 74 8 8} 9 9 94 28 64 64 74 8 84 9 9" 94 10 10| 11 30 7| 8 84 9" 94 10 104 104 11 114 12 32 9 9 94 104 10 1 11" 114 12 12| 13 SCHEDULE FOR RED, YELLOW, AND BLACK SCALES. Circumference trees 40-80 feet. 40 42 44 46 48 50 52 54 56 58 60 62 64 66 68 70 72 74 76 78 80 (Distance around.) 34 10 10 104 11 114 12 124 13 134 14 15 36 11 111 12 124 13 134 14 15 15 16 16 38 12" 13 13" 14 15" 15 16 16 17 18 18i 40-: 13 14 15 15 16 16 17 18 18 19 19 42 I 15 154 16 164 17 18 184 19 194 204 21 44 % 16" 17 17 18 19 19" 20 21 21 22 224 46 S 18 19 194 204 21 22 22 23 24 244 244 48 1 19 194 20j 21 22 224 234 24 25" 254 26 50 g 21" 21" 22 23 24 244 254 26 27" 274 28J 52 224 23 24 244 254 26" 27 274 284 294 30 54 " 24 244 254 264 274 28 284 294 30" 304 314 56 254 264 27 284 29 30" 304 31 32" 33„ INSPECTION AND QUARANTINE. In most of the counties of the citrus belt there are special ordinances pertaining to the quarantine of certain citrus fruit pests. The grower or nurseryman should consult his county horticultural commissioner regarding these before making any interchange of nursery or other stock. The section of the state law relating to the duties of county boards of horticulture, approved March 6, 1909, is given below : Section 2322a. It shall be the duty of the county horticultural commissioner in each county, whenever he shall deem it necessary, to cause an inspection to be made of any premises, orchards or nursery or trees, plants, vegetables, vines, or fruits, or any fruit-packing house, storeroom, salesroom, or any other place or article in his jurisdiction, and if found infected with infectious diseases, scale insects, or codling moth, or other pests injurious to fruit, plants, vegetables, trees, or vines, or with their eggs or larva?, or if there is found growing thereon the Russian thistle or saltwort, Johnson grass or other noxious weeds, he shall in writing notify the owner or owners, or person or persons in charge, or in possession of the said places, or orchards or nurseries, or trees, or plants, vegetables, vines, or fruits or article as aforesaid, that the same are infected with said diseases, insects or other pests, or any of them, or their eggs or larvae, or that the Russian thistle or saltwort, Johnson grass or other noxious weeds is growing thereon, and require such person or persons, to eradicate or destroy the said insects, or other pests, or their eggs or larvae, or Russian thistle or saltwort, Johnson grass, or other noxious weeds within a certain time to be therein specified. Said notices may be served upon the person or persons, or either of them, owning or having charge, or having possession of such infested place or orchard, or nursery, or trees, plants, vegetables, vines, or fruit, or articles, as aforesaid, or premises where the Russian thistle or saltwort, or Johnson grass, or other noxious 6— b214 512 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION. weeds shall be growing, or upon the agents of either, by any commissioner, or by any person deputed by the said commissioner for that purpose in the same manner as a summons in a civil action ; provided, however, that if any such infected or infested articles, property or premises as hereinabove specified belong to any non-resident person and there is no person in control or possession thereof and such non-resident person has no tenant, bailee, depositary or agent upon whom service can be had ; or, if the owner or owners of any such articles, property or premises can not after due diligence be found, then such notice may be served by posting the same in some conspicuous place upon such articles, property or premises, and by mailing a copy thereof to the owner thereof at his last known residence, if the same is known or can be ascertained. Any and all such places, or orchards, or nurseries, or trees, plants, shrubs, vegetables, vines, fruit, or articles thus infested, or premises where the Russian thistle, or saltwort, or Johnson grass, or other noxious weeds shall be grow- ing, are hereby adjudged and declared to be a public nuisance ; and whenever any such nuisance shall exist at any place within his county, and the proper notice thereof shall have been served, as herein provided, and such nuisance shall not have been abated within the time specified in such notice, it shall be the duty of the county horticultural commissioner to cause said nuisance to be at once abated, by eradicating or destroying said diseases, insects, or other pests, or their eggs, or larvae, or Russian thistle or saltwort, or Johnson grass or other noxious weeds. The expense thereof shall be a county charge, and the board of supervisors shall allow and pay the same out of the general fund of the county. Any and all sum or sums so paid shall be and become a lien on the property and premises from which said nuisance has been removed or abated in pursuance of this chapter. A notice of such lien shall be filed and recorded in the office of the county recorder of the county in which the said prop- erty and premises are situated, within thirty days after the right to the said lien has accrued. An action to foreclose such lien shall be commenced within ninety days after the filing and recording of said notice of lien, which action shall be brought in the proper court by the district attorney of the county in the name and for the benefit of the county making such payment or payments, and when the property is sold, enough of the proceeds shall be paid into the county treasury of such county to satisfy the lien and costs ; and the overplus, if any there be, shall be paid to the owner of the property, if he be known, and if not, into the court for his use when ascertained. The county horticultural commissioner is hereby vested with the power to cause any and all such nn Usances to be at once abated in a summary manner. STATION PUBLICATIONS AVAILABLE FOR DISTRIBUTION, REPORTS. 1896. Report of the Viticultural Work during the seasons 1887-93, with data regard- ing the Vintages of 1894-95. 1897. Resistant Vines, their Selection, Adaptation, and Grafting. Appendix to Viti- cultural Report for 1896. 1902. Report of the Agricultural Experiment Station for 1898-1901. 1903. Report of the Agricultural Experiment Station for 1901-03. 1904. Twenty-second Report of the Agricultural Experiment Station for 1903-04. BULLETINS. Reprint. Endurance of Drought in Soils ofj No. 186. the Arid Region. 187 No. 128. Nature, Value, and Utilization ofj Alkali Lands, and Tolerance ofj 188. Alkali. (Revised and Reprint,] 1905.) •] 189. 133. Tolerance of Alkali by Various Cultures. j 190. 147. Culture Work of the Sub-stations. 191. 149. California Sugar Industry. 192. 151. Arsenical Insecticides. 153. Spraying with Distillates. 193. 159. Contribution to the Study of Fer- mentation. 161. Tuberculosis in Fowls. (Reprint.) 194. 162. Commercial Fertilizers. (Dec. 1, 1904.) 195. 165. Asparagus and Asparagus Rust in California. 197. 167. Manufacture of Dry Wines in Hot Countries. 168. Observations on Some Vine Dis- eases in Sonoma County. 198. 169. Tolerance of the Sugar Beet for 199. Alkali. 200. 170. Studies in Grasshopper Control. 171. Commercial Fertilizers. (June 201. 30, 1905.) 172. Further Experience in Asparagus 202. Rust Control. 174. A New Wine-cooling Machine. 203. 176. Sugar Beets in the San Joaquin Valley. 204. 177. A New Method of Making Dry Red Wine. 205. 178. Mosquito Control. 179. Commercial Fertilizers. (June, 206. 1906.) 180. Resistant Vineyards. 207. 181. The Selection of Seed- Wheat. 208. 182. Analysis of Paris Green and 209. Lead Arsenic. Proposed In- 210. secticide Law. 183. The California Tussock-Moth. 211. 184. Report of the Plant Pathologist to July 1, 1906. 212. 185. Report of Progress in Cereal 213. Investigations. The Oidium of the Vine. Commercial Fertilizers. (Janu- ary 1907.) Lining of Ditches and Reservoirs to Prevent Seepage and Losses. Commercial Fertilizers. (June, 1907.) The Brown Rot of the Lemon. California Peach Blight. Insects Injurious to the Vine in California. The Best Wine Grapes for Cali- fornia ; Pruning Young Vines ; Pruning the Sultanina. Commercial Fertilizers. (Dec, 1907.) The California Grape Root- Worm. Grape Culture in California ; Improved Methods of Wine- making ; Yeast from California Grapes. The Grape Leaf-Hopper. Bovine Tuberculosis. Gum Diseases of Citrus' Trees in California. Commercial Fertilizers. (June, 1908.) Commercial Fertilizers. (Decem- ber, 1908.) Report of the Plant Pathologist to July 1, 1909. The Dairy Cow's Record and the Stable. Commercial Fertilizers. (Decem- ber, 1909.) Commercial Fertilizers. (June, 1910.) The Control of the Argentine Ant. The Late Blight of Celery. The Cream Supply. Imperial Valley Settlers' Crop Manual. How to Increase the Yield of Wheat in California. California White Wheats. The Principles of Wine-making. CIRCULARS. No. 1. Texas Fever. 5. Contagious Abortion in Cows. 7. Remedies for Insects. 9. Asparagus Rust. 11. Fumigation Practice. 12. Silk Culture. 15. Recent Problems in Agriculture. What a University Farm is For. 17. Why Agriculture Should be Taught in the Public Schools. 19. Disinfection of Stables. 29. Preliminary Announcement Con- cerning Instruction in Practical Agriculture upon the University Farm, Davis, Cal. 30. White Fly in California. 32. White Fly Eradication. 33. Packing Prunes in Cans. Cane Sugar vs. Beet Sugar. 36. Analyses of Fertilizers for Con- sumers. 39. Instruction in Practical Agricul- ture at the University Farm. No. 46. Suggestions for Garden Work in California Schools. 47. Agriculture in the High Schools. 48. Butter Scoring Contest, 1909. 50. Fumigation Scheduling. 51. University Farm School. 52. Information for Students concern- ing the College of Agriculture. 53. Announcement of Farmers' Short Courses for 1910. 54. Some Creamery Problems and Tests. 55. Farmers' Institutes and University Extension in Agriculture. 58. Experiments with Plants and Soils in Laboratory, Garden, and Field. 59. Tree Growing in the Public Schools. 60. Butter Scoring Contest, 1910. 61. University Farm School. 62. The School Garden in the Course of Study.