UNIVERSITY OF CALIFOBNIA PUBLICATIONS COLLEGE OF AGRICULTURE AGRICULTURAL EXPERIMENT STATION BERKELEY, CALIFORNIA THE PEACH TWIG-BORER (Anarsia lineatella Zeller) BY WILLIS P. DURUZ BULLETIN No. 355 March, 1923 UNIVERSITY OF CALIFORNIA PRESS BERKELEY 1923 David P. Barrows, President of the University. EXPEEIMENT STATION STAFF HEADS OF DIVISIONS Thomas Forsyth Hunt, Dean. E. J. Wickson, Horticulture (Emeritus). , Director of Eesident Instruction. C. M. Haring, Veterinary Science; Director of Agricultural Experiment Station. B. H. Crocheron, Director of Agricultural Extension. C. B. Hutchinson, Plant Breeding; Director of the Branch of the College of Agriculture. H. J. Webber, Citriculture; Director of Citrus Experiment Station. William A. Setchell, Botany. Myer A. Jaffa, Nutrition. Ealph E. Smith, Plant Pathology. John W. Gilmore, Agronomy. Charles F. Shaw, Soil Technology. John W. Gregg, Landscape Gardening and Floriculture. Frederic T. Bioletti, Viticulture and Fruit Products. Warren T. Clarke, Agricultural Extension. Ernest B. Babcock, Genetics. Gordon H. True, Animal Husbandry. James T. Barrett, Plant Pathology. Walter Mulford, Forestry. W. P. Kelley, Agricultural Chemistry. H. J. Quayle, Entomology. Elwood Mead, Rural Institutions. H. S. Eeed, Plant Physiology. L. D. Batchelor, Orchard Management. W. L. Howard, Pomology. *Frank Adams, Irrigation Investigations. C. L. Eoadhouse, Dairy Industry. E. L. Adams, Farm Management. W. B. Herms, Entomology and Parasitology. John E. Dougherty, Poultry Husbandry. D. E. Hoagland, Plant Nutrition. G. H. Hart, Veterinary Science. L. J. Fletcher, Agricultural Engineering. Edwin C. Voorhies, Assistant to the Dean. DIVISION OF POMOLOGY W. L. Howard W. P. Duruz W. P. Tufts L. C. Barnard E. L. OVERHOLSER I/. H. DAY A. H. Hendrickson J. L. Stahl F. W. Allen C. L. Austin J. P. Bennett M. J. Heppner G. L. Philp * In cooperation with Division of Agricultural Engineering, Bureau of Public Roads, U. S. Department of Agriculture. THE PEACH TWIG-BORER (Anarsia lineatella Zeller) By WILLIS P. DURUZ CONTENTS PAGE Introduction 419 Review of Literature 421 Description of the Insect 424 Systematic Position 424 Names of the Insect 425 Life History 426 The Larvae 426 The Pupae 429 The Adults 430 The Eggs 431 Larvae of Second Generation 434 Larvae of Third Generation 434 Hibernation of Last Brood of Larvae 435 Parasitism 437 Life History Experiments 438 Evidences of a Second Generation 438 Evidences of a Third Generation 442 Spraying Experiments 1921 443 Details of the Experiments 444 Discussion of Results 445 Spraying Experiments 1922 447 Details of the Experiments 447 Discussion of Results 455 Conclusions 459 Recommendations 460 Summary 461 Acknowledgments 462 Literature Cited 462 INTRODUCTION The peach twig-borer or peach worm, Anarsia lineatella Zeller, is an Old World insect, probably coming to this country many years ago on fruit trees from Asia. It has become a serious pest in this country and causes great loss every year. Records show that it is present in at least fifteen states, including California, Colorado, Dela- ware, District of Columbia, Georgia, Illinois, Idaho, New Jersey, 420 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION New York, Maryland, Mississippi, Oregon, Texas, Virginia, and Washington, as well as in Canada, and probably occurs the world over, wherever its host plants are grown. It is particularly serious on the Pacific Coast, and in California is one of the three or four most destructive insects found on stone fruits. It attacks not only the peach, but the almond, apricot, nectar- ine, plum and prune. Every season severe damage is done to the buds and young terminal shoots, particularly on trees one to four years old, and still greater is the loss by injury to the fruit. It is estimated that in California the loss averages from ten to forty per cent of the entire crop and amounts to over one million dollars annually. At various times since the discovery of the peach twig-borer, investigators have studied its habits and attempted its control. Ex- periments conducted in 1902 by Warren T. Clarke, 5 * in Placer County proved conclusively that this insect could be controlled by a home- made lime, salt, and sulfur spray applied as the buds were swelling. Many years of experience seemed to prove the effectiveness of this treatment. Gradually the commercial preparation of lime-sulfur with the salt omitted, displaced this homemade mixture and became the standard remedy for spraying against the peach twig-borer. During the last three or four years, however, some doubt has arisen as to the advisability of using lime-sulfur at all, particularly on apricot trees, for fear of injuring the fruit. Many fruit growers in California have also questioned the efficacy of lime-sulfur as a control for the peach twig-borer, because they have observed considerable injury from this insect even when this spray was applied in the recommended manner. It has been felt, too, that additional spray materials ought to be tested out, especially on host plants other than the peach. Moreover, there has been much controversy among entomologists regarding the life history of the insect. Some authorities have be- lieved that there are from two to four generations a year, while the observations of others convinced them that there is but one irregular brood which extends over the entire season. All this uncertainty and the great economic importance of the insect made a new investigation of the peach twig-borer necessary. It was desirable, first, that the life history and habits of the insect be carefully observed, and second, that a satisfactory means of com- bating it be found. This bulletin is a report of three seasons' study and experiment dealing with the points above mentioned as well as with other miscellaneous factors. The observations and experiments * Reference to literature cited on page 462. Bulletin 355] THE PE ACH TWIG-BORER 421 were conducted at Davis, Esparto, and Winters, Yolo County ; Vaca- ville, Solano County; and Auburn, Newcastle, Loomis, and Penryn, Placer County. Certain of the observations and results herein reported agree with the findings of some investigators, but disagree with those of others. Some hitherto unnoted habits of the insect have been observed and its life history at several places carefully determined. Certain details regarding remedial measures have been learned which make the control of this insect more complete and satisfactory by permitting the fruit grower to attack it at three or four different stages. Other miscellaneous matters have been discovered that lead to advice which, if followed, will prove helpful in preventing serious injury from this pest in the future. EEVIEW OF LITERATURE A brief review of the important literature of previous writers is here presented to show the development and accumulation of informa- tion relating to the peach twig-borer. The first published account of the peach twig-borer was the original description by Zeller in Germany in 1839. 37 Clemens 6 in 1860 described the same insect in this country, assigning it to a different species, however, and doubtfully referring it to the genus Anarsia (Anarsia pruinella). But in 1872 7 he identified it with the insect described by Zeller. Riley also obtained specimens of the same moth from peach twigs, and on submitting samples to Zeller, they were pronounced identical with the European insect. In 1872 Saunders 31 described an insect attacking the crown and root of the strawberry and believed it to be the peach twig-borer. This theory was shared by subsequent writers until Cordley 11 in Oregon in 1897 pointed out the fact that the peach twig-borer and the strawberry crown-borer were distinct insects. In July 1872 Glover 17 reported the peach twig-borer as occurring in Maryland and Virginia and doing damage for the first time in the United States. He described the nature of the injury and sug- gested cutting off the withered shoots in May and June. Comstock 8 in 1878 briefly described the twig-boring habit of the larvae of this insect and the pupation of a second generation on the peach. Lintner 22 in 1882 gave a bibliography and quotations of previous writers and further described the habits of the insect. He reported it as occurring in eight different localities in New York State and 422 UNIVERSITY OF CALIFORNIA— EXPERIMENT STATION referred to the existence of a chalcid parasite {Copidosoma of Ratze- burg) on the pupa. He also recommended cutting off the wilted shoots in May and June. Klee 21 in 1888 described the damage caused by the twig-borer to various plants, including strawberries in California. He stated that it was subject to parasites, which might account for its disappearance in some localities. He recommended scraping off the rough bark of trees and removing wilted young twigs, as well as guarding against introducing the pest on fruit boxes into non-infested districts. Coquillett 10 in 1891, referred to the working of an insect suspected to be Anarsia lineatella in Kern County on trees brought from Ala- meda, California. He described the working of the insect in terminal shoots. Fully eight hundred apricot trees were reported attacked, from four to six of the youngest twigs being destroyed on each tree. Spraying with Paris green (1 pound to 180 gallons of water) was reported to be an effective control measure. The next work of economic value was that of Ehrhorn, reported by Craw 13 in 1893. Results of Ehrhorn 's investigations in the Santa Clara Valley, California, showed that the insect winters in the early larval stages in hollow chambers in crotches of the branches. Eggs of the last brood are placed in the fall; the larvae hatch and grow very slowly at the point indicated and construct chambers for passing the winter. When new growth starts in the spring they leave their burrows in the bark and enter the new shoots. The later brood works in the fruit. Remedies suggested were; coal oil or resin solution, or lime-sulfur-salt mixture sprayed in January or February. Clipping off the wilted shoots was also suggested. He considered the trial of parasites advisable. In 1898 Gossard 19 briefly described the insect's habits and the injury it did. Kerosene emulsion was recommended, but its effective- ness was doubted. Marlatt 23 in 1898 published the fullest account of the peach twig- borer up to that time. He thoroughly reviewed the work of previous investigators, including descriptions of the insect, its habits, life history, and control measures. He told of a minute parasitic native mite (Pediculoides ventricosus) and a chalcid parasite, alluded to by Comstock 8 and later described by L. 0. Howard as Copidosoma variegatum. A new parasite was reported from material submitted by Ehrhorn and identified by Ashmead as Oxymorpha livida. The remedies advised were clipping off the wilted shoots in May and spraying with kerosene emulsion in January or February. The Bulletin 355] THE PEACH TWIG-BORER 423 possibility of control by arsenicals in the fall and spring was also suggested, but at the same time doubt was cast upon their effective- ness. Unfortunately the work done by Marlatt 23 was not conducted under natural field conditions and in many respects does not agree with observations made in California. Likewise other eastern observations have been fragmentary and require verification before being used on the Pacific Coast as a basis for a plan of control. The best work on the control of the twig-borer in California was done by Clarke 5 who published his results in 1902. Clarke reported observations on the activity of the insect and gave the results of spraying experiments in Placer County. Many points in the life history were cleared up, several observations being at variance with previous published accounts. Conclusions drawn from the experi- ments warranted the recommendation to spray with lime-sulfur-salt mixture at the time the buds are swelling. Piper 25 in 1905 writing of ' ' Orchard Enemies of the Pacific North- west," includes the peach twig-borer as an important pest. He tells of the insect being " usually noted in late varieties of peaches, the earlier ones being exempt as a rule. ' ' The type of injury and extent of damage is described. Piper states, "lime-sulfur-salt mixture shows no appreciable effect." Kerosene emulsion proved the most reliable remedy. In 1907 Taylor 32 working in Colorado made the following sum- mary of spraying experiments: "Former recommendations for the control of this insect have been for spring applications of lime and sulfur washes. This has in fact been a most successful treatment, but the use of lead arsenate against the twig-borer of the peach is destined to meet with equal popularity when its efficiency, cost, and convenience of preparation and application are considered." Taylor's counts showed 97 per cent benefit from spraying with arsenate of lead, as against 90 per cent with lime-sulfur, the spray being applied as the blossoms were showing pink. Yothers 36 in 1914 held the opinion that the "regular San Jose scale spraying (either with lime-sulfur or crude oil emulsion) would reduce the work of the peach twig-borer to a minimum in the state of Washington. In 1915 Wilson 35 published a very complete account of this insect in Oregon. He reviewed its life history and admitted that the ques- tion of the number of generations per year in Oregon was puzzling. At Corvallis only a single generation was found, while in eastern and southern Oregon two or three generations appeared. Results 424 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION of a series of spraying experiments were tabulated, showing that when applied in April, lime-sulfur, 1-12, in combination with arsen- ate of lead, 2-50, gave almost perfect control. "Black Leaf 40," 1-2000, with lime-sulfur, 1-12, also gave very high control, as did arsenate of lead, 2-50, with "Black Leaf 40," 1-2000. Arsenate of lead and "Black Leaf 40" alone also gave good control. Essig 14 in 1915 in his publication on "Injurious and Beneficial Insects of California, ' ' gives a most complete summary of the present information on the peach twig-borer. The life history, nature of work, distribution, food plants, natural enemies, and control are all very thoroughly discussed. Essig shared the opinion of G. P. Weldon that the insect had but one uneven brood a year. The control sug- gested was "a thorough application of lime-sulfur spray when the buds begin to swell." Howard's and Home's 20 observations in 1920 in experiments with brown rot showed that the peach twig-borer was almost completely controlled with commercial lime-sulfur 1-10, and by dry lime- sulfur, 12-50. They further remark, however, "This was especially true where trees were sprayed twice before they came into bloom. Spraying after the trees came into bloom with either of the lime-sul- furs had little effect against the borer. Bordeaux mixture and oil sprays afforded no protection against the insect." In 1921 Wakeland 33 called attention to the seriousness of the peach twig-borer in Idaho on peaches and prunes. He recommended spraying with lime-sulfur at the time the buds are swelling and doubted that a combination of lime-sulfur and arsenate of lead would prove worth the additional expense. Although, admitting cases where such sprays brought the desired results, arsenate of lead alone, he states, "is likely to prove unsatisfactory." DESCRIPTION OF THE INSECT Systematic Position. — The peach twig-borer belongs to the order Lepidoptera, and has been assigned to the family Gelechiidae 2 . The original description of the genus Anarsia and the species lineatella as given by Zeller 37 is quoted below : "17. Anarsia Zell. Palpen des Mannchens wie bei Ateliotum, die des Weibchens, dessgleichen die Kopfhaare, die Junge, der Pliigelbau u. beider Geschlechter wie bei Ypsolophus. 1. Decolorella Zell — grosser als Anchin. bicost.; die Vorderfl. blass lehmgelblich, an den Gegenrandern aschgrau, im Mittelraume mit eini- gen Langsreihen schwarzer Punctehen. — I. M. aus Sicilien. Bulletin 355] THE PE ach TWIG-BORER 425 2. Spartiella Schr. Grosse von Ypsol. striatellus ; die Vorderfl. aschgrau, braunlich unrein, mit braunlichen Schragstrichelchen am Vorderrande. Gegen 30 M. und W. erhielt ich im Juni aus Kaupen von Genista tinct. 3. Lineatella FK. von 2 nur dadurch verschieden, dass sie schwarze, ungleichmassige Langstriche im Mittelraume hat. I M. aus Oesterreich, in FBs Sammlung. ' ' Clemens 6 describes the same insect thus : "Head and face pale gray; thorax dark gray. Labial palpi dark fuscous externally, and pale gray at the end; terminal joint gray, dusted with dark fuscous. Antennae grayish, annulated with dark brown. Fore wings, gray, dusted with blackish-brown, with a few blackish-brown spots along the costa, the largest in the middle, and short blackish-brown streaks on the median nervure, subcostal in the fold, and one or two at the tip of the wing; cilia fuscous gray. Hind wings fuscous gray; cilia gray tinted with yellowish." The larva has been decribed by Saunders 31 as follows : "The head is rather small, flattened, bilobed, pale brownish-yellow, darker in color about the mouth, and with a dark brown dot on each side. The body above is semitransparent, of a reddish-pink color, fading into dull yellow on the second and third segments; anterior portion of second segment smooth and horny-looking, and similar in color to the head. On each segment are a few shining reddish dots (yellowish on the anterior segments), or faintly elevated tubercles, from each of which arises a single, very fine, yellowish hair, invisible without a magnifying power; these dots are arranged in imperfect rows, a single one across the third, fourth and. terminal segment, and a more or less perfect double row on the remaining segments. The under surface is of a dull whitish color, becoming faintly reddish on the hinder segments, with a few shining whitish dots; those on the fifth, sixth, eleventh and twelfth segments, being arranged in transverse rows, in continuation of those above. The feet and prolegs are yellowish-white, the former faintly tipped with dark brown. It spins a slight silken thread, by which it can suspend itself for a time, at a short distance from its place of attachment. ' ' Names of the Insect. — The peach twig-borer is known scientifically as Anarsia lineatella Zeller. There are many common names applied to it, including the following: peach worm, bud worm, peach moth, bud moth, peach and prune twig-borer, and prune and peach twig miner. The simple name of twig-borer is liable to be confusing with the coleopterous branch, and twig-borer (Polycaon confertus Leconte). In California " peach twig-borer" is the name recognized by au- thorities. 426 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION LIFE HISTOEY The Larvae. — In central and northern California the larvae may be found in the hibernating chambers or hibernaculae from September 1 to March 15. The presence of hibernating larvae would be hard to detect were it not for the presence of small reddish brown chimneys, or tubes sticking up from the surface of the bark (fig. 1). These Fig. 1. — Crotch showing chimney of hibernating peach twig -borer. (Enlarged.) chimneys consist of tiny pieces of bark fastened together with silk. They are constructed by the burrowing larvae always on the upper surfaces in the crotches of the younger branches. They are rarely found in the crotches of branches that are more than three years of age. As Clarke 5 states, there seems to be something in the composi- tion of the tissue at these points which makes them a favorable loca- tion for winter quarters. On cutting into one of these chambers it will be found that they extend well beneath the bark into the cambium layer. The burrow is from two to three times longer than the larva within it and has a silk lining which projects well up into the tube above (fig. 2). This silk lining affords protection from the weather and apparently from some spray materials. The exact function of this peculiar tube is not definitely known. Bulletin 355] THE PEACH TWIG-BORER 427 The larvae pass the winter months in these burrows apparently without feeding, as they do not increase perceptibly in size. With the warm weather of spring they become active and work their way out of the cells. The time of emergence seems to be correlated with the sap flow of the tree. On almond trees which start growth relative- ly early the larvae seem to become active before they do on peach or plum trees in the same locality. This time is usually when the buds on the tree are swelling. Freshly opened hibernaculae were Fig. 2. — Burrow laid open, showing the worm in its winter quarters under the outer bark. (After Ciarke.) found on almond trees at Davis, Yolo County, March 2, while at Auburn, Placer County, larvae were found emerging on plum trees as late as March 22. Upon leaving the hibernation chambers, the larvae crawl about for a couple of days, then go to the base of a bud or in between the expanding leaves and begin to eat their way down and into the tips of the twigs, gaining in size as they feed. Frequently the larvae merely bore into a bud, then withdraw, and attack another. This occurs when they attack newly placed scions of grafts; they eat off every bud on a scion, but do not go into the harder tissue. The most usual manner of attack, however, is to bore into the pith of a chosen shoot, taking a downward course, eating all of the interior, and leaving only the bast and wood fibres to hold the twig. This causes 428 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION the characteristic wilting of the twig (fig. 3), which later dries up and breaks off. When the larvae reach the harder wood they bore their way out, leaving a circular exit hole in the side of the twig (fig. 4). Each larva may attack several shoots in this way and thus multiply the injury. Fig. 3. — Shoots and twigs showing characteristic wilting caused by larvae of the peach twig-borer. Fig. 4. — Base of almond twig showing exit hole of larva. (Enlarged.) Bulletin 355] THE PEACH TWIG-BORER 429 By destroying the terminal growth of a shoot, serious injury is done, particularly to nursery stock and young trees. New cells must be formed and length growth revived at great expense of energy and stored plant food. Three or four larvae may seriously devitalize or even completely destroy a young tree by repeated attacks on the new growth. The attacks are not so injurious to older trees (five years and upward), and do not prove fatal. It has been the theory of some entomologists that later emerging larvae of the first or winter generation attack the developing fruit. Fig. 5. pupating. -Portion of bark showing silken web spun over place where larva is This theory was disproved by experimental counts (p. 441) which showed that all the larvae emerge at nearly the same time and feed on buds and shoots first, then give rice to second and third generation larvae which feed on the fruit or twigs or both. The fourth genera^^r tion of larvae do not feed, but at once begin to construct hibernaculae^ in which they pass the winter, and these constitute the first generation larvae of the following season. The Pupae. — When the larvae are full-grown and ready to pupate, they seek a secluded spot in old pruning wounds, in curls of bark, or in rough crevices on the main trunk of the tree and occasionally in curled leaves. The larva invariably spins a characteristic silk web over the entrance to the place of concealment (fig. 5). By the last of April at Davis, all of the larvae had disappeared from the burrows in the twigs and many were found pupating in the various places just mentioned. 430 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION The larva forms an extremely flimsy web out of a few threads of whitish silk, which serve only to hold the pupa in place, and not for protection. The abdomen of the pupa is attached to this support by a little button of silk. The pupa or chrysalis (fig. 6) is about six millimeters long, rather broad, and dark brown in color. The segments on the abdomen are pronounced, but only the last three are flexible, which accounts for a slight twitching movement when the pupa is held in the hand. Fig. 6. — Pupae of the peach twig-borer, curled leaves. (Enlarged.) Occasionally pupation takes place in The pupation period in the case of the first generation lasts about fourteen days. With the second generation the time is much shorter, being only two to four days, while with the third generation it varies from 7 days in Esparto, to 20 days in Newcastle, California. This is due apparently to climatic conditions in the different sections. The Adults. — The adult moths of the first generation emerge be- tween May 1 and May 15, according to the climatic factors. Adults of the second generation emerge in general from August 1 to August 10. The last brood of moths appears about the first week in Sep- tember. The moths are seldom observed, being very small and extremely quick in their movements and flying with great rapidity when dis- turbed in their hiding places. They are from ^4 to % inch long and dark steel gray in color (fig. 7). It is interesting to note that Clarke 5 Bulletin 355] THE PEACH TWIG-BORER 431 was unable to trap these moths by lantern traps even when present in large numbers, although scores of other closely related species were easily enticed. The Eggs. — Eggs of the first brood of moths are deposited on the twigs (fig. 8), the second and third broods on the fruits or twigs and Fig. 7. — Adult moths of the peach twig-borer. (Enlarged.) Fig. 8. — Eggs of peach twig-borer in position on twig. (After Clarke.) 432 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION Fig. 9a. — Fruit showing damage from peach twig-borer. Note two distinct types of injury. The upper picture shows working around the pit and the lower picture shows surface injury. Bulletin 355] THE PEACH TWIG-BORER 433 the fourth apparently on the young branches near the crotches. The eggs are very minute and appear as tiny droplets of water without any definite arrangement. Clarke 5 described the egg as follows : "The newly placed egg is pearly white and shows under the micros- cope a rather coarse reticulation. Before hatching, the color changes to a deep yellow, almost orange color and at this stage the egg is quite conspicuous. It is about two-fifths of a millimeter in length by one- fifth in breadth, being a rather long oval in shape, about twice as long as broad." Fig. 9b. — Fruit showing characteristic injury to plums and apricots. 434 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION Larvae of the Second Generation. — Between June 5 and June 10 larvae of the second generation appear at Davis. These larvae attack fruit, if any is present on the tree. If fruit is not present, they bore into the shoots in the same manner as larvae of the first generation. Sometimes they may feed for a short time on the shoots and later go into the fruit. In the majority of cases the larvae enter the fruits at the stem end, probably because it is the first reached. They may also enter through the side as well, especially when two fruits are in contact, entrance being made at the point of contact. After gaining entrance through the skin they begin to eat out the flesh, often making a large hole which fills with a gummy substance, (figs. 9a, 9b). The skin above often turns black, thus indicating the presence of the larva. Injuries of this nature account for the name "fruit miner," as the insect is sometimes called. Following another common habit, the larva works its way straight to the pit, and if the latter is not already hardened, the larva will bore through to the kernel and seems to eat that with relish. This is one cause of the characteristic "split pits" of the stone fruits. When the larvae have penetrated to the pit their pres- ence may be detected by small bits of masticated fruit and gum which are thrown out by the insect on the surface of the fruit (figs. 9a, 9b). In either case the injury is the same, the fruit being rendered unsuitable for shipment as a fresh product or for commercial canning. The California Fresh Fruit and Vegetable Standardization Act for- bids the packing of "wormy" fruit and canners refuse to buy it. Therefore many fruit growers must discard large quantities of in- fested apricots, nectarines, peaches, and plums that are otherwise perfect. It is not an uncommon sight to see ten to twenty lug boxes (each forty pounds net) of "wormy" fruit culled out of a single packing-house each day of the picking season. When picking the late clingstone peaches in certain districts, pickers leave enormous quantities of "wormy" fruit on the ground. Most growers make no attempt to salvage this fruit while some prevent complete loss by using it for drying or home-canning. Larvae of the Third Generation. — Warren T. Clarke, E. 0. Essig, and the writer have made careful observations and have secured evidence of a distinct third generation of larvae. During the season of 1921 serious injury was evident to late clingstone peaches in Placer County, California, and this was attributed by L. H. Day of the Division of Pomology to a later brood of larvae. On Septem- ber 30, 1921, Day stated as follows in correspondence: Bulletin 355] THE p EACH TWIG-BORER 435 "I have neglected to report to you of my findings in regard to the peach work at Newcastle. I went up there a week ago last Tuesday. I found that there was a distinct brood of the twig-borers which had begun to hatch about three weeks before that date. Evidently many of these worms on hatching had immediately gone into hibernation, while others were attacking the fruit. The ones that were in hiberna- tion were of the usual small size, that is to say, % 6 of an inch long, while those that were feeding in the peaches would average around Ys to y± of an inch long. ' ' There were a few growers who lost 50 per cent of their peaches and the Silva-Bergtholdt people lost about 20 per cent of their Phillips Clings and Levi Clings. There were a very small number of larger worms ready to pupate and a few in the pupating state. A few evidently had recently emerged as adults. On the ground under the infested trees were quite a number of green fruits that had been lying on the ground for some weeks and in which there had been larger worms which evi- dently had emerged some weeks before. This seems to indicate that there was a distinct brood at this time. I found quite a number of the hibernating larvae in the old trees and in a nursery just over the fence from an infested orchard I found quite a large infestation of the hibernating larvae. I made counts in a few trees and will go up a little later and make another count to see if there has been an increase in the infestation. In a small nursery tree I found 12 hibernating larvae. "This infestation of nursery stock, as I had told you before, is not new, as I have often found several dozen hibernating larvae in one nursery tree. Some years practically all nursery stock in the state contain large numbers of these hibernating larvae, while other years there will be practically none, or very few. The growers reported that there were practically very few worms in the midseason peaches such as the Elberta, probably as much as 1 or 2 per cent infestation. Down at Penryn, which is at a lower elevation, Mr. Butler of the Penryn Fruit Company told me that the infestation of worms began a little bit earlier, attacking the Orange Clings which ripen a week or two earlier than the Phillips. " Some of these late larvae apparently go into hibernation while many others attack the fruit. This observation is substantiated by Yothers 36 in Washington, Wilson 35 in Oregon, Clarke 5 in California, and by other observers. According to Clarke, the larvae of the third generation "are the only ones that enter the fruit immediately on hatching" — that is, they do not act as "twig-borers." At first they make very minute burrows contrasting strongly with the freshly made burrows of the preceding generation. Hibernation of Last Brood of Larvae. — The last eggs are laid in trees in the vicinity of Davis about the last of August, as far as our observations indicate. In Placer County, Clarke states, and Day con- firms, that egg laying continues well into September. The very 436 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION minute larvae (fourth generation) from these eggs begin constructing hibernaculae at once in Yolo County, while in Placer County some of them eat into late peaches and there attain considerable size before hibernating. Fig. 10. — An important natural enemy of the peach twig-borer is another insect which devours the hibernating larvae. It is a hymenopterous parasite named Eyperteles lividus (Ashmead). Winged adult and larva shown above. (Original drawings. Enlarged.) Bulletin 355] THE PEACH TWIG-BORER 437 Parasitism. — In most sections of California hibernating larvae of the peach twig-borer are attacked by natural enemies. During the winter 1921-1922, a small hymenopterous larva, Hyperteles (Oxymor- pha) lividus (Ashmead), (fig. 10) was found destroying from 70 to 95 per cent of the immature larvae in many orchards. The parasite devours the body of the larva and leaves only the empty head. When Fig. 11. — Exit hole of parasite from burrow of hibernating larva. (Enlarged.) the parasite has accomplished this it bores its way out through the bark, leaving a small exit hole at the base of the chimney (fig. 11). The original description of this parasite by Ashmead 1 is as follows: "Male: Length .14 inch. Uniform dark blue including legs, ex- cepting the first three tarsal joints, which are pale or white, and the upper surface of the thorax which has a greenish metallic tinge; the antennae are black and hairy; thorax punctate, abdomen is very long and slenderly pointed; wings, hyaline, with pale yellowish veins, the marginal vein is long and thickened, the stegnal short, while the post- marginal vein is long. Description from one male specimen swept from bushes in a low swampy meadow. This genus was found by Doctor Furster in 1856, ' Hymenopterogische Studies 11, Chalcidino and Proctorrupii, p. 145, ' and this is the first species described in our fauna. " 438 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION It is stated by Marlatt 23 that in California a minute mite (Pedicu- loides ventricosus) destroys from 75 to 95 per cent of the larvae. Professor Clarke was "unable to confirm the statement made by Marlatt." The writer has not seen this parasite either. Lintner 22 and Comstock 8 described the work of a chalcid parasite (Copidosoma variegatum Howard) which destroyed the pupae of the peach twig-borer. So far as the writer could learn, thr parasite has not been found in California. Fig. 12. — Trees inclosed in cheese-cloth tents for the purpose of making life- history studies. (Photographs taken after tents had been torn and studies com- pleted.) LIFE HISTORY EXPERIMENTS Evidences of a Second Generation. — As previously stated, there have been conflicting theories regarding the number of generations of the peach twig-borer. Evidence is here presented to prove the existence of a distinct second generation (as well as a third and fourth proved later on), rather than one uneven brood that extends through the season. A few investigators claim to have evidence of one irregular brood. Weldon 34 found newly constructed chambers as early as May 19 in Ventura County, on June 23 in San Joaquin County, and again at Hanford, Kings County, on July 24. On the basis of these observa- tions he concludes, "the presence of only one strung-out brood of this insect, instead of three or even four, as have been previously reported. ' ' This conclusion may be misleading since it is highly probable that these few larvae may have been "freaks" of the brood that carried over in a single generation, while the great majority went through Bulletin 355] TIIE PEACH twig-borer 439 two or three generations. "This latter supposition would also ac- count for the existence, during the winter, of larvae of different sizes," Wilson 35 states. The writer has followed closely the life history of the peach twig- borer at Davis (fig. 12) as well as in Placer County (fig. 13), and his findings are presented under "Life History" (p. 426). Careful counts were made on each of 562 almond seedlings at the University Farm, Davis, between April 1 and 21 and between June 10 and June 13, Fig. 13. — One of the experimental plots in Placer County, Sierra Foothill District. respectively (figs. 14 and 15). The counts made April 1-21 were primarily to determine the effectiveness of the different spray treat- ments and are discussed in full under "Spraying Experiments," (p. 443). In making the counts, the wilted tips were sought and opened to reveal the larvae. It should be noted that the unsprayed trees had an actual average of 5.2 larvae per tree at this time (table 1). After the first count was made the trees were observed for further wilting of the shoots, but no additional infestation could be found. The wilted twigs dropped off and new lateral shoots were sent out in their place. During this time the insects were observed going through their pupation and emergence as adults. 440 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION On June 8 large numbers were again noticed attacking the new shoots on the same trees. The second count was then made in the same manner as the first (fig. 15). The significant facts are that, first, the number of larvae this time averaged 12.5 per tree, an increase of 150 per cent; and second, the infestation was general throughout the entire orchard. Sprayed trees which at the first count had no larvae, contained exactly the same average, i.e., 12.5, as the un- 1 , ^ l*:V - ri t— o- o» V/> uo = ^- HhHttSHuH - (X> 0 to ^- i^ ^-o>oo b ri « w ^ - rt en * ± ri r- n Ntf N - Co — ■>*■ MHNN * +fej-<>)t-'i* J, »i!j » __!» H-4 -i hNyggEl&iya N&b NpHHtfUtfElB-BUlitiUHkll?* * 1 1 -T> V o V o ooooNH^°° 0000 °° — oooorio— yjEJbJo m o o *i i 5 =f *^ _i '3 -» 2 Isv HNHHHHBHEitilHHMBH Hfc ■> rt -J -§ci 4* cr fc d e . oooooooNhH ooOoo NBHHMg HMM Ub| H^HMP *- tfooooooEJNHoooooooo w. ao-rtri + g^M-roo rt - •+ !3H H HH|iJfelBNNaHWtEjHNE)E CD * .y- i 4 * 1 5 -^ r?" 5- -t> ,*> * -+c 01 9 v -o ? v C -o T ^ c/3 ^ CP o» V r > 6^ or fc ^H Nh MNNH MM*!* M H N M NMNHH M M^H 4- •> si 1" 00 O °£ .2 2 -4-» Qj O 5H l-H © be© § S 03 •a-s © a Bulletin 355] THE PEACH TWIG-BORER 441 sprayed trees. The infestation had been spread by the moths flying about the orchard. In addition to the above facts, another point of interest was that larvae taken at the same time from peach and apricot fruit at Winters (twelve miles west of Davis) were brought to Davis and placed in jars, indoors, by the side of similar jars containing infested twigs taken from the trees at Davis. All these larvae transformed to adults and emerged within three days, showing that in this locality the be d nMHM c3 ± » S $= * £ 3 2-3= * rt "• »» jO ^ rt — ■ 0\A te t — ti "rt--ri rt «< "> W 5 ft £ f* o» + £ 5 **» ^ f—^-^ ■*■ -a -H - rt __ * s mHM t — t- C— v, * h BH6 - 1 b {« £* - ~ to *" ..■s ± * ±± #$& ± $ ^z *Z « *iBBBNaa&Btftf@B B B B — — — 1— rt — — — i * t = pd 2 En S ^OoOoloto 2«J°~flHy° - °~~ * — <*> t r V be * NN^ttrtgflMN itf BHNH i F a; d 5h O o-be«j_<3 fJo-Ovo p|<| - 1— 1 r^ ^rmtjo + o^^j^s :£ I? -» S V» t - 1 <» 5 i5S r O * i tiers' * rSS 3 •- c , m O bjog nBNBNMWHhhmH h..M * t 3: 3 5 3., i 0? W C 13 ij^r pi .2 O !* = * o-o-.£ rt@§M>» , Ocri »• «« 05 — f- -3 14 4-sMf ri5rta^? fl|sr52<»oc * 5 5- »*- vZ» &~o -O- '£. •* — 2- n< « 0) ., «.a NttNNBN : flll*fllUtf|B a? .£ 5 8 bo •S.S BnINShNN B*&hS«N* -3 g, HBNWM^||HNBi|g|HBH sr- cr "t "^^N^S = ^"«?9o-fir -• 1 1 1 : «2 S pi 3 "■* *-S2 ^-i^i^lNH---- ^~ = 5 0- <^ c^ ^ * e3 BBHHH|NBw6a5|BBHge O MMrtRHrtttHBBaaHaiiHBE BNHNHHgKHWtfHM u 6 A 1 1 NHNI HnH-HBBBHHE id SRS^SSSS-SSaA-Sr.r'P bb •rH 442 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 4a * * 03 c t^ ooo TJH OHH OQ O O t^OOOOOH^ t-"c CC COCO cbo'd oo cd o a> o os CO rH O100l> rH H^ OOrH CO Ph ° 1 1 03 3 Ma),) co Orf< CO t^ CO to CO iO lO I> l> to ( _ i Numbe larvae found -f oo oq o ooH.£ P a 5^ p"g ?p p A 1 E 5 ill ^7 E 0) cu nfl cu J 3 ©"G 111 l|l H Ph O tn 3 a -^ fl S to o ^ 5 ^ c3 o O-jh +; ^ Q ^tsj r? pq P CP Ph >j (D fa c3 a J ^ cc ^ Oh S-, £<3 03 V ^ o> C<1 o> C* Oi a o- rH rH »0 Ol Ol Ol i-h Ol O H(NH(NHH^ "5 fe co CO C0~^ " "" o3 o3 Oft , W(N CM cM(M l> CdO C (M o "5 OC i— i CO l> Ol o r O (M CO CO 00 Ol 'r (N (N ^CC > HHrtH > 03 -O 03 ft ft 03 QJ o3 -a il £ > 93 d "0 > 03 to-* X o a -C bfi * 03 > 03 "2 d d Xi T3 03 >> 03 x) O ft ■j Oj o (-. ^ ^J -2 03 "tf O si >. +j a > ki o si tH > 03 t. * J3 •^J3 d 03 03 -G ^ > X3 c3 si ■fl 00 fl ee) o .2 O ed S® - "S o^ fl P S 03 ^ 03 *J 03 040 B 03 J^03§ rt 03 fl R — I-.J3 03 -o^^" 03 -^^3 2 s a . 00 CO 10 ^ 00 CT> rH 14 3 W g 3 O O 5 1 H 4 o s fe hJ ;- *9 O 00 o CO CO *C CM ^(NO i-i CO GO 00 N N O o ic id > a o o '-£ 3 3 d -A J9 £d a II |g 1 02 ^h S iO.S s ^ 5 a 3 o g a cr 03 ^ * I 02 S 0J o ft b3 hQ 0) "o '3 g o .a s ^^^Q^'^lzj'E^ ^ TjH 00 O rH o nn ogo CM tO CM rH CO S I 3 3 08 O CO ^ CO CO CO O rH CO O b- CD rH rH CO CO 1 oo oo oo oo oo oo c 14-. © o'-3, JM iO CN iO H ^ I &*o o rH O O O O O CO rH CO CM oo\ CO oo\ : : o o !: 5? » to o k O H ^ rt rt IO H o x I \i O O I I tO CO MN rH CO TJH CO cq ^Ph- I X o a% H -r- 02 03 PQ pq > > ts — ' m i O .s gq a> d a r^ o -Jags -5 o ^ s s o 3 3 C£ c72 _ d ft ^ 03 ih O 02 02 d 73 O ft XT r- * <2 hH £ e~ O CD qJ" § cd '55 £ § 3 , 03 at mi H rri ft ^H VJ a; d > P «1 1.55. ►2 c Bulletin 355] THE PEACH TWIG-BORER 451 The writer repeated and enlarged upon the 1921 experiments at the University Farm, Davis, and on test plots at Vacaville secured through the cooperation of growers there. Details of the Experiments. — The spraying experiments at Davis were conducted on the 562 almond seedlings that were used in 1921. The planting was divided into check rows and test rows which were sprayed at different stages (fig. 17). Counts were made of infested twigs the first week in May (table 4). The same trees were again sprayed on May 11 to combat the second generation of larvae and counts were made early in June to determine comparative effectiveness of the spray (fig. 18). N a N rt W H ^3 bX o o o o o - O ri M ri 1 | U N N N <*> tt to -* r — oooo H o o rt cn rt - B — O O co o rt ri 02 12 1 o o - o o o - o o o - o - H H O o - o o rt _. O o o rt rt o o v> o ri o - " O ^ $ riOOrt-Ortri- 2 rt ^ qj ® ^-roVr>£»Woocr,Tj-0 - - O W >9 to — cp O o ri rt — +— «> . 2 C i/» fi— *- v 0) — *— % 3-C •» 0-3 O «h 03 TH p=j - O - O - NNNnwhhMN H H H r- O O rt + <$-«■> — — <0 H -V- -- c ■> 0/ o a X 03 O a) 4> o^oo --o M oooo o DD QQ Hoooooooo M0ooooo°- N O O - O - o v -- 55" C u " - o . - - - . 3"~*- M "* • C ^»' fl CO o >-> i3 ^ ^OOOoo^q oooooooo N H H o - - H to M H w C QQ "Si 2 "^ /; a, 3 s C s ? c I ° n-i 11 w 02 «W 02 o ^ o t~n » V) i|- - mm t^Ori-O*-***! H oooo - o o w + - ri 1 1 i— 1 OO- ri — — r? o» IS O O + O - bi) NH HQ Hg^ N H H MH H 452 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION Fourteen plots (fig. 13) in Placer County were selected for the purpose of testing those materials which in 1921 proved to be the most promising. Ten trees on each plot were set aside to be sprayed with each material and an adjoining row of ten trees was sprayed in the pink stage, with lime-sulfur in order to compare the test spray with the standard remedy. Unfortunately, in only a few cases could unsprayed trees be left as checks. Counts of twig and fruit infestations were recorded and percentages computed. Table 5 Spraying Experiments University Farm, Davis Summary of Results, 1921-1922 Material and Type of Application Per Cent Control Per Cent Control 1921 1922 96.7 80.5 25.0 70.6 74.4 100.00 41.66 4.0 43.0 97.4 95.5 100.0 46.7 87.5 7.0 77.5 6.0 46.0 100.0 80.8 100.0 100.0 100.0 Trees Dormant Liquid Lime-sulfur Dry Lime-sulfur Nicotine Sulfate Buds Swelling Liquid Lime-sulfur Dry Lime-sulfur Spra-Mulsion Nicotine Sulfate Arsenate of Lead Full Bloom Liquid Lime-sulfur Dry Lime-sulfur Spra-Mulsion Zinc Arsenite Nicotine Sulfate Arsenate of Lead The H. Hartwig orchard at Esparto was selected for the purpose of comparing the effects of nicotine sulfate, arsenate of lead, and lime-sulfur, during different stages of blooming, on apricots, peaches, and plums. Counts of infested fruits were made and percentages of control compared. The Winters test plots were on the A. Wolf skill ranch and consisted of lime-sulfur and arsenate of lead sprays on apricot and plum trees. Fruit infestation was counted as in the other plots. Bulletin 355] THE PEACH TWIG-BORER 453 The Vacaville experiments were in the orchard of E. I. Power and involved nectarines, peaches, and plums. These trees were sprayed with lime-sulfur plus arsenate of lead as the buds were swelling, and also received a second spray of arsenate of lead alone on May 11, for the purpose of controlling the second generation larvae. Some trees in this orchard were unsprayed, while others received only one spraying with lime-sulfur. P< ~ | _JlTtfM * 1 bhHBNiBfe nnN «. be N B N h| N 02 Jhh N&Mfcl H O INhh^NMN N N H^B b 13 IhHhmh^N^ H^^ IT > u |*Hrifj|fc|HMNHHtt gtf&BHt: Q <& |H«Ip>ViC"-i--Vo j ci » ■*- o ciri-^-^-t-tnUiciriO 5 ^3. o bJO 0+--— OciC— «o + r* O W ro •+ ■* r t 1 S~ £ O «ie— rt o — 4- ct 4" — ci — j ■*- ■- a _£T 02 ^1 O (JoorfmMn-fiJdiiort+riJ- £" HI s^-M s OOn-(i)rl(i)^.(tit-0 lorfOf) - £- Si!»;"» r s + oocn*rt — H H o ri ri «i o *o co o- m r? rt c*> O O «o — n>*-0CnOc?O* toco NNH h a h^ - I 6' 3 oJ J rl w rt *-0 e, pi IT 4- « c .-+o "~ f ^ II-. m r Jl ei_i s-tlS-SlsBJiJ 3 HhNhmnmH & H B tf Ml= 5 cr- cr- — * , ra 1 ^« h 1* © tf 3 H^HNHHNHHH H 7fi r-L-i? r s rd MNNNnNrt ^IhNNMHHH^n 5 _c *t :DC" Sri 3 5 C V CD — <*-*<0«)c>i-0— c? — w? fo^-ef 5" d st cV n3 «l O O «lt?- — OOO-«ncc-O0 — ^ s 2 O 0«?OOcr>--*9-OO- o •*- — « — co ; "ea Q mm O O A — — 00«0 — - — — OO— rj o OJWOO-^WO^-'O'*- O OO*- s g- »- c^«Of«Cl>r?>O0f?C0000«0 — cr?^ «- t »* to T-l is jib * ffi srn * 8 D S^rst • .rH 454 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION Table 6 Spraying Experiments Placer County— 1922 Counts of infested twigs made May 18, 1922 Material and Type of Application Lime-sulfur (Pink stage, 3/17/22) Unsprayed Arsenate of Lead (Full bloom, 4/3/22) Unsprayed Bordeaux Mixture Arsenate of Lead (Pink, 3/23/22) Unsprayed Lime-sulfur (Full bloom, 4/4/22). Lime-sulfur (Pink 3/22/22) Arsenate of Lead (Pink 3/18/22).. Arsenate of Lead (Pink, 3/18/22). Lime-sulfur (Pink, 3/18/22) Lime-sulfur (Pink, 3/18/22) Arseniteof Zinc (Pink, 3/20/22)4 Arsenite of Zinc (Full bloom, 4/2/22). Nicotine Sulfate (Pink, 3/20/22) Nicotine Sulfate (Full bloom, 4/2/22). Home-made lime-sulfur-salt (Pink, 3/20/22) Unsprayed Lime-sulfur (Pink, 3/22/22) Lime-sulfur plus Arsenate of Lead, Hy- drated Lime Dust (Pink, 3/22/22) Unsprayed Lime-sulfur, plus Arsenate of Lead (Pink, 3/20/22) Lime-sulfur (Pink, 3/20/22) Nicodust (Pink 3/22/22) Lime-sulfur (Pink, 3/22/22). Nicodust (Full bloom, 4/4/22) Lime-sulfur (Pink, 3/17/22) Orchard Van Riper, Newcastle Silva-Bergtholdt, No. 3, Newcastle E. Appleton, Newcastle F. Midgely, Newcastle H. W. Tudsbury : Newcastle C. V. Freed, Newcastle H. E. Butler, Penryn H. N. Hansen, Loomis J. J. Brennan, Loomis E. L. Rippey, Loomis No of Trees No. of Infested Twigs 10 6 11 74 10 10 9 10 10 10 10 24 10 18 30 13 (Plums) . 10 (Peaches) 10 13 (Plums) 10 4 (Peaches) 20 10 10 21 10 16 10 38 10 48 1 20 17 17 1 10 1 10 4 10 10 5 10 20 10 2 Average Infes- tation 0.6 6.7 0.9 1.0 2.4 1.8 0.4 1.3 0.4 0.5 2.1 1.6 3.8 4.8 20.0 .1 0.4 0.5 0.2 0.2 Bulletin 355] THE PEACH TWIG-BORER 455 R. Amaden of Dunnigan and E. C. Schrader of Arbuckle con- ducted spraying tests in their almond orchards with lime-sulfur to compare with non-spraying. The infestation in these orchards, how- ever, was so slight that counts were abandoned. Millard Sharpe of Vacaville also applied various spray materials to a number of trees, but the number of larvae in his orchard was so small as to make the experiment of little value. Discussion of Results. — The 1922 experiments did not result in as definite comparisons as those of 1921, primarily because there were so few larvae in unsprayed trees. Taking this into consideration, we must limit our conclusions somewhat. Results of the Davis experiments are shown in tables 4 and 5. Referring to these results, it will be noted that lime-sulfur has shown itself to be uniformly good in controlling the twig infestations at all stages. Nicotine sulfate has also given good control, results being about the same as in 1921. The arsenicals also proved valuable as remedies particularly during the time of blooming. Dry lime- sulfur was in all cases inferior to the liquid lime-sulfur. The oil sprays were not at all effective. Table 7 Spraying Experiments Placer County, 1922. Counts of Infested Fruits. Orchard Variety of Peach Kind of Spray Condition of Blossoms at Time of Application No. of Trees Per Cent of Loss 1. C. V. Freed & R. F. Moss 2. Freed & Moss.... 3. H. W. Tudsbury 4. G. Lammiman... 5. Freed & Moss.... 6. Freed & Moss.... Freed & Moss.... Freed & Moss.... 7. M.E. Van Riper 8. F. Midgeley 9. J. Brennan J. Brennan 10. E. L. Rippey 11. H. E. Butler 12. H. E. Butler 13. E. Appleton 14. H. Hansen Tuscan Tuscan Elberta Levi Tuscan Tuscan Tuscan Tuscan Elberta Levi Phillips Phillips Elberta Levi Levi Salway Levi Nicotine Sulfate and Soap Nicotine Sulfate and Soap Arsenate of Lead Arsenate of Lead Arsenite of Zinc Arsenite of Zinc Home-made Lime-sulfur... Home-made Lime-sulfur. . . Lime-sulfur Nicodust Lime-sulfur Nicodust Lime-sulfur Arsenate of Lead (Dust) .. Lime-sulfur Bordeaux mixture and Ar- senate of Lead Lime-sulfur and Arsen- ate of Lead Pink Full Bloom Pink Pink Pink Full Bloom P.'nk Full Bloom Pink Pink Pink Pink Full Bloom Pink Pink Pink Pink 10 10 10 10 10 10 10 7 10 10 34.5 28.9 0.2 0.6 20.8 18.0 0.5 29.3 1.0 2.1 4.3 0.1 0.8 1.0 0.1 0.4 456 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION Table 8 Summary of Spraying Experiments, H. Hartwig Orchard, Esparto, 1922 Kind of Fruit Type of Spray Date of Date of No. Fruits No. Fruits Per Cent Spraying Count Examined Infested Control Apricots Lime-sulfur 4/23 6/15 630 30 95.3 (Royal) (Full Bloom) .... 4/23 6/15 400 9 97.8 I 4/23 6/15 306 15 95.2 4/23 6/26 351 89 Average 74.7 90.7 (Formosa) (Full Bloom) .... 4/24 6/26 297 151 454 433 237 57 154 484 533 185 196 178 167 122 346 59 446 299 543 103 170 34 10 43 66 40 18 37 47 69 36 36 36 39 13 55 13 50 49 77 19 21 88.5 93.4 91.5 84.8 83.2 68.5 76.0 90.3 87.1 80.6 81.7 79.8 76.7 89.4 84.2 78.0 88.8 83.6 85.9 81.6 87.7 Nicotine Sulfate 4/19 6/7 349 100 42 Average 19 88.0 84-0 Apricots 81 (Royal) (Full Bloom) 100 100 100 500 355 486 400 178 167 200 177 500 472 774 27 24 14 79 43 21 16 3 3 7 5 26 27 37 Average 73 76 86 84.2 87.6 95.9 96 98.3 98.9 96.7 97.8 94.8 94.3 95.1 90.4 Bulletin 355] THE PEACH TWIG-BORER 457 Table 8 — (Continued) Kind of Fruit Type of Spray Date of Date of No. Fruits No. Fruits Spraying Count Examined Infested 4/19 6/20 1731 61 6/22 300 24 6/28 87 5 6/28 737 89 6/28 598 80 Average 6/26 138 10 6/20 327 36 265 28 257 20 6/20 437 52 Per Cent Control Plums (Formosa) Nicotine Sulfate (Full Bloom) 96.5 92.0 94.3 88.0 86.1 91.0 Apricots (Royal) Plums (Formosa) Peaches (Alexander) Unsprayed. Unsprayed. Unsprayed. 92.8 89.0 89.4 92.3 88.1 From figure 18 it will be observed that the second generation of larvae was reduced by both arsenate of lead and nicotine sulfate sprayed about May 15. The arsenate of lead spray reduced the infestation from an average of 3.5 larvae per tree in the unsprayed trees, to an average of 1.4, while nicotine sulfate reduced the average to 2.6. Tables 6 and 7 show the results of counts on the fourteen test plots in Placer County. Table 6 shows the effects of various sprays in reducing twig injury, while table 7 shows the per cent of loss of fruit. It is unfortunate that unsprayed trees were so lightly infested, yet we were able to make a few observations. Lime-sulfur seems to be a satisfactory spray, particularly when the application is made at the pink stage. The arsenicals and nicotine sulfate also proved very effective in controlling the insect. Addition of arsenate of lead to either lime-sulfur or Bordeaux mixture made a satisfactory com- bination. Homemade lime-sulfur and salt in these tests has been inferior to commercial lime-sulfur. The dry dusts, Nicodust or arsenate of lead, did not prove good remedies. In the Hartwig orchard at full bloom, lime-sulfur gave 90.7 per cent control on apricots (Royal) and 84.0 per cent on plums (For- mosa). Nicotine sulfate gave 90.4 per cent and 91.0 per cent, respec- tively, on the same kind of trees at full bloom (table 8). In the A. Wolfskill orchard at the pink stage lime-sulfur showed a benefit of 98.8 per cent on apricots, while arsenate of lead showed the same per cent control on plums at full bloom, and on peaches in the pink stage it gave 96.8 per cent control (table 9). 458 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION Table 9 Summary of Spraying Experiments, A. Wolfskill Orchard, Winters, 1922 Kind of Fruit Type of Spray Date of Spraying Date of Count No. Fruits Examined No. Fruits Infested Per Cent Control Apricots (Royal) Lime-sulfur (Pink stage) Arsenate of Lead (Full Bloom) .... Arsenate of Lead (Pink) 4/1 4/1 4/1 6/16 6/16 6/20 6/20 6/28 8/16 1200 1000 500 1820 5000* 2000 81 2 1 Average 62 63 92.3 99.8 100.0 99.05 98.8 Plums (Formosa) Peaches (Elberta) 98.8 96.8 * Estimated. Table 10 Summary of Spraying Experiments, E. I. Power Orchard, Vacaville, 1922 Date of Date of No. Fruits No. Fruits Per Cent Kind of Fruit Type of Spray Spraying Count Examined Infested Control Nectarines Lime-sulfur and (Cardinal) Arsenate of Lead (Buds swelling) .. Arsenate of Lead.. 2/20) 5/11/ 7/19 9500* 20 99.8 Unsp rayed 75.0* Nectarines Unsprayed 7/19 1050 275 74.0 (Quetta) Unsprayed 7/19 75.0* Peaches Unsprayed 8/10 60.0* (Elberta) Lime-sulfur and Arsenate of Lead (Pink) 8/10 98.0* Nectarines Lime-sulfur (Quetta) (Buds swelling) .. Arsenate of Lead 2/15) 5/25/ 7/17 26980* 100 99.7 Arsenate of Lead.. 5/25 8/5 35000* 3 99.02 Unsprayed 8/5 300 27 91.0 Peaches Arsenate of Lead 5/15 6/9 200 100.0 (Alexander) (Summer spray) Arsenate of Lead 200 200 200 2 100.0 100.0 98.0 (Summer spray) 5/25 7/17 26980* 100 99.7 * Estimated. Bulletin 355] THE PE ach TWIG-BORER 459 The experiments conducted by E. I. Power at Vacaville were remarkable in showing the outstanding benefit of lime-sulfur and arsenate of lead in the pink stage, and of arsenate of lead in the early summer for the second generation of larvae (table 10). Power stated that he had never been able to produce worm-free nectarines before, and in these tests, with arsenate of lead and lime-sulfur and a summer spray of arsenate of lead alone, he was able to secure 99.8 per cent control on nectarines, also on peaches. In these tests arsenate of lead proved beyond a doubt that it will give perfect con- trol when used as a summer spray on early and mid-summer varieties of nectarines and peaches. CONCLUSIONS The habits of the peach twig-borer have been studied and its life history carefully worked out. Evidence has been secured which proves the existence of distinct second and third generations and sometimes even a fourth, rather than one uneven brood, as heretofore believed. New features in control measures have been ascertained which make it possible to successfully combat the attacks of this pest. In these experiments nicotine sulphate, % of a pint to 100 gallons of water, with three pounds of soap as a spreader, gave the most consistent and highest control of the peach twig-borer. Arsenate of lead, 3 pounds to 100 gallons, with % of a pound of casein spreader, gave excellent control at the pink and full bloom stages, as well as a summer spray. Liquid lime-sulfur, 1 in 10, was very satisfactory at all stages, being best at the pink stage. For the full bloom stage, arsenate of lead added to lime-sulfur increased the efficacy of the latter. Bordeaux mixture and arsenate of lead sprayed just before blossoming time proved to be a satisfactory combination. The home- made lime-sulfur and salt mixture in these experiments was inferior to the commercial preparation. The dry dusts and the oil sprays are not satisfactory remedies for this pest. On account of the presence of a natural parasite, Hyperteles livi- dus (Ashmead), hibernating larvae in certain years have been almost completely eradicated in some districts. Most of the damage of the peach twig-borer is caused by larvae of the second and third generations. The present trouble arising from these later generations is due to a number of factors, chief of which are the lack of uniform control of the first generation and failure to destroy or properly dispose of "wormy" fruit and pruning brush. 460 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION KECOMMENDATIONS On the basis of the foregoing observations and experiments and from discussions of this subject with Essig and others, the writer suggests the following remedies for the peach twig-borer. 1. Spray with commercial liquid lime-sulfur at the rate of 1 gallon to 9 of water, plus basic arsenate of lead powder, 3 pounds to 100 gallons, in the spring at the pink stage, that is, just previous to blossoming. This combination will control diseases and insect pests other than the peach twig-borer. Because of the frequent damage resulting from lime-sulfur in coastal districts, it is considered best not to use this spray on apricots. Therefore, Bordeaux mixture, plus basic arsenate of lead, 3 pounds to 100 gallons, seems to be the best combination on apricots when brown rot or shot hole fungus and peach twig-borer are to be controlled. This latter spray also should be applied at the pink stage. 2. Nicotine sulfate, % of a pint to 100 gallons of water, with 3 pounds of soap as a spreader, is a good remedy for the peach twig- borer, and may be used alone in a few limited cases where diseases and other insects are not troublesome. 3. A summer spray of arsenate of lead, basic or neutral (never acid), at the rate of 3 pounds to 100 gallons of water with % pounds of casein spreader, may be used as an additional insurance against "wormy" fruit. This spray should be applied not less than two weeks before the fruit is picked. 4. Too much emphasis cannot be placed upon the necessity of proper spraying at the right time. It is essential to cover the entire surface of the tree, particularly the newer and outer portions of the branches. Use at least 175 pounds pressure and preferably 250 pounds. 5. All prunings should be collected and particularly the small and newer wood should be burned before spring, because this material harbors the larvae. 6. Cull fruit should not be carelessly left about the orchard or packing house. All wormy fruit should be collected and properly dis- posed of. It should be fed promptly to pigs or other stock, or de- stroyed by burying or burning. A quick and simple manner of destroying worms in the cull fruit is to place the discarded fruit in a pile or in a trench, saturate with oil or cover with wood, and ignite. The resulting heat from the fire will be sufficient to kill the larvae in the fruit. Another means is to boil the fruit for fifteen minutes. Bulletin 355] THE peach TWIG-BORER 461 SUMMARY 1. The peach twig-borer (Anarsia lineatella Zeller) is a serious pest in deciduous orchards of California. 2. The injury is caused by the larvae boring into the buds, twigs and fruit of the almond, apricot, nectarine, peach, plum, and prune. 3. The insect passes the winter in the larval stage underneath the bark in small burrows constructed in the crotches of young branches. In early spring the larvae come out and begin feeding on the buds and shoots. 4. When the insects are full grown they crawl down the branches to the trunk where they pupate in the curls of the rough bark. The adult moths emerge in early summer and begin egg laying on the twigs. 5. About the first week in June a second generation of larvae begins to attack the twigs and particularly the fruit. 6. Later in the summer a third generation emerges in some sec- tions and causes serious injury to late ripening varieties of the fruits attacked. 7. The fourth and last generation of larvae comes out late in September and begins at once to construct chambers and go into hibernation for the winter. These are also known as the first gene- ration larvae of the following year. 8. A parasitic larvae, Hyperteles lividus (Ashmead), has been found in certain districts. In some seasons it destroys as high as 95 per cent of the hibernating larvae. 9. Results of spraying experiments show that this insect can be controlled by a number of materials and at different times. 10. Nicotine sulfate and arsenate of lead have, in these experi- ments, proved to be slightly better than lime-sulfur in controlling this pest, but in view of the fact that lime-sulfur is an all-round fungicide and insecticide, it is advisable to use lime-sulfur at the pink stage of the opening buds, with the addition of arsenate of lead in serious attacks. 11. Bordeaux mixture and arsenate of lead, applied at the pink stage, is considered best on apricots in the coastal region because of the danger of lime-sulfur injury to the fruit. 12. The lime-sulfur substitutes controlled the worms less per- fectly than the commercial liquid lime-sulfur. The oil sprays and 462 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION the dry dusts cannot be considered satisfactory remedies for this insect. Arsenate of lead applied as a summer spray has proved very efficacious on almonds, nectarines, and peaches. 13. Stress is placed upon spraying at the proper time and upon thorough application. 14. Spraying must be supplemented by proper disposal of prun- ings and of cull fruits, because they aid in carrying over the insect from one generation to another. ACKNOWLEDGMENTS The writer wishes to express his gratitude to E. 0. Essig for his valuable advice and assistance and especially for reading and correct- ing the manuscript of this bulletin. W. L. Howard also has been exceedingly helpful in making valuable corrections to the manuscript. The assistance and cooperation of W. P. Tufts have largely con- tributed to the success of this project. A great many useful sug- gestions have been contributed by W. T. Clarke, E. R. de Ong, and L. H. Day which have been valuable in the completion of this in- vestigation. Miss Edna Russ and W. C. Mathews have been particu- larly helpful in making charts and photographs. Valuable assistance has also been rendered by members of the Division of Pomology, and by R. D. McCallum, C. K. Turner, W. H. Cudaback, and W. D. Norton. LITERATURE CITED 1 ASHMEAD, W. H. 1886. Trans. Am. Entom. Soc, vol. 13, p. 135. 2 Barnes, S. B. and McDunnough, J. 1917. Check List of Lepidoptera of Boreal America, p. 159. s Chambers, V. T. 1872. Canadian Entomologist, vol. 4, p. 208. 4 Chambers, V. T. 1878. U. S. Geol. and Geog. Surv. Terr., Bull., vol. 4, pp. 112, 129. s Clares, W. T. 1902. The Peach Worm, Calif. Agr. Exp. Sta., Bull. 144. e Clemens, Dr. B. 1860. Proc. Acad. Nat. Sci., Philadelphia, p. 169. 7 Clemens, Dr. B. 1872. Tineina of North America (Stainton edition), p. 128. Bulletin 355] TnE PEACH TWIG-BORER 463 1878. Proc. West N. Y. Hort. Soc, p. 13. 9 COMSTOCK, J. H. 1879. Report U. S. Dept. of Agr., p. 255. 10 COQUILLET, D. W. 1891. Insect Life, vol. 6, p. 206. 11 CORDLEY, A. B.. 1897. Oregon Agr. Exp. Sta. Bull. 45, p. 123. 12 CORDLEY, A. B. 1897. U. S. Dept. of Agr., Div. Ent., Bull. 9, pp. 71-75. is Craw, A. 1893. Calif. State Board of Hort., Bull. 67, p. 9. 14ESSIG, E. O. 1915. Injurious and Beneficial Insects of California, Sup. Mon. Bull. Calif. State Conim. Hort., vol. 4, no. 4, pp. 443-445. is Forbes, S. A. 1882. Twelfth Report State Entom. Illinois, p. 76. is Forbes, S. A. 1883. Trans. Miss. Valley Hort. Soc, vol. 1. 17 Glover, T. 1872. Entom. Record, Mon. Bull. U. S. Dept. Agr. (July), pp. 304-305. is Glover, T. 1873. Ann. Report U. S. Dept. Agr., 1872, p. 112. 19 GOSSARD, H. A. 1908. Ohio State Agr. Exp. Sta. Bull. 198, p. 63. 20 Howard, W. L. and Horne, W. T. 1921. Calif. Agr. Exp. Sta., Report (1919-1920), p. 43, and Bull. 326, p. 80. 21KLEE, W. G. 1888. Calif. State Board of Hort., A Treatise on the Insects Injurious to Fruit and Fruit Trees, p. 43. 22 Lintner, J. A. 1882. First Ann. Report N. Y. State Entomologist, p. 151. 23 Marlatt, C. L. 1898. U. S. Dept. Agr., Div. Entom. n.s., Bull. 10, p. 7. 24 Marlatt, C. L. 1898. U. S. Dept. of Agr., Farmers ' Bulletin 80. 25 Piper, C. V. 1902. U. S. Dept. of Agr., Farmers' Bulletin 153. 26 Qaintance, A. L. 1905. U. S. Dept. of Agr., Yearbook, pp. 344-346. 27 Riley, C. V. 1883. Prairie Farmer, Nov. 24. 28 Riley, C. V. and Howard, L. O. 1888. Insect Life, vol. 1, p. 196. 464 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION 29 Riley, C. V. and Howard, L. O. 1894. Insect Life, vol. 6, p. 373. so Sanderson, E. D. 1912. Insect Pests of Farm, Garden and Orchard, pp. 650-652. si Saunders, William. 1872. Entom. Soc. Ontario, Canada, Ann. Report., p. 15. 32 Taylor, E. P. 1907. Colorado Agr. Exp. Sta. Bull. 119, p. 8. 33WAKELAND, C. 1921. Better Fruit, vol. 15, no. 10 (April), p. 8. 34WELDON, G. P. 1914. Calif. State Com. of Hort., Mon. Bull., vol. 3, no. 7, p. 287. 35 Wilson, H. F. 1915. Oregon Agr. Exp. Sta., Second Biennial Crop Pest Report (1913- 1914), p. 113. 36 YOTHERS, M. A. 1914. Wash. State Agr. Coll., Pop. Bull. 61. 37 Zeller, C. P. 1839. Isis (Leipzig, Germany), p. 190.