BULLETIN No. p 4 DECEMBER, 1900. m , N. Y. SAN JOSE) SCALE INVESTIGATIONS. I. The Development of the Female. V. H. LOWE and P. J. PARROTT. PUBLISHED BY THE STATION. BOARD OF CONTROL. Governor Theodore Roosevelt, Albany. Stephen H. Hammond, Geneva. Austin C. Chase, Syracuse. Frank O. Chamberlain, Canandaigua. Frederick C. Schraub, Lowville. Nicholas Hallock, Queens. Lyman P. Haviland, Camden. Edgar G. Dusenbury, Portville. Oscar H. Hale, North Stockholm. Martin L. Allen, Fayette. OFFICERS OF THE BOARD. Stephen H. Hammond, President. William O\'Hanlon, ¦ Secretary and Treasurer EXECUTIVE COMMITTEE. Stephen H. JHLammond, Martin L. Allen, Frank O. Chamberlain, Frederick C. Schraub, Lyman P. Haviland. Nicholas Hallock. STATION STAFF. Whitman H. Jordan, Sc. D., Director. George W. Churchill, Agriculturist and Superintendent of Labor. William p. Wheeler, First Assistant {Animal Industry}! Fred C. Stewart, M.S., Botanist. Lucius L. VanSlyke,Ph.D., Chemist. Christian G. Jenter, Ph.C, * William H. Andrews, B.S., J. Arthur LeClerc, B.S., ^[Amasa D. Cook, Ph.C, Frederick D. Fuller, B.S., ^TEdwin B. Hart, B.S., * Charles W. Mudge, B.S., * Andrew J. Patten, B.S., Assistant Chemists. Harry A. Harding, M.S., Dairy Bacteriologist. Lore A. Rogers, B.S., Assistant Bacteriologist. George A. Smith, Dairy Expert. Frank H. Hall, B.S., Editor and Librarian. Victor H. Lowe, M.S., fF. Atwood Sirrine, M.S., Entomologists. Percival J. ParroTT, A.M., Assistant Entomologist. Spencer A. Beach, M.S., Horticulturist. Heinrich Hasselbring, B.S.A., Assistant Horticulturist. Frank E. Newton, Jennie Terwilliger, Clerks and Stenographers. Adin H. HorTon, Computer. Address all correspondence, not to individual members of the staff, but to the New York Agricultural Experiment Station, Geneva, N. Y. The Bulletins published by the Station will be sent free to any farmer applying for them. * Connected with Fertilizer Control. f At Second Judicial Department Branch Station, Jamaica, N. Y. •[[Absent on leave. Mm BULLETIN No. 193. SAN JOSE SCALE INVESTIGATIONS. I. THE DEVELOPMENT OF THE FEMALE. V. H. LOWE and P. J. PARROTT. SUMMARY. * The females were found to pass through three well defined periods during development: The period of activity which follows very soon after birth and during which they move about freely; the period of growth at the beginning of which they insert their mouth parts into the tissue and begin to suck the sap and to form the scale; and the period of reproduction at the close of which they die. The young scale insects under observation remained active for an average period of 27.7 hours at temperatures above 700 F. Temperatures below 6o° F. caused them to settle very quickly. During the period of activity the larvae can cling to insects of various species and may be carried by them to new localities to which these larger insects happen to go from the infested trees. The duration of the period of growth was found to average 49.5 days. Four distinct stages in scale formation were apparent, the cottony stage, the tufted stage, the black stage and the mature stage. The temperature experiments showed the larvae to be unable to develop at an average temperature of 350 F. but able to develop to the black stage at a temperature of 450 F. Adult females were able to survive this temperature three months and to produce young soon after being removed to a temperature of 700 F. At 580 F. some of the larvae developed to the adult stage. INTRODUCTION. The past three years have demonstrated that the San Jos6 scale will thrive in some of the best nursery and fruit-growing sections of the State. This fact, together with its well-known destructive powers, makes it an important factor in the business of New York nurserymen and fruit-growers. There is, therefore, much demand for information concerning this important species. With a view to meeting the requirements of the situation, extensive series of investigations have been planned bearing upon its development, distribution and control. The present bulletin deals principally with the development of females of the late broods. The investigations aim to present an exhaustive study of the subject and much pains is being taken to work out each phase in detail as it is believed that only by such thorough work can the true nature of this as well as other species be fully understood. Such investigations should form the basis for practical experiments having in view the control of such pests. As the work was not actively begun until last fall the results thus far obtained are necessarily somewhat fragmentary. Further investigations along the same and similar lines are being carried on. PERIODS OF DEVELOPMENT. The Coccidce present a marked difference in the development of the male and female. The stages preliminary to the mature form are well marked in the former while in the latter they are not. After the female larva settles down there is a uniform development with little change except in size. There are, however, at least three well defined periods through which both forms pass as follows : The period of activity, the period of growth and the period of reproduction1. The sexes were found to be practically indistinguishable in the early stages, there being no definite relation between sex and size of larvae, but later develop- 1 With the male the period of reproduction is also a period of activity as it flies readily. 353 ments of the specimens under observation showed a small percentage of males. Hence the facts recorded for the female larvae apply also to the males. PERIOD OF ACTIVITY. Duratio?i.—This period includes the time from birth until the larva settles down. Its duration is influenced greatly by temper" ature as will be seen by comparing the following table which gives the records of larvae kept in the insectary and laboratory at temperatures of from 700 to 76°F. with the records of larvae kept in rooms at lower temperatures, on page 365. Tabi/h: -I.—Length of Active Period of San Jose Scai,e Larv^s in Insectary and Laboratory. Number of larvae in Date of Date transferred Settled. Remarks. each lot. birth. to apple. 2O Sept. 1 Sept. 2 28 hrs. Insect ary. 3 " 4 17 to 28 hrs. One larva of this lot was active for 48 hrs. 2O 9 " 10 18 < 3 Cl 12 (< 13 18 < 10 Oct. 5 Oct. 6 12% \' 4 24 Not transferred 2 in 36 \' 2 in 36 to 48 l 280 Sept. 8 Sept. 9 28 \' Laboratory. 120 9 " 10 28 \' 90 " 10 " 11 28 * " 16 ,« 1? 28 \' The total number of larvae recorded in this table is 747. None of them settled in less than 12^ hours, while a number remained active for from 36 to 48 hours, making the average number 27.7 hours, or a little over one day. The larvae probably remain inactive for a short time after birth. To secure data on this point the scales were removed on Sept. 25 from three adult females and on Oct. 8 from three more. Up to Dec. [3 the six gave birth to 263 larvae, 20 of which were born enclosed in the amniotic sack. Until the sack was ruptured they appeared as minute, oval, light-yellow bodies. Most of the imprisoned larvae did not succeed in freeing themselves but those that successfully ruptured the sack escaped in 354 from one to 48 hours. Those that were born free remained motionless near the anal plate of the mother for from one-half hour to four hours. Distayice the larva migrate.—During the active period the larvae move about very freely. The distance they can migrate unaided naturally varies with the character of the surface over which they travel and with the temperature. It is not probable that they travel very far over loose earth, but to determine this point more observations are needed. During our investigations the nearest approach to data on this phase of the subject was in the case of an infested apple placed on the ground about four inches from the base of a small apple tree growing in the shade in the insectary. The soil about the tree was well packed and moderately moist. The apple remained for three weeks during which time the larvae were numerous and active but none were found on the tree. It is possible that the larvae did not attempt to leave the fruit, but a large number of cases were observed in the laboratory where they wandered freely from infested apples kept under similar conditions, thus indicating that they have a definite tendency to migrate from the fruit. A more definite illustration of the power of the larvae to migrate was furnished by a simple experiment with a single larva. December 27 a young larva measuring 0.2 mm. in length was placed on a smooth piece of paper at 10:05 A-M- The temperature of the room averaged about 74°F. The larva traveled almost continously, with occasional stops, for six hours, during which time it had covered io}^ feet, or about 16000 times its own length. The larvae appear to have a tendency to seek sheltered places on the bark and fruit before settling down. This is especially noticeable in cases of moderate infestation. On fruit, the blossom end or stem end is usually sought by a majority of the larvae, the former often being preferred. It is possible that the position of the fruit may have some influence ; as after the fruit turns down the blossom end is less often, if at all, in the direct rays of sunlight. With this in mind 20 larvae were placed on each of ten smooth-skinned apples. Immediately after being infested half of the apples were placed on shelves in the laboratory stem end 355 down and half blossom end down. In two days all had settled and in every case about three-fourths settled on the under side where there was the least light, the remaining one-fourth being scattered. It is also very noticeable that on infested apple and pear fruits a majority of the young scales will be found grouped about the adults. An examination of a large number of infested fruits including apple, pear, quince, plum and peach, showed about eight-tenths of the young scales gathered about the adults that had made slight depressions in the fruit, probably as a result of sucking the juice and the consequent withering of the tissue, while but comparatively few were found about those that had not made a depression. A number of typical groups are shown much enlarged at Plate II, Figs. 1,2,3 and 4. At Fig. 3 a male scale is shown with a number of young about it. At Plate IV, Fig. 1 a large group is shown, also much magnified. Mortality of the larvce.—The active larvae are very small and comparatively delicate and probably under ordinary conditions a large percentage do not succeed in passing the active period. To ascertain the mortality among larvae kept as near normal conditions as possible, seven adult females were kept under observation for several weeks. They were enclosed in cells like those described on page 369. The temperature of the room in which they were kept varied from 700 to 75°F. during the day and dropped to about 6o° at night. The scales were removed from three of them. The mortality among the larvae from these females is shown in the following table : TabIvK II.—Mortality of San Jose: Scai^e Larv^ , During Active Period. Number r Number lived Num- Percent- No. Reproductive young to settle ber age of Remarks. period. produced. down. died. mortality. I Sept.25to]S[ov.I; \\ 59 52 7 II Scale not removed 2 12 2 10 83 << < 1 3 26 2O 6 23 < < (< 4 87 67 20 23 < t << 5 14 4 10 70 Scale removed. 6 61 34 27 44 (< <( 7 12 9 3 25 << «< Totals...... . 271 188 83 Average 39-8 356 In two of the records the percentage of mortality is very high while in the remainder, with the exception of No. 6, not more than 25 per ct. perished. Although all of the females and young were kept under the same conditions, no reason for the much higher percentage of mortality in some cases than in others could be ascertained. As shown by the table the average mortality was almost 40 per ct., leaving about 60 per ct. that lived to settle down. The comparatively small number produced by each female is noticeable but it. is not exceptional to our experience with a large number of other females of the fall broods kept under observation. It is not improbable that females of the late broods give birth to fewer young than those of earlier broods. PERIOD OF GROWTH. Duration.—The period of growth lasts approximately from the time the larva settles down until the beginning of the reproductive period. In the field there is much variation in the duration of this period. In the laboratory and insectary there was also much variation, especially in the case of 19 of the larvae under observation. Fifteen of these were transferred to smooth-skinned apples and kept in the insectary and four were placed on the smooth bark of a young apple tree also in the insectary. The results are shown in the following table : Table III.—Length of Period of Growth of San Jose Scale Larv^. Larva Date settled No. down. I Sept. 6 2 6- 3 6 4 6 5 6 6 6 7 6 8 6 9 6 IO 6 ii 6 12 6 13 6 14 7 15 6 16 / 17 V Aug. 29 18 ) 19 < 29 Datebegan to reproduce. No. days. Remarks. Oct. 24. " 27. None to Dec. 31. Oct. 28. None to Dec. 31. Oct. 25. None to Dec. 31. Oct. 29. On Nov. 11 had 25 larvae None to Dec. 31. Oct. 7 had together 101 larvae. Oct. 12. Average 5i 52 49 53 _44_ 49-5 On apples in laboratory hibernating in adult stage Nos. 16, 17, 18 kept in one cage and were overlooked untilOct. 7. On apple tree in insectary. On apple tree in " days. Plate I.—i-6, Successive Stages of Scale Formation ; 7, Female Scale ; 8, Female with Scale Turned Back. (Original.) .. -,\' va Plate II.—i, Female Scales, Nipples Lateral ; 2 and 4, Adult Females with Young; 3, Male Scale; 5, Adult Female, Natural Size, on Apple; 6, Discoloration of Fruit by Growing Scales. (Original.) 357 The table shows that but ten or a little more than half of these females produced larvae. With these, however, the period from date of settling down until young were produced was fairly uniform varying from 44 to 53 days with an average of 49.5 days. At Plate I, Fig. 1, some larvae are shown that have just settled down and are about to begin forming scales. It is during this period also that the discoloration of the tissue begins. The irregular blotches produced by the young scale individually and collectively on fruit and leaves are shown at Plate II, Fig. 6 and Plate IV, Fig. 2. Formation of the scale.—In the formation of the scale by the female there were usually apparent four well defined stages based upon its outward appearance as follows : (1) The white or fluffy stage, (2) the tufted stage, (3) the black stage and (4) the fully formed stage. The white or fluffy stage.—The first indication of the formation of the scale is the secretion of white cottony filaments that cover the body at first sparingly but finally become quite dense until the insect has the appearance of a white oval mass of fluffy cottony fibres loosely woven together. This first covering is very delicate and can be easily removed. The scales under observation showed a variation in the time of the first appearance of the white secretion of from 6 to 24 hours, but in all cases when the young scales were kept in a warm room or the insectary this stage was reached within 24 hours after the larvae had settled down. The secretion of the filaments is normally quite rapid, as the larvae were usually completely covered with them within six or eight hours after they first appeared. Plate I, Fig. 2. The tufted stage.—At the beginning of this stage a denser layer of waxy threads is seen projecting from beneath the loose threads over the margin of the body. This is the true scale. As the insect increases in size this portion of the scale is enlarged. The loose white filaments form a central tuft which in many cases becomes three or four times the diameter of the scale, as shown at Plate I, Fig. 3. The true scale soon begins to turn dark passing through several shades of dirty gray until it becomes nearly black. The tuft grows smaller slowly, probably weathering away, until it finally disappears, leaving a crater-like depression at the 358 apex of the scale. (Plate I, Fig. 4 and Plate II, Fig. 4; the small scale on the left.) The black stage,—This stage is characterized by the dull black color of the scale and usually at first by the crater-like depression at or near its apex, which is later filled by the nipple. It begins when the white tuft has disappeared. During this stage the scale becomes thicker and its texture is more compact than at any previous time. In the latitude of New York State the insect hibernates in this stage, hence its duration varies greatly with the time of year. Plate I, Fig. 5, and frontispiece. The mature stage.—As the insect grows the scale is enlarged by the secretion of the white waxy fibres which may often be seen projecting from beneath the scale as shown at Plate I, Fig. -6. This white mass soon turns dark, usually a dull dirty gray, and forms a large part of the scale. The mature scale is characterized by its comparatively large size, the prominent, usually central, nipple and the light-yellowish areas caused by the molted skins showing through the scale. In many cases the nipple is near the margin as shown at Plate II, Fig. .1. The two large scales in this picture are adult females. The first molt causes the whole central area of the scale to appear a lighter shade than the remainder. The white cottony mass which is forced beyond the edges of the scale turns dark forming a dark, ring. The second molt forms a lighter area which, as it shows only toward the edge, the scale now being much thinner at the edges than toward the apex, forms a lighter ring. Thus there are two more or less distinct broad light bands with a narrow dark band between. Plate I, Fig. 7. At Plate I, Fig. 8, a mature scale is shown turned back exposing the living insect. The dark area forming the posterior extremity of the insect\'s body is the anal plate. It is by means of the microscopic characters of this plate that the species may be definitely determined. Plate III, Fig. 1 is from a photomicrograph of the anal plate of the San Jose scale and Fig. 2 of Aspidiotus czstreczformis, a species common in this State that is sometimes mistaken for it. While the above description of scale formation is fairly typical, there is much variation. In this connection the following notes giving the details of the formation of the scales of a number of III.—AnaIv Plate OF Aspidiotus pemiciosus; 2, Anal Plate of Aspidiotus cestrecBformis. From photomicrographs. (Original.) 359 individuals kept under the same conditions may be of interest. All of the larvae were placed on smooth-skinned apples and kept in the laboratory or insectary. No. i.—Ten larvae born Sept. 4. By Sept. 8 they were completely covered by the white cottony secretion. On this date the cottony mass was removed, but by Sept. 10 it was replaced by another covering of waxy filaments which were more closely matted together than the former. The scales were white like the first and on this date showed a faint indication of a central nipple but no ring about the nipple. By the following day a slight ring-like depression had formed about the nipple. Until Sept. 19 there was no apparent change but on that date the scales appeared to be turning darker in color. By Sept. 21 they had begun to turn very dark, nearly black on the outer margin, and on Sept. 28 were black over their entire area except the white nipple at the center. At this point further change in the scales ceased and the insects are now dormant. No. 2.—One larva born Sept. 12. By Sept. 14 the white cottony substance had formed a prominent tuft near the center with the yellow body of the insect showing around the margin. The following day the entire body was covered. Sept. 17 a small white fluffy tuft had formed a little to one side of the center with the remaining portion of the scale white but more dense and firm. Sept. 19 the margin was turning dark with the nipple still white. The gradual change to darker shades continued and on Oct. 4 the scale was much darker with a white tuft at center surrounded by a narrow ring of yellow, caused by the first molt, and a second ring of yellow at the margin caused by the second molt. By Oct. 8 the main portion of the scale was dark brown and by Oct. 12 it was black, the white nipple still persisting. There was no further development of this scale as it gradually became dormant. No. 3.—Under this number are included ninety larvae born Sept. 3 and transferred to apples, six on each apple, the following day. They were kept in the insectary and the formation of the scale was so uniform that the lot may be discussed as a whole. - An examination, Sept. 6, showed them to be completely covered by a grayish-white scale with a central nipple just apparent. By Sept. 8 the nipple had turned to light gray 360 and was surrounded by a dark brown indented ring followed by a broad base of dark gray. By Sept. 14 the whole scale, except a narrow brown margin, was black. Sept. 17 most of the scales showed a narrow band of white on the margins caused by the pressing out of the white cottony substance secreted by the insect. Plate I, Fig. 6. Sept. 21 the scales were black or very dark gray but still showed the white extension. Oct. 8 the first molt of one of the scales had taken place. Nearly simultaneous with the molt the discoloration of the skin of the fruit appeared. Oct. 12 some of the specimens showed second molt and the males were now distinguishable by the elongation of one side of the scale. By Oct. 16 one male showed first and second molt areas, light yellow in color. A narrow dark-brown ring separated the two areas. The lateral extension was light gray. Oct. 30 one of the female scales was mature. The first and second molts showed the broad light yellow bands with the narrow dark band between and the margin dark brown. The entire scale was covered with a white pollinose substance. The remaining scales had all reached the black stage and were dormant. No. 4.—This group included eight larvae born Sept. 18 and kept on apples in the laboratory. They were not examined until Sept. 29. On this date they could be divided into two lots based on the outward appearance of the scale. Lot 1 was well covered with a tuft of white cottony substance. Lot 2 had molted. All of this lot had a white nipple at the center surrounded by a narrow slightly-depressed band, deep brown in color. On the outer margin of this depression was an elevated ring of the same color and covered with a white pollinose substance. From this elevated ring the scales sloped down to a nearly flat surface which formed the boundary of the oval figure and was composed largely of the molted skin. This area was light brown in color in nearly all cases, with a narrow black extension on the margin. After this date there was no further development of either lot. PERIOD OF REPRODUCTION. This period probably begins very soon after full development. Owing to the fact that many of the scales under observation have yet passed only to the hibernating stage we are able to present the 361 records of but seven females which are given in the following table. It will be noticed that the average number of days is 30.2 while the highest number of young produced in a single day was 8 and the average for the entire number was but 1.07. Table IV.—Number of Larvje Produced by Seven Females with Daily Record of Each.3 1 2 3 4 5 6 7 Oct. 14 23 26 4 5 27 18 1 8 4 28 2 0 4 0 5 29 7 0 2 0 3 30 0 2 1 2 8 31 1 0 3 6 0 Nov. 1 1 0 4 4 1 2 1 1 2 1 i 3 2 2 1 0 0 4 2 0 0 2 2 5 3 0 0 1 2 6 5 0 0 0 4 7 0 0 0 0 0 8 5 1 0 1 2 9 5 3 0 0 0 10 1 1 2 0 0 11 1 0 0 0 2 52 12 0 0 0 0 5 3 13 0 0 2 0 0 0 14 1 1 2 1 7 2 15 6 0 0 0 1 1 16 1 0 0 0 0 1 Remarks. Temperature dropped tO5S°F., which evidently checked development. Nov. 17 20 21 22 II 27 28 29 3O Dec. 1 3 4 5 6 7 8 10 11 12 13 14 15 26 4 I 5 I I rV rv Remarks. 2 1 o 5| ;| oj o| 5 1 2 CO o o o! 0\' 000,0 No. of days........................ No. of larvae...................... Average number per day............ General average.................... Total number of larvae for each female 58 42 43 14 Av. 30.2 da. 1.07 76 14 341 56 88 12 81 3 Numbers in Italics represent number of larvee born when observations were corn menced. 362 MOI/TING : HOW ACCOMPLISHED. Laboratory observations upon individuals from which the scale had been removed showed that in molting the skin splits along the anterior margin and for a short distance along the lateral margins. It is then forced off the posterior end of the body by the motions of the segments. The following observations upon the molting periods are from 320 males and females kept in the laboratory. For convenience they were divided into lots as follows : Lot 1 consisted of 160 larvae born Sept. 4. Sept. 17 one larva showed first molt. About half the remainder did not show first molt until Oct. 1, while nearly all the other half showed the second molt on the same date. The majority of the scales were dark gray in color at the time of first molt. Lot 2 consisted of six larvae born Sept. 5. They showed first molt Sept. 19. Lot 3 consisted of one larva born Sept. 25. Oct. 6 showed first molt. The scale at time of first molt was white with white central nipple. Lot 4 consisted of 150 larvae born Sept. 3. Oct. 8 two individuals showed first molt. In both cases the scales were black. Oct. 12 the same specimens showed second molt. On this date, also, all of the males showed second molt and the lateral projection of the scale was becoming apparent. Up to the time of writing, Dec. 31, the remaining larvae have not molted but are dormant in the black stage. Lot 5 consisted of one larva born Oct. 5, first molt Oct. 30. At the time of molting the scale was light gray in color with crater-like depression at the center. To Dec. 31 there is no trace of a second molt. The insect is now dormant. Lot 6 consisted of ten larvae born Sept. 11. They were on a young apple tree in the insectary. Oct. 12 no appearance of first molt. Oct. 26 one female had passed second molt. The remainder are dormant (Dec. 31) without showing first molt. Lot 7 consisted of one larva born Sept. 25. By Oct. 14 it had passed the second molt. At this time the white central tuft still remained. By Oct. 25 it had disappeared. The first and second molt-areas were dirty yellow and the remainder of the scale gray. 363 Lot 8 consisted of five larvae born Aug. 25 and placed on young apple trees in the insectary. Oct. 5 all showed second molt and were characterized by a central light-yellowish area and black band toward margin. Oct. 7 a number of larvae were born from these females. Lot 9 consisted of one larva born Aug. 31. There was no indication of first molt until Oct. 5 ; after which the insect became dormant. Summarizing the above: The first molts of 91 larvae were recorded and the period from birth to molting found to vary from 11 to 35 days, the average number being 20.7. The second molts of 87 larvae were observed and the number of days from birth found to vary from 14 to 45 days or an average of 29^ days while the period from the first to the second molt in the case of five larvae was four days. In all cases there was no constant relationship between the stage of development of the scale and the molts. Rate of growth of the scale.—The table on following page shows the rate of growth of the scales of three larvae during the first half of the period of growth. None of the scales lived to mature. As the growth of the insect and its scale is probably at nearly the same rate the measurements are of interest as indicating the rate of growth of the insect as well as its scale. EFFECTS OF TEMPERATURE ON DEVELOPMENT. The effects of temperature on the development of the scales is well understood in a general way. It is a matter of common observation that the larvae are usually more numerous and active during warm than cool days. Also that the half-grown insects withstand severe cold, otherwise they could not endure our winters. But it is not yet fully understood whether young scales attached to fruit or nursery stock kept in cold storage will continue to develop, are merely checked or cannot survive. Also whether mature scales under the same conditions will survive and produce young when brought into higher temperatures. The following data was obtained from larvae placed on apples and kept in rooms having temperatures as follows : Checks kept in insectary and office temperature 72-75^ developed normally. Room 1 had an average temperature 35°F., Room 2, average tern- 364 Table V. -Rate of Growth of Scale. Rate of growth. Date Larva No. 1. Larva No. 2. Larva No. 3. JKemarics, Sept. 27 . . .254 mm. \' 28 . . .293 « \' 30 . . .400 \' Oc t. 1 .. .418 \' \' 2 . . .418 ( 3 •• .420 \' .325 mm. 5 •• .420 \' .327 " 6 .. .436 \' .33O " 7 .. •455 \' • 345 <( 8 .. .200 mm. 9 •• .637 \' •273 \' .364 " ( 11 .. .655 \' .290 \' .364 " ( 12 .. .655 \' .309 ( .400 " 1 13 . . .655 \' •364 \' .418 u 1 14 .. .655 \' .368 \' .418 \'* ( 15 •¦ .655 \' .368 • .418 (< 1 16 .. .655 \' .368 \' .418 " * 17 ¦ .655 \' .372 \' .418 " 1 18 .. .655 \' .436 " \' 19 • • •655 \' ¦372 \' • 473 {i \' 20 .. .658 \' •374 \' • 473 " No 2. No change after Oct 20. 1 21 .. .658 \' •473 " * 22 .. .658 < •473 " 1 23 .. .673 * • 473 " \' 24 .. .673 ( • 473 {i \' 25 .. .673 * • 473 *\' • 24 . . .673 \' • 473 " 1 25 .. .673 \' •473 " ( 26 .. .691 \' •473 " \' 27 .. .69 r « •473 4< 1 29 .. .728 < 1 30 •• .728 \' •473 " 1 3i •¦ .728 • Nov. 1 . .746 ( •473 " " 2 . . .746 \' •473 " No. 1. Nearly mature on Nov. 2 but no further growth. " 8.. .491 " No. 3. No change after Nov. 8. Averages . .6 •33 " •43 <4 perature 45°F., Room 3, average temperature 58°F. The young scales were divided into lots and placed upon sound apples which were then placed in the cold storage rooms with the following results: Room 1,—Average temperature 35°F. Lot 1 consisted of Plate IV.—i, Portion of a Group of Scales on an Apple; 2, Infested Pear Leaves Showing Discolorations Caused by Growing Scales. Plate V.—i, Cotton Bands and Cells on Young Apple Tree used Confine Active Larvae ; 2, Cells on Apple in which Active are Confined and Growing Scales Isolated. to 365 twenty larvae, born September 9, and transferred to apples September 10. They were immediately placed in Room 1. In half an hour all had settled down. The following morning each was covered with the white fluffy scale. September 14 no change was apparent except with two laivae, one of which had pushed the scale nearly off from the body1 while the scale of the other had begun to turn light brown. September 22 the scales of two larvae were somewhat more dense than the others but otherwise there was no apparent change. From this time on there were no further signs of development and by December 20 they were dead. Lot 2. This lot consisted of 13 larvae born October 5 and transferred, the following morning, to an apple which was at once placed in Room 1. They settled down almost immediately. October 8 they were dormant and naked with the exception of two which showed faint traces of cottony threads. One was sparsely covered with them. Examinations were made every other day but no further development was apparent. November 17 they were carefully examined and found to be dead. Summary.—The effect of an average temperature of 35°F. upon the young larvae is here indicated and definitely shown so far as the larvae under observation were concerned. They settled down almost immediately and attempted at once to cover themselves with a scale. More than half succeeded in doing this, but all perished before reaching the normal hibernating stage. Room 2.—Average temperature 45° F. Lot 1 consisting of 84 larvae born Sept. 4 and transferred to apples the following morning. Sept. 6. All had settled, a few of the white fibres showing in every case but one and this larva was naked. Sept. 8. Nearly all showed the white central tuft. From this time on there was no further development until Oct. 24 when six infested apples (36 larvae) were transferred to the insectary where the average temperature was 750 F. By Oct. 27 a slight indication of development was apparent. Oct. 30 the white fibres of the new addition to the scales were apparent on most of the specimens. The scales continued to enlarge slowly in this way until Nov. 9 when the insects apparently ceased their JThis has been observed in the laboratory. It is done by a movement of the posterior segments. 366 activities and still remain dormant. Nearly all of them reached the normal hibernating stage. The effect of this temperature upon the adult females was shown by a number that were kept three months in this room and then removed to the laboratory. Within two days after the change some of them were producing young. Summary.—These results are interesting in showing that the young larvae, although apparently unable to develop to the hibernating stage in a temperature of 450 F. were still able to resist this temperature for six weeks and when transferred to a room of higher temperature to continue development to the normal hibernating stage ; also that the adult females may withstand it and produce young soon after being removed to a higher temperature. Room 3.—Average temperature 580 F. Lot 1 consisted of ten larvae born Sept. 1 and transferred to one apple Sept. 2 which was immediately placed in the cool room. The scales were not again observed until Sept. 29 when they could be easily divided into three groups according to the external appearance of the scale as follows : Group i, four larvae, scales light-brown ; Group 2, five larvae,scales dark gray approaching black,with small white central tuft. Group 3, one larva, side black. Oct. 3, Group 1 light-brown, quite convex, with black addition to margin. Groups 2 and 3, no change. Oct. 5, Group 1 has passed first molt. The scales show characteristic light central area with narrow black band at margin of the scale. Group 2, no change. Group 3 has passed first molt. Oct. 8, Group 1 very dark brown, nearly black. Group 2, no change. Group 3, black with dark brown nipple. From this time until Oct. 30, Group 1 showed steady growth passing the second molt and becoming full size about this date. Groups 2 and 3 showed no further change. Summary.—In this case the temperature of 580 F. was not sufficient to materially check growth until the normal hibernating stage was reached and one insect succeeded in reaching full development. General summary.—These experiments are of practical interest in indicating the temperature required in a cellar for cold storage of trees or fruit to prevent the development of young larvae or to kill the the adult females which if able to survive the cold 367 would probably produce young, as was the case with the adults referred to on page 366 very soon after being brought into warmer temperatures. This is of especial interest in connection with cold storage of fruit. It will be noticed that at a temperature of 45° F. development was merely checked and continued when the scales were brought into higher temperature, while at 35 F. none of the young scales survived. MEANS OF LOCAL DISTRIBUTION. It is during the active stage that the insect is distributed locally. There are three principal agencies which aid in local distribution. First, the activity of the larva which enables it to migrate from one place to another ; second, the wind which may carry infested leaves and twigs about; and third, insects, birds and similar agencies. The ability of the larva to migrate over smooth surfaces has been previously referred to. Wind.—To ascertain the probability of the larvae being carried on foliage by the wind, 200 pear leaves were picked and carefully examined Oct. 1, and although the larvae were numerous on the trees none could be found on the leaves. Ten leaves were then placed on the ground and a larva on each. In one hour all had gone except two which remained three hours. Oct. 4, when the larvae were numerous and active on the infested pear trees, 1680 green leaves on the trees were carefully examined and but 54 larvae were found. A larva was then placed on a pear leaf which was released from a point about 10 feet from the ground. It was carried by a light breeze about 16 feet and when examined the larva had disappeared, evidently having been blown off by the wind. This was repeated six times, the leaves being carried about the same distance each time. In every instance but one the larva was blown off and when the leaf to which the larva had successfully clung was again released from the same place the larva did not succeed in clinging to it. Insects.—At various times from Aug. 26 to Oct. 11 insects that were found on infested trees were caught and examined to see if larvae were clinging to them. The following is a list: Grasshoppers. On Aug. 26 one grasshopper was found with four larvae clinging to it; and on Aug. 29, another with one. Aphis lion, Chrysopa. On Aug. 29 two aphis lions, with one larva caught in the hairs on the upper surface of posterior wing of each were found. Flies, Sarcophagi dee. One individual was found on the same date with a larva clinging to one of its legs. Beetles. A specimen of Euphoria inda was found Sept. 1 with seven larvae clinging to it. At various times also twelve wasps representing four species, 30 honey bees, 24 ants and two dragon flies were examined, all of which were taken from trees upon which the young larvae were very numerous and crawling about actively, but no larvae were found. In the case of the Hymenoptera it is not improbable that their cleanly habits account for the lack of San Jose scale larvae. CONTROLLING THE INSECTS FOR THE PURPOSE OF STUDY. One of the difficulties in the way of accurate and extensive observation upon the development of this species has been the difficulty of keeping the active forms within sufficiently narrow limits. To obviate this difficulty, two simple methods were resorted to. First the use of bands of cotton wool tied about the trunks of small nursery trees or the small limbs of larger trees. These bands were placed from one to two inches apart and prevented the escape of latvae placed on the bark between them. Plate V* Fig. 1. Second, cells made by cementing glass or metal rings to the bark or fruit with melted paraffin. Half-inch brass curtain rings proved very satisfactory. Thin circular cover glasses, the same as used in microscopical work, were placed over the rings and held in place by paraffin. Enough paraffin was always used to entirely cover the ring. To admit air small holes were made with the point of a fine needle through the paraffin just under the cover glass. Plate V, Fig. 2. In our studies sound apples were found very convenient. A single female could be isolated and her offspring easily counted, or a single larva could be kept within narrow limits for close observation.