LIBRARY rATE PLANT BOARD January 1%7 E-7H United States Department of Agriculture Agricultural Research Administration Bureau of Entomology and Plant Quarantine REPORT ON COOPERATIVE EXPERIMENTS CONDUCTED BY THE BUREAU 07 ENTOMOLOGY AND PLANT QUARANTINE AND THE CALIFORNIA STATE DEPARTMENT OP AGRICULTURE RELATIVE TO THE FUMIGATION OF FRUIT AND NURSERY- STOCK HOSTS OF THE ORIENTAL FRUIT MOTH l/ Zj By A. C. Johnson, C. H. Bowen, and G. L. Phillips, Division of Control Investigations The secretary of the Western Plant Board, in letters dated December 11, 1942, and January 12, 1943, transmitted a request from the Board to the Bureau of Entomology and Plant Quarantine for stud- ies to be undertaken on the development of treatments for host fruits originating in areas quarantined by Western States because of the oriental fruit moth (Granholitha molesta (Busck)). The answer from the Bureau, dated January 23, 1943, pointed out that such studies were already under way on a limited scale in the Division of Control Investigations, but only on fumigation schedules for summer-maturing fruits intended for immediate consumption. It was stated that funds were not available to undertake studies of fall-maturing fruits in- tended for storage. In February 1943, the late D. B. Mackie, of the California State Department of Agriculture, proposed that a cooperative project be undertaken on this problem, and it was finally arranged that the State of California would allot to the Bureau a sum not to exceed $8,000, to be available during the fiscal biennium of 1944 and 1945, to aid in carrying out studies along the line proposed in the orig- inal request by the Western Plant Board. Later,at the request of the California State Department of Agriculture, studies were also made with hibernating larvae in an effort to reduce the dosage sched- ules and the temperature requirements in effect for the treatment of nursery- 8 tock hosts. l/Thls report was submitted to the member States of the Western Plant Board, November 15, 1945, and is now reproduced in substantially the original form for the information of others interested in this subject. 2/These investigations were under the immediate supervision of Randall Latta. JAN 2 7 1947 - 2 - The cooperative agreement with California terminated June 30, 1945* This report is a presentation of the studies made during the period covered "by the agreement. OBJECTIVES The objectives of the study were threefold: (1) To develop fumigation dosage schedules for the treatment of fresh -fruit hosts of the oriental fruit moth. (2) To study further the dosage schedules needed for the destruc- tion of hibernating larvae on nursery-stock hosts, in an effort to de- velop fumigation schedules at temperature levels "below 60°P. and to re- duce the schedules now authorised at 60c and 70°. (3) To study the tolerance of host fruits to fumigation schedules that are effective against this insect. METHODS All the tests were conducted at St. Louis and Louisiana, Mo., by the Division of Control Investigations of the Bureau. The University of California Citrus Experiment Station supplied all oriental fruit moth eggs and hibernating larvae of California origin. Hibernating larvae from New Jersey were supplied by the Division of Fruit Insect Investigations of the Bureau. Stark Eros. Nursery, Louisiana, Mo., assisted in taking nursery-stock storage shed temperatures and humidity records, which are shown in figure 1. The experimental fumigations were performed in portable chambers, which were in excellent condition. Commercial cold-storage facilities were utilized for the storage of s-opies. Except where otherwise noted, all fruit 8 were purchased from local sources, and were especially se- lected for condition. All dosages are expressed in pounds of methyl bromide per 1,000 cubic feet of space. For conciseness the dosage schedules are abbre- viated as indicated in the following example: A schedule of 3 pounds per 1,000 cubic feet for an exposure of 2 hours at 70°E. is shortened to 3 lb./2 hr. at 70°. As certain portions of the experimental test9 were finished, cor- roborative tests were made in California to check the results under their conditions. These tests were reported by Arm it age and Steinweden in March 1945. 3/ 3/Armitage, H. H., ejri& Steinweden, J. 2. Development of methods of fumigation for control of the oriental fruit moth. Dec. 1944 - Mpr. 1945. Unpublished report of Anaheim Stetion, California State Department of Agri culture. The results are presented under the following headings: ( l) Fumi- gation of fresh-fruit hosts of the oriental fruit moth, (2) mortality of larvae exposed to cold storage, ( 3) fumigation of hibernating larvae, and (4) tolerance of fruits to methyl "bromide fumigation. FUMIGATION OF FRESH- FRUIT HOSTS OF THE ORIENTAL FRUIT MOTH All studies relative to the fumigation of fresh- fruit hosts were limited to the summer broods of the oriental fruit moth. The results of tests with each stage of this insect are given. Overwintering larvae were considered only in their relation to dormant nursery stock and are the subject of another section. Larvae Tests in an effort to develop fumigation schedules for larvae of the oriental fruit moth embedded in fresh fruit were first made in the summer of 1943. At first green apples were infested by enclosing them in cages with infested peach twigs; later naturally infested fruit was ob- tained. Dosages of methyl bromide ranging from 1 to 2 pounds per 1,000 cubic feet were used at temperatures of 60° and 70°F. The results of these tests pre given in table 1. Complete mortality occurred at all dosages except 1 lb./? hrs. at 60°, where 1 larva and 2 pupae survived. In 1944 plans were made to infest fruit artificially so that greater quantities would be available. Through the courtesy of the University of California Citrus Experiment Station, eggs, deposited on sheets of wex paper, were supplied at frequent intervals ( 2 to 3 days) by air mail. Bushel lots of apples were infested by placing a small piece of wax paper containing about 6 eggs in contact with each apple. Nineteen bushels in- fested in this manner proved to have an average infestation of slightly more than one larva per apple. Apples were ready for use in fumigation tests in about 6 days if immature larvae, or about 12 to' 15 days if mature larvae, were desired. Fifty-nine tests were made with dosages ranging from 0.5 to 2,5 lb. at temperatures from 40° to 80CF. A total of 4,247 apples were used, containing 4,455 larvae. It was considered desirable to develop fumigation schedules suitable for the treatment of fruit that had been refrigerated, or placed in cold storage, as well as for freshly picked fruit. A minimum of 40 eF* was used, since it was considered that most fruit coming from cold storage would be at approximately that temperature by the time it had been made ready for fumigation. The results of these tests are given in table 2. The minimum dosage schedules causing complete mortality of larvae were 0.75 lb./2 nr. at 80°, 70°, and 60°F. and 1 lb./2 hr. at 50° and 40c. The location of surviving larvae within the apples varied. No particular area, such as the center, was noted where survival would most likely occur - 4 - Table 1. — Results of 1943 tests on methyl bromide fumigation of fresh fruits infested with oriental fruit moth larvae. Fumigation for 2 hours unless otherwise noted Treatment : Total : Condition of larvae Temperature* • • — • Do sage ' * i Date s fruit : • • • Total • • Mortality Of Mm ^ ounus Number jDtumoor i" ere en v Apples 70 2 5/13 6 32 100 1.5 5/13 6 27 100 5/19 . 16 94 100 5/19 1/ 16 75 100 60 2 6/23 19 67 100 JL«0 6/23 20 1UU 1 7/20 29 9 2/ 89 Peaches 5/ 70 1*5 7/26 37 12 100 7/28 75 16 100 1 7/26 33 22 100 8/4 32 5 100 60 1.5 8/12 100 12 100 Pears 2J 70 1 8/4 32 5 100 i/Fumigation 1.5 hours. ,2/Two live pupae also found, under skin of apples. 2/Naturally infested fruit. Table 2. — Resulte of 1944 teats with 2-hour methyl bromide fumiga- tion of fresh fruit infested with oriental fruit moth larvae Treatment Tenperature: Dosage 80 Pounds 0.5 .75 1.0 Total tests Number 2 3 5 Apples Number 34 280 490 Condition of larvae Total : Mortality Number 35 176 519 Percent 91 100 100 70 .5 2 .75 2 1.0 4 1.25 5 60 .5 1 .75 2 1.0 1 1.5 5 2.0 1 50 .5 1 .75 1 1.0 2 1.25 1 1.75 5 2.0 2 2.5 1 40 .5 1 .75 1 1.0 1 1.25 2 1.5 1 2.0 6 2.5 1 92 70 91 183 161 100 441 370 100 500 686 100 53 19 89 63 38 100 112 57 100 626 644 100 150 189 100 40 21 52 39 19 63 66 50 100 43 48 100 300 427 100 39 51 100 22 22 100 41 31 74 42 39 92 44 35 100 64 29 100 46 20 100 413 650 100 24 49 100 - 6 - Ho difference in reaction was observed between the different larval stages. The mortality obtained in artificially infested apples was compared with that in naturally infested fruit collected near St. Louis, These data are given in table 3. The naturally infested fruit required slightly higher dosages than the artificially infested fruit. Single survivors appeared with a dosage of 1 lb. at 50° and 60°E. and it would apparently require a dosage of 1.25 lb. for complete kill at these temperatures. With a dosage of 0.75 lb., survival occurred at 70°, indicating that a dosage of 1 lb. would be necessary at this temperature level. Fumigations at the 40°F. temperature level would probably be on fruit either refrigerated or from cold storage. In order to determine whether a period of cold storage would change the susceptibility of larvae to fumigation, a series of tests was made wherein infested apples were removed from cold storage at weekly intervals and fumigated with a dosage of 2 lb./2 hr. at 40°. The apples were placed in storage Septem- ber 25, 1944, and contained both mature and immature larvae. The results are given in table 4. No survivals occurred. However, all larvae in the check samples were deed from cold storage alone at the end of the eighth and ninth weeks. Eggs The results of fumigation tests with oriental fruit moth egge, at Beltsville, Md., in 1939, reported in 1942, 4/ showed some hatching with schedules of 1.5 and 2 lb./4 hr. at 60C]T. Later it appeared that these schedules might be excessive because of certain errors connected with the use of too small a fumigation chamber. Therefore, further tests were conducted in 1944 with eggs supplied by air mail from the University of California Citrus Experiment Station. Pieces of wax paper upon which eggs had been deposited were fumigated without other load in a 20-cubic foot temperature-controlled chamber. Since experience had shown that the displacement by a load is usually greater than the absorption by it, results in an empty chamber are valid. Tepts were made between 50° and 70°P. with exposures of 2, 3, and 4 hours in an attempt to develop fumigation schedules for eggs comparable to those used for larvae in fresh fruits. A check sample was kept from each shipment of eggs. The results are given in table 5. 4/Johnson, A. C., Livingstone, E. M. , and Bulger, J. W. Methyl bromide fumigation to control oriental fruit moth on dormant nursery stock. Jour. Econ. Ent. 35i 674-677. 1942. - 7 - Table 3. — Comparison of mortality obtained by fumigation of artificially and naturally infested fruit. (Numbers of larvae involved are given in parentheses) * Mortality at treating temperatures of — Do sagft * : 40°?. : 50 °P. { 60°?. : 70 °F. 5 80°Po ; : _j i : Pound g Percent Percent Percent Percent Percent Artificially infested apples, treated July 17 to Oct. 31, 1944 1.5 100 ( 20) 1.25 100 (29) 100 (48) — 1.0 100 ( 35) 100 ( 50) 100 ( 58) 100 ( 370) 100 ( 522) .75 97 ( 36) 100 ( 40) 100 ( 16l) 100 (176) .5 90 (19) 87 ( 69) 94 (17) Naturally infested pears, treated Nov. 1 to 7, 1944 1.75 100 (8) — 1.5 100 (7) 1.25 100 ( 8) 100 ( 7) ' 1,0 100 (5) 100 (8) .75 90 (10) 100 (8) 100 (6) ,5 — 100 (10) 100 (7) Naturally Infested apples, treated Nov. 14 to 19. 1944 1.75 100 (8) 1.5 100 (16) - 1.25 100 (8) 100 (12) 1.0 88 (8) 90 (10) .75 85 (7) 100 (8) 100 (12) ,5 91 (11) 100 (10) - 8 - Table 4.-- .Results of weekly fumigations of infested apples from cold storage, with a dosage schedule of 2 lb./2 hr. at 40°F. Storage Check samples Fumigated samples >eriod • s < Apples ' , , , i Total larvae ! Mortality • * • • Apples ' • Total larvae ! Mortality • * t Weeks Number, Number Percent Number Number Percent 0 12 9 0 1 12 10 100 2 12 8 100 3 12 6 100 4 12 9 100 5 12 13 100 6 12 10 90 12 8 100 7 12 7 86 12 6 100 8 24 16 100 12 7 100 9 51 21 100 - 9 - Table 5. — Hatching of eggs fumigated with methyl "bromide at temper- atures between 50° and 70°F. Tests conducted March to June, 1944. Treatment fn_ _ i i xocai • tests ! Results of hatching i emp e rs w u.r© # x>o sag© • • « If' «*- .»-. A A •>« «. A # Jaxposure f • Total eggs Eggs S hatching 6F. Pounds Hours Number Nua ier Percent 50 1 2 4 1,009 82.3 3 2 413 63a] 4 2 403 4,9 1.5 2 4 808 32.3 3 2 379 0 4 2 336 0 2 2 3 795 0.7 3 1 168 0 4 1 190 0 2.5 2 2 401 0 1 169 \j 4 1 166 0 3 2 1 228 0 55 1 2 3 755 36.3 3 1 191 1.5 4 1 211 0 1.5 2 2 414 24.4 3 1 168 0.5 4 1 197 Xw r ft 2 2 3 R92 ft Q 3 1 209 0 4 1 232 0 2.5 2 2 443 o 3 1 163 0 3 2 1 203 0 60 1 2 4 1,160 7.8 3 2 407 2.4 4 1 2?5 0 1.5 2 3 1,057 0.6 3 1 170 0 4- 1 188 0 - 10 - Table 5.— Continued Treatment Total i Results of hatching • in , • Tempera ture, • Dosage • • Expo sure tests : Total » eggs "66' : hatching op. Pound? Hours Number Number Percent 60 2 2 3 690 0 2.5 ' 2 3 670 0 65 1 2 3 4 3 1 1 824 191 142 16.0 0 0 1.5 2 3 4 3 1 1 663 139 130 0 0 0 2 2 2 431 0 2.5 2 1 215 0 70 1 2 2 443 0.4 1.5 2 2 457 0 2 2 1 200 0 Check e 44 5,271 93,6 - 11 - It is evident from the results shown that the ejcposure period can "be shortened to 2 hours to conform with schedules for the fumi- gation of larvae. The minimum schedules for the 2-hour exoosure at vhich no eggs hatched were as follows: c7. Pounds 50 55 60 65 70 Pupae Specific tests were net made with pupae. However, it has been observed that, wherever pupae were included with larvae, they gen- erally showed grerter mortality than did the larvae. For example, a test with a dosage of 1 lb./2 hr. at 60CF. showed 14 dead larvae out o^ a. total of 18, and complete mortality among 25 pupae. Adults No further tests were made against adults eince it had been pre- viously shown that they were very susceptible to methyl bromide fumi- gation (0.25 lb./4 hr. at 70°F.) . "Discussion Dosage schedules for fresh fruits should "be sufficient to destroy not only larvae, but eggs and pupae as well, tfh.il e pupae are seldom found on the fruit, they could be present in containers. Adults prob- ably would not be present, but they are the easiest to kill of all stages of this insect. A. review of the results obtained with artificially infested fruit ( table 2) shows that complete mortality was obtained with the following schedules: 0.75 lb./2 hr. at 80c, 70°, and 50 °F. 1 lb./2 hr. at 50c end 40° Tests with naturally infested fruit (tables 1 and 3) show that slightly higher schedules are needed, as follows: 2.5 2.5 2 1.5 1.5 1 lb./2 hr. at 70 °F. 1.25 lb./2 hr. at 50° and 60° - 12 - Tests with eggs ( table 5) indicated them to be more resistant than summer-brood larvae, and the following schedules were the mini- mum causing complete mortality: 2.5 lb./2 hr. at 50CF. 2 lb./2 hr. at 60° 1.5 lb./2 hr. at 70° It would appear then, on the basis of the available data herein 5/, that a satisfactory series of fumigation schedules for fresh fruit in- fested with oriental fruit moth, or suspected of being so, would be: Z lb./2 hr. at 40°?. 2.5 lb./2 hr. at 50° 2 lb./2 hr. at 60° 1.5 lb./2 hr. at 70° 1 lb./2 hr. at 80° Owing to the discovery of the oriental fruit moth in California in 1942, and the subsequent program of regulation and control of this insect in 1943 during which tons of fruit and thousands of containers were fumigated, it was necessary to select dosage schedules for that, purpose before much of this experimental work was performed. The dosage schedules set up by California, in 1943 of 1.5 lb./2 hr. at 70°P., 2 lb./2 hr. at 65°, and 2.5 lb./2 hr. at 60° are substantially con- firmed by the results of the present studies. MORTALITY OP LARVAE EXPOSED TO COLD STORAGE Following the discovery that the viability of larvae in apples held in cold storage was seriously affected, as shown in the check sam- ples -in table 4, tests were conducted to obtain further evidence on this point. Two bushels of infested apples placed in cold storage on September 18, 1944, were sampled at weekly intervals for 10 weeks, and the condition of the larvae was noted. One bushel contained mostly immature larvae, and the second mostly mature larvae. The results of the weekly examinations are shown in table 6. There was no evidence of development of the immature larvae after en- tering cold storage, and all were dead in samples removed at the 5th to the 10th weeks. The mature larvae were hardier, and one survived in the sample examined the 10th week, although all others were dead in the sample taken the 9th veek. There was no evidence of migration from the apples during the storage period. 5/Armitage and Steinweden (see footnote., page 2) in California had no survivors in artificially infested fruit fumigated at the following schedules, in series repeated four times on Dec. 5, 1944, Jan. 2, Jan. 28, and Fab. 24, 1945: 1 lb. at 80°F., 1.25 lb. at 70°, 1.5 lb. at 30c, 1.75 lb. at 50°, and 2 lb. at 40°, - 13 - Table 6.— Mortality of larvae in infested apples held for various periods in cold storage at 34° to 36°P. Storage : Apples ! x nuns, wur o larvae larvae period : examined : Total 5 • • Mortality'* Total ! 1 1 Mortality Weeks Number Number Percent Number Percent 0 12 21 0 8 0 1 12 14 0 13 0 2 12 11 36 5 20 3 12 11 64 13 15 4 12 19 95 8 38 5 12 8 100 6 83 6 12 12 100 9 89 7 12 11 100 11 91 8 12 7 100 15 93 9 24 13 100 21 100 10 1/ 17 100 2] 30 93 l/36 apple 8 examined. 2/54 apples examined. LIBRARY STATE PLANT BOARD - 14 - Since some survival occurred after storage for 2 l/2 months, furthsr tests were made for periods of 3 and 4 months. At 3 months two temperature levels were compared, 33° to 34°F. and 35° to 35°. The 4-month test material was stored at 35° to 36°, The mortality in the 3 lots was almost, but not quite, complete. In the "bushel stored for 3 months at 35° to 36CF.,4 live larvae were recovered from a total of 129. In attempts to rear out these larvae at room temperature, one died the 4th day, one the 5th, and the third the 7th day. The fourth larva survived to maturity. Prestorage examination of a sample of 12 apples showed 19 live larvae and none dead. The bushel contained 195 apples of which 35 were soft and rotten at the end of the experiment. In the second bushel stored for 3 months, at 33° to 34°F. , ' 1 live larvs was found in a total of 214. This larva was weak and died 6 days later. Prestorage examination of a sample of 12 apples showed 8 live and no dead larvae. The bushel contained 219 apples of which 19 had rotted. In the bushel stored for 4 months at 35° to 36°F., 1 moribund larva was found in a total of 176. It died 12 days later. The bushel contained 165 apples, 9 of which had rotted. It is evident from these tests that there is little danger of oriental fruit moth larvae being disseminated by fruit which has been subjected to any considerable amount of cold storage at temperatures below 36CF. On the other hand, a cold-storage treatment would not appear to be entirely acceptable as a means of certifying fruit under oriental fruit moth quarantines. The occurrence of live hibernating larvae in used baskets often utilized as containers for fruit to be certified under oriental fruit moth quarantines is an additional complication. Even though the bas- kets would be subjected to fumigation at schedules used for summer broods of this insect, a hazard would still exist, since the dosage schedules for infested fruit are considerably less than those for hibernating larvae. FUMIGATION OF HIBERNATING LARVAE Experimental Work 1938-40 The dosage schedules now required by member States of the Western Plant Board, with respect to nursery-tree hosts of the oriental fruit moth, are based on experimental work carried on by the Bureau of Ento- mology and Plant Quarantine from 1938-40 (See footnote p. 6) . The first tests were conducted at Moorestown, N. u, , in 1938, with hiber- nating larvae provided by H. W. Allen and associates of the Bureau. The larval material was held at a storage temperature of approximately 40°F. until treated. After treatment many lots were divided, the - 15 - larvae in one lot being removed from their cocoons following treat- ment and held for observation. The remaining larvae were stored in an outdoor shelter and observed in periods ranging from 2 months to 2 weeks. It was found that the mortality of the larvae held for later examination was greater than of those removed from their co- coons soon after treatment. Tests were made at Beltsville in the winter of 1938-39, with larvae from the same source, but kept in outdoor storage. Mortality occurred at lower dosages than when stored at a constant of 40CF., and no apparent difference existed in lots removed from cocoons immediately after treatment, and those held for a considerable period. The original recommendation in 1938 for treatment was for a dosage of 3.5 lb./4 hr. at 70°F. In 1939 this was modified to 2 lb./ 4 hr. at 70°, or 3 lb./4 hr. at 60°. These latter schedules have been in effect since that time. Recent Experimental Work In 1943, further studies were initiated for two purposes: ( l) To attempt to reduce the dosage schedules then in effect, and (2) to attempt to develop fumigation schedules for lower temperature levels. Approximately 15,000 hibernating larvae were provided for these tests by the University of California Citrus Experiment Station. Upon their arrival on December 5, 1943, these were placed in storage at 32°F., and the temperature was increased later in the season to 48° to 50° in order to reproduce to some extent conditions comparable to those in nursery storage sheds. Six series of tests were made with these larvae between February and May, each series including fumigation at temperatures between the current minimum level and 70°F. The larvae were conditioned to the temperature at which they were fumigated for the periods indicated in table 7. Past experience in other studies had indicated that with each temperature drop of 10°, the dosage of methyl bromide needs to be increased. Since the tests in 1938 had shown the need for an in- crease of 1 pound per 1,000 cubic feet in dropping from 70° to 60°, the dosage increase was used in the first series of tests made February 18 to March 2 - i.e., 2 lb. at 70°, 3 lb. at 60°, 4 lb. at 50°, 5 lb. at 40°, and 6 lb. at 30°, Before the second series was started, it became evident that this rate of increase was insuf- ficient, so the dosages were changed to 4 lb. at 50c, 6 lb. at 40°, and 8 lb. at 30°. The results of these tests are given in table 7. Table 8 contains a summary of the essential data for tests of 2, 3, and 4 hours' duration. It is evident from table 7 that under the conditions of these tests, with 4-hour exposures, that dosages of 8 lb. at 30°, 6 lb. at 40c, and 4 lb. at 50°F. were not sufficient - 16 - Table 7. — Adults emerging after treatment of hibernating larvae at intervals during the storage season. Larvae of 1943 California origin. Samples of series A contained approximately 20 larvae each, of series B about 25, and of series C-P about 50 larvae. Treatment Storage^ Condi- ' temper-* tioning ature ' period * • t 1 Adults emerged from lots exposed for — Temper-: ~ Dosage ature : & 2 : 2.5 : 3 : 3.5 : 4 , _hours • hours : hours : hours : hours CP. Pounds eF. Hours Number Number Number Number Number Series A, treated Feb. 18-Mar. 2, 1944 30 6 32 2 7 3 2 13 12 35 5.5 32 3 7 20 4 6 18 40 5 32 12 8 10 11 8 2 45 4.5 32 17 8 10 2 0 0 50 4 32 18 5 2 2 o o 55 3.5 32 24 1 2 0 1 0 60 3 32 27 3 0 1 0 0 65 2.5 32 48 0 0 0 0 0 70 2 32 48 2 1 1 0 0 Series B, treated Mnr. 7-24, 1944 30 8 32 2 9 — 6 — 0 35 7 32 3 1 1 2 40 6 32 15 2 0 0 45 5 32 18 4 0 0 50 4 32 18 1 0 0 55 3.5 32 24 4 0 0 60 3 32 24 1 0 0 65 2.5 32 48 1 0 0 70 2 32 48 3 0 0 Series C, treated Apr. 5-20, 1944 35 8 34 None 8 18 9 18 10 40 6.5 50 3 24 19 4 5 5 45 5 48 3 9 15 5 1 3 50 4 50 None 5 1 0 0 0 55 3.5 48 16 7 0 0 0 0 60 3 48 16 1 0 0 0 0 65 2.5 48 36 5 0 0 0 0 70 2 43 48 10 1 0 0 0 - 17 - Table 7. — Continued Treatment Temper-: Storage temper- ature Condi- tioning ueriod Adults emerged from lots exposed for— 2 hours 2.5 hour 8 3 hours 3.5 hours 4 hours Wait t\ A a ■rounds Houxe Number Number xmm.Qex n umu Series D, treated Apr. 5-20, 1944 35 7.5 34 None 13 17 25 19 n 40 6.5 48 3 12 11 16 5 19 45 5 48 3 9 12 6 5 1 A *x 50 None 1 4 1 0 O 55 3.5 48 16 3 0 0 1 0 o 48 72 4 0 1 0 0 65 2.5 48 60 10 1 1 0 0 70 2 48 72 2 2 0 0 0 Series E, treated Apr. 29-May 3, 1944 45 5 48 18 12 7 2 50 4 48 3 14 5 9 60 3 48 20 5 1 0 70 2 48 36 7 0 0 Series F, treated May 4-11, 1944 45 5 50 15 15 1 7 50 4 50 None 5 3 4 55 3.5 48 15 12 4 1 60 3 48 36 8 3 0 65 2.5 50 36 1 0 0 70 2 1/ 48 0 0 0 l/Taken out of storage at 48°P. and subjected to room temperature varying from 55° to 70° for one week, then held at 70° for 48 hours. - 18 - Table 8. — Mortality of hibernating larvae of 1943 California origin following treatment at interval? during the storega season; data of table 7 summarized for each treatment temperature and exposure Treatment : Total : tests : Average i : larvae : : per J • f a a f I • xesv « Mortality of larvae exnosed for — Temper- : ature : j-'o sage 2 : hours : 3 hours : 4 hours Pounds Number Number Percent Percent Percent 30 6 3 17 65 82 43 8 o do 65 74 100 35 5.5 3 20 63 76 22 ry f n «3 do y/ 7.5 3 49 75 46 78 Q O i o HA O 1 S3 O A 84 fo A A 40 c O di. DO A Q 4o OA yo 6 3 25 93 100 100 C. K D, 0 6 66 79 75 45 4.5 1 o 65 91 100 5 15 45 77 63 94 50 4 18 39 85 95 95 55 3.5 15 42 87 93 99 60 3 18 46 92 98 100 65 2.5 15 42 92 99 100 70 2 18 40 90 99 100 - 19 - to produce complete mortality in all series. The schedules of 3 lb. at 60°, and 2 lb. at 70° did, however, produce complete mortality. It is also noted that as the treatment was done later in the season, the larvae tended to become more resistant to methyl bromide fumiga- tion. This i* contrary to results obtained in previous tests. The program was amplified further in 1944-45. The previous conflicte in results could have been due to the source of larvae or to the conditions of storage. Therefore, larvae vere obtained from both California and New Jersey and stored under ( l) cold-storage temperature conditions, (2) simulated nursery-stock storage conditions, and (3) outdoor winter conditions. For cold-storage conditions the larvae were placed in commercial apple storage. For simulated nursery- stock storage the larvae were placed in a thermostatically controlled mechanical refrigerator which was periodically adjusted so as to follow the weekly averages of hygrothermograph records taken concur- rently in a nursery- storage shed in Louisiana, Mo. The weekly mean tempera ture in this selected storage shed, and the current outdoor temperature means are given in figure 1. The relative humidity in this shed remained at 100 percent until almost the end of the season. For outdoor conditions the larvae were placed in a battery jar in a sheltered location outdoors at St. Loui6. Tests with larvae of New Jersey origin. — Approximately 10,000 hibernating larvae were received from Moorestown, N. J.t on November 5, 1944. These were divided into four equal portions and stored as follows: Portion 1 - cold storage at 32c to 38°F. , portions 2 and 3 - simulated nursery-stock 6hed storage, and portion 4 - outdoors. Larvae from cold storage (portion l) were fumigated at approxi- mately monthly intervals frota January 25 to April 25. Since some tests in each series were at temperature levels different from that orf storage, the larvae were conditioned for a period prior to fumigation. The original series of dosage schedules, ranging from 2 lb. at 70° to 6 lb. at 32°F. was again used. In each test the larvae were removed from their cocoons follow- ing fumigation, and kept in petri dishes for observation. Final re- sults were based on the emergence of adults from these larvae. The results are given in table 9. They showed no tendency for the larvae to become more 'resistant to fumigation as the sea.son pro- gressed. This was a reversal of the results given in table 7. In series A, survival occurred at 32°F. vith all exposures and at 40° and 70° with 2-hour exposures. In series B, one month later, a single survival occurred at 40° with a 2-hour exposure. In the remaining two series, no survivals occurred in any test. - 20 - Table 9.— Adult a emerging after treatment of hibernating larvae at Intervals during the storage season. Larvae of 1944 New Jer- sey origin, kept in apple- storage rooms at a temperature of 32° to 34°F. from Nov. 5, 1944, to Feb. 26, 1945, and at 36° to 38° from Feb. 27 to end of tests. Samples contained from 19 to 75 larvae each. Treatment Condi- ' ' tioning period Adults emerged from lots exposed for — • Temperature) Dosage • 2:35 4 hour 8 : hours : hours °P. Pounds Hour 8 Number Number Number Series A, treated Jan. 25-27, 1945 32 6 0 12 25 9 40 5 .75 1 0 0 50 4 1.5 0 0 0 60 3 2.25 0 0 0 70 2 3 2 0 0 Check (untreated) • 10 adults from 36 larvae Series B, treated Feb. 27-Mar. 3, 1945 32 6 0 0 0 0 40 5 .75 1 0 0 50 4 1.5 0 0 0 60 3 2.25 0 0 0 70 2 3 0 0 0 Check (untreated) . . . . 9 adults from 37 larvae Series C, treated Mar. 26-30, 1945 40 5 0 0 0 0 50 4 .75 0 0 0 60 3 1.5 0 0 0 70 2 2.25 0 0 0 Check (untreated) 1 adult from 61 larvae Series D, treated Apr. 25-28, 1945 40 5 0 0 0 0 50 4 .75 0 0 0 60 3 1.5 0 0 0 70 2 2.25 0 0 0 Check (untreated) 12 adults from 29 larvae - 21 - A similar series of tests was mads with larvae held under simulated nursery- stock storage shed conditions. It was desired to compare the mortality of larvae taken from storage following fumigation, with that of larvae replaced under nursery-cto'ck storage conditions for the remainder of the season. To do this, a double amount of lerval material (portions 2 and 3) was included in each test. The larvae from one portion were removed from their cocoons following fumigation, and held in petri dishes at room temperature for observation. The remaining larvee were re- turned undisturbed to simulated nursery storage and held until they were about to pupate (as indicated by examinations of check samples), before they were removed from their cocoons. This additional stor- age period amounted to 98 days in series A, 63 days in series B, 43 days in series C, 14 days in series D, and 6 days in series E, The emergence from both portions is given in table 10. The number of adults was less from larvae returned to storage than from those placed tuider observation immediately following fumigation. - 22 - Table 10.— -Adults emerging after treatment of hibernating larvae at intervals during the storage season. Larvae of 1944 New Jersey origin, kept in simulated nursery- stock storage. Samples contained approximately 30 larvae each in series A, E, and C, and 40 larvae and pupae mixed in series D and S . : : Adults emerged from i Treatment : Condi- : lots removed to : tionine : room temperature : Adult 8 emerged from lot 8 replaced in nursery storage Temper-: « : period : 2 : 3 : 4 ature : ■Uosage: .hours • hours j hours « 2 » 3:4 hours • hours » hours °F. Pounds Hours Number Number Number Number Number Number Series A, treated Jan. 22-24, 1945 32 6 0.75 11 19 17 10 5 9 40 5 0 1 11 4 3 0 2 50 4 .75 2 0 0 0 0 0 60 3 1.5 0 0 0 0 0 0 70 2 2.25 1 0 0 1 0 0 Check (untreated) • • e 9 adults from 28 larvae 9 adults from 30 larvae Series B, treated Feb. 22-Mar. 1, 1945 40 5 0 2 8 0 0 0 0 50 4 .75 0 0 0 0 0 0 60 3 1.5 0 0 0 0 0 0 70 2 2.25 0 0 0 0 0 0 Check ( untreated) . . 7 adults from 28 larvae 5 adults from 30 larvae Series C, treated Mar. 19-20, 1945 50 4 . 75 4 1 0 4 0 0 6030 00000 0 70 2 .75 0 0 0 0 0 0 Check (untreated) . . 6 adults from 23 larvae 10 adults from 30 larvae Series D, treated Apr. 17-20, 1945 50 4 . 75 1 0 0 5 0 0 60 3 0 0 0 0 0 0 0 70 2 .75 0 0 0 0 0 0 Gheck (untreated) . • 20 adults from 41 larvae 13 adults from 27 larvae and pupae and pupae Series E, treated Apr. 30-May 3, 1945 50 4 . 75 1 0 0 0 0 0 60 30 00000 0 70 2 .75 0 0 0 0 0 0 Check (untreated) 3 adults from 3 pupae - 23 - The mortality following fumigation of lervae kept in cold stor- age can be compared with that of larvae kept in simulated nursery- stock storage by referring to table 9 and the results of immediate examinations given in table 10. There were fewer instances of sur- vivals from larvae held -in cold storage than from those stored under simulated nursery-rtock conditions. In table 9, series A, there were no survivals from 3-and 4-hour exposures at 40CF. , or after 2 hours at 50°, none in series B after 3 hours at 40°, none in series C after 2 and 3 hours at 50°, and none in series D after 2 hours at 50c. Sur- vivals occurred at all of these points with larvae held in simulated nursery- stock storage. Additional tests were made April 9 to 11 with larvae stored out- doors (portion 4) . These larvae had been exposed to normal winter temperatures for approximately 5 months. Tests were made at 50°, 60c, and 70°F. , with exposures of 2, 3, and 4 hours at each temperature level. No adults emerged from any of the tests. The check samples yielded 135 adults from 222 larvae and pupae. Tests with larvae of California origin.— Larvae were" received from California in three shipments on November 15, 1944, December 29, 1944, and January 26, 1945. Since this made the prefumigation storage dif- ferent, seasonal series of tests were made with each lot. The November shipment was paired with the New Jersey material so that the series of tests would be directly comparable. This shipment was divided into three portions, and stored with the New Jersey larvae as follows* Portion 1 - cold storage -at 32° to 38CF., and portions 2 and 3 - sim- ulated nursery-stock shed storage. Larvae from cold storage (portion l) were fumigated at approxi- mately monthly intervals in* the same tests with New Jersey larvae. The results of these tests ere given in table 11. There was no evi- dence that there was any appreciable change in the resistance of the larvae with the advance of the season. With the 40_-oercent schedule for 3 hours a single survivor occurred in series B, C, and D. With the exception of survival at 70 CF. for 2 hours in series A, no sur- vival occurred in any series at any schedule »t 50° or above. Series of tests were also mode with the November shipment of larvae held under simulated nursery- stock storage. These were again paired with New Jersey larvae from the same storage in series of tests at intervals through the storage season. A double amount of larvae was used (portions 2 and 3), one portion being removed from the co- coons following fumigation, and the other being replaced in simulated nursery-stock storage until nearly ready for pupation. The emergence from both portions is given in table 12. The mortality was greatest when the treated larvae were replaced in nursery- stock storage, both from the standpoint of the number of tests showing no emergence, and in the fever numbers of adults emerging. - 24 - Table 11. — Adult b emerging after treatment of hibernating larvae at intervale during the storage season. Larvae of 1944 Califor- nia origin, shipped Nov. 15, and kept in apple- storage rooms at a temperature of 32° to 34°F. until Feb. 26, and at 36° to 38° from Feb. 27 to end of the tests. Samples contained from 24 to 70 larvae each. Treatment Temperature] Dosage Condi- tioning period Adults emerged from lots exposed for — 2 hours 3 hours 4 hours 32 40 50 60 70 Pounds Hours Number Number Series A, treated Jan. 25-27, 1945 6 5 4 3 0 .75 1.5 2.25 7 10 5 0 0 4 16 0 0 0 0 Number 12 0 0 0 0 Check (untreated) 11 adults from 25 larvae Series B, treated Feb. 27 -Mar. 3, 1945 32 6 0 1 1 0 40 5 . 75 0 1 0 50 4 1.5 0 0 0 60 3 2.25 0 0 0 70 2 3 0 0 0 Check (untreated) . 22 adults from 25 larvae Series C, treated Mar. 26-30, 1945 40 5 0 0 1 0 50 4 .75 0 0 0 60 3 1.5 0 0 0 70 2 2.25 0 0 0 Check (untreated) 10 adults from 53 larvae Series D, treated Apr. 25-26, 1945 40 5 0 4 1 0 50 4 . 75 0 0 0 60 3 1.5 0 0 0 70 2 2.25 0 0 0 Check (untreated) 15 adults from 27 larvae - 25 - Table 12. — Adults emerging after treatment of hibernating larvae at intervals during the storage season. Larvae of 1944 California origin, shipped Nov. 15, and kept in simulated nursery-stock storage. Samples contained from 17 to 29 larvae each in series 5, unu C, and from 13 to 54 larvae and pupae mixed in series D and E. • • Adults emerged from : Adults emerged from Treatment : Condi-: lot 8 removed to : lot 8 replaced in : tioning: room temperature : nurnery storage Temper-! : period: 2:3:4 : 2 : 3 : 4 ature : Dosage. hours . hours . hours . hours • hour 8 . hour 8 Pounds Hours Number Number Number Number Number Number Series A, treated Jan. 22-24, 1945 32 6 0.75 11 25 17 11 4 10 40 5 0 19 19 15 6 5 1 50 4 .75 14 2 1 0 0 60 3 1,5 5 0 0 0 0 0 70 2 2.25 7 0 0 0 0 0 Check (untreated) ... 12 adults from 27 larvae 8 adults from 24 larvae Series B, treated Feb. 22-K?r. 1, 1945 40 o 0 5 7 0 0 0 0 50 4 .75 0 0 0 0 0 0 oU 1.5 0 0 0 0 0 0 70 2 2.25 0 0 0 0 0 0 Check (untreated) • . 9 adult 8 from 24 larvae 10 adults from 24 larvae Series C, treated Mar. 19-20, 1945 00 4 .75 7 5 1 1 0 0 60 3 0 0 0 0 0 0 0 70 2 .75 0 10 0 0 0 Check (untreated) . . 11 adults from 25 larvae 10 adult s from 24 larvae Series D, treated Apr. 17-20, 1945 50 4 .75 5 2 0 1 0 0 60 3 0 10 0 0 0 0 70 2 .75 0 0 0 0 0 0 Check ( untreated) • Q 22 adults from 41 larvae 28 adults . from 42 larvae and pupae and pupae Series B, treated Apr. 30-May 3, 1945 50 4 .75 0 10 5 0 0 60 3 0 0 0 0 0 0 0 70 2 .75 0 0 0 0 0 0 Check (untreated) from 11 larvae and pupae - 26 - Additional tests with larvae kept tinder simulated nursery- stock storage were made with the December and January shipments. The results of these are given in tables 13 and 14. In these tests the additional storage amounted to 48 days for series A, 26 days for series B, 15 days for series C, and 6 days for series D. These series of tests showed less survival than the November shipment. The cause for this difference is not known. Less emergence occurred from larvae replaced in storage, as was the case in the tests with the November shipment. - 27 - Table 13. — Adults emerging after treatment of hibernating larvae at intervals during the dormant season. Larvae of 1944 California origin, shipped Dec. 29, and kept in simulated nursery-stock storpge. Samoles contained from 15 to 68 larvae each. Treatment : Condi-: : tloning:. Temper-: ^ : period: a*we { _i L Adults emerged from lots removed to room temperature 2 hours 3 hours 4 hours Adults emerged from lots replaced in nursery storage 2 hour 8 3 hours 4 hours Pounds Hours Number Number Number Number Number Number Series A, treated Mar. 14-16, 1945 0 0 50 4 0.75 12 7 0 3 0 60 3 0 2 2 0 1 0 70 2 .75 8 0 0 2 0 Check (untreated) . . 18 adults from 64 larvae 9 adults from 60 Series B, treated Apr. 4-7, 1945 504 .75 00 0 0 0 0 60 30 000000 70 2 ,75 0 0 0 0 0 0 Check (untreated) . . 6 adults from 53 larvae 12 adults from 60 larvae Series C, treated Apr. 17-20, 1945 504 . 75 000000 60 3 0 0 0 0 0 0 0 70 2 .75 0 0 0 0 0 0 Check (untreated) . . 10 adults from 20 larvae 0 adults from 9 larvae Series D, treated May 1-3, 1945 50 4 .75 0 0 0 0 0 0 60 3 0 0 0 0 0 0 0 70 2 .75 0 0 0 0 0 0 Check (untreated) 6 adults from 16 larvae - 28 - Table 14.-- -Adults emerging after treatment of hibernating larvae at intervale during the storage season. Larvae of 1944 California origin, shipped Jan, 26, 1945, and kept in simulated nursery-stock storage. Samples contained from 41 to 72 larvee each. Treatment : , Condi- ! tioning period ! Adult 8 emerged from i : lots removed to i : room temperature Adult 8 emerged from i lots replaced in nurserv storage Temper-: Dog i ature : I : 2 : 3 : 4 > hours • hours ; hours - : 2 1 3 1 4 I hours • hour 8 j hours °7. Pounds Ho\trs Number Number Number Number Number Number. Series A, treated Mar. 14-16, 1945 50 4 0.75 11 2 1 2 0 0 60 30 200000 70 2 .75 1 0 0 0 0 0 Check (untreated) - - 23 adults from 66 larvae 10 adults from 60 larvae Series B, treated Apr. 4-7, 1945 50 4 . 75 0 0 0 0 0 0 60 30 000000 70 2 .75 0 0 0 0 0 0 Check (untreated) . . 10 adults from 62 larvae 10 adults from 60 larvae Series C, treated Apr. 17-20, 1945 50 4 .75 000000 60 30 000000 70 2 .75 0 0 0 0 0 0 Check (untreated) . . 18 adults from 56 larvae 8 adults from 37 larvae Series D, treated May 1-3, 1945 50 4 .75 0 0 0 0 0 0 60 3 0 0 0 0 0 0 0 70 2 .75 0 0 0 0 0 0 Check (untreated) • • 4 adults from 26 larvae - 29 - Discussion To analyze the data better, the tests from tables 9 through 14 have been summarised in table 15. In these tables, the results from larvae immediately removed from cocoons, and of those replaced in storage, as given in tables 10, 12, 13, and 14, have been combined. The combined data in tables 8 and 15 show that the first objective, that of reducing the present dosages at 60° and 70°F., cannot be ful- filled. It is true that under certain circumstances reduced schedules were effective, but taken from the overall standpoint, a reduction would not be advisable. The experimental tests were planned to dupli- cate conditions often associated with nursery-stock fumigation, i.e., treatment at any date between January and May, replacement in nursery storage after fumigation, the shipment of stock immediately following fumigation, possible differences in resistance of larvae in different localities, and different storage conditions. Therefore a satisfac- tory fumigation schedule should be one that produces complete mortality under all of these conditions in experimental tests. The same conclusion was reached by Armitage and Steinweden in corroborating tests in California ( see footnote, p. 2) . In series of tests with hibernating larvae fumigated for 3 and 4 hours with 2 lb. at 70°, and 3 lb. at 60°F., in December 1944, January, February, and, March, 1945, there were survivors with 3-hour exposures under both 60° and 70° schedules in February with larvae that had been in hiberna- tion 7 1/2 weeks, and in a March test with 3 lb. for 3 hr. at 60° with larvae that had been in hibernation for 9 weeks. It is also shown that on the basis of available data, the second objective, that of developing additional dosage schedules for lower temperature levels, cannot be fulfilled. The two projected series of dosage schedules, i.e., 4 lb. at 50°F.; 6 lb. at 40°; and 8 lb. at 30° (table 8); and 4 lb. at 50°; 5 lb. at 40°; and 6 lb. at 32° (table 15) were both insufficient to produce complete mortality of larvae under all the nursery-stock fumigation conditions tested. This does not mean that such schedules cannot be developed, but rather that the selected dosages were not high enough. Until further studies are made, therefore, schedules for fumigation at 50°, 40c, and 32° cannot be recommended. Further analysis of the data demonstrates these additional points. (l) Tests with larvae from the two sources showed that those from California consistently yielded slightly higher survival than those from Hew Jersey. This could be interpreted to mean that larvae from different localities or areas will not react exactly the same. On the other hand, it could mean that the differences in handling and rearing methods were responsible. ( 2) Hibernating larvae held in cold storage at 32° to 38°F. showed less survival than those kept under simulated nursery-stock storage conditions. - 30 - £8888 fc H rl H rt S . •*» CM lot I Q I O «-4 H in in 5 o> I 00 I O) I O) r*- i cn i on i o> O O i to I cn I oo m n i cn I cn I cn O a 3 o A CM 55 i-4 cm cn m co to to to to to 88888 rH rH rH rH O +> G3 O o cn o o o o >< co cm ■*> © © u -r> to in CO cm © © u 9 co 3< 35 to rs o © o CO °" 8 S °- © o - 31 - (3) Larvae returned to simulated nursery- stock storage follow- ing fumigation showed a lower survival than those subjected to higher temperatures following fumigation. These two conditions of post fumi- gation handling are the same as those associated with the handling of nursery stock, where some stock is fumigated and replaced in stock piles or order bins, while other stock may he shipped soon after treat- ment . (4) Tests with larvae stored outdoors over winter were limited, but the results compared favorably with tests made at approximately the same date using larvae stored under controlled conditions, and indi- cates that outdoor storage did not materially increase the resistance of the larvae to fumigation. (5) The previous evidence (table 7) that larvae became more resistant as the season progressed was not substantiated in the 1944-45 tests (tables 10 through 14). Rather, the resistance appeared to be about the same throughout the season. (6) Of incidental interest was the fact that live adults were found in check samples while still in simulated nursery- stock storage beginning May 4. No adults emerged, however, from check samples as long as they remained in cold storage. TOLERANCE OP FRUITS TO METHYL BROMIDE FUMIGATION Summer- Maturing Fruits Intended for Immediate Consumption Tests were made as opportunity permitted to study the tolerance of summer- maturing fruits. Fruits maturing in early or midsummer, which moved directly to consumer markets were included in this classi- fication. These may have been subjected to refrigeration, but were not intended to be stored for winter marketing. Samples of fruits were fumigated with dosages of 1 and 2 lb. at 70°F. , and 1.5 and 3 lb. at 60°. Two schedules at each temperature level were selected, since the final results of tests with eggs and larvae were not known at the time the tests were made. Likewise, the higher schedules helped to determine if a sufficient margin of toler- ance existed. The condition of fumigated fruit was compared with that of untreated checks at intervals following treatment. Auricotsi— The variety Royal (California origin)was used in tests of July 12, 1944. This fruit was firm and well ripened. It was ob- tained in the St. Louis fruit market, had been shipped under refrigera- tion, and was in fruit storage at 60°F. when purchased. After fumiga- tion it was held at room temperature (85°) for observation. There was no evidence of injury, and all treated samples reacted similarly to the check. - 32 Apples. — At St. Louie, the applee infested for mortallt7 studies were closely observed for symptoms of Injury from the fumigation. These included the varieties Wealthy, Black Twig, Lowland Raspberry, Duchess, and Golden Delicious in all stages of maturity. Ho evidence of injury was observed with dosage schedules ranging from 0.5 lb. at 80° to 2.5 lb. at 40°?. The State Entomologists Office of Colorado kept records of ship- ments into that State in 1942, when their oriental fruit moth regula- tions were amended to allow apples to be received under fumigation certificates. These records were supplied to the Bureau by courtesy of F. H. Gates, State entomologist. A sample was removed at destina- tion from each carload and kept under observation for effect of the treatment on quality. Ho injury or decrease in quality was observed in 21 carloads of early apples. These included some fumigated with 4-hour exposures as follows: Number of cars Origin Variety of apple Dosage schedule 13 Delaware Delicious 2 lb./4 hr. at 70°?. Gano 3 3 2 Kansas -do- -do- 2 lb./4 hr. at 70° 3 lb./4 hr. at 60* 2 lb./2 hr. at 70° In other experimental studies by the Division of Control Investi- gations, it has been shown that the variety Williams Early Red is sus- ceptible to injury under certain circumstances. The same studies showed no injury to Wealthy or Starr apples. It appears from these observations that most varieties of summer apples can be fumigated without risk of injury. Cherries. — Local Montmorency cherries were purchased in June 1945, and fumigated with dosages of 1.5 and 3 lb. at 60 °F. , and 1 and 2 lb* at 70° for 2-hour exposures. The cherries were well ripened and in excellent condition, all with stems on. There was no evidence of in- jury1 in fact, the treated samples maintained a higher percentage of marketable cherries over a 2 weeks' period than did the checks, owing to a greater amount of "nesting * in the check samples. Hectarlnes. — The variety John Rivers (California origin) was pur- chased in the St. Louis fruit market on July 12, 1944. It had been shipped under refrigeration and was in fruit storage at 60 °F. when pur- chased. The fruit was firm and in excellent condition. After fumiga- tion the samples were placed in room storage (85°7.) and compared daily with untreated checks. There was no evidence of injury, and all treated samples reacted similarly to the checks. - 33 - Pears.— Bartlett pears (California origin) were purchased on the St. Louis fruit market on August 9, 1944. These pears were firm but well ripened. After fumigation internal injury showed in all pears, being more severe with the heavier schedules. Typical injury is shown in figure 2. It was suspected that the maturity of the pears might have been a contributing cause. Therefore additional Bartlett pears of California origin were obtained, which were selected as being less mature than the first purchase. These pears were in fruit storage at 60°?. when obtained. The entire lot was warmed to 70°. Two samples were fumiga- ted with 1 and 2 lb. for 2 hr. as soon as they reached 70°, Two more samples were allowed to ripen at 70° for an additional 2 days, and a third pair of samples were ripened for 4 days before treatment. The results are given in table 16. They show that as the pears became more mature, the amount of internal Injury increased markedly. Table 16. — Injury in Bartlett pears fumigated upon removal from storage, and after 2 and 4 days' ripening at 70°F. Fumigated at 70° with 2-hour exposures Ripening period after : Dosage ! Pears showing internal removal from storage * injury on 6th day i/ * I Day Pounds Percent 0 1 7 2 0 2 1 60 2 87 4 1 100 2 100 i/ Check samples shoved all pears sound on the 4th day, and 7 percent unmarketable on the 6th and 7th days. - 34 - Further tests were made with unref rigerated pears of local origin. These were of the varieties Kieffer and Garber, which at this season were very green and hard. Samples of these were fumigated with the same schedules used with the Bartlett pears. No evidence of injury occurred even after several weeks of observation. The evidence from these tests suggest that fully mature pears may be susceptible to injury from methyl bromide. Plums. — The variety Duarte (California origin) was purchased in the St. Louis fruit market on August 9, 1944. These plums had been shipped under refrigeration and were in storage at 60°?. when purchased. They were firm and in excellent condition. After fumigation the sam- ples were placed in room storage at 85° and compared daily with un- treated checks. There was no evidence of injury, and all treated sam- ples reacted similarly to the checks. Peaches. ^-Five lots of ripe peaches, variety unknown, of local origin were fumigated in St. Louis in July and August 1943. No injury was observed. Fall-maturing Fruits Intended for Cold Storage In the development of fumigation schedules for the host fruits of oriental fruit moth, it was necessary to consider the treatment of late- maturing fruits that normally are placed in storage for various periods before marketing, as well as the treatment of summer- maturing fruits intended for immediate consumption. Apples are the principal class of host fruit going into storage; therefore attention was con- fined to them. As shown in previous sections of this report, fumigation schedules were developed for the treatment of fruit at temperatures as low as 40°?* The problem of the reaction of apples to such treatments remained to be studied. In experimental work done by Phillips et al. §] in Canada, the apples were injured unless they were stored for 6 weeks after picking before treatment. Further tests by Phillips and Monro 7j indicated a varietal difference in tolerance. While most of these tests had been made under conditions of vacuum fumigation, they indicated that the problem of fumigating apples immediately prior to storing, or after a period of storage, required thorough study. £/tehillips, W. H. , Monro, H. A. U., and Allen, C. E. Some obser- vations on the fumigation of apples with methyl bromide. Sci. Agr. 19: 7-20, 1938. 7/Phillips, W. R. , and Monro, H. A. U. Methyl bromide injury to apples. Jour. Scon. Ent. 32: 344-345, 1939. - 35 - Teste were planned In 1943-44, to give evidence of the reaction of apples fumigated before being placed in storage, as well as after various periods of storage. As many varieties as could be obtained were to be included to study varietal tolerance. The apples were to be fumigated with a dosage schedule appropriate for the temperature level existing at the time of treatment, as follows: 1.5 lb./2 hr. at 70°FD 2 lb./2 hr. at 60° 2.5 lb./2 hr. at 50° 3 lb./2 hr. at 40° To provide information on the points listed above, four series of tests were made at Louisiana, Mo. Series A.-- Apples were fumigated at packing-shed temperatures as soon as picked. One half was placed in cold storage at 32° to 38°!\, and the other half at marketing temperatures of 40° to 55°, Series B.— Apples were held 2 weeks at packing -shed temperatures, then fumigated. One half was placed in cold storage, and the other half a» marketing temperatures. Series C— Apples were held 1 month in cold storage, then fumi- gated at 40°F. One half was replaced in cold storage, and the other half was held at marketing temperatures. Series D. — Apples were held 3 months in cold storage, then fumi- gated at 40°?. One half was replaced in cold storage, and the other half was held at marketing temperatures. It was not possible to obtain a sufficient quantity of all vari- eties to carry them through the four series. Three varieties, Commerce, Black Ben Davis, and Giant Geneton, were used in Series A and B only, while small lots of Northern Spy, R. I. Greening, and Rambo were used in series A only. The following varieties were used in all four series: Black Twig King David Starking Golden Delicious Red Delicious Staymen Wine sap Grimes Golden Red Winesap Willow Twig Jonathan Rome Beauty York In the varieties used in all four series, six bushel lots were used, with one exception, divided as follows: one and one-half bushels in each series, subdivided into one-half bushel for cold storage, one- half bushel for marketing temperatures, one-fourth bushel for cold storage check, and one-fourth bushel for marketing temperature check. Pertinent data relative to these treatments are given in table 17. - 36 - Table 17. — Date relative to the treatment of apples in series A, 3, 0, and D, all exposures for 2 hours Variety ! Date I picked ] Quantity^ used \ Date j fumigated. Apple • tempera-** ture ; Dosage Bushels 1943 J? m w9i loo Ay treated at picking Bl«rlf Ben D«vi« io h 1 10/8 60 Blnrlc Twl v in l\ p 1.5 10/13 64-65 & in /7 1 10/8 ou A f~l •? ■ p f f» a t ^ r vxiauv « oil c u ii in /7 y 1 10/8 An flrt 1 on Dal 1 r>\ ah a 9 /P5 1.5 9/26 4&.4A P 5 urimc8 VXOJ.Q.OU Q /l A 1.5 9/19 UO~UC *> Q /l 7 1.5 9/18 o c, Kin^r David 9/l4 1*25 9/18 c 1 9/26 9 A Ho I0 Greening 9/25 0.25 9/26 46-48 2.5 Rambo 9/25 1 9/26 46-48 2.5 Red Delicious 10/2 1.5 10/3 62-63 2 Red Wine sap 10/16 1.5 10/18 52-53 2.5 Rome Beauty 9/25 1.5 9/26 46-48 2.5 Starking 9/23 1.5 9/24 58 2 Staymen Wine sap 10/2 1.5 10/3 62 2 Willow Twig 10/6 1.5 10/8 60 2 York 10/6 1.5 10/8 60 2 Series B, treated 2 weeks after picking Black Ben Davis Black Twig Commerce G-ipnt Geneton Golden Delicious Grimes Golden Jonathan King David Red Delicious Red Wine sap Rome Beauty Starking Staymen Wine sap Willow Twig York 10/7 10/12 10/7 10/7 9/25 9/18 9/17 9/14 10/2 10/16 9/25 9/23 10/2 10/6 10/6 1 10/23 56-58 2 1.5 10/26 53 2.5 1 10/23 56-58 2 1 10/23 56-58 2 1.5 10/9 59 2 1.5 10/3 63 2 1.5 10)3 9/30 63 2 1.25 63-64 2 1.5 10/17 50 2.5 1.5 11/1 56 2 1.5 10/9 59 2 1.5 10/9 59 2 1.5 10/17 50 2.5 1.5 10/23 56-58 2 1.5 10/23 56-58 2 Table 17.— Continued Variety \ Date ] Quantity \ Date | picked used [ fumigated) 1943. Bushel s. I94£ Apple t tempera-s Dosage ture ; Series C, treated after 1 month of cold storage Black Twig Golden Delicious Grimes Golden Jonathan King David Bed Delicious Bed Wine sap Borne Beauty Starklng Staymen Wine sap Willow Twig York 10/12 9/25 9/18 9/17 9/14 10/2 10/16 9/25 9/23 10/2 10/6 10/6 Series D, treated after 3 months of cold storage Black Twig Golden Delicious Grimes Golden Jonathan King David Bed Delicious Bed Wine sap Borne Beauty Starking Staymen Wine sap Willow Twig York 10/12 1.5 9/25 1.5 9/18 1.5 9/17 1.5 9/14 . 1.25 10/2 1.5 10/16 1.5 9/25 1.5 9/23 1.5 10/2 1.5 10/6 1.5 10/6 1.5 1/15/44 1/1 1/1 12/31 12/31 1/2 1/15 1/1 H1 1/2 1/2 1/2 39 38 38 36- 40 36 37- 38 38- 39 38 38-41 37-38 38 38 Pounds 1.5 11/9 37 3 1.5 10/25 40 3 1.5 10/17 36-38 3 1.5 . 10/17 36-38 3 1.25 10/14 36 3 1.5 11/1 39 3 1.5 11/16 36 3 1.5 10/25 38 3 1.5 10/24 36 3 1.5 10/31 39 3 1.5 11/7 36 3 1.5 11/7 36 3 3 3 3 3 3 3 3 3 3 3 3 3 LIBRARY STATE PLANT BOARD - 38 - The samples held at marketing temperatures were examined at approximately 10-day intervals until they were no longer of marketable quality. Those in cold storage were examined at Intervals throughout the storage period. No external nor internal injury was discovered on any variety in series A, B, or D. External injury only was present on, two varieties in series C, In Grimes Golden, 19 percent of the apples had from mild to severe spotting of the skins (see figure 3) in the sample held at marketing temperatures, hut only 8 percent of those held in cold stor- age. In Jonathan apples, 14 percent of those held under marketing temperatures were spotted, while 5 percent of those in cold storage showed injury ( figure 4) . Evidence of injury showed up on apples held under marketing tempera- tures earlier than on those returned to cold storage. Spotting was pres- ent at the first observation of the former samples on the 9th day, but did not appear until the second examination of the cold-storage apples on the 22nd day. In each case the Injured area increased somewhat after its first appearance. Since no injury appeared in apples fumigated before cold storage, and none appeared in apples fumigated after 3 months of cold storage, further tests were confined to the periodical treatment of apples in the earlier part of the cold storage period. These tests were made in the 1944-45 season. The two apple varieties which showed injury in Series C of the 1943-44 tests, Grimes Golden and Jonathan, were selected for these tests, with a third variety, Starking, which had shown no injury. Seventeen bushels of each variety were placed in cold storage within a day after picking. Samples were withdrawn from storage and fumigated at intervals up to 17 or 18 weeks. On each date two samples of each variety were fumigated, one with 2 lb./2 hr. at 40°F. and one with 2 lb./4 hr. at 40°. The two dosage schedules were used in order to better delimit the margin of tolerance. Each sample was divided after fumigation, one half being returned to cold storage, the other half being placed at room tempera- tures of 55° to 75°. Check samples were handled and divided similarly. The results are presented in table 18. It is evident that the apples under the conditions of these tests were more susceptible to in- jury during the first few weeks of storage. In each instance the sus- ceptibility appeared to reach a peak after the start of the storage period, then recede until no injury occurred after the 5th or 6th week. As would be. expected, more apples showed injury with the 4-hour exposures than with the 2-hour. Also, apples held at room temperature following fumigation showed more injury than those returned to cold storage, in fact, Jonathan and Starking showed no injury to apples fumigated for 2 hours and returned to cold storage. 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