E-484 July 1939 
 
 United States Department of Agriculture 
 Bureau of Entomology and Plant Quarantine 
 
 THE USE OF METHYL BROMIDE FOR THE TREATMENT OF QUARANTINED PLANT PRODUCTSl/ 
 By Lon A. Hawkins, Division of Control Investigations 
 
 As a treatment for living hosts infested with insect pests under quar- 
 antine regulations, fumigation with methyl bromide in many cases meets the 
 requirements for an effective treatment which is noninjurious to the host for 
 the purpose for which it is intended. 
 
 Methyl bromide is a gas at ordinary temperatures, its boiling point 
 being 40.1° F. As a liquid it has a specific gravity of 1.732 and as a gas 
 it is approximately 3.5 times as heavy as air. As commercially produced, 
 methyl bromide is approximately 99.5 - 99.8 parcent pure. It is soluble in 
 most common organic solvents but is only very slightly soluble in water. In 
 an impure state it is used in fire extinguishers in France and England. 
 
 The first use of methyl bromide in insect control was made in France, 
 about 193,r. when it was applied as a blanketing gas with ethylene oxide. As 
 there were indications of its insecticidal value, however, it was then tested 
 as a fumigant alone. Its first recorded use in this country against insects 
 was by D. B. Mackie in 1935. Mackie carried on considerable work with it, 
 both of an experimental and of a practical nature. He has shown that numerous 
 fruits and vegetables and other commodities can be fumigated with methyl 
 bromide with safety, and he has also used it for killing rodents and termites 
 in California. Some of his results are given in his several publications on 
 the subject. 
 
 Methyl bromide was used experimentally by this Bureau in the summer of 
 1936 in the fumigation of fruits and vegetables for the adult Japanese beetle, 
 and the results obtained in this investigation indicated that it might be 
 valuable against other insects affecting fruits, vegetables, and nursery stock. 
 Since that time work has been taken up on the destruction of insects which are 
 under quarantines, both Federal and State, on a number of plant products. This 
 work has been carried on by A. C. Johnson, E. M. Livingstone, H. C. Donohoe, 
 J. W. Bulger, Randall Latta, S. S. Easter, and H. H. Richardson, of the Divi- 
 sion of Control Investigations, but most of it has been in cooperation with 
 other divisions of the Bureau of Entomology and Plant Quarantine, various 
 
 1/ This paper was presented at the meeting of the Central States Plant 
 Board at St. Paul. Minnesota, on March 22, 1939. 
 
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 State departments of agriculture, shippers, railroads, nursery men, and 
 others. The list of collatorators is too long for mention to be made of each, 
 but the excellent cooperation received has contributed markedly to the success 
 of the work. It is very much appreciated. 
 
 In cooperation with the divisions of this Bureau concerned, experimenta- 
 tion has been under way since 1936 on adults and larvae of the Japanese beetle, 
 in developing a treatment for fumigating carloads of fruits and vegetables in 
 the regulated area so that they can be shipped outside that area without 
 danger of carrying live adult beetles, and in the treatment of nursery stock 
 so that it will be freed of any infestation by adults or larvae. It was deter- 
 mined that in green string beans, v/hite potatoes, northern-grown sweetpotatoes, 
 lima beans, sweet corn, peppers, tomatoes, and a number of other types of green 
 vegetables and fruits shipped in the living condition, the fumigant could be 
 applied at a dosage sufficient to kill the beetles in the package without 
 damage to the commodity. This investigation has been extended since its incep- 
 tion, and during the past summer, in cooperation with the various interested 
 agencies, a method was developed for fumigation of produce in refrigerator 
 cars for the adult Japanese beetle. 
 
 The method employed in truck-growing regions of New Jersey, Delaware, 
 Maryland, and Virginia in 1937 to insure freedom fiom infestation of shipments 
 of such commodities during the Japanese beetle flight period was to prefumigate 
 refrigerator cars for fruit and vegetable shipment, screen them, and then 
 free the fruits and vegetables from beetles by other methods before loading 
 them. This involved fumigating and screening some 15,000 cars at considerable 
 cost, whereas only about 4,000 of them moved out of the regulated area. It 
 v;as decided that it might be practical to fumigate and screen only the loaded 
 cars that were to be shipped out of the regulated area, eliminating the cost 
 of prefumigation and screening in other cases. The cars destined for un- 
 infested territory were therefore fumigated at diversion points and allowed to 
 move from the shipping point possibly a day's run to this point without screens. 
 In this way fumigation was localized and all was done at three points. The 
 cars traveled under ventilation in the usual manner to the particular diversion 
 point and were fumigated after the contents had been sold. In this work some 
 2,771 cars were fumigated during the past season. The dosage was 2 pounds 
 per 1,000 cubic feet, or 5 pounds per refrigerator car having a capacity, 
 including ice bunkers, of 2,500 cubic feet, and it was applied at a temperature 
 of 70° F. or above. The fumigant was agitated by a blower for part of the 
 time the fumigation was in progress — sufficiently to mix it thoroughly with 
 the air in the car. Tests of the efficacy of the method were made by arti- 
 ficially infesting 16 cars with approximately 45,000 Japanese beetles. There 
 were no survivals after fumigation. 
 
 In connection with this work, one point which deserves consideration is 
 the retention of methyl bromide by fumigated products. A cooperative project 
 with the Public Health Service has been under way for the last year and a half 
 ya the amount of methyl bromide retained by fumigated plant products and the 
 effect of ingestion of tl-ese products by warm-blooded an'mals. H. C. Dudley, 
 
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 of the Public Health Service, has been carrying on this study and presented 
 a paper on his work at the Richmond meetings. In general it has been found 
 that only a small amount of methyl bromide is retained by most fumigated plant 
 products tested — considerably less than would be dangerous for ingestion. 
 
 A method of fumigating strawberry plants in field baskets, or packed 
 in crates, for Japanese beetle larvae was worked out on a commercial basis 
 and authorized. A fumigation room with apparatus for circulating the air- 
 gas mixture throughout the room was developed, built, tested, and found 
 satisfactory . 
 
 Extensive investigations on fumigation of nursery stock for Japanese 
 beetle larvae, in which some 4,000 plants of 575 varieties, representing ap- 
 proximately 200 genera, were used, with a total of around 20,000 larvae of 
 the Japanese beetle, show that complete mortality of the larvae can be ob- 
 tained by fumigating at a dosage of 2-1/2 pounds of methyl bromide for a 
 period of 2-1/2 hours, at temperatures of 63° F., or above. The treatment so 
 far is limited to 8-inch pots or soil balls, but investigational work is under 
 way on larger soil masses, in the hope of extending the treatment to the 
 general run of balled and burlapped stock. 
 
 It is of interest to note that this treatment has been applied to 25 
 varieties of hydrangeas with no damage and in most cases a noticeable accel- 
 eration of growth. Ninety-two varieties of azaleas have been treated and 
 only two of these have shown definite injury. This treatment has been 
 authorized, and shipments of fumigated plants are being made at the present 
 time . 
 
 Oriental Fruit Moth 
 
 Work with the oriental fruit moth, taken up at the suggestion of J. 
 Carl Dawson, State entomologist of Missouri, in 1936, when a few small lots 
 of peach nursery stock in which hibernating larvae had been placed were fumi- 
 gated, was continued during the winter of 1936-37 with approximately 25,000 
 hibernating larvae of this insect. The larvae were in cocoons in corrugated 
 paper, or had spun cocoors among twigs or in holes in small branches pre- 
 pared for that purpose. 
 
 In carrying out this project it was necessary to design a fumiga- 
 tion box that was tight and that could be heated readily and brought up to a 
 fairly constant temperature. Such a box was built of galvanized iron, in- 
 sulated and equipped with a fan for mixing the methyl bromide with the air and 
 an electric heater thermostatically controlled. The box was self-contained 
 in that it was only necessary to plug it in in a light circuit to make it 
 ready for use. 
 
 In the experimental work the cocooned insects were placed in among 
 brush in the box in as nearly natural conditions as possible, and after fumi- 
 gation most of the insects were placed at outside temperatures for a period 
 to simulate natural conditions. Dosages of from 1 to 4 pounds were used, and 
 it was found that 3-1/2 and 4 pounds of methyl bromide per 1,000 cubic feet 
 
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 for a period of 4 hours gave a complete kill in all cases. Some 50 experi- 
 ments were carried out with this treatment and there was indication that a 
 lower dosage might be employed. 
 
 The process was tested out on nursery stock in connection with three 
 com.mercial nurseries, one in Missouri and two in Maryland. In the tests in 
 Missouri 26 varieties of nursery stock — in all about 1,000 trees — were 
 treated. The dosages were 3 pounds for 5 hours, 3-1/2 pounds for 4 hours, 
 and 4 pounds for 4 hours at approximately 70° F. The stock was stored and 
 planted out with an equal number of checks that had not been fumigated, to 
 determine the comparative effect of the fumigant on the trees. Somewhat 
 similar experiments were carried on in Maryland. The plantings were inspect- 
 ed at intervals throughout the summer. In most cases there was apparently no 
 effect that could be attributed to the fumigant. In som.e cases there was a 
 stimulation of growth and in a few instances a retardation, the latter oc- 
 curring particularly in some varieties of apples. There was less damage to 
 apples at the lower dosage of 3-1/2 pounds than at 4 pounds, although in some 
 cases a definite retardation of the rate of growth was noted in the fumigated 
 trees, even at the lower dosage. The work is being continued during the 
 present season with a probability that a lower dosage may be effective and 
 possibly a lower temperature. As a result of the work so far, seven of the 
 Western States have modified their State quarantines to admit nursery stock 
 from infested areas when fumigated by this method, and stock is being treat- 
 ed and shipped commercially into these States. 
 
 Sweetpotato Weevil 
 
 In connection with the eradication of the sweetpotato weevil, experi- 
 ments were begun in the summer of 1937 in devising a method for destroying 
 the sweetpotato weevil in seed potatoes, and with the further idea of de- 
 veloping a method of treating potatoes for culinary purposes so that they 
 could be shipped outside the regulated area with no danger of carrying the 
 insect. This involved determining the time and dosage necessary at various 
 temperatures to kill all stages of the insect on and within the sweetpotato 
 and sweetpotato plants. This was done for several temperatures and complete 
 mortality was attained at 70° F. and above with a dosage of 3-1/2 pounds 
 per 1,000 cubic feet and an exposure of 4 hours. It was found rather easy 
 to kill the weevil within the sweetpotato, but the effect on the host 
 was rather disturbing. When sweetpotatoes v/ere taken from the kiln where 
 they were maintained at a temperature of around 50° F. and fumigated at 
 these low temperatures, even when the dosage was only 10 ounces per 1,000 
 cubic feet, they were liable to break down. In some sizable experiments, 
 involving on the whole a hundred bushels or more of sweetpotatoes, practical- 
 ly a complete breakdown occurred in the treated potatoes and only a slight 
 deterioration in the control. It was found, however, that by raising the 
 temperature of the sweetpotatoes to above 70° F. a few days before fumiga- 
 tion, treating them at this temperature, and then holding them for 2 or 3 
 days before bedding, this difficulty could be largely obviated. Two sizable 
 experiments were carried on last year on a commercial basis with excellent 
 results in that the fumigated potatoes produced an excellent crop of drav'3. 
 Treatment with methyl bromide markedly ac ^lerates the production of shoots 
 
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 and new growth in sweetpotatoes . Approximately 2,000 bushels have been 
 fumigated and planted this year in cooperation with 40 or 50 growers, with 
 a view of getting the process on a commercial basis, and ironing out any 
 flaws in the procedure. 
 
 White-fringed Baetle 
 
 Investigations have shown that methyl bromide can be used in the 
 fumigation of potted plants and greenhouse stock for the white-fringed 
 beetle. A method has been developed for fumigating this stock at atmos- 
 pheric pressures and at a temperature of 85° F. with a dosage of 1 pound 
 of methyl bromide per 1,000 cubic feet. Out of 33 plants, mainly herbaceous 
 perennials, some 24 can be fumigated without injury. Treatment of potting 
 soil with a dosage of 40 cc per cubic yard gave a complete kill of the 
 larvae of this insect at a cost of approximately 10 cents per cubic yard. 
 
 Fumigation of Miscellaneous Imported Plant Products 
 
 Experiments are under way in developing treatment for imported 
 plant products, and this work so far is largely concerned with determining 
 the effect of the fumigant on the numerous plants and plant products that 
 are imported into this country in commercial quantities. It is planned to 
 test the effect on the insect when sufficient numbers are available in 
 commercial shipments of infested stock. When the effect on the host plant 
 of fairly heavy dosages is known, the work can be completed rapidly when a 
 sufficiently heavy infestation is found to furnish material for determining 
 the effect on the insect. 
 
 In fumigation with methyl bromide, most of the evergreen plants 
 and rose stocks, and nursery stock of such types, can be treated at a 
 reasonably high dosage without injury to the plants. Some injury has been 
 obtained with cacti and succulent plants. A number of experiments with 
 Cattleya orchids which were infested with a coleopterous leaf miner were 
 carried out during the past season, and complete mortality of the leaf 
 miner was obtained by fumigation under 15-inch vacuum at a dosage of 3 
 pounds per 1,000 cubic feet, the orchids being in a dry condition. There 
 was little or no injury to the orchids. Cipollini bulbs recently shipped 
 from Morocco to New York were found infested with larvae of Exosoma lusi^ 
 t anica , a chrysomelid beetle not known to exist in this country, and it 
 was possible to obtain some information on the effect of fumigation on both 
 bulbs and insects. These bulbs were in dormant condition, and fumigation 
 at a concentration of 4 pounds per 1,000 cubic feet in 15-inch vacuum for 
 2 hours did not injure them and killed all the larvae that were found on 
 later inspection. About a thousand cases of these bulbs were fumigated. 
 
 Similar work in connection with shipments of green lima beans from 
 Cuba, infested with Maruca te stu lalis . one of the bean pod borers, was carried 
 out. Shipments arriving in New York were fumigated with a concentration of 
 4 pounds of methyl bromide per 1,000 cubic feet in a 15-inch vacuum for a 
 
UNIVERSITY OF FLORIDA 
 
 3 1262 08537 0962 
 
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 period of 4 hours. Complete kill of the insects found in the pods has been 
 obtained in a total of several thousand hampers. No injury to the lima beans 
 was evident. The fumigation has been successful even at temperatures around 
 40° F. These results are being checked in Puerto Rico, where this insect 
 is abundant, and sufficient data should soon be available for definite recom- 
 mendations as to the treatment. 
 
 Studies are under way on the treatment of scale insects and certain 
 other insect pests. 
 
 In general, methyl bromide seems to be specially adapted to the 
 fumigation of plants or plant products which are transported and marketed 
 in a living condition. It does not appear probable that it will take the 
 place of other fumigants as an all-purpose fumigant but rather that it will 
 extend the field for gaseous insecticides. It injures some plants and may 
 accelerate or retard the growth of others. It appears to be a distinct ad- 
 dition to the means of combating insect pests, especially as a quarantine 
 treatment . 
 
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