August 19UB ^753 United States Department of Agriculture Agricultural Research Administration Bureau of Entomology and Plant Quarantine REPORT ON EXPERIMENTS WITH METHYL BROMIDE AS A FUMIGANT FOR STORED TOBACCO By W. H. White . Division of Truck Crop and Garden Insect Investigations V The experimental work on methyl bromide as a fumigant for control of the cigarette beetle (Lasioderma serricorne (F.)) and the tobacco moth (Ephestia elutella (Hbn.)) in stored tobacco is reported herein. This report does not constitute a recommendation of this material as a fumigant for tobacco. Tobacco was fumigated with methyl bromide both in vacuum chambers and under atmospheric pressures. Most of the studies were conducted at Richmond and Newport News, Va., during 1939-41. Data were obtained on the fumigation of a cigar factory at Selma, Ala., in April 1948. Vacuum Fumigation Laboratory tests.— In an effort to determine the relative effec- tiveness of methyl bromide and hydrogen cyanide at reduced pressure, a series of replicated tests were conducted in an experimental vacuum chamber, 33 cubic feet in size, as described by Brubaker and Reed. %/ In each test or fumigation, three bales of imported Turkish tobacco were used, one of which was not fumigated, but was held as a check. These bales weighed approximately 140 pounds each. Conditions in all tests were as uniform as possible. Tobacco and air temperatures were constant at approximately 70° F., and the moisture content of the tobacco was about 13 percent. A perforated, hollow-steel test spike containing large, nearly mature cigarette beetle larvae were driven into each bale. These larvae had been reared under laboratory conditions and were selec- ted at random. Each spike held the larvae at depths of 1, 3, 5, 7, and 9 inches in the tobacco, with 25 larvae being used at each depth. Fumi- gation was performed with a vacuum of 28 to 29 inches as recorded on a standard mercury gauge. After fumigation the chamber was air washed twice to remove as much gas as possible, and the tobacco then removed from the chamber. The test insects were allowed to remain in the tobacco for 72 hours after fumigation^ They were then removed to glass-covered l/This report was prepared by J. N. Tenhet. The work was performed by J. P. V^nzant (resigned Sept. 15, 1940), P. K. Harrison, R. W. Bru- baker, and J. N. Tenhet. Prior to 1942 the work was under the direct supervision of W. D. Reed (resigned June 13, 1946). 2/Brubaker, R. W., and W. D. Reed. 1943. Fumigation of tobacco at reduced pressures. Jour. Econ. Ent, 36t 200-303. SEP -2- dishes for a 7-day period of observation for mortality. Each fumigant was tested at dosages of from 1 to 4 pounds per 1,000 cubic feet, at an exposure of 3 hours, and every test was replicated 6 times or more. Results of these tests are presented in table 1. Under the condi- tions of this experiment it can be seen that either 2 or 3 pounds per 1,000 cubic feet of methyl bromide gave 100 percent mortality of the test insects, and that 4 pounds of hydrogen cyanide were required to produce the same results. Commercial experiments: To obtain information on the behavior of methyl bromide under commercial conditions, a large-scale experiment was conducted in 1940. In a series of replicated tests at moderately low temperatures, Turkish tobacco was fumigated at Richmond and at Newport News, Va. In the first series of tests at Richmond, bales of Turkish tobacco were fumigated in commercial vacuum chambers of 1,028 cubic feet capacity, each. The chambers were filled to capacity with bales of tobacco, evacu- ated to approximately 29 inches on a standard mercury gauge, and a dos- age of 4.62 pounds of fumigant per 1,000 cubic feet was introduced. After an exposure of 4 hours the chambers were air washed twice and the tobacco was then removed. As in the laboratory tests insects were in- serted into the tobacco by means of perforated steel test spikes and allowed to remain in the tobacco for 72 hours after fumigation. Mortal- ity was recorded at the end of 7 days after fumigation. During the course of the tests tobacco temperatures ranged from 30 to 43° F. In this first series of tests, 6 replicates of each test were com- pleted with hydrogen cyanide and 4 with methyl bromide. A total of 3,168 eggs of the tobacco moth, 1,568 eggs of the cigarette beetle, 90 larvae of the tobacco moth, 749 larvae of the cigarette beetle, and 191 .cigarette beetle pupae were exposed to hydrogen cyanide. A total of 2,342 tobacco moths eggs, 715 cigarette beetle eggs, 60 tobacco moth larvae, 495 cigarette beetle larvae, and 193 cigarette beetle pupae were exposed to methyl bromide. Mortality of all stages was 100 percent for both insects, except that in two tests with methyl bromide some eggs of the tobacco moth sur- vived. The second series of tests were conducted at Newport News at slightly higher temperatures. In this experiment the vacuum chambers of 3,026 cubic feet capacity, each, were also evacuated to a pressure of approximately 29 inches on a standard mercury gauge. The dosage of fumigant was 5 pounds per 1,000 cubic feet and the exposure period was 4 hours. Following fumigation the chambers were air washed twice before removing the tobacco. Mortality data on test insects were obtained by the test-spike method previously described. During this experiment tobacco temperatures ranged from 57° to BC° F* A total of 5 replica- tions or separate fumigations were completed for both methyl bromide and hydrogen cyanide. A total of 832,000 pounds of tobacco were fumi- gated with methyl bromide and 778,000 pounds fumigated with hydrogen cyanide. A total of 2,250 eggs and 1,672 larvae of the cigarette beetle and 224 larvae of the tobacco moth were exposed. -3- Table l.~ Mortality of 50 large cigarette beetle larvae exposed at indicated depths in bales of Turkish tobacco to fumigation at reduced pressure for 3 hours at 70 F. Richmond, Va,, 1941. Fumigant, lbs» i i per 1,000 tPercent mortality in tobacco at depths of: cu» ft. s 1 in. s 3 in. j 5 in. i 7 in. i 9 in. : Average Fumigation with methyl bromide 1 96 100 100 100 100 99.2 86 100 100 100 100 97.2 26 16 62 56 56 44.4 96 100 100 100 100 99.2 100 100 100 100 100 100 6 86 78 96 90 71,2 76 98 100 96 94 93.2 Av. 75.1 86.0 91.4 92.6 91.4 86.9 2 (Av. 6 tests) 100 100 100 100 100 100 3 (Av. 6 tests) 100 100 100 100 100 100 4 (Av. 6 tests) 100 100 100 100 100 100 Check (Av. 25 tests)!/ 0.6 2.3 2.3 0.6 1.7 1.5 Fumigation with hydrogen cyanide 1 100 100 96 92 98 97.2 100 100 100 98 96 97.8 100 98 92 90 98 95*6 98 94 86 88 96 92.8 100 100 100 100 98 99.6 100 100 100 100 98 98.6 AV. 99.7 98.7 95.7 94,7 97.3 97.2 2 100 100 100 98 100 99.6 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 98 100 99.6 100 100 98 100 100 99.6 Av. 100 100 99.7 99.6 100 99.7 3 100 100 100 98 100 99.6 100 100 100 100 100 100 100 100 100 100 ioo 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 98 100 100 99.6 Av. 100 100 99.7 99.7 100 99.9 4 Av. 100 100 100 100 100 100 Check(Av. 24 tests )l/ 1.3 1.7 1.5 1.0 2.2 1.5 1/ Only 25 larvae used at each depth in each test. r -A- Ifertality of test insects was 100 percent at all depths in the tobacco in all tests with both gases. Following fumigation, the tobacco used in this experiment was stored in separate warehouses — that fumigated with methyl bromide in warehouse 22-A, and that fumigated with hydrogen cyanide in warehouse 22»T. The weekly insect-trap catch from the two warehouses is shown in table 2» The insect population was appreciably higher in the warehouse containing tobacco fumigated with methyl bromide. However, the tobacco moth passes the winter outside of the mass of tobacco j hence, perhaps the large emergence of moths in warehouse 22»A could be attributed in part, at least, to a heavier population in this warehouse the preceding year. Table 2.-- Weekly catches in suction light traps in warehouses containing tobacco fumigated in March. Newport News, Va., 1941. Period : Warehouse 22-A, tobacco ending : fumigated with methyl bromide Warehouse 22-T, tobacco fumigated with HCN ;Tobacco moths: Cigarette beetles iTobacco moths t Cigarette beetles Aug, 2 3 44 300 100 48 28 19 10 2 2 3 26 44 68 150 71 51 59 5 49 110 100 96 43 0 0 0 0 0 1 4 0 3 2 5 3 5 2 1 4 0 16 8 5 6 0 0 2 1 0 2 18 30 40 29 22 12 8 3 4 1 3 30 29 30 9 20 7 0 4 9 13 8 12 0 0 0 0 0 3 0 1 0 2 5 1 1 0 1 0 1 6 1 1 10 1 0 0 0 Total 1,433 68 343 34 Weekly average 57 2.7 13.7 1.4 -5- Atmo spheric Fumigation Warehouse fumigation. — Four tobacco warehouses were fumigated at Richmond in 1941. Two of them contained hogsheads of cigarette tobacco of the flue-cured type, and two contained bales of Turkish tobacco. One warehouse of each type of tobacco was fumigated with methyl bromide and the other with hydrogen cyanide. The warehouses were comparable in every way, except that one was somewhat smaller. Each of three of the ware- houses were approximately 239,000 cubic feet in size, while the fourth was only 177,000 cubic feet. Each of the larger storages contained about 1,500,000 pounds of tobacco, while the smaller contained about 1,100,000 pounds. Prior to the fumigation on September 11 , no insect control meas- ures had been practiced in these buildings in 1941, except the operation of suction light traps , The tests were uniform in respect to the sealing of the buildings and the introduction of the fumigants. The dosage of fumigant used was 12 ounces per 1,000 cubic feet, with an exposure of 72 hours. Test lots of eggs and adults of the cigarette beetle and the tobacco moth were exposed in the air space of each warehouse at three elevations from the floor, and lots of cigarette beetle larvae were placed in the tobacco in each warehouse (by means of test spikes) at depths of 1^ 3, and 5 inches. At the beginning of the experiment the air temperature was 76 F. Unfortunately, bad weather developed and the temperature dropped to 49 F. for two nights of the 3-day period. Mortality of eggs and adults of both kinds of insects exposed in the air space was 100 percent in all four warehouses. Mortality of the cigarette beetle larvae in tobacco is given in table 3. The penetration of methyl bromide was definitely superior to that of hydrogen cyanide. In one warehouse fumigated with hydrogen cyanide the sealing of the door was broken by the wind, permitting loss of an unknown amount of gas. This loss would in part account for the comparatively low mortality of test insects in the tobacco in this building. Table 3. — Percent mortality of 150 cigarette beetle larvae per test in tobacco fumigated at atmospheric pressure with methyl bromide and hydrogen cyanide. Richmond, Va., 1941. i Fumigant : Type of : : tobacco i ; Percent mortality at depths in of tobacco 1 inch : 3 inches i 5 inches Methyl bromide Turkish Flue-cured 100 100 98.7 100 9903 99.9 Hydrogen cyanide Turkish }/ Flue-cured 93,3 100 54,7 98.7 47,3 65.3 None Flue-cured 23.3 28,0 32.7 1/ Wind broke the sealing of the door on the warehouse and prob. affected the results. r -6- Weekly trap catches of cigarette beetles and tobacco moths in the fumigated warehouses are shown in table 4* The relative insect popula- tions in the four warehouses after fumigation indicate that there was little difference in the control, given by the two insecticides, although the control of the tobacco moth was slightly better with methyl bromide than with hydrogen cyanide. Cigar factory fumigation. — A cigar factory at Selma, Ala., was fumi- gated in April 1948. This two-story brick building was over 900,000 cubic feet in size, and held a considerable stock of cigars, as well as filler, binder, and wrapper tobacco. A dosage of lg- pounds of methyl bromide per 1,000 cubic feet was used with an exposure of 44 hours. The air tempera- ture ranged from 65 to 85° F., and the weather was calm and fair. Cigars were made with a perforated capsule containing 25 cigarette beetle larvae rolled within the tobacco. Each of these cigars was placed at random in a box of 50 cigars in a rack of such boxes. Twenty-five cigarette beetle larvae were also placed in each compartment of test spikes that were inserted into bales of wrapper, binder, and filler tobacco, and into a bag and pile of loose, -strip-filler tobacco^ Mortality of the test insects was high, as shown in table 5. Penetra- tion of the gas was excellent. The larvae in cigars were all killed, except in a single instance where 3 survived out of a total of 275 exposed. In bales of Connecticut Broadleaf , mortality was 100 percent at all depths to 9 inches, and in bales of Wisconsin binder, at depths of 7 inches or less, but there was some survival at 9 inches. In bales of Florida wrapper, mor- tality was 100 percent to a depth of 3 inches, and 76 percent at 5 inches; at greater depths than 5 inches kills were light. No effect of the funigant upon the tobaccos was noted, and no odor of gas could be detected after 20 hours of aeration. -7- © t3 1 to •H r-l to OOlOOWN^HO a> "* A CM rH rH 10 ft • O O 53 B © tf •• X fH © < -p +> bO 1 •H © O in o CMiHOGOCMCMLOCOO to LO 5 © u 10 rH O tO tO CM CM CM JO •n • 00 rH CM 1 fl> -P ■P — o 53 •• CM S3 o5 « i CM In at © o ^tOHtOKJlOlOHH fc» LO hO -d r-i IO rH rH ^ 0) •H •H 00 X) O s • •d o o ■>* fi *-. S3 i-H •o ,o •♦ t> 1 & i-i >> 1 r-H i-H X CO O rH cono^^ooiNH o CO >> -p LO N t(i N W H CO 1— t £ s • o iH L, CO © rH © 53 £> 6 © -P x •p «< O. •H © 1 © N 13 CO O CO OCOOOOOOt-tO O CO •H i-H LO tO^CMOLOlOO^tO o CO Tt c CO "d H W CO CO ^ N LO CM © a5 • Tjt CD % -P >> o -P CM 01 o £3 aJ bO •« hO a © < "A a © O 1 o t2 OOiOOLOiOOcMO t- o -P u o rH-^CMOCMt-O^rH CM c- CO o -d • CM i-i rH rH rH CO © CO 5 6 O 3 3 o o o m M X o <«J CD • a5 1 J-. i-H £> © CM 05 "■* O -a i—l O OOOLOOCMC-rHLO G) co ■e en Eh •H LO CONCDCMO^Hrl C- O) r-l a • O) i-H CM tO co P o 6 to * : 55 a5 C > f-1 •H b «t * A I W TJ -p CO LO CDNOt-C»lOCMt»^ Oi to CD C £ c- ©©©^^WHH 1— 1 i-H -c 2 a • -tf rH i-H •<* o i-H o 6 o •1 -P X W i-H as o .. ~ *~ 4* ** *• O -H « ex a) j* • to to -p © r-t © i-H TJ hfl fcD >**d 2 • oi • i-H C ^1 r» ^ > ,M at XJ rH O © O © >> © o 6 05 53 P > =3 at s? - O I 1 i a M EH >> 1 © « CO i-H CO • hO © 1-\ COLOCMO)> -P ♦ • sx ex, X X P-. -P > © © 05 © O O CO co E- 1 CO O 53 -8- • fa c © to .H CO Jh © 1 Xc 3: ftto w to o a p p -p CO as u 3 n O © -C +3 OS *• &0-«J« •H B Jh 5 o HH >, -p f- © o © -p > x: • >>P P 2 ■* •H S o> rH r-« csS X +3 P » V< •H • J3 £ at a rH i © <*} i Jh » 3 * lO to al co a 0 © rH H Jh © rO faW ca t-i © P -H feD S3 rH aS © a) Jh o P © Jh Jh ^ © 2 -4 ft a ro © d © Jh aS co P O © S>P •h aS aS O t 8 o © S3 O hH Jh © fa Oi CO © IX o S3 at- 40 ## CO © o S3 H CO © S3 H |to M3 o S3 © & co g P S3>© © n co rH $3 3 CD -H P O «M EH o CO p o © CO S3 p CO (0 TJ p © © X aS © t-i •H (3k Jh S3 © •H * O o © as o Eh to o o o> rH rH rH r-T| o o 00 o o o O 00 CO O O 1 I 1 ? O 00 O O 1 1 1 i o o to o o o o to o o O O to o o o o t- o o o o © o o o o o o o o o o o o o o o o o I 9 I I I I I I o o O CO if} O CO o o in ID LO CM N tO t- LO tO Cvi CO W rH rH rH CM 3 •H Sh £>£> © P O CO •h aj © S3 rH T> u o aS © P lO rCj SH © >» 9 ^ •H rH a P X Jh •H * o *"> & o P r"» fa O T3 r-< © Vh © SH O aS Jh OS © fa «B fa a aS © O «tH CO © © 3 l> CQ © o Jh OS at 4, g r-{ - a aS S3 O £ to o Jh CM .rt P © o |g rH © X X © O CM P Sh O a$ O O Sh •£ » P © t-i P aS P Cm Sh S3 aS S3 © © ■H ft t3 co •H >> CO © o T3 aS H • to O O J» S3 O Sh rH aj T3 O ,o © © a$ P O T3 X rH OS P S-. O >> 3 o 4j X a1 up © S3 © p © CO © T3 •H Sh •h g aS js X o EH -n cvTl -9- Effect of Methyl Bromide on "Sweating" of Tobacco Fumigation has been suspected of adversely affecting the "sweating" or fermentation of tobacco. In 1940 and 1941 large quantities of Turkish and flue-cured tobacco were fumigated with methyl bromide in vacuum and at atmospheric pressure. Careful records were made as to the sweating of this tobacco. In all instances the tobacco fumigated with methyl bromide sweated normally and no injurious effects of any kind were noted. Reports of Methyl Bromide Injury to Cigar "Tobaccos In the experiments on methyl bromide fumigation no injury of any character was noted. In 1940, however, an investigation was made of a report of an objectionable odor in tobacco following fumigation. It was found that a lot of Puerto Rican cigar tobacco (strip filler) in New York had been fumigated in vacuum with methyl bromide at a dosage of 5 pounds per 1,000 cubic feet. A part of this tobacco had developed such an ob- jectionable odor that it was worthless. Samples of the affected tobacco were found to be high in bromine content, which constituted some evidenoe that perhaps the odor had been caused by methyl bromide. No evidence could be found to eliminate the methyl bromide fumigation as the respons- ible factor. In the spring of 1948 another report was received, that since 1941 in the course of commercial fumigation of cigar tobaccos in Havana, Cuba, there had been at least two instances in which tobacco fumigated with methyl bromide developed objectionable odors. Danger to Warehouse Workers CAUTION.— METHYL BROMIDE IS A POISONOUS GAS AND SHOULD BE HANDLED ONLY BY ESPECIALLY TRAINED OPERATORS* However, it also may present a hazard to workmen employed in the handling of tobacco after fumigation. The fact that the odor of this gas in low concentrations is not very noticeable, increases the danger. During fumigation, tobacco absorbs a considerable amount of the gas which is gradually released over a period of days. It is often necessary for laborers to work in a warehouse immediately after fumigation. Even though the concentration of poison gas may be too low to be noticed, continued exposure for several days may result in acute illness. For example, a crew of laborers at Winston-Salem, N. C, were handling tobacco that had been fumigated with methyl bromide. After several days spent in moving the bales of tobacco, two of the men developed typical cases of acute methyl bromide poisoning. They eventually re~ covered after a prolonged period of illness. In experiments at Newport News in 1940, data on the concentrations of gas which would develop under certain conditions were obtained through the cooperation of the Research Department of the Dow Chemical Company. After being fumigated in vacuum and air washed, bales of Turkish tobacco were brought from the fumigation chambers and stored in a tobacco warehouse 100 by 100 by 18 feet. The doors and ventilation openings on two sides of UNIVERSITY OF FLORIDA -10- 3 1262 09239 1860 the warehouse were screened and the other two sides were brick firewalls. This is customary in many tobacco warehouses, but affords rather poor ventilation. Before opening the doors at 8j00 a.m., after this warehouse had been closed overnight, 13 samples of air were taken from various points in the building. By chemical analysis the average concentration of methyl bromide was found to be 37.4 parts per million. The maximum amount of gas in any sample was 50.6 p. p.m. and the minimum 19 p. p.m. After the building had been aerated the concentration of gas dropped rapidly. At 8 $10 a.m. the average of 3 air samples showed 29.4 p. p.m., and at 9:10 a. ia«, 27.7 p. p.m. At 2 locations near the door the methyl bromide content of the air had dropped from 19 to 12»2 p. p.m. and from 30 to 17.6 p. p.m.} in the center of the warehouse the concentration had dropped only from 39»3 to 38.5 p. p.m. After thorough ventilation the highest eoncentra* tion of methyl bromide was 16 p. p.m. and the lowest 4,5 p. p.m. The average of 12 samples taken near the doors was 8.3 p. p.m. Under similar conditions, in the same warehouse, shortly after storage of 105,000 pounds of tobacco just fumigated in vacuum with methyl bromide, tests of the air with a halide detector showed concentrations of gas ranging from 20 to 200 p. p.m. Summary Extensive and carefully replicated experiments have shown that methyl bromide is an affective fumigant against the cigarette beetle, (Lasioderma serricorne (F,)) and the tobacco moth (Ephestia elutella (Hbn)j In laboratory tests at reduced pressure 2 pounds of methyl bromide was as effective as 4 pounds of hydrogen cyanide. In commercial-scale tests at reduced pressure methyl bromide was found to be approximately equal in effectiveness to hydrogen cyanide at the same dosage. In atmos- pheric fumigation of flue-cured and of Turkish tobacco methyl bromide was found to be more effective than hydrogen cyanide at the same dosage - giving bettor penetration. No injurious effects were noted to cigarette-type tobaccos from fumigation with methyl bromide. However, injury to cigar tobaccos has been reported. After fumigation with methyl bromide, cigar tobaccos h*ve been known to develop obnoxious odors. Bad odors after fumigation with this gas are rare, bu-c until some explanation of this occurence can be made or until some remedy for it can be found, it should be recognized that the use of this gas on cigar tobaccos involves a risk. For several days after fumigation with methyl bromide low concen- tration of the gas remains in the tobaccq, where it constitutes a health hazard to workmen, particularly since there is little or no warning odor.