Fumigation Efficiency as Affected by Exposures, Formulations, and by Insect Species and Stages1

Abstract

During 1958 and 1959, various stored-grain insect species and stages were fumigated under laboratory conditions to determine (1) relative toxicities of carbon tetrachloride (CCl4), carbon disulfide (CS2), and CCI4 formulated with CS2, methyl formate (C2H2O2) and ethyl formate (C3H6O2) and (2) sorption of 80:20 (CCI4:CS2 by volume) after various exposure periods. Fumigations were conducted at 80°#xb1;2° F. in l-gallon or 20-liter fumatoria containing Hard Red Winter wheat at 12 ±0.1% moisture with less than 1% dockage. Formulations containing 80% or less CS2 failed to produce significantly higher mortalities than 100% CCI4 to adult rice weevils ( Silophilus sasakii (Takahashi)), confused flour beetles ( Tribolium confusum Jacquelin du Val), saw toothed grain beetles, Oryzaephilus surinamensis (L.), or first- and third-instar rice weevils. The average order of resistance for adults to all formulations was weevils <confused flour beetles=saw-toothed grain beetles and for weevil stages was adult=first instar <third instar. Formulations of 80: 20 (CCl4: C2H2O2 or CCI4: C3H6O2 by volume) were significantly less toxic than 80: 20 (CCl4: CS2) or CCl4 alone to adult weevils, confused flour beetles, and saw-toothed grain beetles. Decreasing the percentage of C2H2O2 or C3H6O2 formulated with CCI4 increased formulation toxicity to confused flour beetles. This effect was not indicated by weevil or saw-toothed grain beetle mortalities. The order of resistance was saw-toothed grain beetles> confused flour beetles = weevils, considering average effectiveness of all formulations containing C2H2O2or C3H6O2 components. Sorption and toxicity studies were conducted with 80:20 (CCl4:CS2) by fumigating various insect species and stages in wheat for exposures of 8, 24, and 48 hours. Approximately 43% and 8.5% of the fumigant was sorbed during the initial 8- and 24- hour exposures, respectively. Extending exposures to 48 hours increased sorption to approximately 90%. The average order of resistance for adults tested for all exposures and all mortality levels was weevils < confused flour beetles <saw-toothed grain beetles. In general, the relative susceptibility of adults compared with immature weevils was less at 8 hours' exposure and greater at 48 hours' exposure.