Effects of Carbamates on House Fly Fecundity, Longevity, and Food Intake12

Abstract

Topical application of sublethal but knockdown-inducing doses of Isolan® (1-isopropyl-3-methyl-5-pyrazolyl dimethylcarbamate) to house flies, Musca domestica L. resulted in substantial reduction of egg laying but did not affect mating, longevity, or egg fertility. Significant reductions in fecundity were obtained whether the insecticide was applied before or after mating and whether the insects had prior access to milk or not. Increasing the doses above the sublethal level had a greater repressing effect on fecundity but did not cause complete sterility. Thus, a sublethal dose of 0.3 μg per fly reduced total egg production by 35.8%, while doses of 0.6 and 1.0μg, representing LD10 and LD30 levels, respectively, reduced egg production by 43.1% and 77.2%, respectively. The effect of the treatments was long lasting: the daily egg production in flies treated with 0.6 μg did not equal that of the control until the 19th day after treatment; by the use of p32 milk it was found that treated flies consumed as much as 51.8% less milk than the untreated flies even 8 days after treatment. Tests with other carbamates indicated that while pliysostigniinc and Pyrolan® (3-methyl-1-phenyl-5-pyrazolyl dimethylcarbamate) had no effect on fecundity, dimetilan, carbaryl, Bayer 39007 ( o -isopropoxyphenyl methylcarbamate) and Hercules 5727 ( m -isopropylphenyl methylcarbamate) caused significant reduction in egg production. Although the precise nature of the interaction between the insecticide and the physiological processes that are significant in reproduction remains unresolved, the available evidence indicates that cholinestcrase inhibition is not directly responsible for the suppression of egg production.