Age-dependent variations in the response of several species of diptera to insecticidal chemicals

The toxicity of carbaryl to three species of fleshflies Sarcophaga bullata Parker, S. crassipalpis Macquart, and S. argyrostoma (Robineau-Desvoidy) varied considerably with age and sex. In contrast, the susceptibility of a blowfly, Phormia regina (Meigen) to carbaryl decreased with age and that of two muscid flies, Musca autumnalis DeGeer and Stomoxys calcitrans (L.), remained relatively constant. The synergistic activity of piperonyl butoxide varied inversely with the innate toxicity of carbaryl to each species suggesting that the observed age- and sex-dependent variations in carbaryl toxicity result mainly from differences in detoxifying capability. This was supported by in vitro measurements of oxidative microsomal metabolism. It was further established that differences in the rates of penetration and excretion of carbaryl and in the susceptibility of the head cholinesterase to carbaryl inhibition were of little importance in determining the susceptibility of the flies to this insecticide.