Toxicity and metabolism of carbaryl in the European corn borer

Larvae from two strains of the European corn borer, Ostrinia nubilalis (Hübner), were compared for differences in their tolerance and metabolism of carbaryl (1-naphthyl N-methylcarbamate). The Geneva strain was about twice as susceptible to carbaryl, but both Valley and Geneva borers converted carbaryl to oxidative metabolites at similar rates in vivo and in vitro. Maximum carbaryl-metabolizing activity was present in last-instar larvae, particularly in the fat body and gut tissues. However, the specific activity of gut homogenates was highest in the Geneva strain and the specific activity of fat body was highest in the Valley strain. Other differences in the mixed-function oxidase systems of gut and fat body were also found. The major metabolite in vivo and in vitro was hydroxymethyl carbaryl.