Abstract
In vivo metabolism of [methoxy-14C] fenitrothion topically applied to the organophosphorus-resistant (Mizobe) and -susceptible (Sapporo) strains of the diamondback moth was examined. There was no difference in the rate of penetration between the two strains. Significant differences were found in the formation of internal metabolites, i. e., fenitroxon levels were 3 to 4 times higher in the Sapporo strain, while the levels of dimethyl phosphate, a hydrolysis product of fenitroxon, were 2 times higher in the Mizobe strain. To confirm the differences in vitro metabolism of [methoxy-14C] fenitroxon was examined. In both strains, fenitroxon was detoxicated mainly by the hydrolysis in the soluble fraction, but the hydrolytic activity was 2 times higher in the Mizobe strain. Based on these results, it was proved that the increased fenitroxon hydrolysis in the soluble fraction plays an important role for fenitrothion resistance in the Mizobe strain.
