Relation of metabolism and translocation of propaphos in rice plant to insecticidal activity against two strains of green rice leafhopper

Some behaviours of propaphos (O, O-di-n-propyl O-4methylthiophenyl phosphate, Kayaphos®) in the rice plants grown in water culture and in the two strains of green rice leafhoppers fed on these rice plants were examined to elucidate its insecticidal activity. In the rice plants, propaphos absorbed and accumulated in the roots was translocated gradually to the sheaths and the leaf blades, in which the chemical was oxidized to its sulfoxide and selfone derivatives. Especially in the top part of the leaves, marked concentration of sulfone was detected. When the leafhoppers were fed on these rice plants, it was found that there were several high correlations between KT50 of the insects and the concentrations of propaphos and its oxidative metabolites in the rice plants. Based on the results of analysis of propaphos and its oxidative metabolites in the rice plants and in the insects, it was indicated that (1) the oxidative metabolites in the rice plants were similarly insecticidal against the leafhoppers, (2) the insects fed on the rice plants containing high concentration of the chemicals were found to have higher concentration than the lethal threshold, (3) there was a correlation between the concentration of the chemicals in the rice plants and that in the insects, (4) propaphos was oxidized to its sulfoxide and sulfone derivatives in the insects at a higher rate than in the rice plants, (5) the insects of resistant strain seemed to detoxify the chemicals faster than the susceptible strain.