Mechanism of resistance to malathion in the green rice leafhopper, Nephotettix cincticeps uhler

In order to clarify mechanism of the malathion-resistance in the green rice leafhopper, effects of some synergists, penetration and metabolism of malathion, and sensitivity of ChE were determined using two organophosphate-resistant strains (M and P) and one susceptible strain (S). Any distinct difference was not found in penetration of malathion and sensitivity of ChE to malathion and malaoxon among S, M and P strains. Although malathion was metabolized relatively quickly to aqueous metabolites in the three strains both in vivo and in vitro, the degradation activity in M and P strains was twice that in S strain. The main aqueous metabolite was malathion monoacid. Other unknown metabolites appeared 1-2 hr after treatment and increased gradually, but a distinct difference was not found in the patterns of aqueous metabolites among S, M and P strains. Malaoxon was evidently accumulated in the body of S strain but not detected in M and P strains. Consequently, extremely small amount of malaoxon in the resistant strains was explainable to the resistance to malathion in these resistant leafhoppers. (auth.)