Glutathione S-transferases as antioxidant defence agents confer pyrethroidresistance in Nilaparvata lugens

Selection of a laboratory colony of the brown planthopper Nilaparvata lugen s with the pyrethroids permethrin and lambda -cyhalothrin increased its res istance to both insecticides. Biochemical analysis and synergistic studies with metabolic inhibitors indicated that elevated glutathione S-transferase s (GSTs) with a predominant peroxidase activity conferred resistance to bot h pyrethroids, whereas esterases conferred part of the resistance to permet hrin. Purified esterases hydrolysed permethrin at a slow rate, but incubati on of either pyrethroid or their primary metabolites with partially purifie d GSTs had no effect on the metabolic profile. Although GSTs were sensitive to inhibition by both pyrethroids, they did not serve as binding proteins, as previously hypothesized [Grant and Matsumura (1988) Insect Biochem. 18, 615-622]. We demonstrate that pyrethroids, in addition to their neurotoxic effect, induce oxidative stress and lipid peroxidation in insects. Pyrethr oid exposure induced lipid peroxides, protein oxidation and depleted reduce d glutathione. Elevated GSTs in the resistant strains attenuated the pyreth roid-induced lipid peroxidation and reduced mortality, whereas their in viv o inhibition eliminated their protective role. We therefore hypothesize tha t the main role of elevated GSTs in conferring resistance in N. lugens is t hrough protecting tissues from oxidative damage. Our study extends the GSTs range of efficacy to pyrethroid insecticides and possibly explains the rol e of elevated GSTs in other pyrethroid-resistant insects.