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.