Insecticide Susceptibility and Detoxication Enzyme Activities in Permethrin-Selected Diamondback Moths

Abstract

Selection of larvae of the diamondback moth,Plutella xylostella(L.), with permethrin increased resistance. After 21 generations of continuous selection pressure, resistance to permethrin was over 600-fold in this strain compared with the unselected parental strain. The permethrin-selected strain was also cross-resistant to all pyrethroids tested, but remained susceptible to organophosphorus, carbamate, cyclodiene, chloronicotinyl, avermectin, and microbial insecticides tested. Detoxication enzyme assays revealed that activities of microsomal oxidases (epoxidases, hydroxylases, sulfoxidase,N-demethylase, andO-dealkylases), glutathioneS-transferases (DCNB, CDNB, and PNPA conjugation), hydrolases (general esterase, carboxylesterases, β-glucosidase, acetylcholinesterase, and carboxylamidase), and reductases (juglone reductase and cytochrome c reductase) and levels of cytochrome P450 and cytochrome b5were similar in the permethrin-selected and parental strains. There was no difference in the rate of cuticular penetration of permethrin between the two strains. Synergist studies showed that neither piperonyl butoxide (microsomal oxidase inhibitor) norS,S,S-tributyl phosphorotrithioate (DEF, esterase inhibitor) reduced the level of resistance to permethrin. The results indicated that pyrethroid resistance observed in this strain was most likely attributed to decreased target site sensitivity.