INSECTICIDE SUSCEPTIBILITY AND DETOXICATION ENZYME-ACTIVITIES IN PERMETHRIN-SELECTED DIAMONDBACK MOTHS

Selection of larvae of the diamondback moth, Plutella xylostella (L.), with permethrin increased resistance. After 21 generations of continu ous selection pressure, resistance to permethrin was over 600-fold in this strain compared with the unselected parental strain. The permethr in-selected strain was also cross-resistant to all pyrethroids tested, but remained susceptible to organophosphorus, carbamate, cyclodiene, chloronicotinyl, avermectin, and microbial insecticides tested. Detoxi cation enzyme assays revealed that activities of microsomal oxidases ( epoxidases, hydroxylases, sulfoxidase, N-demethylase, and O-dealkylase s), glutathione S-transferases (DCNB, CDNB, and PNPA conjugation), hyd rolases (general esterase, carboxylesterases, beta-glucosidase, acetyl cholinesterase, and carboxylamidase), and reductases (juglone reductas e and cytochrome c reductase) and levels of cytochrome P450 and cytoch rome bg were similar in the permethrin-selected and parental strains. There was no difference in the rate of cuticular penetration of permet hrin between the two strains. Synergist studies showed that neither pi peronyl butoxide (microsomal oxidase inhibitor) nor S,S,S-tributyl pho sphorotrithioate (DEF, esterase inhibitor) reduced the level of resist ance to permethrin. The results indicated that pyrethroid resistance o bserved in this strain was most likely attributed to decreased target site sensitivity. (C) 1996 Academic Press.