MECHANISM OF RESISTANCE TO DELTAMETHRIN IN CYDIA-POMONELLA (L.) (LEPIDOPTERA, TORTRICIDAE)

The pathways for deltamethrin detoxification were studied in fifth ins tar larvae of two resistant strains of Cydia pomonella obtained by mas s selection (with deltamethrin (Rv) or diflubenzuron (Rt)) of resistan t field populations from southeastern France. Compared to a laboratory susceptible strain (S), these strains exhibited respectively a 3170- and 1600-fold resistance ratio to topically applied deltamethrin. The esterase inhibitor S,S,S-tributyl phosphorotrithioate synergized delta methrin in both resistant and susceptible strains, whereas the mixed-f unction oxidase (mfo) inhibitor piperonyl butoxide (PBO) synergized de ltamethrin only in R strains (Rv and Rt). The two inhibitors together totally overcame the deltamethrin resistance of Rv and Rt strains. Whi le ethoxycoumarin deethylase activities, measured at individual level in microtitration plates, were higher in R strains than with S, those of glutathione S-transferases showed little difference and those of es terase showed no difference. Moreover, the involvement of mfo in the r esistance to deltamethrin was confirmed by in vivo metabolization of [ C-14] deltamethrin by guts of fifth instar larvae. Metabolites resulti ng from the ester bond hydrolysis, such as phenocyanol and PBald, were common to S and R strains. The mfo-dependent hydroxylated derivatives (t or c-CHO-t-deltamethrin, 4' or 5-HO-deltamethrin and 4' or 5-HO-PB -acid) were generated only in Rv and Rt strains and were inhibited by PBO. These results may provide the basis for further studies in geneti c of resistance in C. pomonella. (C) 1997 Academic Press.