Mechanism of resistance to deltamethrin in Cydia pomonella (L.) (Lepidoptera: Tortricidae)

The pathways for deltamethrin detoxification were studied in fifth instar larvae of two resistant strains of Cydia pomonella obtained by mass selection (with deltamethrin (Rv) or diflubenzuron (Rt)) of resistant 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 deltamethrin in both resistant and susceptible strains, whereas the mixed-function oxidase (mfo) inhibitor piperonyl butoxide (PBO) synergized deltamethrin only in R strains (Rv and Rt). The two inhibitors together totally overcame the deltamethrin resistance of Rv and Rt strains. While 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 esterase showed no difference. Moreover, the involvement of mfo in the resistance to deltamethrin was confirmed by in vivo metabolization of [C-14] deltamethrin by guts of fifth instar larvae. Metabolites resulting 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 genetic of resistance in C. pomonella. (C) 1997 Academic Press.