MONOOXYGENASE, ESTERASE, AND GLUTATHIONE TRANSFERASE-ACTIVITY ASSOCIATED WITH AZINPHOSMETHYL RESISTANCE IN THE TUFTED APPLE BUD MOTH, PLATYNOTA-IDAEUSALIS

Azinphosmethyl-selected tufted apple bud moths were compared to suscep tible and reverted strains with respect to possible metabolic mechanis ms of resistance within the third instar, fifth instar, and adults. Ba sed upon bioassays conducted by topical application with azinphosmethy l, LD(50)s were as high as 867-fold in the selected strain as compared to that seen in susceptible bud moths. The LD(50) of the reverted str ain was intermediate to that of the susceptible and selected insects a t all stages studied. Glutathione transferase activity measured with 1 -chloro-2,4-dinitrobenzene was elevated in the selected strain 1.6- an d 2.2-fold as compared to third and fifth stadium susceptible bud moth s, respectively. No consistent strain differences were noted for 1,2-d ichloro-4-nitrobenzene. Cytochrome P450 content and P450 mRNA was not significantly different in fifth instars of the susceptible and select ed strain. However, there was a 2.7- and 1.9-fold increase in benzphet amine and p-nitroanisole metabolism, respectively, in the guts of azin phosmethyl-selected fifth instars. Benzo[a]pyrene metabolism was eleva ted 2.4-fold in the carcass of selected bud moths and no differences w ere noted for methoxyresorufrin in either gut or carcass. Susceptible fifth instars demonstrated a reduced rate of metabolism of azinphosmet hyl to the oxon and methyl benzazamide. Piperonyl butoxide failed to s ynergize azinphosmethyl toxicity. Esterase activity measured with 1-na phthyl acetate and p-nitrophenyl acetate was elevated in selected larv ae compared to that seen in susceptible tufted apple bud moths in both larvae and adults. This increased esterase activity was attributed to several isoforms as resolved by analytical isoelectric focusing. One of these forms was consistently overexpressed in ail of the life stage s examined. Pretreatment of selected fifth instars with S,S,S-tributyl phosphorotrithioate increased the toxicity of azinphosmethyl 400-fold and had minimal effect on toxicity in susceptible insects. It appears that multiple hydrolases are the primary metabolic factor in azinphosm ethyl resistance in the tufted apple bud moth. (C) 1996 Academic Press , Inc.