Correlation of azinphosmethyl resistance with detoxication enzyme activity in the light brown apple moth Epiphyas postvittana (Lepidoptera: Tortricidae)

Abstract

Bioassay using diet incorporation of azinphosmethyl showed six strains of light brown apple moth to have varying levels of resistance to azinphosmethyl (3- to 15-fold) compared with three susceptible strains. Two of these strains were products of a selection and backcrossing program providing resistant insects that had a common genome with that of one of the susceptible strains. Individual male moths from each strain were tested for (i) glutathione S-transferase and (ii) non-specific esterase activity. Larvae were assayed for (iii) mixed function oxidase activity. Each enzyme group was assayed with two substrates. Significant positive regressions between LC 50 and enzyme activity were observed for all three groups: (i) r 2 = 0.84 for 3,4-dichloronitrobenzene conjugation, (ii) 0.64 for α-naphthyl acetate hydrolysis, 0.54 for α-naphthyl butyrate hydrolysis, and (iii) 0.88 for p-nitroanisole oxidation and 0.86 for aniline oxidation. No correlation with the LC 50 was found for 1-chloro-2,4-dinitrobenzene conjugation ( r 2 = 0.001). Activities of all three groups were significantly higher in the two backcross resistant strains compared to the susceptible parent strain ( P < 0.05). The gene(s) for high enzyme activity had thus been successfully transferred with the factor for resistance. The results suggest a close relationship between detoxication enzyme activity and azinphosmethyl resistance.