AZINPHOSMETHYL RESISTANCE IN THE OBLIQUEBANDED LEAFROLLER, CHORISTONEURA-ROSACEANA - REVERSION IN THE ABSENCE OF SELECTION AND RELATIONSHIPTO DETOXICATION ENZYME-ACTIVITY

Larvae of the obliquebanded leafroller, Choristoneura rosaceana (Harri s) (Lepidoptera: Tortricidae), were collected from apple orchards in D eux-Montagnes, Quebec, Canada, where leafroller populations were docum ented to be resistant to azinphosmethyl. Larvae were bioassayed for az inphosmethyl resistance over five generations of rearing in the labora tory in the absence of insecticide selection pressure; resistance leve ls reverted to susceptibility in approximately four generations in 199 5 and three generations in 1996. In 1996, activities of esterases and glutathione transferases were assayed in adult moths concurrently acro ss generations. Reversion of resistance was significantly correlated w ith decreasing esterase activities in both male and female moths when either alpha-naphthyl acetate or a-naphthyl butyrate was used as the t est substrate. Glutathione transferase activities were correlated with resistance levels only in male moths when 3,4-dichloronitrobenzene (D CNB) was the test substrate; no correlations between activity and resi stance were observed for females with DCNB or for either sex when acti vity was assayed with 1-chloro-2,4-dinitrobenzene (CDNB). The instabil ity of azinphosmethyl resistance in the obliquebanded leafroller, coup led with the apparent involvement of esterases in resistance developme nt, should make this pest amenable to a resistance management strategy involving the rotation of azinphosmethyl with other control materials that are not primarily metabolized by esterases. (C) 1998 Minister of Public works and Government Services Canada.