Variation in response to insecticides in two species of univoltine leafrollers (Lepidoptera: Tortricidae)

Abstract

AbstractPopulations of fruittree leafroller, Archips argyrospila (Walker), and European leafroller, Archips rosana L., were obtained from eight sites in the Okanagan Valley, British Columbia, and assayed for their responses to five insecticides using a leaf-disk bioassay and neonate larvae. Lethal concentration ratios (LCR values) were calculated for all populations compared with the most susceptible strain, and significant variation was detected in both species. LCR values ranged from 1.04 to 9.06 for azinphosmethyl, from 1.29 to 53.15 for tebufenozide (Confirm®), from 1.85 to 24.69 for methoxyfenozide (Intrepid®), from 1.59 to 2291.4 for indoxacarb (Avaunt®), and from 1.92 to 1.98 for spinosad (Success®). Methoxy fenozide was approximately 100-fold more toxic to neonate leafrollers than was tebufenozide, and spinosad was the most toxic of all materials tested. Correlation analysis indicated that there was cross-resistance between azinphosmethyl and tebufenozide. At the LC50 level, the responses of the two species were not significantly different for each insecticide. Analysis of equivalency and parallelism of dose-response lines revealed that A. argyrospila and A. rosana had equivalent responses to azinphosmethyl. LC50 values for the response of A. argyrospila to azinphosmethyl were not different from values obtained almost 20 years earlier. Cross-resistance between azinphosmethyl and tebufenozide suggests that resistance management for these two species of univoltine leafrollers should not include rotation of azinphosmethyl and benzoylhydrazine insect-growth regulators. The high level of resistance to indoxacarb found in one population indicates that baseline tolerance screening is desirable before indoxacarb is introduced for use in Canadian orchards.