Cross-resistance between azinphos-methyl and acetamiprid in populations of codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae), from Washington State.

Codling moth, Cydia pomonella (L.), has been intensely managed with the organophosphate insecticide azinphos-methyl for 50 years, and populations have developed resistance. New management programs have been developed and implemented that rely more heavily on other classes of insecticides. A prerequisite for developing effective resistance management strategies for these compounds is to establish their current levels of effectiveness. Adult and neonate larval assays were conducted to assess the response of field-collected codling moth populations from apple in Washington State. Male codling moth populations exhibited a range of responses to a discriminating concentration of azinphos-methyl in a survey of 20 populations. Populations from certified organic orchards were more susceptible than those from conventional orchards. Mean fecundity was inversely related to azinphos-methyl tolerance. Male responses to azinphos-methyl and acetamiprid varied significantly among populations and were correlated. The residual effectiveness of field applications of both insecticides varied significantly against neonate larvae. Neonate bioassays with insecticide-dipped fruit found significant differences among populations with azinphos-methyl, acetamiprid, methoxyfenozide and spinosad, but not with esfenvalerate. These results support a concern that alternation of insecticides with different modes of action may not be a sufficient strategy to avoid the evolution of broad-spectrum insecticide resistance by codling moth.