Resistance of codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae), larvae in Michigan to insecticides with different modes of action and the impact on field residual activity.

Background: The codling moth is one of the principal pests of apple in the world. Resistance monitoring is crucial to the effective management of resistance in codling moth. Three populations of codling moth in neonate larvae were evaluated for resistance to seven insecticides via diet bioassays, and compared with a susceptible population. In addition, apple plots were treated with labeled field rate doses of four insecticides. Treated fruit were exposed to neonate larvae of two populations from commercial orchards.

Results: Two populations of codling moth expressed two- and fivefold resistance to azinphos-methyl, seven- and eightfold resistance to phosmet, six- and tenfold resistance to lambda-cyhalothrin, 14- and 16-fold resistance to methoxyfenozide and sixfold resistance to indoxacarb, but no resistance to acetamiprid and spinosad. The impact of the resistance to azinphos-methyl, measured as fruit damage, increased as the insecticide residues aged in the field. In contrast, fruit damage in methoxyfenozide- and lambda-cyhalothrin-treated fruit was observed earlier for resistant codling moth. No differences in efficacy were found for acetamiprid.

Conclusions: Broad-spectrum insecticide resistance was detected for codling moth. Resistance to azinphos-methyl, lambda-cyhalothrin and methoxyfenozide was associated with reduced residual activity in the field. Broad-spectrum resistance presents serious problems for management of the codling moth in Michigan.