Broad-spectrum insecticide resistance in obliquebanded leafroller Choristoneura rosaceana (Lepidoptera: Tortricidae) from Michigan.

Nineteen insecticides, belonging to nine chemical classes, were bioassayed by dietary exposure against two strains of obliquebanded leafroller, Choristoneura rosaceana, collected from Michigan apple orchards. Berrien is a putatively organophosphate-resistant strain from a commercial orchard with a history of insecticide use, and Kalamazoo a susceptible strain from an isolated and unsprayed orchard. The Berrien strain was moderately resistant (about 25-fold) to organophosphates such as azinphos-methyl and chlorpyrifos. Very low resistance (< 10-fold) was also observed to pyrethroids such as cypermethrin, zeta-cypermethrin, bifenthrin, deltamethrin and esfenvalerate, to the ecdysone agonists tebufenozide and methoxyfenozide, and to the chlorinated pyrrole chlorfenapyr. Endosulfan and carbamates such as thiodicarb, methomyl and carbaryl had low intrinsic toxicities against both strains, with little difference in sensitivity between them. There was no resistance to spinosad. Emamectin benzoate was found to be the most toxic insecticide against C rosaceana, with slightly higher lethal doses required for the Berrien strain. Unexpectedly, Berrien exhibited a very high level of resistance (> 700-fold) to indoxacarb, which has never been used in Michigan to control this insect pest. The active metabolite of indoxacarb, DCJW, was considerably more toxic than the parent compound, but the resistance against DCJW was comparable to that seen with indoxacarb. This indicates that a failure to activate indoxacarb was not the mechanism of resistance in Berrien. The low level of resistance to several chemistries recorded in Michigan C rosaceana can be managed at this stage by adopting a rotation of chemistries having different modes of action.