Eighteen insecticides were bioassayed by dietary exposure against two obliquebanded leafroller strains collected from Michigan orchards: a putatively organophosphate-resistant strain (Berrien) obtained from a commercial apple orchard with a long history of insecticide use, and a susceptible strain (Kalamazoo) from an isolated and unsprayed orchard. Berrien was moderately (25- to 50-fold) resistant to organophosphates such as azinphosmethyl and chlorpyrifos compared to Kalamozoo, and low level differences in sensitivity were also observed with pyrethroids such as cypermethrin, zetacypermethrin, bifenthrin, deltamethrin and fenvalerate, with the ecdsyone-mimics methoxyfenozide and tebufenozide, and with the chlorinated pyrrole, chlorfenapyr. Carbamates, including carbaryl, methomyl and thiodicarb, and endosulfan had low intrinsic activities against both strains with little difference in sensitivity between them. Spinosad was equally toxic to both strains. An unexpected result was obtained with the new insecticide, indoxacarb, which has never been used to control this insect. Nevertheless, Berrien showed a very high level of resistance compared to Kalamazoo (approximately 800-fold). The active metabolite of indoxacarb, DCJW, was considerably more toxic than the parent compound, but the difference in sensitivity between the strains was comparable to that seen with indoxacarb itself, indicating that a failure to activate indoxacarb was not the mechanism of resistance in Berrien. Similar result were obtained in less extensive tests with a second leafroller strain collected from a different commercial orchard. The mechanism of the Berrien strain's resistance to indoxacarb is under investigation.
Species 1: Lepidoptera Tortricidae Choristoneura rosaceana (obliquebanded leafroller)
Keywords: Indoxacarb, Organophosphate
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