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Green apple aphid, Aphis pomi De Geer, and Aphis spiraecola Patch (both Hemiptera: Aphididae), are sympatric aphid species that are pests of apples (Malus spp.) and other crops. A. spiraecola has been shown to be significantly more tolerant to several insecticides compared with A. pomi. To establish the mechanisms contributing to this difference in insecticide response, clones of both species were collected from British Columbia, Canada, and Washington state. Dose–response bioassays were conducted to determine relative tolerances to the insecticides pirimicarb, dimethoate, and imidacloprid; these results have been reported previously. Samples of adult aphids from each clone were assayed for the activity of esterase enzymes often involved in the detoxification of insecticides. A. spiraecola had higher esterase activity compared with A. pomi; this was apparent for two model substrates, α-naphthyl acetate (α-NA) and α-naphthyl butyrate (α-NB). Aphid clones of both species collected from Washington had higher esterase activity than clones collected from British Columbia. Clones from both species and locations hydrolyzed α-NA to a greater extent than α-NB. Esterase activity measured with both substrates was significantly positively correlated with the relative response to pirimicarb and dimethoate; a significant positive correlation also was found for hydrolysis of α-NB and imidacloprid. The apparent involvement of esterases in the differential response of A. pomi and A. spiraecola to insecticides indicated that the choice of control chemicals for A. spiraecola should not involve chemistries that are metabolized predominantly by esterases.
Journal of Economic Entomology is published bimonthly in February, April, June, August, October, and December. The journal publishes articles on the economic significance of insects and is divided into the following sections: apiculture & social insects; arthropods in relation to plant disease; forum; insecticide resistance and resistance management; ecotoxicology; biological and microbial control; ecology and behavior; sampling and biostatistics; household and structural insects; medical entomology; molecular entomology; veterinary entomology; forest entomology; horticultural entomology; field and forage crops, and small grains; stored-product; commodity treatment and quarantine entomology; and plant resistance. In addition to research papers, Journal of Economic Entomology publishes Letters to the Editor, interpretive articles in a Forum section, Short Communications, Rapid Communications, and Book Reviews.