Resistance of Greenhouse, Laboratory, and Native Populations of Western Flower Thrips to Spinosad

Abstract

Western flower thrips (Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae)] collected from greenhouse, laboratory, and native populations were evaluated for resistance to the insecticide spinosad. Individual cut stems of transvaal daisy (Gerbera jamesonii H. Bolus ex Hook. f.) were inoculated with 25 adults from 1 of 9 thrips populations and maintained in isolation chambers. Treatments of no spray, water spray, spinosad at one-half label rate (0.41 mL·L-1) and spinosad at the recommended label rate (0.81 mL·L-1) were applied to the flowers. Three days after treatment, the number of live and dead thrips was recorded. Significantly more thrips were recovered from the control treatments than the spinosad treatments. Thrips survival varied by treatment and insect population. Based on an odds ratio analysis, the likelihood of recovering live thrips was greater in the IL-GH1 (Illinois greenhouse) population than in the NV-N1 (Nevada native) reference population for both spinosad treatments, suggesting resistance to spinosad in the IL-GH1 population. The IL-GH1 population was collected from a greenhouse regularly sprayed with spinosad whereas the NV-N1 population was collected in Incline Village, Nev., on wildflowers with no history of exposure to spinosad. This is the first documented indication of spinosad resistance in a thrips population. In comparison to the NV-N1 reference population, none of the populations collected from laboratory or native nonagricultural environments exhibited evidence of resistance to spinosad. Resistance to an insecticide with a novel mode of action, such as spinosad, indicates the necessity of rotating insecticides and implementing alternative methods of managing western flower thrips. Chemical names used: spinosad including spinosyn A and spinosyn D (Conserve SC).