Western Flower Thrips (Thysanoptera: Thripidae) Resistance to Insecticides in Coastal California Greenhouses

Abstract

Field populations of western flower thrips, Frankliniella occidentalis (Pergande), showed high levels of resistance in laboratory tests to four classes of insecticides Commonly used for insect control in ornamentals. The resistance ratios (RR at LC90) to the pyrethroids permethrin and bifenthrin were very high, ranging from 138-fold (Bifenthrin, San Diego-1 [SD-1] location) to 8,716-fold (Permethrin, SD-1) Compared with a susceptible strain (UC89). Piperonyl butoxide significantly synergized permethrin up to 50-fold (SD-2), indicating that mixed-function oxidizes are a Cornponent of the overall resistance mechanism. There was moderate to high intensity of resistance to methomyl, a carbonate; RR values ranged from 41-fold (SD-1) to 378-fold (SD-2). Field resistance to chlorpyrifos, an organophosphate, was Comparatively low, with the RR values ranging from 17-fold (Santa Barbara-2 [58-2]) to 31-fold (SD-2). Although not registered for western flower thrips control, abamectin (a macro cyclic lactone) showed low to high levels of resistance (RR values ranging from 18-fold [SD-1] to 798-fold [S8-1]). The development of resistance to abamectin is the first documented case of resistance to this chemical in the field. In a separate field trial conducted at SB-1, all the chemicals tested including chlorpyrifos (microencapsulated formulation) performed poorly. Maximum adjusted control was only 53% (Pounce), confirming the field failure for all the insecticides tested at this greenhouse. Resistance to Commonly used insecticides and the likelihood of losing many more registrations emphasize the need for better and practical pest management strategies.