Population Densities of Tetranychus spp. (Acari: Tetranychidae) After Treatment with Insecticides for Amyelois transitella (Lepidoptera: Pyralidae)

Abstract

In field studies in four California almond orchards, effects of azinphosmethyl, carbaryl, diazinon, permethrin, flucythrinate, and cyfluthrin on abundance of web-spinning spider mites, Tetranychus spp., and their predators were compared. Except for trees treated with azinphosmethyl, those sprayed with each of the insecticides had a significantly greater abundance of spider mites than untreated control trees in the year of treatment. Only the trees treated in May with azinphosmethyl at one test site gave this result. During the year after treatment, population abundance of web-spinning spider mites on trees treated with only pyrethroids was significantly greater than on trees treated with the other insecticides or on untreated controls. Although numbers were low at each site, pyrethroid treatments tended to have greatest impact on predators during the year of application. In the year after treatment, predator populations were significantly greater on permethrin-treated trees in all but one location. Predator abundance was also greatest on trees treated with the two highest flucythrinaterates during the year following treatment. Results of this study suggest that use of pyrethroid foliar sprays on almonds may compromise California’s current spider mite management program.