Toxicity of elm spider mites, Tetranychus schoenii, to their natural enemies on American elms treated with imidacloprid

Like several other ornamental plants, American elms treated with imidacloprid, a systemic neonicotinoid insecticide, exhibit increased damage associated with the spider mite, Tetranychus schoenii. Although reasons for these elevated populations of mites are not fully understood, a possible contributing factor could be that mites feeding on treated plants become toxic to their natural enemies. Mites raised on elms treated with imidacloprid or untreated elms were fed to spider mite destroyers, Stethorus punctilum, and green lacewing larvae, Chrysoperla rufilabris. Feeding rates and mobility were compared between the two treatments. S. punctilum and C. rufilabris consumed fewer mites per unit time when exposed to mites from treated rather than untreated plants. S. punctillum presented with mites from treated plants also showed a lower mobility after 1 hour of exposure to the mites. C. rufilabris exhibited a similar response after 2 hours. Disruption of feeding and mobility of natural enemies may help explain why spider mites become so numerous on plants treated with imidacloprid.