Monday, December 10, 2007 - 8:41 AM

Indirect effects of imidacloprid on natural enemies of the boxwood spider mite, Eotetranychus buxi

Scott Creary, and Michael Raupp, University of Maryland, Department of Entomology, 4112 Plant Sciences Bldg, College Park, MD

Like several other ornamental plants, boxwoods treated with imidacloprid, a systemic neonicitinoid insecticide, exhibit increased damage associated with the boxwood spider mite, Eotetranychus buxi. Although reasons for these elevated populations of mites are not fully understood, a contributing factor could be that mites feeding on treated plants become toxic to their natural enemies. Mites raised on boxwoods treated with imidacloprid or untreated were fed to spider mite destroyers, Stethorus punctilum, and green lacewing larvae, Chrysoperla rufilabris. Feeding rates and mobility were compared between the two treatments. Stethorus punctilum and C. rufilabris consumed fewer mites per unit time when exposed to mites from treated rather than untreated plants. Stethorus punctillum presented with mites from treated plants also showed a lower mobility after 1 hour of exposure to the mites. Chrysoperla 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 imidacloprid-treated plants.

Species 1: Acari Tetranychidae Eotetranychus buxi (boxwood spider mite)
Species 2: Coleoptera Coccinellidae Stethorus punctilum (spider mite destroyer)
Species 3: Neuroptera Chrysopidae Chrysoperla rufilabris (green lacewing)