Monday, December 10, 2007 - 10:41 AM

Impacts of imidacloprid applications on non-target soil and litter arthropods in eastern hemlock forests

Wm. Nicholas Reynolds, wreynold@utk.edu1, Ernest C. Bernard, ebernard@utk.edu2, Rusty Rhea3, and J. F. Grant, jgrant@utk.edu2. (1) University of Tennessee, Entomology & Plant Pathology, 2431 Joe Johnson Drive, Room 205, Knoxville, TN, (2) University of Tennessee, Entomology and Plant Pathology, 2505 E. J. Chapman Drive, 213 Biotechnology Bldg, Knoxville, TN, (3) USDA Forest Service, Forest Health Protection, 200 Weaver Boulevard, Asheville, NC

Hemlock woolly adelgid (HWA, Adelges tsugae) is a major pest of eastern hemlock (Tsuga canadensis) in the U.S., and threatens this foundation forest species with extirpation in most of its native range. Imidacloprid (IMI), a broad-spectrum neonicotinoid insecticide, is widely and effectively used for control of HWA. The effect of this pesticide on non-target forest soil arthropod communities is unknown. In laboratory microcosms, an LD50 of 1.38 mg IMI / kg dry soil and an ED50 of 0.598 mg IMI / kg dry soil were observed for Folsomia candida (Collembola: Isotomidae). A replicated field experiment was established to determine the effects of four application methods and controls(imidacloprid soil drench, soil injection, trunk injection, and foliar horticultural oil spray) on soil arthropods and active ingredient availability. In the field, the LD50 and ED50 concentrations of imidacloprid in soil for F. candida were consistently exceeded in the drench plots, and less consistently so in the soil injection plots as determined by high-performance liquid chromatography (HPLC). Each quarter for two years, arthropods were extracted from soil cores. The microarthropods in soil drench plots had decreased richness and dissimilar species composition when compared to control plots. Mites comprised >50% of microarthropod abundance, and had no response to treatments. Collembolan species abundance, richness, evenness, and composition were severely impacted by the soil drench treatments. These results have implications for HWA chemical management by elucidating non-target impacts of common HWA application methods on soil microarthropods, which are important members of the decomposer food web.