Hemlock woolly adelgid (HWA, Adelges tsugae) is a major pest of eastern hemlock in the U.S., and threatens the existence of this important forest species. Imidacloprid, a broad-spectrum neonicotinoid insecticide, is widely and effectively used for control of HWA. The effects of this pesticide on non-target forest arthropod communities are unknown. A replicated field experiment was established to determine the effects of four application methods (imidacloprid soil drench, soil injection, trunk injection, and horticultural oil foliar spray) on soil arthropods within the drip line of hemlocks. Untreated trees in each block serve as controls. Each quarter, active surface arthropods are collected with pitfall traps and soil arthropods are extracted with high-gradient Tullgren-type funnels. For each replicate, imidacloprid is extracted from soil and quantified with high performance liquid chromatography. In the first six months of this study, numbers of soil arthropods, primarily Collembola and Acari, were lower in soil drench and soil injection treatments than in the other treatments, and these two treatments also had higher imidacloprid concentrations, which were negligible in the other treatments. Both Collembola and Acari are being identified to species level to estimate individual sensitivities to imidacloprid. Other aspects of this research now in progress are the deployment of litter bags to assess the effects of imidacloprid on litter turnover and the determination of lethal doses (LD50) of imidacloprid for several species of edaphic Collembola.