Impact of Hemlock Woolly Adelgid Imidacloprid Treatments on Water Quality and Aquatic Macroinvertebrate Communities

Imidacloprid treatments are used in integrated pest management (IPM) programs for the suppression of hemlock woolly adelgid (Adelges tsugae [Annand]) (HWA) (Hemiptera: Adelgidae). As part of a retrospective analysis of Great Smoky Mountains National Park’s (GRSM) HWA IPM program, the presence of imidacloprid and possible effects on aquatic macroinvertebrate communities in streams associated with HWA imidacloprid treatment areas were assessed.

Ten conservation areas in which hemlocks in riparian areas were given soil imidacloprid applications were selected.  Stream sampling sites were chosen upstream and downstream from each conservation area, for a total of ten paired upstream – downstream sites.  Surface water samples and aquatic macroinvertebrate samples were collected from each sampling location.

Concentration of imidacloprid in parts per trillion (ppt) was determined using liquid chromatography mass spectroscopy (LC/MS).  Aquatic macroinvertebrate communities were assessed as indicators of water quality.

Imidacloprid was detected in seven of ten downstream locations.  Concentrations ranged from 28.5 to 379 ppt, which are below USEPA chronic and acute aquatic macroinvertebrate aquatic life benchmarks.  Aquatic macroinvertebrate taxa from upstream and downstream sites were similar. While potential impacts of HWA imidacloprid treatments on surface water quality are minimal, the extent of treatments should be carefully considered for overall system health.