Macroinvertebrate community response to repeated short-term pulses of the insecticide imidacloprid

This study examined stream mesocosms in the same design as Berghahn et al. 2012 to identify impacts from multiple imidacloprid pulses. Imidacloprid was applied in three consecutive weekly 12h pulses of 12 µg/L. Neureclipsis spp. caddisflies were the most sensitive and reacted to the first pulse, while other larvae including ephemerids and dipterans only reacted negatively after repeated pulses. Total abundance of all macroinvertebrates did not show a significant response to imidacloprid, but some taxa showed abundance effects, including a significant difference in Tanypodinae abundance. Emergence was significantly reduced in the treated mesocosms, with ephemerids displaying the strongest effects. Gammarus roeseli abundance was not affected, and they appeared to be able to detoxify the imidacloprid in the 7 days between pulses. The dipteran and ephemerid larvae declined more after the second and third pulse in each series, indicating that they may not be able to detoxify imidacloprid in 7 days.