Effects of low-doses imidacloprid pulses on the functional role of the caged amphipod Gammarus roeseli in stream mesocosms

The authors examined the long-term effects of imidacloprid on Gammarus roeseli shredding efficiency. Crustaceans like gammarids are less sensitive to imidacloprid than insects in short-term toxicity tests, so the authors wanted to evaluate chronic impacts. The 70-day experimental length included the second generation offspring from the initial individuals. The experimental design was a stream microcosm including gammarids and different litter materials (alder leaves and straw) that were dosed with 12-hour weekly pulses of 12 µg/L imidacloprid. They did not identify an effect of the imidacloprid pulses on population growth or litter decomposition, but there was a reduction in the number of brood carrying females in the last three weeks. This decline in brood carrying females appeared before the end of the second pulse series and continued through the end of the experiment. The reduction could indicate delayed reproductive effects of imidacloprid pulses that would eventually impact the population, and thus their functional role as shredders.