Imidacloprid perturbs feeding of Gammarus pulex at environmentally relevant conditions

The authors explored individual feeding rates of Gammarus pulex during and after a four day exposure to imidacloprid. Exposures were designed to represent 0.2-20% of the 96 hour LC50 and were 0.81 µg/L, 2.7 µg/L, 9.0 µg/L, 30 µg/L, and 100 µg/L. The gammarids were exposed to imidacloprid for four days and then had a three day recovery phase. Gammarid feeding was inhibited in the exposure phase with increasing concentration, with significant impacts at concentrations greater or equal to 30 µg/L (this could not be explained by an inability to reach the food due to immobility as gammarids were always observed to be in contact with the leaf disks). During the recovery phase, gammarids that did not show significant effects during the exposure phase (0.81 µg/L, 2.7 µg/L, and 9.0 µg/L) ate significantly more food than they did during exposure. The observed compensational feeding could result directly from feeding impacts or from additional energy requirements, such as detoxification. One limitation of the experimental design they noted was that the feeding rate of individuals was not stable throughout the week, so the design would need to be altered for longer experiments. Effects on feeding were seen at concentrations two orders of magnitude lower than those that caused mortality, suggesting that low-level contamination could pose a risk. The researchers noted that changes in gammarid feeding at low doses of imidacloprid seen in this study could impact leaf litter breakdown and lead to shifts in the population and the ecosystem. Multiple pulses of imidacloprid may also affect G. pulex more because of their relatively long lifespan.

Agatz, A., R. Ashauer, and C.D. Brown
Environmental Toxicology and Chemistry
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