The insecticide imidacloprid causes mortality of the freshwater amphipod Gammarus pulex by interfering with feeding behavior

This experiment evaluated the response of Gammarus pulex to imidacloprid under constant and pulsed exposures, as well as a starvation trial that did not include imidacloprid for comparison. The pulsed treatment groups were exposed to 90 µg/L of imidacloprid every 4 or 8 days for 14 days, and the constant treatment group was exposed to 15 µg/L of imidacloprid for 14 days. The 21 day experiments included pulses of 140 µg/L imidacloprid every 4 or 11 days, and a constant exposure of 15 µg/L. Immobile gammarids were removed and frozen for later internal imidacloprid analysis, and mobile gammarids were also sampled at the end of the treatment. Chemical stress modeling was applied to data on their mobility over time to discern if the pulsed treatments had a different mechanism for survival and mobility than the constant exposure. The constant 14 day treatment inhibited feeding, and the pulsed treatments showed a less pronounced effect. In the 21 day treatments, constant exposure reduced feeding but pulsed exposure did not. Internal concentrations of imidacloprid declined fairly quickly, with about 60% of the imidacloprid left after 2 days. The 21 day constant imidacloprid treatment also reduced lipid content in the G. pulex. From the results of their modeling, the authors show that there are likely different processes that govern mobility under constant and pulsed exposure scenarios, although they cannot rule out the possibility of the differences being caused by varying proportions of dead and immobile gammarids since the model treats them equally.

Nyman, A-M., A. Hintermeister, K. Schirmer, and R. Ashauer
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