Biochemical and Behavioral Responses in the Killer Shrimp Dikerogammarus villosus Following Acute Exposure to Thiacloprid and Calypso®.

Neonicotinoids are insecticides that are used globally and can persist in soil and surface water, posing a threat to ecosystems. In this study, we exposed the invasive freshwater amphipod Dikerogammarus villosus to environmentally relevant and relatively high concentrations of thiacloprid, a widely used agricultural neonicotinoid active ingredient and its commercial form Calypso® for two days. The acute effects were investigated at the behavioral (immobility time) and biochemical [glutathione S-transferase (GST) and acetylcholine esterase (AChE) activity] levels. Calypso® concentrations of 10 µg/l and 100 µg/l a significantly increased the immobility time, while thiacloprid exerted such an effect only at 100 µg/l. The GST enzyme activity did not change in the thiacloprid-treated groups; however, the 10 µg/l and 100 µg/l Calypso® concentrations significantly increased the GST activity. All Calypso® concentrations significantly decreased AChE activity until the highest Calypso® concentration was reached, and an interesting outcome was the 'U-shaped dynamics' of AChE activity. In contrast, thiacloprid had no significant blocking effect on AChE activity at any of the concentrations tested. Neonicotinoid insecticides are neurotoxins that selectively target nicotinic acetylcholine receptors in the insect central nervous system. However, their widespread use has a growing impact on nontarget animals. This study confirms the risk of neonicotinoids to aquatic invertebrates by providing evidence that neonicotinoids can also affect both behavioral and biochemical processes in D. villosus.