Effects of environmentally realistic concentrations of neonicotinoid insecticides on an aquatic invertebrate community

Neonicotinoid insecticides represent 24 % of the global market, and their use is increasing globally. Among them, clothianidin, imidacloprid, and thiamethoxam are widely used systemic insecticides, but are also used for lawn and garden care, and pest control. Residential usage has been linked to the occurrence of toxic level of pesticides in urban water bodies. Neonicotinoids are highly soluble in water and persistent in soil, and even though they are not intended for use in water bodies, they may enter in the aquatic compartment via spray drift, runoff or leaching, and contribute to downstream aquatic toxicity. Neonicotinoids interfere with the insect nervous system, and exhibit very high selectivity for insect nicotinic acetylcholine receptors. However, although insects appear to be the most sensitive, some studies have shown effects of neonicotinoids on the crustaceans Ceriodaphnia dubia and Daphnia magna, but also on honeybees and bumble bees, flies, and birds. Moreover, neonicotinoid contamination is likely to induce a top-down trophic cascade in a community dominated by invertebrate predators. Very little is known concerning the impact of neonicotinoid mixtures on the environment, and their combined toxicity on invertebrate community. Thus, our study aimed to test the effect of a mixture of imidachloprid, clothianidin and thiamethoxam on an aquatic invertebrate community at concentrations measured in the environment, and explore the community-level effects. The experiment was conducted in outdoor microcosms. The community was sampled before the insecticide application and throughout the month following the treatment. Environmental parameters (water temperature, pH, conductivity, chlorophyll a) were measured in every microcosm on each sampling date. Results will be discussed during the presentation. Keywords: neonicotinoid insecticides, mixture, aquatic invertebrates, community-leve