Is Actara® a less toxic neonicotinoid formulation? A multigenerational study using the non-target organism Chironomus xanthus.

Neonicotinoids are highly consumed systemic insecticides that mimic acetylcholine (ACh) with a specific mode of action at the nicotinic acetylcholine receptors (nAChRs). The insecticide Actara® (active ingredient thiamethoxam- TMX) is a commercial formulation widely used for the control of various agricultural pest species. However, negative effects of TMX have been observed in non-target organisms. This work aimed to evaluate the biological effects of the commercial formulation Actara® on the aquatic non-target and non-biting larvae of Chironomus xanthus (Diptera). The lethal (LC 50 ) and sublethal (body length, head capsule width, cumulative emergence, and mean time to emergence-EmT 50 ) effects were determined in two subsequent generations (P and F1). The estimated 48 h LC 50 for C. xanthus larvae exposed to Actara® was 73.02 µg TMX/L. By looking at the sublethal effects of Actara on the life cycle parameters of C. xanthus, we determined that none of the concentrations used induced a significantly different response in the organisms, compared to the control treatment (NOEC > 2 µg TMX/L). However, the head capsule width in the parental (P) generation exposed to Actara (≥ 0.9 µg TMX/L) was significantly bigger than the head capsule width of control animals. Overall, our results highlight that, at environmentally relevant concentrations, the commercial formulation Actara® is non-toxic to C. xanthus.