Imidacloprid ingestion alters the behavior of the natural enemy <i>Mischocyttarus cassununga</i> (Hymenoptera: Vespidae)

Neonicotinoid pesticides, while effective against pests, contribute to pesticide resistance, environmental contamination, and harm to beneficial arthropods. Social wasps provide valuable ecological services, such as pest predation and pollination, yet the effects of agrochemicals on their behavior and colony dynamics remain poorly understood. Here, we investigated the effects of lethal and sublethal concentrations (LC50 and LC10) of the neonicotinoid imidacloprid on the predatory social wasp Mischocyttarus cassununga. In controlled bioassays, we assessed individual- and colony-level responses using the pesticide at concentrations below the minimum label rate (1,800 mg active ingredient/L). We evaluated individual mortality, antifeeding effects, locomotion, and social interactions. The bioassays revealed a concentration-dependent mortality in foragers, with no evidence of feeding repellence or inhibition. Wasps ingested contaminated food regardless of the pesticide concentration, highlighting their susceptibility to oral exposure. Sublethal effects included impaired locomotion, marked by reduced walking distance, increased meandering, and more frequent stops, which likely affect their foraging efficiency. At the colony level, imidacloprid exposure reduced nest departures, trophallaxis, cell inspection, and aggression. These behavioral disruptions led to reduced overall colony activity, characterized by prolonged pause periods and general lethargy. Our findings demonstrate that imidacloprid disrupts key behaviors essential for colony maintenance, such as foraging, food distribution, and brood care. This study provides novel insights into imidacloprid's sublethal colony-level effects on social wasps. Given the widespread use of neonicotinoids and the ecological importance of social wasps, our results emphasize the need for more comprehensive ecotoxicological assessments to ensure that pest control strategies support the conservation of beneficial nontarget species.