Long-term impacts of a single uptake of imidacloprid on brood care and reproduction in ant founding queens

Ants are key components of most terrestrial habitats and contribute to various ecosystem services. They live in social colonies composed of reproductive (males and queens) and non-reproductive (workers) castes. Most ant colonies are founded independently by a single queen directly after the mating flight. Any pesticide-induced impairment during the critical founding period can have long-lasting consequences for colony establishment and growth, yet empirical data on pesticide effects on colony founding ant queens are absent.,We experimentally addressed this knowledge gap by orally exposing founding queens of the common garden ant, Lasius niger, once to the neonicotinoid imidacloprid and quantifying early (3 weeks) and delayed (12 weeks) effects. Queen survival was significantly reduced at high doses. Egg production of surviving queens decreased during the first two weeks, whereas egg size remained unaffected. Sublethal effects persisted, with treated queens showing significantly reduced reproductive output, likely due to impaired brood care behaviour that resulted in inadequate prevention of mite infestation and increased egg and larval mortality.,Our findings demonstrate for the first time, long-term effects of a single exposure to imidacloprid on reproduction and brood care behaviour in colony founding L. niger queens. These results highlight the complex and potential long-term impacts of pesticides on social insect colonies and indicate that standard short-term assessments may fail to detect such effects. Our results show that behavioural effects, such as reduced brood care, can impose long-term effects which are rarely considered in current risk assessments for e.g. pesticides and insecticidal proteins in genetically modified crops.