Effects of two nAChR agonists on wood ants: acetamiprid induces lethality and immediate hypoactivity, while flupyradifurone causes time-delayed hyperactivity

Neonicotinoids and related compounds, such as acetamiprid and flupyradifurone, are widely used in agriculture to control pest insects. Due to their broad mode of action, their effects are not restricted to target species, potentially causing harm to other animals as well. Investigating these effects on non-target organisms is crucial for environmental protection, biodiversity conservation, and ecosystem sustainability. In the present study, we examined lethal and sublethal effects of acetamiprid and flupyradifurone on wood ants (Formica polyctena), a key species in wood ecosystems, within a dose range of 0–30 ng active substance/mg body weight (ng a.s./mg bw). Acetamiprid significantly reduced survival at doses above 143 ng/individual (equivalent to > 10 ng a.s./mg bw) with an LD50 of 323.4 ng/individual at 72 h (equivalent to 23.1 ng a.s./mg bw). Moreover, acetamiprid induced tremors and comatose states and restricted ant mobility with significantly reduced distances and lower walking speeds. Flupyradifurone exhibited less severe effects on survival and physical condition but induced a time-delayed hyperactivity 48 to 72 h post-treatment. In summary, these findings suggest distinct impacts of two nAChR agonists, acetamiprid and flupyradifurone, on Formica wood ants and emphasize the importance for species-specific research across a diverse array of organisms, particularly in the context of risk assessment.