Abstract:

Imidacloprid, a commonly used insecticide, has been shown to adversely affect non-target insects at concentrations typically used in agricultural fields. While the bulk of studies have focused on the effects of imidacloprid on pollinators through ingestion, recent findings indicate that soil insects may also be at risk from direct contact with contaminated soil. Currently, there is no standardized approach for assessing the impact of pesticides on non-target soil insects with realistic field applications. In this study, we introduce a novel method designed to evaluate the effects of soil mediated contact exposure on the behaviour and survival of the soil-nesting ant species, Lasius neoniger. We found that exposing colonies to a soil drench representing 25% of the recommended imidacloprid application rate led to complete colony mortality. Furthermore, even minimal exposure levels—0.03% of the typical application rate—significantly decreased the ants' ability to move soil and halted colony growth altogether. These results mirror those seen in target insect species. Our testing method is both field realistic and replicable for evaluating the ecological risks of imidacloprid and potentially other pesticides. This new approach holds promise for advancing research in agricultural ecotoxicology across North America and may be adapted for use with other contaminants and other soil-nesting insects.