A novel method for testing the impacts of pesticide exposure on soil-nesting insects: a case study using the ant Lasius neoniger and the neonicotinoid insecticide imidacloprid

Soil nesting insects are exposed to soil drench pesticides via several routes of exposure, including through contact with the soil matrix. To date, only ∼20% of insecticide toxicity studies have investigated the impacts of insecticide exposure on non-target insects. Our study aims to address these gaps by creating a novel method for laboratory rearing and ecotoxicological testing using a native, agriculturally common North American soil-nesting ant, Lasius neoniger. We developed a novel soil bioassay method that tests both the acute and chronic effects of exposure to the neonicotinoid insecticide imidacloprid resulting from a soil drench applied to a sandy-loam soil commonly found in southern Ontario farms, to whole colonies of a soil dwelling eusocial insect, L. neoniger. This method could be applicable to a wide range of different pesticides, as a reliable, replicable, cost-effective tool for assessing contact toxicity in soil-dwelling insect ecotoxicology research. Our laboratory results show that soil drench applications of imidacloprid at levels below 0.06% (0.02202 μg/ml) of recommended application concentrations have deleterious sublethal or lethal impacts on L. neoniger. These impacts, following the soil drench application of imidacloprid, included significant reductions in motor function and soil excavation, and increased levels of queen and worker mortality.