Acute toxicity of neonicotinoid insecticides to ground beetles (Coleoptera: Carabidae) from Pennsylvania.

Abstract

Predatory soil arthropods are under-represented in insecticide toxicity studies, severely limiting our understanding of how insecticides affect soil-invertebrate communities in agroecosystems. As a step toward addressing this issue, we conducted novel acute oral, topical, and soil-based toxicity assays on 9 ground beetle species (Coleopetera: Carabidae) in response to the neonicotinoid insecticides clothianidin, thiamethoxam, and imidacloprid. From these assays, we calculated 24 h TD50, TC50, LD50, and LC50 values, measured 24 h feeding activity, and recorded beetle survival for 7 d after exposure. Field-realistic oral, topical, or soil-based exposure to neonicotinoids rarely led to acute (<24 h) beetle mortality. Field-realistic topical and oral exposure of multiple tested species did, however, lead to significant sublethal effects-changes to mobility and feeding behavior-and decreased week-long survival. Under field conditions, carabids exposed to neonicotinoid sprays or contaminated food will be at higher risk of mortality from other factors (eg predation and starvation) which may affect their ability to contribute to biocontrol in agroecosystems. Similar toxicity assays with other carabid species, immature life stages, and additional taxa of predatory soil arthropods will further improve our understanding of how these insecticides affect soil-invertebrate communities in agroecosystems.