Toxicity of thiamethoxam seed treatments on key natural enemies of soybean aphid

Thiamethoxam is a widely used neonicotinoid compound applied as a seed treatment in soybean crops. During the last few years there has been a growing concern about the impact of thiamethoxam on beneficial insects in soybean crops. Negative impacts on beneficial arthropod communities are based on the fact that neonicotinoid residues can be present in soybean vegetative tissue, host insects and flower tissues making them toxic to pollinators and natural enemies. Therefore, the risk characterization of neonicotinoids to natural enemies needs to be developed through the evaluation of multiple routes of exposure to the insecticide. The objective of this study was to evaluate the toxicity of thiamethoxam on key natural enemies of soybean aphid exposed to residues in vegetative tissue and in insect prey. To achieve this objective, the predators Orius insidiosus and Crysoperla rufilabris where exposed to different concentrations of thiamethoxam in soybean leaves and in soybean aphid using different laboratory methodologies. The results show that the concentrations required to kill more than 50% of the evaluated insects were higher than the concentrations that the insects are exposed to in the field. The influence of the laboratory bioassay methodologies in the evaluation of the toxicity of neonicotinoids on natural enemies is also discussed.