Thiamethoxam Toxicity and Effects on Consumption Behavior in Orius insidiosus (Hemiptera: Anthocoridae) on Soybean

Neonicotinoid residues can be present in soybean vegetative tissue, prey insects, and flower tissues, possibly making them toxic to pollinators and natural enemies. Baseline information on the toxicity of neonicotinoids to beneficial insects other than pollinators through multiple routes of insecticide exposure is limited. The objectives of this study were 1) to evaluate the toxicity of thiamethoxam to the hemipteran predator, Orius insidiosus Say, exposed to residues through treated vegetative tissue and insect prey, and 2) to evaluate the effect of thiamethoxam on the abundance of this predator species in soybean fields. Predators were exposed to thiamethoxam in soybean leaves and Aphis glycines Matsumura using a systemic bioassay. Abundance of the predator was evaluated in thiamethoxam seed-treated fields during two different soybean seasons. Our results indicate that concentrations required to kill >50% of the evaluated insects were higher than the concentrations that the insects are likely to encounter in the field. Consumption of A. glycines by O. insidiosus was affected at 10 ng/ml and 5 ng/ml of thiamethoxam at 24 h of evaluation. There was significant mortality for O. insidiosus at 24 h after exposure to thiamethoxam-treated aphids at these concentrations. In soybean fields, there were no significant differences in O. insidiosus number between the plots treated with thiamethoxam and the control. Thiamethoxam may have significant effects on the predators if O. insidiosus feeds on early soybean vegetative tissue or contaminated prey. These results suggest that the compatibility of thiamethoxam with IPM programs for A. glycines needs further evaluation.