Residues of thiamethoxam/mefenoxam in soybean plants and potential effects non-target insects

During recent years, serious concerns have been raised among the scientific community and public in general on the impact of neonicotinoids seed treatments on beneficial insects in soybean crops. Negative impacts on beneficial arthropod communities are based on the hypothesis that neonicotinoid residues can be present in vegetative tissue, host insects and floral tissues, making them toxic to pollinators and natural enemies. Neonicotinoids are commonly used in combination with a variety of systemic fungicides. However, few studies have examined the impact of seed treatment mixtures on beneficial insects. Although fungicides have generally low acute toxicity to insects, they can have synergistic, additive or antagonistic effects, increasing or reducing the toxicity of insecticides on beneficial insects. In this study, we evaluated the translocation of thiamethoxam and mefenoxam applied as seed treatments in soybean crops and the potential toxicity of this mixture on beneficial insects. Field studies were performed by monitoring O. insidiousus and Chysoperla sp. on soybean fields treated with thiamethoxam alone, and in combination with the fungicide. Residues analysis were performed to identify the concentrations of the insecticide and the fungicide in soybean flowers and leaves from different soybean fields in Nebraska. We found low concentrations of thiamethoxam and clothianindin in flowers and higher concentrations of both compounds in soyben leaves.  Mefenoxam was detected at very low concentrations in the analyzed samples. Our results suggest that the addition of mefenoxam to thiamethoxam seed treatments in soybean do not pose a significant risk to the evaluated non-target species.