Study of the translocation of thiamethoxam/mefenoxam seed treatments to soybean flowers

Neonicotinoids are a group of insecticides that have dominated the pesticide market during the last 19 years, and thiamethoxam is one of the most widely used neonicotinoids in the United States. Thiamethoxam, like other neonicotinoids, is highly water soluble with a low molecular weight. These characteristics allow the movement of the insecticide through plant vascular systems and the accumulation of the compound in vegetative and floral tissues. A possible link between honeybee Colony Collapse Disorder (CCD) and the use of neonicotinoids has raised questions concerning the risk of systemic pesticides to beneficial insects in several crops. Neonicotinoid residues have been identified in leaves and flowers of different crops including canola, corn, sunflower and cucumber. Currently, there is no information available on neonicotinoid residues in soybean floral tissue. Neonicotinoids are often applied in combination with systemic and non-systemic fungicides. However, the research on ecological risks of neonicotinoids has been focused on the analysis of these compounds without considering their interaction with other agrochemicals. The objective of this study is to identify the concentration of thiamethoxam in soybean flowers applied singly and in combination with the systemic fungicide mefenoxam. A field experiment with four treatments and four replicates was conducted. Treatments consisted of: thiamethoxam-mefenoxam, thiamethoxam only, mefenoxam only, and untreated seeds. Flowers were collected at reproductive soybean stages R1-R2. Quantification of the insecticides was done using liquid chromatography coupled to mass spectrometry analysis (LC-MS). The consequences of the translocation of thiamethoxam to soybean flowers on beneficial insects in soybean are discussed.