Uptake and translocation of neonicotinoid insecticides in soybean and its influence on soybean aphid, Aphis glycines (Hempitera: Aphididae), feeding behavior

The soybean aphid, Aphis glycines Matsumura, is an important economic insect pest throughout much of the soybean-producing region of North America. Seed treatments containing the neonicotinoid insecticides thiamethoxam and imidacloprid have become increasingly popular even though inconsistent control has often been observed under field conditions. In this study, electronic penetration graphs (EPG) documented the effect of seed treatments on A. glycines feeding behavior. This research raised further questions about the chemical properties of seed-applied insecticides. Hence, the uptake and translocation of neonicotinoid seed treatments were explored at the Bayer CropScience research facility in Monheim am Rhein, Germany. Individual seeds were treated with [¹⁴C]imidacloprid or [¹⁴C]clothianidin. Randomly selected potted soybean plants were subjected to either low moisture stress or no stress conditions. Plants were harvested at the VC, V1 and V2 vegetative stages. Distribution of the radiolabeled compounds in the plant was visualized using phosphor-imaging technology. These images documented rapid systemic and acropetal movement through the xylem to the distal parts of the leaves. Concentrations were highest in the cotyledons, but remained present in the trifoliates of V2 stage plants. The presence of low moisture stress conditions appeared to significantly influence insecticide movement in the plant. Concentrations of radiolabeled material in the roots, stem, cotyledons and trifoliates are currently being quantified. Results of this study will be presented in the Student Competition at the 2013 NCB meeting in Rapid City, South Dakota.