Characterization of neonicotinoid uptake in seed-treated soybeans

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 have become an increasingly popular method for management of soybean aphids. Unfortunately, limited information is available on how these seed-applied insecticides are distributed throughout the soybean plant. The objective of this study was to document the uptake and translocation of neonicotinoid ([¹⁴C]imidacloprid and [¹⁴C]clothianidin) and butenolide ([¹⁴C]flupyradifurone) insecticides. At the VC soybean stage, plants were assigned to one of two moisture treatments: low moisture stress (≈40-60% soil moisture) or no stress (continuous water). Plants were harvested at the VC, V1 and V2 stages and distribution of the radiolabeled compounds in the plants was visualized using phosphor-imaging technology. All insecticides displayed rapid systemic and acropetal movement through the xylem to the distal parts of the leaves. Roots, stems, cotyledons, unifoliate and trifoliate leaves were then separated and combusted in order to quantify radioactive concentrations present in the plant parts. At all vegetative stages, concentrations were significantly greater in the cotyledons compared to the other plant tissues. Low moisture stress did not significantly impact the total amount of imidacloprid and flupyradifurone recovered in V1 and V2 soybeans. However, significantly less clothianidin was recovered from the low moisture stress treatment compared to the no stress treatment in V2 soybeans. Interestingly, concentrations for the three insecticides were similar between the low moisture stress and no stress treatments in the unifoliate and trifoliate leaves.