Effects of neonicotinoid seed treatments on soybean aphid (Aphis glycines) feeding behavior and soybean physiology

The soybean aphid, Aphis glycines Matsumura, is an important economic insect pest throughout the soybean-producing region of North America. Neonicotinoid seed treatments have grown in popularity; however, efficacy under field conditions has remained inconsistent. This research investigated A. glycines feeding on thiamethoxam-treated soybeans using electronic penetration graphs (EPG). Aphid feeding was recorded continuously for 9 h on V2 and V4 (second and fourth trifoliate, respectively) soybean plants. Significant differences in pathway, xylem, and sieve element feeding were not detected among the treatments. These results suggest early exposure (< 9 h) to seed treatments has no effect on aphid feeding. In a subsequent study, thiamethoxam-treated soybeans were evaluated for efficacy against Biotype 1 soybean aphids under growth chamber conditions. At all time points evaluated (4, 8 and 11 days after aphid introduction), thiamethoxam-treated soybeans had significantly fewer aphids compared to untreated plants. This research represents the first report of A. glycines feeding behavior after initial exposure to thiamethoxam-treated soybeans.