Effect of host plant resistance and seed treatments on soybean aphids and natural enemies

The soybean aphid, Aphis glycines Matsumura (Hemiptera: Aphididae) is an important pest of soybean in the North Central region.  Management tools include resistant varieties and insecticidal seed treatments, used alone or in combination, which may have variable effects on different pest or natural enemy species.  We conducted a field study on aphid-resistant soybeans containing the Rag1 gene, with or without insecticidal seed treatment, in 2011 and evaluated the impact on soybean aphids and natural enemies.  Aphid-resistant Rag1 soybeans significantly reduced soybean aphids compared to controls.  Peak aphid densities were maintained below the economic injury level, and just above the economic threshold.  Inclusion of Rag1, thiamethoxam seed treatment, or both together, significantly reduced cumulative aphid days and significantly increased yield.  Rag1 soybeans, and thiamethoxam-treated soybeans were found to have lower natural enemy populations than in the controls.  Harmonia axyridis Pallas and Orius insidiosus Say were the dominant predators in the study.