The soybean aphid is one of the greatest recurring constraints to U.S. soybean production. An economic analysis of the impact of this pest on soybean production predicted that without effective plant resistance, a range of $3.6-4.9 billion could be lost annually. Our research identified and characterized the first known resistance to the aphid in soybean germplasm. We also mapped the first resistance genes (Rag1 and Rag2). The first commercial soybean cultivars with the Rag1 were grown on limited acreage in 2008, and are now widely grown. The United Soybean Board supported this research. Additional research on the soybean aphid is needed to determine the inheritance of virulence and to determine the effect of biotype-specific endosymbionts on virulence. We plan to improve average U.S. soybean yields by increasing the level of plant resistance to environmental stress, targeted pests and diseases in elite germplasm.

Achieving the objectives
• Several antibiotics were evaluated before proper treatments were devised to create endosymbiont-free aphid clones for testing
• Evaluation of the importance of endosymbionts to aphid virulence, or ability to overcome resistance showed that endosymbionts were not involved

Not achieving the objectives
• Some difficulties were encountered with maintaining live soybean aphid clone colonies. Throughout the study techniques at rearing and maintaining these clones were improved.
• Not all possible aphid biotype crosses have been made. So far those tested show a strong maternal influence for virulence, beyond that expected genetically.