Interactions of biological control, host plant resistance, and seed treatment in soybean aphid management

The soybean aphid, Aphis glycines, is a major economic pest of Midwest soybean, and several control options are currently available for soybean aphid management.  Understanding how these control options interact with one another is a critical component in developing an effective soybean aphid integrated pest management (IPM) plan. We investigated the interactions of three aphid management options – Rag1 host plant resistance, neonicotinoid (thiamethoxam) seed treatment, and biological control in both the laboratory and field. In lab we conducted survival studies of the predator Orius insidiosus on Rag1 resistant and seed-treated soybean.  We reared O. insidiosus adults on field-collected leaves to assess treatment survival effects.  In field we conducted a two-year trial with replicated plots to examine the response of natural enemy abundance to Rag1 resistance and seed treatment. Whole-plant aphid counts were utilized to estimate aphid abundance, and sweep nets and visual observations were used to estimate natural enemy abundance.  Survival study results demonstrated no significant treatment effect on survival  of O. insidiosus.  Field results demonstrated that Rag1 resistance and seed treatment did slow development of aphid populations, and aphid abundance was consistently lowest in plots combining both Rag1 resistance and seed treatment.  Natural enemies, however, did not demonstrate a consistent treatment response to either Rag1 resistance or seed-treatment over the 2-year study.  These results indicate neither Rag1 host plant resistance nor thiamethoxam seed treatment are negatively impacting soybean aphid biological control, further indicating that these management options can successfully be utilized together in a soybean aphid IPM plan.