Do aphid resistant soybeans affect natural enemies of the soybean aphid?

The soybean aphid, Aphis glycines Matsumura, is a major pest of Midwest soybean production. Management of this pest often relies on integrated pest management (IPM), however the compatibility of different management options is not always known. The recent development of aphid-resistant soybean varieties, such as those containing the Rag1 gene, has provided another tool for soybean aphid management, but whether resistant varieties are compatible with conservation of natural enemies is not yet known. A field study was conducted in summer 2009 at Rosemount, MN to investigate the effects on natural enemy populations of Rag1 resistant soybean in comparison to three foliar insecticides: the commercial standard insecticide lambda cyhalothrin and the two biorational insecticides spirotetramat and pyriproxyfen. Based on cumulative aphid days (CAD), spirotetramat demonstrated comparable aphid suppression to the standard insecticide, while Rag1 resistant plots showed intermediate control compared to the untreated control. Mean density of total natural enemies was higher in the untreated control compared to all treatments, although this trend was not consistent within individual guilds of natural enemies. In comparison to all insecticide treatments, Rag1 plants averaged higher parasitoid numbers but lower numbers of coccinellids and Orius insidiosus.