Protecting Soybeans from Aphids, as Easy as (Rag) 1, 2, and 3
Although soybean aphid can be patchy within fields and between growing seasons, it is considered the most economically important Iowa soybean insect pest since 2000. Soybean aphid can significantly reduce yield, and therefore regular scouting and timely foliar insecticides have been the primary way to protect yield. Advances in soybean breeding have produced varieties with single, double and triple gene combinations of soybean aphid host plant resistance. These naturally-occurring genes dramatically suppress aphid populations and will reduce the reliance of insecticides in soybean. Farmers using aphid-resistance genes will save on input costs and minimize negative effects to pollinators and beneficial insects associated with insecticides.
During 2016, we focused on two objectives. Objective 1 (Screen new aphid-resistant gene combinations) required laboratory testing for biotype survival on new Rag gene combinations. We maintain four soybean aphid biotypes at Iowa State University and have sufficient growth chambers to test these biotypes on aphid-resistant varieties. Replicates of each variety were artificially infested in the vegetative stage (V2-3) with 5 aphids and their population growth was measured over 14 days. Objective 3a (Small cage studies) takes the top-performing aphid-resistance varieties outside. We used caged plants to evaluate aphid performance. Soybean aphid infestations can be highly variable in both time and place, and therefore, using caged plants ensures the data can be collected every growing season. This approach included growing plants in small plots, caging ten plants with mesh around a PVC frame, and artificially infesting caged plants with field-collected aphids. We compared four Rag gene combinations, or treatments, with all four soybean aphid biotypes. Each variety x biotype treatment was compared with “caged” and “uncaged” replications. In total, there were 64 plants at each location where aphid abundance was measured for several weeks.
We completed Objective 1 in 2016. Our results confirm that the Rag1+2+3 pyramid effectively manages all known soybean aphid biotypes. Our results indicate that Rag1+2+4 would be an effective management option for biotype-1, biotype-2, and biotype-3 soybean aphid, but had a negligible impact on biotype-4. We also completed the first year of work for Objective 3a in 2016. Soybean aphid responded to resistant gene combinations similar to the laboratory testing. A second summer of work in 2017 will confirm our findings.
Impacts and Contributions/Outcomes
A journal manuscript summarizing Objective 1 was prepared and submitted to the Journal of Economic Entomology in March 2017. Erin Hodgson also was actively presenting and writing about host plant resistance for soybean aphid to farmers and people working in agriculture (2 Extension proceedings, 2 Extension newsletter articles, 15 Extension presentations, and 1 Extension Videos). Preliminary results from Objective 3a indicate aphid-resistant soybean suppressed the aphid population.