Soybean Aphids are Resistant to Pyrethroids, Now What? Webinar

Soybean aphids have been a challenge for Midwest soybean producers since 2000, but farmers were able to manage them relatively well using insecticides. However, by 2015, insecticide controls like pyrethroids were starting to fail, and resistance was suspected.

Dr. Matt O’Neal’s and his research team have been working to confirm resistance and map the spread. There are two main ways to confirm resistance: collect live aphids, provide them with insecticide-treated soybean leaves and observe the result or perform a DNA analysis and look for specific molecular markers that are present in resistant populations.

Confirming Soybean Aphid Resistance

From 2021 to 2023, O’Neal’s team surveyed soybean fields before and after pyrethroid applications. The results were apparent: there was no difference in the number of infested plants or the number of aphids per plant after spraying. DNA testing was used to confirm that resistance was present and showed that 99.9% of soybean aphids in Iowa carry at least one mutation that makes them resistant to pyrethroids.

Even more striking were the results that came from the experimental control, which received no pyrethroid spray application. The number of aphids actually decreased. Researchers have seen this result before, and they believe it occurs because the natural predators help reduce aphid populations—when they aren’t killed by insecticide applications. However, when the spray kills the aphid’s natural insect predators, the aphids continue to thrive. At this point, spraying pyrethroids can make the soybean aphid infestation worse.

Now What?

Besides insecticides, there are two other strategies for managing soybean aphids: planting aphid-resistant soybean varieties and using biological controls like parasitoid wasps. Aphid-resistant soybean varieties include at least one “resistance against Aphis glycines” (RAG) gene. Several RAG genes have been developed, and ideally, farmers should look for a soybean variety that has at least two RAG genes. This will provide excellent protection against soybean aphids. These resistant soybean varieties may be difficult to find, but they offer a long-term, sustainable solution.

Other insecticides, such as thiamethoxam, pyrifluquinazon, and chlorpyrifos may still offer some protection, but they come at a higher cost. Not only do these options have a higher price, but they come with more risks to people and the environment as well.

For more information about soybean aphids and aphid migration tracking, check out the Suction Trap Network and Iowa State’s Integrated Crop Management website.

Presenter