While soybean aphids did not pose as much of a threat in fields this summer as spider mites did, the saga of the aphid, which began in 2000, is now further complicated by a recent arrival of one of its natural enemies, a tiny Asian wasp, that was first spotted in Minnesota fields just last year.

The wasp species, Aphelinus certus, was initially studied in USDA and University of Minnesota (U of M) quarantine labs and was found to be effective in feeding on nearly every aphid species that it was offered. The wasp poses no threat to humans or any other organism besides aphids. However, the USDA and U of M made the decision to not release the wasp to control for aphids based on their findings.

“If we released this, it would pose a high risk to native aphids, so the decision was made not to release,” says Joseph Kaser, a U of M department of entomology graduate student and project lead.

This wasp was inadvertently introduced in the U.S. from an unknown source, and it was first noticed in 2005 in Pennsylvania. It has since been found in Canada, and last summer, in Minnesota. The wasp was again found in Minnesota this year, possibly due to the mild 2011/2012 winter weather.

“Now we’re trying to figure out if and to what extent it’s controlling the soybean aphid, and if it’s impacting other aphids,” Kaser says.

The U of M, in partnership with the USDA, successfully released a different species of wasp that preys on the soybean aphid. In 2007, they received permission to release the Binodoxys communis wasp species, which is native to China, and they started large-scale releases in fields that year. However, any parasitoid release requires a long and careful research process and USDA approval, which can take years. And the inadvertent introduction of the aphid’s enemies, such as the U of M and USDA-rejected Aphelinus certus, further complicates the process.

Finding alternatives

Research efforts to continue to fight the soybean aphid are promising, though. Another wasp species similar to Aphelinus certus was just named. The species, Aphilinus glycinis, originated in Korea and has proven to be particularly effective against soybean aphids in lab tests.

“It’s a super promising one, and we’re just one hurdle away from having a permit to release that one. In some ways, it’s more promising than Aphilenus certus,” says George E. Heimpel, PhD., principal investigator and director of graduate studies, U of M department of entomology.

Meanwhile, seed companies have begun releasing soybean aphid-tolerant varieties in the past few years to fight the pest. Initial control methods typically involved insecticides, but since 2000, seed companies have been developing varieties that deter and reduce the population of the aphids on soybean plants.

“As the issue escalated and became broader scale, that’s when Monsanto really stepped it up and said ‘hey, we need to do something to address this problem,’” says Tony White, Monsanto soybean product development manager. Monsanto released its Genuity Roundup Ready 2 soybean varieties for aphid control in 2011 and is working on a second-generation variety.

In the pipeline

As of now, seed companies have only released soybean aphid-tolerant varieties, which survive despite aphid feeding while maintaining good yields, but resistant varieties are still in the pipeline, says Steve Schnebly, DuPont Pioneer senior research manager, soybeans. Schnebly says DuPont Pioneer is a couple years away from developing early resistant varieties. Still, the resistant varieties likely won’t ward off every single soybean aphid without other management strategies, such as the use of insecticides and regular scouting.

“There’s not one management strategy that’s likely going to totally eliminate soybean aphids. The idea is really using a management strategy that uses several tactics, like biocontrol, insecticide, plant resistance and other ways,” says Megan Carter, masters research assistant, U of M department of entomology. “It’s an integrated pest management strategy.”