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Biocontrol Option for Soybean Aphid Tested

A program supported by university researchers, farmers and soybean groups is introducing tiny parasitic insects to control soybean aphids in South Dakota and neighboring states.

South Dakota State University soybean research and Extension entomologist Kelley Tilmon said there have been 10 releases of the insect, Binodoxys communis, at points in eastern South Dakota since the program won federal and state approval to proceed in 2007.

Tilmon is part of a group of 14 scientists from five north central states and the U.S. Department of Agriculture who are overseeing the Binodoxys communis release in South Dakota and the larger region.

“The thing to understand about these releases is that they’re not mass releases of insects like butterflies at a wedding,” Tilmon said. “Rather, these are small inoculations at various points with the hope that over time, a population will become established in that area and ultimately spread from there to soybean fields throughout the state.”

In the long term, Tilmon said, the insects could make it necessary to use pesticides less often to control soybean aphid, an insect from Asia that was first discovered in the U.S. in 2000.

“Soybean aphid is actually seldom a pest in Asia, largely because there is a large suite of natural enemies that are particularly adapted to prey upon the soybean aphid,” Tilmon said.

“This is a very common pattern: When an herbivorous insect — something that’s going to be a crop pest — gets in accidentally, it usually gets in without the natural enemies that help control it in its land of origin, and as a consequence, usually becomes a much larger pest in the new range than in its native range.”

One solution, Tilmon said, is to try to restore that balance by what’s called “classical biological control.” In this case, scientists performed research in the soybean aphid’s native range, evaluated enemies of the pest insect and selected some for further study.

University of Minnesota entomology professor George Heimpel said scientists brought several parasitoids back to a federally-approved quarantine lab at the University of Minnesota, specially designed to prevent accidental release.

The parasitoids pose no threat to humans or pets, but scientists wanted to evaluate whether they would harm other aphids besides the soybean aphid.

At the Minnesota quarantine lab, researchers selected one that preys almost exclusively on soybean aphid. Scientists filed an application with the U.S. Department of Agriculture in January 2006 for permission to release the parasitoid.

Permission was granted in April 2007, after two experts from the U.S., two from Canada and two from Mexico gave approval.

Tilmon said because Binodoxys communis is a soybean aphid specialist, it’s not likely to cause problems for other non-pest insects. In addition, the parasitoid doesn’t stray far from the habitat of its host insect, making it unlikely to become a nuisance for humans.

“These parasitoids are wasp relatives,” said Tilmon.

“They’re in the same family as wasps, but they’re not wasps in the sense that we think of large, stinging creatures. These are really more the size of gnats,” she described.

“I measured one once and it’s about the size of a comma at the end of a sentence in your typical printed text. They are biologically incapable of stinging people.”

As part of its reproduction cycle, Tilmon said the female Binodoxys communis deposits an egg inside a living aphid. The egg hatches into a larva that feeds inside the aphid. The aphid eventually dies and forms a protective shell or “mummy” around the developing parasitoid pupa. The adult parasitoid then exits, leaving the mummified aphid shell behind.

Tilmon cautioned that only about half of the parasitoid introduction attempts over the decades have resulted in successful establishments. Even if the Binodoxys introduction is successful, it won’t mean that producers need to stop monitoring for soybean aphid and using pesticides to control aphid, but it may mean they’ll need to spray less often. And if Binodoxys gets established, whatever biological control it provides will be free; producers won’t have to pay year after year for it.

The South Dakota Soybean Research & Promotion Council helps fund Tilmon’s ongoing work.

"For soybean farmers, I think it will be very helpful to have more options to control soybean aphids,” said Astoria producer David Iverson, chairman of the South Dakota Soybean Research & Promotion Council.

“Currently farmers can control aphids with pesticides,” he said.

“To have the aphid population reduced with natural predators would be great for soybean producers and good for the environment as well. We are fortunate to have Kelley Tilmon doing this type of research.”

In addition, the North Central Soybean Research Program and the Iowa Soybean Association use checkoff dollars to support the biological control project against soybean aphid. The NCSRP was recently nominated for the International IPM Achievement Award for supporting this regional project, which has resulted in releases in seven states.

In South Dakota, it’s a collaborate effort involving not only SDSU research, but also the South Dakota Cooperative Extension Service and South Dakota farmers. “Seven out of our 10 release sites were done with the cooperation of Extension educators in their respective counties, and they were done with the cooperation of soybean producers on their farms,” Tilmon said.

“The soybean producers donated the space to set up the release points and have helped to get this project going.”

“It’s really nice that this project has involved not just the university, but also the grassroots of the soybean producers in the state.”

As a result of her research and Extension work on several fronts, Tilmon won the Sherwood and Elizabeth Berg Faculty Award for 2007, given to an SDSU faculty member in the early stages of a career.

Tilmon used the award to help fund her travel to attend the International Congress of Entomology in Durban, South Africa, in 2008. The congress meets every four years in a different part of the world. Tilmon presented work on the Binodoxys communis project at the conference.

Heimpel notes that the University of Minnesota’s quarantine lab and a USDA-sponsored quarantine lab in Delaware are studying two other parasitoids for possible release against soybean aphid.

SDSU soybean research entomologist Kelley Tilmon scouts for soybean aphid eggs on a host plant, buckthorn, in early spring.

SDSU soybean research and Extension entomologist Kelley Tilmon raises the parasitoid Binodoxys communis in an SDSU greenhouse for release in South Dakota soybean fields. The parasitoids are natural enemies of soybean aphids.

Jeanne Jones Manzer | Newswise Science News
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