BROOKINGS, S.D. -- South Dakota State University researchers put out tiny Asian parasitic wasps at a dozen sites across eastern South Dakota this year to see if they have an impact on soybean aphids.
Kelley Tilmon, SDSU extension and research entomologist, says the Binadoxis communa, a stingless wasp, is a natural predator for the soybean aphid and might be part of the battle against it.
"The idea of classic biocontrol is to introduce (crop) pests that may have left some its natural enemies behind in its land of origin," Tilmon says. "You explore in its native area to find out what the specialist natural enemies that focus on it."
Parasitoids aren't capable of harming people but are studied to make sure they don't attack native species or other nontarget insects. Some of this work was done at the U.S. Department of Agriculture's Beneficial Insect Research Unit in Newark, Del., and the University of Minnesota in St. Paul.
More research, including an exacting economic assessment, will have to come before the parasitoid will be a recommended control, Tilmon says.
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In 2007, the wasp was approved for release by USDA. Soybean aphids have been in the United States since 2000.
"We know it to be fairly effective in laboratory settings for killing soybean aphids, and we know it is safe," Tilmon says. "We don't know if it'll establish and spread."
One issue is whether the parasitoid has specialized fungi that will attack it.
The lifecycle of the wasp plays a part.
Wasps insert eggs inside the host. The egg hatches inside the host and consumes the aphid host from within. In turn, the larvae pupate into a "resting" form as it transforms into an adult wasp. The dead aphid host body becomes a "mummy," holding the pupae of the wasp inside.
"The most vulnerable stage for them is not as adult wasps but as mummies," Tilmon says. "They are stuck to the plant and are kind of sitting ducks at that time for -- in particular -- generalist predators like lady beetles that also eat the mummies at that point."
The wasp is part of a classical control program that has been going on since 2002 to try to control soybean aphids. It is part of a national effort, funded by checkoff dollars and the U.S. Department of Agriculture,
"These aren't wasps that most people understand the large, stinging insects," Tilmon emphasizes. "These are only very distantly related, and they're biologically incapable of stinging or biting. And they're pretty tiny."
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Tilmon conducted one release last year that was pretty limited.
"We got our permit too late in the year to do much, but this year, we're doing an expanded release," Tilmon says.
This year's soybean aphid population got a slower start than in previous years, the first identifications coming two weeks later than in 2007 and 2006. Soybean aphid activity was increasing into North Dakota the week of July 14, and with soybeans smaller than normal for this year, spray thresholds were difficult to judge.
