Those swarms of soybean aphids that show up this time of year are in for a big surprise. Armies of tiny wasps now wait to eat them for lunch.
Native to China, populations of these natural predators are arriving in North America in numbers large enough to potentially reduce the need for insecticide applications. Although some fields will still have more aphids than their enemies can attack and destroy, what these wasps attempt to achieve is nothing short of heroic.
"We see significant soybean aphid control by a combination of natural enemies and only see a few fields with later infestations that require spraying," says Tracey Baute, entomologist for the Ontario Ministry of Agriculture.
Scientists call them parasitoids, an insect group that describes bugs that live in or on the body of a single host and eventually kill their host. No one is quite sure how the Aphelinus certus (A. certus) wasp migrated to North America and found a home here. Ontario entomologists first spotted the A. certus in 2006. It appeared on a University of Minnesota research farm in 2011 and has continued to spread.
Joe Kaser, University of Minnesota grad student, worked with the Minnesota Department of Agriculture on a 2014 Minnesota survey. "We found A. certus from the Iowa border to the Canadian border," he says.
A. certus is not the only aphid parasitoid flying about Minnesota. After a rigorous approval process, University of Minnesota entomologists worked with USDA to introduce another half-million wasps called Aphelinus glycinis (A. glycinis). This summer, entomologists will comb the state to see if A. glycinis survived the winter and how it might help control soybean aphid numbers.
"We are hopeful that the intentionally introduced wasps, as well as the wasps which got here on their own, will help to reduce soybean aphid numbers below economic thresholds," Kaser says.
The stingless wasps don't work alone. Lady beetles, minute pirate bugs and other insects have lived in grower fields for years since soybean aphids arrived in the U.S. 15 years ago. Canadian entomologists incorporate these natural enemies into their Aphid Advisor scouting tool (www.aphidapp.com).
The desire to keep natural enemies alive and working is one of the main reasons entomologists urge growers to wait until fields reach an economic threshold of 250 aphids per plant before spraying.
"Allow the natural enemies to do their job," urges University of Minnesota Extension entomologist Bob Koch. "Keep in mind that having 100 aphids a plant doesn't mean you will hit 250 or more." He also suggests planting aphid-resistant soybean seed, rotating insecticide modes of action to avoid resistance and thinking about using soybean insecticides such as Transform (sulfoxaflor) that may be gentler on predators than some of the more widely used products.
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