URBANA – Tiny wasps from China may soon help farmers protect soybeans in their fields by turning aphids that feed on them into mummies.
Illinois Natural History Survey entomologist Dave Voegtlin, an aphid specialist, and his graduate student, Doris Lagos, grow the wasps, which are about 1.5 millimeters long – 17 of them end to end would be an inch long – in containers in a laboratory at the National Soybean Research Laboratory.
They're waiting for aphids to show up in East Central Illinois fields. When they do, University of Illinois entomologist Kevin Steffey will put the wasps out in fields in cages to feed on the aphids there and multiply.
The plan: to introduce a population of natural predators that zero in on specific aphid populations but don't threaten other species.
"We don't want something that feeds on every aphid we have," Voegtlin said. "Biological control is a powerful tool because it allows farmers to bypass pesticides, it works year after year and after the initial testing, it costs nothing."
Aphids, an ancient pest, first showed up in Midwestern soybean fields in 2000."My theory is they came here from Asia on edamame," Voegtlin said. "They're native to China but they could have come from anywhere."
Voegtlin was one of the first to hear about the Asian aphids.
"In late July 2000, colleagues from the University of Wisconsin called me wanting to know why they had aphids on their soybeans," he said. "They had identified them as something else. By the next morning, I had a shipment, I identified them and sent them to the Smithsonian, the British Museum and a research station in Florida for confirmation."
Scientists immediately started looking for natural predators. ""We traveled to Asia looking for natural enemies starting in 2001," Voegtlin said. "I was there four times. We found a dozen natural enemies but discarded some because you want a narrow host range. This wasp lives on only a few species that are closely related like the cotton melon aphid, its closest relative."
What the minute wasp does to aphids isn't pretty. It lays an egg inside them; the egg hatches into a larva and it eats the aphid from the inside, forming a cocoon scientists call a mummy. Lagos has perfected a lab hatching system so she knows exactly how long it takes for the larvae to hatch and finish off the aphid and how long it takes the wasp to emerge.
Steffey's keeping a close eye on soybean fields so he knows when enough aphids are in them for wasp populations to thrive. He said he expected that to happen earlier in the year but it's been dry and aphid numbers have been low.
Steffey will put them in bean fields at Urbana, near DeKalb and in northern Mercer County.
"When we get aphids built up inside the cages, we'll put the mummies in, the wasps will emerge and they'll start stinging aphids," he said. "At the right time, we'll open the cages."
Scientists don't know whether or how the wasps will overwinter. "The speculation is they will because they're from China and the climate there is temperate with cold winters," Steffey said.
"My guess is that they'll overwinter on the aphids' winter host, buckthorn," Voegtlin said. "If they survive they'll be everywhere. There's good evidence they're carried by aphids."
Steffey said releases to be done in every state in the Midwest have been planned carefully.
"Everyone asks if they sting," he said. "They sting only aphids. This is a wasp no bigger than a period. No one wants to introduce something that's more of a problem than the problem."