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Stingless wasps unleashed to fight emerald ash borer

By Bill McAuliffe
Minneapolis Star Tribune

The wasps, raised in a USDA lab, go after the ash borer larvae. Minnesota is the eighth state to experiment with their use.

Stingless wasps unleashed to fight emerald ash borer

A boatload of state and federal agriculture and forestry officials stop at a remote island on the Mississippi River with a cooler full of ... stingless wasps.

Last update: September 23, 2010 - 6:34 AM 

VICTORY, WIS. - A boatload of state and federal agriculture and forestry officials zoomed up the Mississippi River on the last day of summer Wednesday, heading for a remote island with a cooler full of... stingless wasps. Watch a video of the release here.

Indeed, this was no picnic. Instead it was an effort to establish a biological beachhead in the effort to stem the advance of the emerald ash borer, an invasive pest that threatens Minnesota's more than 900 million ash trees and millions more in Wisconsin and Iowa.

The release on Island 135, a backwater refuge dominated by hardwood forest, chest-high nettles and mosquitoes, made Minnesota the eighth state in which the wasps have been mobilized. The plan is for the wasps to feed off ash borer larvae, ultimately multiplying to the point where they outnumber the ash borer and stop or slow its spread.

"This is not an eradication tool," said Monika Chandler, biological control program coordinator for the Minnesota Department of Agriculture. "What we're trying to do is find a way to live with" the ash borer.

2wasp092310 by Ewen McKenna-Star Tribune

The tiny wasps, raised in a U.S. Department of Agriculture laboratory in Michigan, are descended from wasps in China, where they live in balance with the ash borer. They prey only on ash borers and won't sting people. That much is known. But researchers say they have a lot more to learn about how effective they might be in North America. One key question is whether they can withstand a Minnesota winter. Ash borers die off at minus 15.

"This insect is raising questions about the biology of ash trees that we haven't even thought of," said Robert Venette, a research biologist with the state agriculture department. The wasps' performance will be a critical concern in northern Minnesota, which has a heavy concentration of black ash, a species that is important in boggy areas and shorelines. In the rest of Minnesota, particularly in urban landscapes, green ash are common.

The ash borer has destroyed tens of millions of trees across 15 states and two Canadian provinces. The bug is believed to have arrived in the United States in packing crates from China delivered to the Detroit area in the late 1980s.

Previously unknown in North America, it wasn't even identified until 2002, by which time it had already killed ash all across southern Michigan.

The wasps destroy ash borers by laying eggs on the bugs' larvae.Wasp_parasitosis of EAB larve

Ash borer larvae destroy ash trees by cutting off the flow of nutrients from the roots to the upper branches as they develop just under the bark.

Female wasps are able to "hear" ash borer larvae under the bark. They then bore into the larvae and lay their eggs in them. As the eggs develop into adults, they nourish themselves on the ash borer larvae, killing them.

Island 135 is across a channel of the Mississippi River from Victory, Wis., site of the first ash borer infestation detected west of Milwaukee. It was chosen as a release site because Minnesota had asked for a federal release permit before neighboring states. Also, being in a federal refuge, the site would provide wasps a chance to prove themselves in an area where infested ash trees weren't being cut down or treated with chemicals.

The island is in Houston County, Minn., which was put under an ash wood quarantine in spring 2009 after the ash borers were confirmed across the river in Victory. That was the first quarantine in Minnesota. A month later, Ramsey and Hennepin counties were restricted after an ash borer infestation was found in St. Paul's Hampden Park neighborhood, near the St. Paul-Minneapolis border. Quarantines mean people cannot move ash wood, from waste to firewood, out of the designated areas without a permit.

Because the ash borer has spread rapidly elsewhere in the past, it's unusual that Minnesota saw no spread of infestations beyond the three quarantined counties this year.

"It's all been good news so far," said Mark Abrahamson, an entomologist and Minnesota's lead ash borer tracker. But he noted that Minnesota has had an apparent advantage in knowing about the bug and how to identify infestations. It arrived as a mystery in states to the east.

"In other places, by the time anybody knew what they were dealing with, it had reached epidemic proportions," Abrahamson said. "Is it going to progress in the same way here? Or because it's been discovered earlier, and we have things we can do about it, we don't reach that situation in five years? It's hard to say which is true."

Abrahamson said aggressive ash-removal programs in both St. Paul and Minneapolis seem to have headed off the ash borer's spread, at least for now. But a recently discovered infestation in the Mississippi River gorge just downstream from the Interstate 94 bridge between the two cities, is worrisome, Abrahamson said. The ash forest in the gorge is thick, and the terrain is too steep for workers to remove trees efficiently. Sending stingless wasps in to do the job might be the way to go, he said, but that probably won't happen until next year.

The bug remains difficult to detect early in infestations. Abrahamson said, and that's a continuing frustration.

"I feel cautious about saying we've got it figured out," he said. "It's been such a short time we've been dealing with it here."

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