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Graduate student Sam Fahrner worked to measure flight patterns of wasps that feed on emerald ash borers and their larvae.

Richard Sennott, Star Tribune

Ash borer battle takes flight anew

  • Article by: BILL McAULIFFE
  • Star Tribune
  • November 27, 2012 - 9:15 PM

Like a kid on a carnival ride, a tiny insect called a Tetrastichus flew in steady circles around a central post, a tiny copper wire glued to its back.

It almost looked like fun. But this wasn't a carnival midway. It was a laboratory at the University of Minnesota's St. Paul campus, where researchers are giving rides free of charge to insects they hope will be a primary weapon in stopping the spread of the emerald ash borer.

Using the "flight mill" as well as a deep freeze, researchers from the U, the state Agriculture Department and the U.S. Forest Service are testing the flight capabilities and cold tolerance of three species of stingless wasps that are the only known predators of the borer, which threatens Minnesota's nearly 1 billion ash trees. Nearly 80,000 of the gnat-sized fliers -- only a fraction of the size of their prey -- have been released since 2010 in the four counties in Minnesota where the ash borer has been found, but researchers don't know what their survival rate has been. They do know that any survivors have been nourished only by emerald ash borers or their larvae.

"We know they're slower" than the ash borers, said Brian Aukema, an assistant professor of entomology, watching the wasp describe a circle nearly 4 inches across at a rate of about 1 mile per hour. "But if we know how far they can go, and how fast they can go, we'll know how best to position them."

Emerald ash borers, thought to have arrived in the United States in the late 1990s in the Detroit area, have spread across 18 states and two Canadian provinces, killing tens of millions of trees along the way. It was first identified in Minnesota in May 2009, near St. Paul's Hampden Park. Since then it has been found in four Minnesota counties -- Hennepin and Ramsey in the metro area and Houston and Winona in the southeast.

The stingless wasps are imports from China, where they live in balance with emerald ash borers. Researchers also want to find out what kind of low temperatures the stingless wasps -- and the borers themselves -- can tolerate. At the U, they're putting the wasps in tiny capsules and then into a freezer while tracking the drop in their body temperatures until they freeze. A warming Minnesota might allow both ash borers and the wasps to survive longer, but could add another annual life cycle for the predators, allowing their numbers to rise, noted Rob Venette, North Research Station research biologist for the Forest Service.

"We're trying to predict where [ash borers] might go in the state, and prevent it, rather than clean up afterward, which is expensive," Venette said.

The three-year flight and cold tolerance research is funded by $500,000 from the state's Environment and Natural Resources Trust Fund.

Bill McAuliffe • 612-673-7646

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