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Tiny beetle-eating species will be released at Riveredge next month in new effort to control tree-killing invader

Three species of tiny wasps — one so small it can fit on the period at the end of this sentence — will be released at Riveredge Nature Center in the Town of Saukville beginning next month as the State of Wisconsin seeks to control the emerald ash borer.

Two species of wasps will be released over six weeks beginning in June, with the third species introduced later in summer or early in fall, said Jane Cummings Carlson, a forest health specialist with the Department of Natural Resources.
Riveredge, which is a stone’s throw from the Town of Saukville woodlot where the borer was first detected in Wisconsin in 2008, was selected for the release because its woods are an excellent habitat for the beetle and the wasp, Cummings Carlson said.

“There’s an emerald ash borer infestation there, so there’s a lot for the wasps to feed on,” she said. Of Riveredge’s 350 acres of forest, 15% of the trees are ash.

Riveredge is excited about the chance to participate in the project, said Executive Director Patrick Boyle.

“We’re honored that they chose Riveredge as the release area,” he said. “We all greatly hope that this project yields some positive results that we can share with the community.”

The fact that Riveredge is near the site where the borer was first discovered was not a factor, Cummings Carlson said.

The wasps, which like the borer are native to China, are natural predators of the beetle. They prey almost exclusively on the borer.

The stingless, parasitic wasps will be released in stages, with 200 of each of the first two species released two weeks apart beginning in early June, Cummings Carlson said. These wasps insert their eggs on the surface or inside the borer larva, while
the third species of wasps deposit their eggs inside the borer’s eggs.

The wasps are delicate, Cummings Carlson said, but the hope is they will colonize and their population will increase on its own, destroying the borer in the process.

The idea of using one non-native species to attack another is not new, nor is the idea of releasing the wasps to fight the borer. Wisconsin will be the tenth state to release them as officials throughout the country seek to mitigate the effect of the borer,
which has killed tens of millions of ash trees since first being detected in the U.S. in 2002.

The wasps are the latest weapon in the arsenal against the borer, which until now has only been fought with chemicals. That process is effective for individual trees, officials said, but impractical in forests.


“We really need an effective biological control to help us preserve our native North American ash forests,” Cummings Carlson said. “The effectiveness of these stingless wasps against the emerald ash borer is uncertain, yet it is clear that reducing
borer populations has a better chance of success when many approaches are employed.

“There is some hope that they (the wasps) may eventually be used on a wide scale to help reduce borer populations, especially in Wisconsin’s forests, where there are more than 700 million ash trees.”

It will take at least five years before scientists will know if the wasps have been effective, Cummings Carlson said.

The wasps, which are being raised in Michigan, will be released by scientists from the DNR, University of Wisconsin-Madison and the U.S. Department of Agriculture’s Animal and Plant Health Inspection Service. The project is being funded for three years by the DNR.

Extensive research has been done to ensure the wasps will affect only the borer, Cummings Carlson said, adding they will be virtually invisible to humans.

“They do not sting. They do not congregate in houses,” she said. “No one will even notice them except, we hope, the emerald ash borer.

“The impact of the wasps is far less than the impact of the emerald ash borer on ash trees, which we know to be devastating.”

The wasps are parasites focused on finding their hosts, the emerald ash borer, said Andrea Diss-Torrance, the DNR forest entomologist.

“Because they are so tiny and at work in the canopy of ash trees, most people will never see them,” she said. “In fact, it is very hard even for trained entomologists to find the adult wasps in the field. To verify if our introductions are successful, we will
have to peel the bark off of infested ash and look for parasitized emerald ash borer larvae.”

Ken Raffa, a UW-Madison professor of entomology, said the wasps “have undergone intense scrutiny by the USDA to safeguard against harm to native species.”

Even as the wasps are being released, the state will be setting fewer of the purple traps intended to track the borer’s movements.

None of the traps will be set in southeastern Wisconsin, where the borer has already been found, said Mick Skwarok of the Department of Agriculture, Trade and Consumer Protection.

Budget cutbacks mean the traps will only be placed where the borer hasn’t been detected before, he said.

“If we were able to trap as much as we want, we could give more communities a heads up that the borer’s coming toward them,” Skwarok said. “But we have to take a realistic view of what the funding is. The reality is there’s less federal money to
support emerald ash borer work.”

In Ozaukee County, he noted, the borer seems to be moving slowly.

“We can only guess the reason for that is there is so much ash where they are that they don’t have to fly far,” Skwarok said. “Why spend that time and energy flying eight miles when you have ash right next door?

“That news (that the bug hasn’t moved far) shouldn’t give anyone in Ozaukee or Washington county reason to let down their guard. We know the emerald ash borer can move some distance on its own.”

Written by: Written by Kristyn Halbig Ziehm
Ozaukee Press