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DNR hopes new allies will slow EAB



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Ash trees that were cut down in Big Foot State Park because of EAB.

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Emerald Ash Borer Associated Press. (click for larger version)
May 15, 2013 | 03:49 PM
Big Foot Beach State Park will be an experimental battleground in Wisconsin's fight against the emerald ash borer, or EAB.

And this time, the state Department of Natural Resources is bringing in some overseas allies to help its fight against the voracious, ash-eating beetle.

Bill McNee, DNR forest health specialist, said two north Asian flying insects with the impressive names of Oobies Agrili and Tretristichus Planipennisi will be released into the state park in an effort to blunt EAB's assault on native species of ash. The two insects, species of stingless wasps, are from China.

The wasps will be released in the park sometime between June and August, McNee said.

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Adults of both species are about a millimeter long and don't at all resemble their larger, North American stinging cousins.

Both Oobies and Tetrastichus have been through field studies in Michigan, which has been hard-hit by EAB.

According to the "Michigan Tech Magazine," when the Tetrastichus were released from a jar onto an EAB-infested tree: "What flies out is nothing like a swarm of wasps. In fact, the tiny parasites are almost too small to see."

Both wasps target EAB almost exclusively, although a few native ash bark borers might also find themselves on the menu, McNee said.

Up close, though, they look pretty ferocious. And what they do to EAB eggs and larvae can only be described as something out of a science fiction horror story.

Oobies injects its eggs into EAB eggs. The Oobies larvae hatch first and feast on the EAB eggs before growing into adults.

Tetristichus injects a paralyzing poison into EAB larvae and then lays eggs on the paralyzed bug.

The eggs hatch and larvae burrow into the paralyzed EAB larvae and devour it from the inside out.

Tactics aside, however, the DNR hopes its two new allies will slow the spread of the emerald pests and give both ash and humans time to find more effective ways to end EAB's arboreal reign of terror.

McNee said he expects the wasps' combined appetites will be 20- to 50-percent effective in controlling the emerald ash borer population.

"It's not a magic bullet that will solve the problem," McNee said.

Helping the two new predators are some native stingless wasps that, according to the University of Michigan, are "acquiring a taste" for EAB.

McNee said he suspects those native-born wasps have been feeding on the EAB here, but their effect has been minimal, because the native wasps still tend to concentrate on native bark-boring bugs.

Although the first hard evidence of EAB infestation wasn't detected in Walworth County until last year, McNee said he believes the beetle arrived in the area a year or two before it was discovered, feeding and multiplying hidden from human eyes under ash tree bark.

EAB is a very stealthy pest, and it takes a year or two before infected ash trees show any sign of infestation, McNee said. "We have a living thing that burrows under bark for 10 months of the year," he said of EAB.

McNee estimated that 30 to 40 percent of the ash in the Lake Geneva area are in decline, with virtually all of the trees infested to varying degrees.

"They've been here for some time," he said.

One of the first creatures to notice the infestation are woodpeckers.

The number of woodpecker feeding holes is a sure sign of the level of infestation, he said. For the woodpeckers, an EAB-infested ash is a smorgasbord.

Unfortunately for the tree, the avian's interest in the ash borers comes too little, too late.

"Once trees are heavily woodpeckered, they don't have much time left," McNee said.

McNees said the trees in Big Foot Beach State Park were cut down because they were diseased. And that posed a danger to humans. Not from EAB, but from EAB- weakened ash tree limbs.

"When ashes go into decline, branches drop quickly," McNee said.

Removal of the ash around the picnic areas and by the beach were necessary to prevent falling branches from injuring park visitors, McNee said.

Some of the ash at Big Foot still stand, waiting for the experimental release of Asiatic wasps.

But they are in swampy areas and marshland, where interactions between humans and falling branches should be a rare occurrence, McNee said.

"If a tree dies and drops a few branches in a swamp, there's little to no risk," McNee said.

The DNR plans to replace the ash with mixed species trees, so no future, unexpected infestation will wipe entire area's clear of tree cover.

McNee said he's unaware of any cost estimate done on the loss of trees to the EAB at Big Foot.

A census of trees cut down was also unavailable at the time.

The DNR is not only taking down infested trees in Big Foot, it is also removing infested trees in other state parks as well.

The economics of an open wooded lot, like a state park, doesn't really allow for saving trees, he said.

However, many ash trees on landscaped state properties are being treated. And parks may also make the effort to save some ornamental ashes, he said.

McNee also said municipalities should consider trying to save what urban ash trees they can.

He said the DNR has found that saving the trees actually saves communities in the long run. Taking down the trees requires some, if not all, to be replaced.

Treating the trees does have a cost, and not all treated trees survive, but while the trees are being treated, the community still has the benefit of the tree.

And those that do survive do not have to be replaced.

Wisconsin has more that 700 million ash trees with trunks more than one-inch in diameter, McNee said. And 20 percent of those ash trees are in urban settings.

McNee also recommended that private homeowners with ash trees take steps to protect their trees from EAB infestation.

EAB has been known to be in Wisconsin since 2008, when an infected tree was identified in Newburg, near West Bend.

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