Imported Chinese bug could destroy Minnesota forests

A half-inch bug is sending chills through Minnesota foresters and entomologists as it threatens to move into state forests.

The emerald ash borer is a Chinese import that's already killed more than 20 million ash trees in southern Michigan, Indiana, Ohio and Illinois. It has no natural enemies here, and North American trees have shown no natural resistance to the metallic-green creature.

The bug's larvae bore into the bark and eat tunnels that block the tree's water supply from moving up through the trunk. Emerald ash borers have killed all sizes and all 17 varieties of ash found in the United States.

Some scientists are predicting that the bug will be even more devastating to Minnesota than Dutch elm disease.

But while Dutch elm affected mostly city trees and southern parts of the state, the emerald ash borer will zero in not just on urban shade trees but also millions of acres of northern forest thick with black ash.

"I dont know if we've ever seen another disease or insect that has done what this can do in Minnesota forests," said Lee Frelich, forest ecologist and director of the Center for Hardwood Ecology at the University of Minnesota. "We could see the end of virtually all ash in the region."

If that happens, Frelich said, few other species are ready or able to take their place. Black ash is the most common lowland species in northern forests, able to thrive in wet areas that most species can't tolerate. It's not clear what that would mean to wildlife or bird species in those areas, he said.

Emerald ash borers first came to attention in the 1990s when ash trees around Detroit and Windsor, Ontario started dying off at an unusually high rate. By the time scientists fingered them as the culprit in 2002, emerald ash borer had already infested almost every ash tree in five counties around Detroit.

Scientists believe ash borers got to the United States in untreated pallets or packing crates from China and escaped in Detroit ports.

The emerald ash borer has quickly risen to the top of the list in a joint federal and state effort to combat exotic pests. The federal government has banned the export of any untreated wood or live ash trees out of Michigan, Ohio, Indiana and Illinois, and state and federal agencies have imposed fines and jail sentences for some violators.

"If we can stop people from moving it and buy some time, maybe we can come up with something, or at least have time to prepare," said Steve Katovich, entomologist for the U.S. Forest Service in Minnesota. "I think it's realistic to say we might keep it out of here for 15 or 20 years or even more if people cooperate."

But efforts so far to stop its spread have failed. Around Windsor, Canadian forest managers cut down thousands of healthy ash trees to create a buffer -- only to realize the bugs had already moved beyond the line, where they continued to spread.

"By the time we figure out where they are, its usually too late. They are hard to find and even harder to kill," Katovich said.

The U.S. Department of Agriculture has already spent more than $100 million on efforts to squash the ash borer. The agency estimates it will cost state and local governments about $7 billion over the next 25 years to remove and replace dead and dying ash trees.

The loss to the forest products industry could rise even higher. Ash is an important source of wood for baseball bats, hockey sticks and carpentry, among other things.

The Minnesota Department of Natural Resources is asking the Legislature to pass laws banning campers from bringing in firewood from out of state into state forests or state parks.

But the greatest hope may lie in a Chinese parasitic wasp recently discovered by researchers. It lays eggs in the emerald ash borer larvae, eventually killing the borer.

But Katovich said it's not clear if the population of wasps would grow fast enough to stay ahead of the ash borers. "It's probably our best chance, but its not a sure thing at all," he said.

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