Pest prevention

WOOSTER TOWNSHIP, Ohio — Researchers here are inching closer to winning the fight to save North America's native ash trees.

The scientists at OSU's Ohio Agricultural Research and Development Center are among a research team from four institutions that recently received $1.4 million from the government to continue working on developing trees that can resist the devastating emerald ash borer. The three-year grant is from the U.S. Department of Agriculture's Animal and Plant Health Inspection Service.

The emerald ash borer, named for its metallic green color, is slowly killing trees in Ohio and much of the Midwest. Its larvae bore through tree bark and destroy the soft tissue layer underneath, gradually cutting off a tree's ability to distribute water and food.

The insect has been found in much of Ohio and across a region that extends from New York to Minnesota and from lower Canada to Tennessee.

The research team has been working on developing resistant trees since 2003, a year after the first infestation of the insect was confirmed in North America. The new grant is a renewal and expansion of previous federal funding for the research, said project leader Dan Herms, an insect specialist at OARDC.

"We've made some pretty good progress over the years," he said — enough that Herms predicted the team will ultimately succeed at producing resistant ash trees.

That progress comes none too soon. The insect continues to spread throughout the state, and where it's established, populations are increasing, Herms said. Within a couple of years, he expects ash tree deaths to be widespread in this region.

That has already happened in southeastern Michigan, where the first North American infestation was found. Almost all of the ash trees within 31 miles of that spot are now dead.

Insecticides can help protect trees in landscapes, but they're not a foolproof remedy, Herms said. And they aren't a reasonable solution for trees in the wild.

That's why the researchers are seeking to grow trees that can fight off the insect naturally.

One approach they're pursuing is crossing Asian ash trees with North American trees. The emerald ash borer is native to parts of Asia, and the researchers have discovered that ash species that grow there produce a chemical that helps them fight off the insect. Emerald ash borers there prey only on ash trees that are weakened, perhaps by drought or damage, Herms said.

The Asian trees, however, don't have the same desirable characteristics as North American ashes, he said. So the researchers are working to develop a hybrid that's mostly North American, one that would have the Asian trees' resistance but the American trees' attractive appearance, good fall color and more desirable growth habit.

In addition, the researchers are studying the rare North American trees that have managed to avoid infestation in hopes of producing more of those super-resistant oddities.

Herms said the researchers have found about 40 trees that have survived unscathed in areas where 99 percent of the ashes have died. "We don't know if they're lucky or naturally resistant," he said.

Those trees are being cloned, and the young offspring will be tested to determine whether they really are resistant to the ash borer. That involves allowing eggs to hatch on the bark and the larvae to enter the tree, and then seeing whether the larvae survive.

If the trees turn out to be truly resistant, the intention is to produce seed for sprinkling in forests and starting trees in nurseries, Herms said.

The researchers are also developing a genetic marker that will help them determine early on which young trees are resistant and which aren't, so they can continue to grow only the resistant ones without waiting till they're big enough to test.

Hybridizing and growing trees takes time, however, so the progress of the research has been slow, Herms said. Nevertheless, he's optimistic about the eventual outcome.

By the end of the three-year grant, he expects the researchers to have bred resistant trees and be at the point where they can evaluate the trees' characteristics and determine which to choose for further breeding.

In addition to OARDC, the team involves representatives from Ohio State's Columbus campus, Wright State University, Michigan State University and the USDA Forest Service stations in Delaware, Ohio, and East Lansing, Mich. Among the lead scientists is Omprakash Mittapalli, another entomologist at OARDC.

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