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A tiny insect recently discovered in two Wisconsin counties could wipe out nearly a quarter of La Crosse’s trees if it gets this far.

State officials last week announced the second confirmed presence of the emerald ash borer, which has wiped out an estimated 25 million trees in Michigan, Pennsylvania, Ohio, Indiana and Illinois as well as Canada.

That has La Crosse city Forester Dan Bonadurer nervous.

Three decades ago, when Dutch elm disease killed half the trees in La Crosse, many were replaced with ash, which now account for about one in four of the trees on the city’s boulevards. The overall city tree population is probably similar, Bonadurer said.

Wisconsin has an estimated 765 million ash trees — about 7 percent of the total tree population. The Department of Natural Resources estimates there are 1.4 to 2.8 million ashes in La Crosse County.

“It’s going to be a heck of a loss” if the insects get to this area, Bonadurer said. “It’s going to kill a lot of trees.”

Unlike Dutch elm disease, which took about a decade to kill the city’s elms, the ash borer is a fast-acting predator.

Metallic green and about a half-inch long, the emerald ash borer came from Asia in the 1990s, most likely in wooden shipping containers. Adults lay eggs in the crevices of ash bark, and the larvae feed on the wood, killing the host, usually in two to four years.

On their own, the insects migrate slowly — about one half to two miles a year. But with human help they can travel great distances in live trees, firewood or other wood products.

The Department of Agriculture, Trade and Consumer Protection has established a quarantine on nursery stock and lumber in four counties in southeastern Wisconsin, including Ozaukee and Washington, where emerald ash borers were found.

Wisconsin state parks already ban users from bringing in firewood from more than 50 miles away or across state lines.

In addition, the state has a management plan, which includes measures such as tree harvesting, the use of pesticides and the introduction of predators, said Darrell Zastrow, director of the DNR’s Office of Forest Sciences.

Should the beetles get a foothold here, Bonadurer figures it would take his department almost two years of constant work to take down all the damaged trees.

“I’m kind of hopeful that scientists will come up with some kind of insecticide,” Bonadurer said. “Even to lessen the shock would be kind of a neat thing.”