A small, glitter-green insect that has killed more than 50 million ash trees in the Midwest and beyond has arrived in the Philadelphia region.

Officials had both dreaded and expected it - just not this soon.

On Wednesday, its presence was confirmed in an ash tree at a condominium neighborhood in Warrington, Bucks County. When officials looked at the surrounding forest, they realized maybe 20 ashes were under attack.

"This is pretty much going to hammer ash trees in Southeastern Pennsylvania almost into oblivion," said Scott Guiser, an educator at Pennsylvania State University's extension service in Bucks County.

The emerald ash borer is an expensive invader.

The ash is a popular street tree, and officials expect municipal budgets will be stressed by the need to take down dead and dying trees that have become safety hazards.

Likewise, homeowners will have to make difficult decisions. Although treatments can be effective - if an infestation is discovered in time, which often is not the case - they can cost several hundred dollars per tree and need to be repeated.

But cutting down a large, half-dead tree next to a house can cost up to $5,000.

Meanwhile, the landscape will change in the region's parks and urban forests, where ashes make up 5 percent to 10 percent of the tree cover.

"For key trees, we have the technology to protect them," said Ken LeRoy, an arborist with John B. Ward Tree Experts in King of Prussia. "But when it starts going through natural areas, that's going to be a scary thing."

The insect could land a hard blow to a region that has spent vast amounts of money and effort to replenish the urban forest through programs like Treevitalize.

Along streets in the region, many of the chestnuts that were lost in the early 1900s to a blight and many of the elms lost in the 1970s to Dutch elm disease were replaced by what was thought to be a hardy survivor - the ash.

Within the state's forests, ashes make up about 4 percent of the trees. Although that may sound small, said Donald Eggen, chief of the division of forest pest management in the state Bureau of Forestry, it amounts to 300 million trees. The ones in the northern tier of the state are an important commercial stand. They're harvested to make Louisville Slugger baseball bats.

The ash borer, about a half-inch long, lays its eggs on the bark of ashes. The larvae burrow inside to feast on the living tissue. Eventually, they girdle the tree, cutting the flow of nutrients and killing it.

Native to China, the insect was discovered in the United States in 2002 in Detroit.

As the borer spread through the suburbs and beyond, leaving ash skeletons behind, the U.S. Department of Agriculture dedicated emergency funding. "Firewalls" were cut. Areas were quarantined. Bans restricted the movement of trees and firewood.

Still, the insect kept spreading.

The borer was detected in 2007 in Pennsylvania. It has since spread as far east as Sullivan County and a turnpike rest stop near Carlisle.

By now, according to the USDA, the insect has cost municipalities, property owners, nursery operators, and forest-products industries "tens of millions of dollars."

The Bucks County infestation was discovered at the Hampton Greens complex by Mark Biresch, an arborist who works for Bair's Tree & Lawn Service in Sellersville. When he arrived for pruning work, he noticed a telltale sign - damage from woodpeckers that had been feasting on the larvae.

Officials are betting that somewhere nearby, someone got a load of firewood in the last few years that contained the insects.

Biresch thinks it's unlikely this is the only infestation in the region.

The Warrington discovery also puts the insect virtually on the doorstep of New Jersey.

Carl Schulze, director of the division of plant industry in the N.J. Department of Agriculture, figured it was inevitable.

"We're sort of resigned to the march of this."

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