Purple bags along central Pa. highways track bugs

Sticky purple traps on I-81 near Harrisburg are another wayof coping with the invasive insect species.
Sticky purple traps on I-81 near Harrisburg are another wayof coping with the invasive insect species. (CHRIS KNIGHT / Patriot-News)
Posted: July 11, 2011

HARRISBURG - Biblical Egypt had to weather insect plagues of lice, flies, and locusts.

Those seem like a collection of gnats compared with what Pennsylvania's woodlands have survived the last several decades: tides of longhorn beetles, gypsy moths, stinkbugs, woolly adelgids, and Sirex woodwasps.

The latter are known for their ability to inject a toxic mucus and fungus into pine trees while they lay eggs. Take that, flies.

This summer, another invader joins the list of pests in central Pennsylvania - the emerald ash borer, a beetle native to Asia.

Its arrival in Cumberland and Dauphin Counties has been followed by the appearance of large purple bags hanging from trees on highways - low-tech monitoring stations for the state Department of Agriculture.

Each week, survey crews check the bags, which lure the beetles with the scent of stressed ash trees, to see if any borers have been caught, and the state tracks the species' spread.

Ash borers are known for their voracious appetite and selective diet; they eat only ash trees, of which Pennsylvania, with its $25 billion timber industry, has 300 million. It is estimated that the borer could cost the state tens of millions of dollars. One small city in Michigan removed more than 2,000 dead or dying ash trees at a cost of $2 million.

The first Pennsylvania sightings were in Butler County, north of Pittsburgh, in 2007. Since then, the insect has spread across much of Western Pennsylvania, primarily by hitching rides on cut wood.

That led to a state campaign to quarantine firewood and to the slogan "Burn it where you buy it." The quarantine has slowed the spread of the insect, buying time for researchers at Pennsylvania State University to try to develop ways to combat it. They have not found a magic bullet but are looking at options including introducing nonnative predators.

When it comes to invasive species, entomologists have two choices: eradication and management. Eradication is easier said than done when a species from halfway around the world arrives in an area with lots of food and no natural predators. More often, researchers look for ways to manage a pest.

And if most modern invasive species seem to arrive from eastern Asia - specifically China - that should not be a real surprise.

Most pests are spread along economic lines of force, said Leo Donovall, a member of the Pennsylvania Invasive Species Council.

"Asia is kind of our highest area of incidents mostly because most of our products are from there," he said. "Asian pests are also so far removed geographically it can be hard to find a congener," or native species of the same genus.

Congeners are important when trying to curb a species because they can provide clues to natural predators or diseases. But vast geographic differences, like those between Asia and North America, can allow insects to evolve in two directions. So a natural disease that limits the spread of a native beetle species might have no effect on its Asian cousin.

But the spread of invasive plants, animals, and insects goes both ways. The United States has presented China with North American species of termites, crayfish, and that New York City staple, the American cockroach.

"So there is some back and forth," Donovall said. "We certainly send a lot of products to other countries . . . so we do ship back a lot of insects as well."

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