2011-07-14 / Local & State

Purple Bags Along Central Pa. Highways Track Bugs

By Nick Malawskey

HARRISBURG, Pa. (AP) – Biblical Egypt had to weather insect plagues of lice, flies and locusts.

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

The latter is known for its ability to inject a toxic mucus and fungus into pine trees while it lays its eggs – take that, flies.

This summer, we add another invader to the list of pests in central Pennsylvania – the emerald ash borer, a type of beetle native to Asia.

Its arrival in Cumberland and Dauphin counties has been heralded by the appearance of large purple bags hanging from trees along the area’s highways.

They’re neither kites nor giant versions of the Japanese beetle traps that adorned area gardens in the late 1990s.

Instead, they’re low-tech monitoring stations for the state Department of Agriculture, as entomologists track the spread of the ash borer across Pennsylvania.

Each week, survey crews attend to the bags, which lure the beetles with the scent of stressed ash trees. The crews check to see if they’ve caught any borers – thus, the state tracks the species’ spread.

Ash borers are known for the voracious appetite and their selective diet – they eat only ash trees, roughly 300 million of which are in Pennsylvania and contribute to the state’s $25 billion timber industry. It’s estimated the borer could cost the state tens of millions of dollars – one small city in Michigan alone removed more than 2,000 dead or dying ash trees at a cost of $2 million.

The first instances of the beetle 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.

The borer’s spread led to a campaign by the state to quarantine firewood – and the slogan “burn it where you buy it.’’ The quarantine has slowed the spread of the insect, buying time for researchers at Penn State University to try to develop ways to combat the spread.

So far, they haven’t found a magic bullet for the species, but are continuing to look at various options, including introducing non-native predators.

When it comes to invasive species, entomologists basically have two options: eradication and management.

Eradication is easier said than done when a species from halfway around the world arrives in a new area with lots of food and no natural predators. Instead, researchers more often look for ways to manage a pest’s population.

And if most modern invasive species seem to arrive from eastern Asia _ specifically China _ well, that shouldn’t be a real surprise.

Most pests are spread along economic lines of force, said Leo Donovall, who is 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,’’ Donovall 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 limit the spread of a species because they can provide clues to natural controls such as predators or diseases. But here’s where evolution steps in – vast geographic differences, like that of Asia to North America, mean that in some cases insects evolve in two directions.

Ergo, a natural disease that limits the spread of a native beetle species might have no effect on its Asian cousin, allowing its population to explode in its new environment.

But the spread of invasive plants, animals and insects is a two-way street.

Aside from Kentucky Fried Chicken and Buick automobiles, we’ve also gifted 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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