ALLENTOWN — When it arrived in these parts from Asia about a decade ago, the brown marmorated stink bug was considered little more than a nuisance — an ugly, shield-shaped insect that oozed a pungent chemical stench when threatened (or crushed) but didn't bite or spread disease.

The biggest concern was that the bugs invade homes in the fall, seeking warm places to spend the winter. That's still a problem, and experts say it may be worse than ever this year because stink bug populations have exploded in many areas.

But now, entomologists and agriculture experts across the country are taking a harder look at stink bugs, because they may become a grave threat to fruit and other crops. They have already been blamed for significant damage to fruit orchards, especially in Maryland and West Virginia.

"Now that it's hitting fruit and hitting it hard, they're starting to pump a lot of money into it and do research on these guys," said Steve Jacobs, an entomologist with Penn State's College of Agricultural Sciences and member of a U.S. Department of Agriculture task force researching the bug.

Allentown has the unhappy distinction of being the first place in America where stink bugs — native to China, Japan and South Korea — were identified, in 2001. Like other nonnative species — emerald ash borers, Asian long-horned beetles — they probably arrived in shipping containers and spread until their numbers grew large enough to be noticed.

They are about 5/8ths of an inch long and get their name from their marbled shell (marmorated means marbled).

The insect is widespread in New Jersey, Maryland, Delaware, West Virginia, and Virginia. Smaller populations have been detected in Mississippi, Ohio, Oregon, and California.

"We're fairly certain now that the primary method of distribution for them is in vehicles — anything from tractor-trailers to motor homes to cars," Jacobs said. "We first had them here, then all the sudden a population cropped up in Portland (Ore.). Like Johnny Appleseed, we're carrying them around and spreading them."

According to a report by the USDA task force, the bugs caused serious damage to apple, pear and peach crops in Maryland and West Virginia last year. Other crops are at risk because the bug has a broad palate.

"I've seen them on all sorts of things — fruits, vegetable, beans, sweet corn, ornamental plants, trees, soybeans," Jacobs said. "My guess is they have such a wide range of potential food sources. Just about anywhere they get dropped off there is something for them to eat, so they get firmly established."