HARRISBURG -- Last year, the insects called brown marmorated stink bugs were a nuisance. This year, they are a serious threat to fruit orchards, and experts are not sure how destructive they might become.

The ubiquitous brown bugs with a citrusy or piney scent are making their way into Pennsylvania homes, previewing the hordes likely to appear late this month and next as the weather cools.

Bloggers share ideas about getting rid of them: Flush them down the toilet, vacuum them up, drop them in a bucket of soapy water, squash them, stick them to duct tape.

They are annoying in homes but don't do much damage. They don't bite people or destroy wood.

To farmers, they have become a destructive pest.

Greg Krawczyk, an entomologist with the Penn State University Fruit Research Center in Biglerville, said some fruit orchards have lost 40 percent of their crops to the bugs. The hardest hit are in Adams County, northern Maryland and West Virginia.

Stink bugs can eat almost anything and so far have no natural predators in the U.S. No one knows if their damage is going to spread to other crops.

"We have a huge list of questions and a very, very short list of answers," Mr. Krawczyk said.

The bugs, originally from Asia, appeared in this country about a decade ago and have spread rapidly.

In the middle of the state, exterminators are just starting to get calls from homeowners and are expecting an onslaught as the bugs seek shelter for the winter.

"This is just the tip of the iceberg," said Heather Meccia, office manager for H.T. Treadway Pest Control, based in York County.

Susan Roselle of Swatara Township has hired Treadway to rid her of the bugs that cover her windows as they try to make their way inside.

"I've seen them for the past five years, but this year they are really, really bad," she said. "If I open the window, they just drop in. Everywhere I turn, there are tons of them."

"Their numbers are amazingly huge," Mr. Krawczyk said.

Penn State entomologist Steve Jacobs said the list of fruits and vegetables they dine on includes "almost anything -- sweet corn, lima beans, peaches, apples, soybeans."

Many orchards have used integrated pest-control management systems to avoid harsh pesticides that kill the good bugs as well as the bad, Mr. Jacobs said. But there's not much that will kill the stink bugs outside the broad spectrum pesticides.

"I don't think anybody had a clue it would be this devastating," he said.

The bugs do their damage by sticking their mouth parts under the skin of the fruit, injecting saliva and sucking out the juice, Mr. Krawczyk said.

The fruit dries out from the inside and becomes brownish and distorted in a characteristic fashion called "cat facing."

Because the stink bugs did not cause much damage before this year, little money has been allocated for research, Mr. Krawczyk said.

"We don't have a good monitoring system," he said. "Because they are so new, we haven't identified a sex pheromone to trap them. We have had native species here forever, but we never worried about them too much."

In previous years, the stink bugs produced one generation a year. But this year, there seems to be at least three generations, he said. That means they can infest a crop at almost any time during the growing season.

"In September, we're still finding nymphs and adults at the same time," he said.

Mr. Krawczyk doesn't know why it's so bad this year. Two months ago, he traveled to West Virginia to learn about the bugs and now he's trying to establish a colony in his lab to do research during the winter.

Ms. Meccia thinks many of the bugs might have survived outside last winter, kept warm in cracks covered by a blanket of snow. She has noticed an increase in all kinds of bugs this year.

Growers from the affected areas met Friday in northern Maryland to discuss the problem.

Mr. Krawczyk said he only can hope that local predators develop a taste for brown marmorated stink bugs. Introducing predators from Asia is a tricky business that could have unintended consequences, he said.

According to Ms. Meccia, "Sometimes it takes a while for an ecosystem to catch up."

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