The brown marmorated stink bug — a dime-sized Asian invader that has been besieging Maryland homes in recent years — has now become a serious farm pest.

Agricultural scientists say the insect's populations have "exploded" this year, and they've demonstrated an unexpected ability to feed during all their developmental stages on a wide variety of crops.

Maryland farmers — especially fruit and vegetable growers in Western and Central Maryland — are seeing a sharp increase in costly damage from the insects.

Bobby Black, owner of Catoctin Mountain Orchard, on U.S. 15 just north of Thurmont, pulled his jackknife through a Pink Lady apple Thursday morning and exposed a dry, tan-colored cavity inside. That's where a stink bug fed on the juice and left its saliva enzymes behind to break down the fruit's flesh. The punctures also cause skin dimpling and blemishes that look like hail damage.

"I can't think of anything that's attacked our farm worse than this that's coming up right now," Black said.

He's taken losses to his peach and apple crops that he estimates at about 20 percent. In some sections closest to woods, 50 percent of the fruit is damaged.

"There's still a lot of good fruit here," he said. His trees and his farm store are full of unaffected apples, peaches and plums. "But I don't want to come back next year with 30 to 40 percent damage. This is almost like a hurricane. We need help now."

Agricultural scientists from New England to Virginia have joined forces to study the invader and find ways to control it. For now, there are few alternatives to chemical insecticides. But researchers are looking at lures, traps and the possible release of predatory insects that attack the stink bugs in their native China.

On Sept. 14, Rep. Roscoe Bartlett, R-Md., whose district includes all of Western Maryland, organized a briefing in Washington on the threat, bringing together federal Department of Agriculture and regional agriculture officials and congressional staff.

"If you wanted to design a terrorist bug, it would have the features of the brown marmorated stink bug," he said. Bartlett is working to enlist colleagues in an effort to free up $3 million in federal funds to address the problem.

Tracy Leskey, an entomologist at the USDA's Appalachian Fruit Research Station in Kearneysville, W.Va., said, "We've seen up to 100 percent losses on some farms. The growers I have worked with are very upset, and they're looking for solutions."

Since it was first found in Allentown, Pa., in 2001, the brown marmorated stink bug has spread to 29 states, with the biggest problems in the Mid-Atlantic. They're present in Southern Maryland and the Eastern Shore, too, but do not yet pose a serious threat there.

Homeowners were the first to notice the insect's arrival in recent years. The adult bugs begin to invade homes in large numbers in early autumn, seeking shelter from the cold. After wintering in the walls or the attic, they emerge in the spring by the dozens looking for a way out of the house.

Homeowners have tried to shoo, sweep or vacuum them away. Those who resort to crushing them quickly discover why the critters are called stink bugs.

Agricultural specialists saw stink bug populations rising on Maryland farms last year, toward the end of the growing season.

"They were causing some damage, but the population wasn't high enough to be concerned," said Joe Fiola, a fruit specialist at the University of Maryland's Western Maryland Research and Education Center in Keedysville.

Now everyone's concerned.

A growth spurt

"The population this year absolutely exploded," Fiola said. "They emerged much earlier in the season than we expected. They were in the orchards in late April and early May when the fruit was really small, especially the peaches. They were causing damage before we even knew they were out there."

It's not clear why the population grew the way it did.

"We're split on it as entomologists," said Jerry Brust, an integrated pest management and vegetable specialist at UM's Central Maryland Research and Education Center, in Upper Marlboro.

"Some of us think the snow cover we had over the winter … acts as a blanket and actually keeps them warm," at least those that over-winter in the open, he said. "And then, because it got so hot, they reproduced much more quickly."

And because populations were so high, the bugs might have "spilled out" from the weeds and trees where they'd been feeding, and moved onto the relatively well-watered farms.

Everyone seemed surprised at how voracious these newcomers have proved to be.

The Asian stink bugs, unlike their native cousins, feed on fruits and other plant parts during each of five development stages, called "instars." And they like just about everything they encounter.

"Not in my history, or in any of the growers' history, have we ever seen something come on this quickly and cause this much damage," Fiola said. "There is continuous pressure in the orchard. And it's not limited to orchards. There are hundreds of acres of sweet corn infested, major losses in vegetables."

Feasting stink bugs have damaged berries, grapes, peppers, tomatoes, squash, field corn and soybeans. "That's what makes it so devastating. It's highly unusual for an insect pest," said Brust.

The bugs don't lay eggs in the fruit and vegetables, Leskey said. "They pierce the fruit with their mouth parts and essentially suck the liquid out, leaving a dry, corky area that can go rather deep into the fruit."

The damage makes the fruit or vegetable unappealing to consumers, and cuts sharply into its value, said Black.

"You can eat it; it's fine. But people have to learn to use a knife again," he said. "You can cut out the blemish and the rest of the apple is quite edible."

Not picture perfect

American consumers, however, expect perfect-looking fruits and vegetables. So most of the affected apples and peaches must be sold — for less than half their value — as seconds, or "utility" fruits, suitable for canning or cider, but not the grocery store or roadside stand.

Stink bugs in the cornfields are a double problem, Black said. They seem to suck juices from the corn silk, which prevents the kernels from developing. "Some ears don't have kernels."