WASHINGTON — After a relative reprieve from the scourge of the brown marmorated stink bug — the infamous pest known for devastating crops and emitting a pungent odor when crushed or irritated — experts caution that it will likely make a reappearance in the mid-Atlantic area this year.

The comeback would come two years after many farmers throughout the region saw their crops extensively damaged by swarms of the brown, shield-shaped insects.

The stink bugs, known to feed on over 300 varieties of host plants, resulted in about $37 million in losses from damage to apple crops alone in 2010; crops of raspberries and blackberries were also ravaged, and many organic farmers saw significant damage to crops of tomatoes, peppers and beans, experts reported.

Lawmakers, entomologists and the agricultural community scrambled for a solution to a problem that was only expected to worsen. A special exemption was approved in 2011 by the Environmental Protection Agency for the use of a highly toxic insecticide to help growers fight the insects. Homeowners braced themselves for the unwelcome presence of the bugs, which seek sheltered places — such as houses, garages and barns — to hibernate for the winter. Farmers prepared for another year of battle in their fields, orchards and vineyards.

But then scientists and farmers alike noticed a sudden and dramatic decrease in the number of stink bugs present during the fall of 2011. Entomologists still aren’t sure how to explain the change. It’s possible, they said, a succession of strong storms late that summer culled the population.

“Just when it was getting really bad, it started getting better,” said Doug Fabbioli, a fruit grower and winemaker who owns Fabbioli Cellars in Leesburg, Va.

But now, scientists caution, the insects appear to be resurgent.

Christopher Bergh, a Virginia Tech associate professor of entomology, said the overwintering population of bugs this past fall was “substantially larger” than that observed in 2011.

“I don’t want to raise any red flags unnecessarily,” he said, “But growers are going to definitely need to remain vigilant starting in the 2013 season.”

Bergh said the early arrival of spring last year also helped farmers and growers avoid the worst of the bugs; many early-season crops got a head start on the insects, which then emerged in smaller numbers.

“There was less opportunity for them to do damage,” he said.

But Tracy Leskey, a research entomologist with the U.S. Agriculture Department, said the reduced population of bugs “essentially rebounded over the course of the growing season” last year, and homeowners saw far more bugs coming inside to overwinter than they did the year before.

“We have been trapping in the late season, and we know the populations are probably at least 60 percent greater this year compared to [2011],” she said. “If they survive over the winter, there will be many more bugs in the spring.”

At Butler’s Orchard in Germantown, Md., co-owner Wade Butler said he and other employees discovered swarms of the insects recently while working in one of the farm’s open barns.

“Between two boards or two pieces of wood, you’d see a couple of hundred stink bugs there,” he said. “It was kind of surprising.”

Still, he said, he was “cautiously optimistic” that the coming year might not be so terrible.

Fabbioli said he noticed a large number of second-generation, young bugs in the autumn, a shift from the previous year.

“We may be having some trouble [this year],” he said. “I hope they’re wrong, but it definitely was more this fall — not as far as the damage to the fruit, but just visually, how many bugs you saw.”

As residents, farmers and growers have welcomed the respite from the stink bugs, entomologists have been busy continuing their research, Leskey said. Much about the bugs is still unknown, and scientists are eager to develop a better understanding of the environmental conditions and natural predators that might affect the insect’s population.

“We are finding that there are a number of different predators and parasites that are attacking them, and it varies according to the different crops and landscapes,” Leskey said.

Despite the progress of ongoing research, Bergh said the region is “not out of the woods” yet.

“We don’t see any pronounced indications of natural enemies suppressing brown marmorated stink bug populations as effectively as we would need to breathe a sigh of relief,” he said.

Leskey noted one particularly hopeful development: Within the last year, scientists have identified and synthesized a pheromone emitted by the bug. Traps baited with the synthetic compound serve as an effective lure, allowing scientists and farmers to better detect their presence, she said.

“That tells growers that the bugs are in the area. It’s an early warning tool, so they know that they need to make management decisions” such as whether to apply insecticides, she said.

Beyond serving as a warning system for farmers, Leskey said, identifying the pheromone will also allow entomologists to more effectively track the population, movement and activity of stink bugs throughout the season — opening the door to a deeper understanding of the insects and how to control them, she said.

“We’ll start to be able to look at their seasonal patterns, and better understand what they’re doing,” she said. “It’s a really exciting development.”

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