The stink bugs are back.

As the hours of spring sunshine lengthen each day, and temperatures climb into the 60s and 70s, the brown marmorated stink bugs that spent the winter hiding under rocks and leaf litter — and in the crevices of homes and buildings — begin to emerge again.

The reappearance of the brown beetle — a menace that sent besieged residents to area hardware stores last year in search of anything that might help control the infestation — is a particularly unwelcome sight for Loudoun County farmers, vintners and other growers, many of whom attended a forum Monday at Woodgrove High School in Purcellville to address the rising stink bug population and its effect on Loudoun’s economy.

The forum, hosted by Rep. Frank R. Wolf (R-Va.) was held in response to concern from Loudoun’s commercial growers, who were hit hard last year as the bugs wreaked havoc on apples, peaches, grapes, soybeans and other fruits and vegetables.

“By 2010, the population densities had increased so dramatically that [stink bugs] were posing a season-long threat,” Tracey Leskey, a research entomologist with the U.S. Department of Agriculture, said at Monday’s forum. “They are known to feed on over 300 different kinds of host plants.”

Although it’s difficult to calculate precisely the amount of losses resulting from stink bugs, Leskey said, the mid-Atlantic region experienced about $37 million in losses last year as a result of damage to apple crops alone. The region’s organic farmers also suffered tremendous losses of tomatoes, peppers and beans, she said.

Some hope has appeared on the horizon: Christopher Bergh, a Virginia Tech associate professor of entomology, told the forum audience about an emergency exemption petition he developed to allow for the use of an insecticide that could help control the bugs. The petition was submitted to the Virginia Department of Agriculture and will be reviewed by the Environmental Protection Agency, Bergh said. He said he hopes the insecticide, Dinotefuran, might be approved by mid-summer, before the annual peak of the stink bug population in August and September.

Dinotefuran has shown promising results in research studies and is used to combat the bug in its native Asia, he said.

“But this is not to be considered a silver bullet,” Bergh cautioned.

Bergh said the stink bug populations here, where the insect has no natural predators, are vastly larger than those observed in Asia, where parasitic wasps and flies help keep the bugs under control.

Leskey said that although the impact of the bugs on the agricultural community is of utmost concern, the pests can also take a psychological toll on homeowners. Many residents become distressed by the sight of the bugs swarming over windows and crawling across walls and ceilings.

“We know of one homeowner [in Maryland] who has removed over 20,000 stink bugs from his home since January,” Leskey said.

For homeowners, she said, the best bet is to focus on physical exclusion: Survey the exterior of homes and barns to look for cracks and crevices where stink bugs might enter, and seal off the structures as much as possible.

That’s no easy task, particularly in western Loudoun, where houses are older and more difficult to bug-proof.

Bergh advised homeowners to avoid “miracle products” that promise an easy fix to the problem, and instead look for products containing the active ingredient permethrin, which can be used to treat exterior surfaces and has proved effective at killing stink bugs.

Leskey said researchers are preparing for another busy season of studying the bugs and are waiting to see whether the 2011 population is affected by the previous winter.

Unfortunately, Bergh said, the population of stink bugs that went into hiding late in the fall appear to be emerging unscathed.

“We can only assume that a substantial number have survived,” he said. “So they will emerge and start doing their thing shortly, once the weather really warms up.”