Warm weather this year has contributed to a resurgence in the mid-Atlantic region’s brown marmorated stink bug population, with researchers estimating at least a 60 percent increase this year in insects that soon will be making their way indoors to escape cooling temperatures.
Record summer heat that lasted through September favored the resurgence of stink bugs, which breed twice a year — in spring and summer. Michael Raupp, entomology professor at the University of Maryland, said the favorable conditions enabled the bugs to complete their second breeding cycle in “spectacular fashion,” meaning they are poised to invade homes and businesses in large numbers.
Some scientists even have speculated that this year’s infestation could rival that of 2010, when swarms of the creepy-looking invasive insect attacked crops and unsettled residents of the mid-Atlantic states.
Far fewer of the bugs were spotted last fall because of cool and wet weather, which made it difficult for them to produce a second generation, Mr. Raupp said. As a result, the stink-bug population was smaller in the spring.
“This gave people the impression that the stink bugs had vanished,” Mr. Raupp said. “The return is kind of a misconception. They never really went away.”
Native to Asia, stink bugs were first found in the United States in Allentown, Pa., in 1998, and have been spreading ever since. The massive 2010 infestation was caused in part by an early warm spring.
“When it warms, it’s a signal that trees are going to have buds, leaves and fruits; then they become active,” Mr. Raupp said.
Characterized by their shield shape and the foul odor they emit when crushed, stink bugs will be looking for refuge indoors as winter approaches. They seek “tight, cool, dry spaces,” such as the insides of windowsill cracks, door jambs, shutters and attics, said Tracy Leskey, an entomologist at the U.S. Department of Agriculture’s Appalachian Fruit Research Station in Kearneysville, W.Va.
Ms. Leskey, who estimated the 60 percent increase from last year, told a Massachusetts newspaper that 2010 proved to be the most devastating year for apple crops damaged by the bug, with $37 million in losses in the mid-Atlantic states. She said even higher numbers of the stink bugs have been seen this year in Maryland and Virginia, among other states.
Swarms of stink bugs have other effects as well.
“It’s the vast number of these big, goofy bugs that freak people out,” Mr. Raupp said, adding that it is not uncommon for several hundred bugs to cluster inside homes.
As the bugs become dormant during winter, they also look for protective spots outdoors, such as underneath the bark of dead trees. In six months last year, Doug Inkley, senior scientist at the National Wildlife Federation, counted 26,000 bugs inside his home in Knoxville, Md., and 30,000 outside.
“They wander inside at nighttime. They will be buzzing around your home,” Mr. Raupp said.
Mr. Raupp said keeping the warmth in and cold air out will help expel the insects from homes. Ways to get rid of them include using a vacuum, dropping them into soapy water and luring them into a light trap.
Mr. Raupp said natural predators including spiders and preying mantises also can rein in the population.
The insects can cause significant damage to crops, feasting on apples, peaches, grapes, corn, tomatoes and soybeans, Ms. Leskey said. This year’s damage estimates are not available because the harvesting season is still under way, she said.
At the Appalachian Fruit Station, entomologists are keeping growers informed of a potentially sizable brown marmorated stink bug population that could be munching on crops next spring. To monitor the population, researchers have identified and synthesized a pheromone that attracts male and female brown marmorated stink bugs to traps.
“This way, the grower doesn’t have to scout the entire orchard; he or she just has to look at the trap,” Ms. Leskey said.
Jayson Harper, a professor of agricultural economics at Pennsylvania State University, said growers need to spray more insecticides on fruits and vegetables to eliminate stink bugs.
“At the end of the season, we used to spray fruits and vegetables with just fungicide. Now we have to use insecticides,” Mr. Harper said.