Adult brown marmorated stink bugs on a crab apple tree. (University of Maryland…)
For months in the spring and summer, homeowners and farmers in Loudoun County braced themselves for the return of the brown marmorated stink bug — the dreaded insect that invaded houses, fields and orchards last year, dealing a hefty blow to the agricultural community and the sanity of local residents.
Scientists cautioned that this year might be even worse, with the population predicted to peak between August and October.
But there was an unexpected turn of luck: When fall arrived, the anticipated tidal wave of stink bugs did not.
“We have no idea as to why that is,” said Christopher Bergh, a Virginia Tech associate professor of entomology. “But there does seem to be an emerging consensus that the populations are down compared with last year.”
Last year, stink bugs — which are known to feed on more than 300 types of host plants — inflicted significant damage to crops of apples, peaches, grapes, soybeans and other fruits and vegetables in Loudoun.
Although experts said it was difficult to determine the total amount of losses caused by stink bugs, they estimated that the mid-Atlantic region suffered roughly $37 million in losses last year because of stink bug-inflicted damage to apple crops. Organic farmers, who avoid using insecticides that might provide some measure of protection from the insects, were hit especially hard.
In response to the rising concern among Loudoun’s commercial growers, Rep. Frank R. Wolf (R-Va.) hosted an April forum to address the growing stink bug population and its impact on Loudoun’s agricultural community, and championed a bill to make stink bug research a top priority for the U.S. Department of Agriculture.
In late June, the Environmental Protection Agency approved a temporary exemption for the use of Dinotefuran, a highly toxic insecticide, to help protect apple, pear and peach crops from the bugs.
Bergh said that some Loudoun farmers did use Dinotefuran, especially on apple crops, but that application of the product was “not widespread.” In some cases, it did not appear necessary, he said.
He said that it would be “extremely difficult” to gauge whether Dinotefuran use might account for the lower levels of damage this season but that growers were generally much more focused on stink bug management this year from the outset of the season, because they were more familiar with the threat.
“They were selecting and using products at times when it would be most effective, and generally speaking, I think growers were much more satisfied with their level of control than they were in 2010,” Bergh said.
Tyler Wegmeyer, who owns Wegmeyer Farms in Hamilton and is a director of congressional relations for the American Farm Bureau, echoed Bergh’s assessment and said area farmers were pleased to see fewer injuries to crops.
“We haven’t had the same numbers of the bugs that we did last year,” he said. “There’s been a little damage — there’s been some — but not the severity of last year. We’re very pleasantly surprised.”
Last year, Wegmeyer said, he lost 50 percent of his raspberry crop to stink bugs – a number that he estimates dropped to about 10 or 15 percent this season. He credits the lower numbers of stink bugs, as well as the heightened awareness of local farmers and growers.
“It wasn’t a surprise situation like it was for us last year,” Wegmeyer said. “This was one of the biggest threats that we’ve had in some time. We really spread the word, and people were looking at their crops and taking precautionary measures to make sure they were on top of it.”
Loudoun homeowners also appear to have experienced a reduced population of insects, Bergh said. Last year, many residents were overwhelmed by the sight of the bugs gathering in windows and doorways and crawling across walls and ceilings.
Many commercial insecticides proved ineffective, and focusing on “physical exclusion,” as experts recommended, was often a challenge, particularly in western Loudoun, where many houses are older and difficult to thoroughly bug-proof.
“Fortunately, we haven’t encountered the same number of calls from homeowners this year as we did last year,” Bergh said. “It’s a mystery to us at this time.”
Bergh said that members of a brown marmorated stink bug working group — including stakeholders, researchers and representatives of the EPA, among others — will gather for a two-day meeting late next month, after the harvest season is over and more data has been collected and analyzed. They will attempt to answer the question of why the stink bug population appeared to drop this year and what factors, environmental or otherwise, might have been responsible.
“It will be a comprehensive meeting,” Bergh said. “We’ll begin to interpret what the data mean and what that tells us about how we should proceed in 2012 and beyond.”