Scientist SWAT team combats stink bug invasion

By Linda Weiford, WSU News

Bug-110PULLMAN, Wash. – An alien pest that smells like dirty socks and devours crops might become Washington state agriculture’s Public Enemy No. 1 in less than five years, government and university researchers are warning.

In the meantime, the scientists are ramping up efforts to blunt this mounting threat to the region’s fruit crop industry.

Washington State University is one of 10 institutions across the nation whose researchers are working to head off an invasion of the brown marmorated stink bug.

Tracy Leskey is an entomologist with the U.S. Department of Agriculture who’s leading this scientist SWAT team.

“One of the most disturbing things about this bug is its scope,” she said from her office in Kearneysville, W. Va. “In a relatively short period, they’ve spread to 40 states; and they’ve made it look so easy.”

Bugs gone wild

Since the brown marmorated stink bug, or Halyomorpha halys, was discovered in Pennsylvania in 1998, the shield-shaped insect from Asia has advanced down the east coast and spread west nationwide – gorging on everything from peaches and grapes to soybeans and corn. In a single year, it took a $37 million bite out of the mid-Atlantic’s apple crop.

A brown marmorated stink bug circles an apple held by WSU entomologist Richard Zack. (Photos by Robert Hubner, WSU Photo Services)

Now that this voracious bug has landed in Washington and elsewhere in the Northwest, “researchers are trying to learn everything they can about this insect to prevent big crop losses as it establishes itself here,” said WSU entomologist Richard Zack.

“Because they’re nonnative to this country, we have no natural enemies to keep their numbers down,” he said. “They keep expanding their geographical reach and they keep multiplying.”

What’s more, the effectiveness of chemicals for pest control remains iffy: “So far, they’re not as susceptible to insecticides as we would hope,” said Zack.

‘We’ll see more’

Right now, brown marmorated stink bugs are overwintering inside people’s homes, sheds and attics and under wood piles. Some are even being stowed away to new locations in vehicles driven by unsuspecting drivers.

But come May and June, they’ll emerge to mate, lay eggs and find food, said USDA’s Pete Landolt, research leader of the Yakima Agricultural Research Laboratory in Wapato, Wash.

“I expect that, in 2014, we’ll see more brown marmorated stink bugs and we’ll see them in more places in Washington,” he said. “Based on what we’ve seen happen in the eastern United States, unless we can figure out a viable strategy to control them, we could see severe crop injuries in less than five years.”

The stink bug is topped with a marbled shield, hence the name “marmorated.”

Unlike most insects, these bugs are “generalist feeders,” meaning they eat many plant species, said Landolt. They plunge needle-like mouthparts into crops and then suck out the juice or sap.

Fruits, in particular, are vulnerable to damage; Washington is the nation’s leading producer of apples, pears and sweet cherries.

“The insect’s expanding presence here has got growers nervous,” Landolt said, “not to mention the researchers who are tracking population levels and working on ways to keep those levels from soaring.”

So far, the bugs are most concentrated in Clark and Skamania counties, just across the Columbia River from infestations in Oregon, said Landolt. Sporadic numbers are appearing in areas such as Klickitat County, the Yakima Valley, Walla Walla and Chelan County. All are fertile agricultural areas where orchards and vineyards stretch across landscapes for miles.

Grape growers on alert

Wine grapes are another major crop in Washington, where more premium wines are produced than any state except California. To date, no brown marmorated stink bugs have turned up in the region’s vineyards, said WSU entomologist Jay Brunner, regional leader of the research team.

But not so in neighboring Oregon, where scientists from Oregon State University have trapped them at three vineyards. OSU is also a member of the scientific group.

“It does attack grapes, including wine grapes,” said Brunner. In addition to puncture wounds, another concern is the potential tainting of aroma and flavor if the bugs find their way into lugs, or crates, during harvest, he said.

This could be a problem considering that “dirty socks,” “spoiled cilantro” and “skunky” are terms used to describe the scent emitted by stink bugs when threatened or crushed.

Interstate travel, innocent bystanders

These bugs can fly, but vehicles best explain how, in Oregon and Washington, they’ve settled in areas off the I-5 interstate and highways.

“They are the most amazing hitchhikers,” said entomologist Michael Bush of WSU’s Yakima County Extension. They catch rides in boxes and crates packed in cars, trucks and trailers or even in a groove between seats, he said.

The thin white bands on its antennae distinguish the insect from native stink bugs that can be beneficial.

Bush works with other WSU extension scientists to teach master gardeners, field workers and the public how to tell brown marmorated stink bugs from our similar-looking native stink bugs.

“Several of our native stink bug species are beneficial because they feed on other insects that damage crops,” he said. “That’s why it’s important to know the difference and not kill them all.”

That said, the easiest way to ID the brown marmorated variety is by the thin white bands on its antennae, he said.

Bring in the wasps?

This tiny parasitic wasp from Asia attacks the eggs of stink bugs. (Photo by M. Roche, “Stop the Brown Marmorated Stink Bug” website)

Back home in Asia, the stink bug’s mortal enemy is a parasitic wasp that lays eggs inside stink bug eggs, destroying them. This tiny terrorist – the size of a gnat – could be released on U.S. soil to serve as a natural pest controller, said project leader Leskey of the USDA.

But first, scientists must do “rigorous screening” to make sure it’s safe to introduce in this country, she said.

Chemicals that lure stink bugs into traps and light intensity levels that attract them are also being looked into, she said.

A WSU guide helps people distinguish between the brown marmorated and native stink bugs and solicits help from the public to track the intruder. See

For more information, go to the Stop the Brown Marmorated Stink Bug national research team’s website at



Richard Zack, WSU entomologist, 509-335-3394,

Jay Brunner, WSU entomologist and regional research team leader, 509-663-8181, ext. 238,

Pete Landolt, USDA Yakima Agricultural Research Laboratory, 509-454-6570,

Linda Weiford, WSU News, 509-335-7209,