Stinkbug Threat Has Farmers Worried

Asian stinkbugs devour American crops, but are predator wasps the answer?

A stinkbug on a drinking glass in a house in Jefferson County, West Virginia.


Part of our weekly "In Focus" series—stepping back, looking closer. Join author Catherine Zuckerman for a live chat about this story on Monday at 3 pm ET (7 pm UTC) using hashtag #NatGeoLive.

Maryland farmer Nathan Milburn recalls his first encounter.

It was before dawn one morning in summer 2010, and he was at a gas station near his farm, fueling up for the day. Glancing at the light above the pump, something caught his eye.

"Thousands of something," Milburn remembers.

Though he'd never actually seen a brown marmorated stinkbug, Milburn knew exactly what he was looking at. He'd heard the stories.

This was a swarm of them—the invasive bugs from Asia that had been devouring local crops.

"My heart sank to my stomach," Milburn says.

Nearly three years later, the Asian stinkbug, commonly called the brown marmorated stinkbug, has become a serious threat to many mid-Atlantic farmers' livelihoods.

The bugs have also become a nuisance to many Americans who simply have warm homes—favored retreats of the bugs during cold months, when they go into a dormant state known as overwintering.

The worst summer for the bugs so far in the U.S. was 2010, but 2013 could be shaping up to be another bad year. Scientists estimate that 60 percent more stinkbugs are hunkered down indoors and in the natural landscape now than they were at this time last year in the mid-Atlantic region.

Once temperatures begin to rise, they'll head outside in search of mates and food. This is what farmers are dreading, as the Asian stinkbug is notorious for gorging on more than a half dozen North American crops, from peaches to peppers.

Intruder Alert

The first stinkbugs probably arrived in the U.S. by hitching a ride with a shipment of imported products from Asia in the late 1990s. Not long after that, they were spotted in Allentown, Pennsylvania. Since then, they've been identified in 39 other states. Effective monitoring tools are being developed to help researchers detect regional patterns.

There are two main reasons to fear this invader, whose popular name comes from the pungent odor it releases when squashed. It can be distinguished from the native stinkbug by white stripes on its antennae and a mottled appearance on its abdomen. (The native stinkbug can also cause damage but its population number is too low for it to have a significant impact.)

For one thing, Asian stinkbugs have an insatiable appetite for fruits and vegetables, latching onto them with a needlelike probe before breaking down their flesh and sucking out juice until all that's left is a mangled mess.

Peaches, apples, peppers, soybeans, tomatoes, and grapes are among their favorite crops, said Tracy Leskey, a research entomologist leading a USDA-funded team dedicated to stinkbug management. She adds that in 2010, the insects caused $37 million in damage just to apple crops in the mid-Atlantic region.

Another fear factor: Although the stinkbug has some natural predators in the U.S., those predators can't keep up with the size of the stinkbug population, giving it the almost completely unchecked freedom to eat, reproduce, and flourish.

Almost completely unchecked. Leskey and her team have found that stinkbugs are attracted to blue, black, and white light, and to certain pheromones. Pheromone lures have been used with some success in stinkbug traps, but the method hasn't yet been evaluated for catching the bugs in large numbers.

So Milburn—who is on the stakeholders' advisory panel of Leskey's USDA-funded team—and other farmers have had to resort to using some chemical agents to protect against stinkbug sabotage.

It's a solution that Milburn isn't happy about. "We have to be careful—this is people's food. My family eats our apples, too," he says. "We have to engage and defeat with an environmentally safe and economically feasible solution."

Damage Control

Research Entomologist Kim Hoelmer agrees but knows that foregoing pesticides in the face of the stinkbug threat is easier said than done.

Hoelmer works on the USDA stinkbug management team's biological control program. For the past eight years, he's been monitoring the spread of the brown marmorated stinkbug with an eye toward containing it.

"We first looked to see if native natural enemies were going to provide sufficient levels of control," he says. "Once we decided that wasn't going to happen, we began to evaluate Asian natural enemies to help out."

Enter Trissolcus, a tiny, parasitic wasp from Asia that thrives on destroying brown marmorated stinkbugs and in its natural habitat has kept them from becoming the extreme pests they are in the U.S.

When a female wasp happens upon a cluster of stinkbug eggs, she will lay her own eggs inside them. As the larval wasp develops, it feeds on its host—the stinkbug egg—until there's nothing left. Most insects have natural enemies that prey upon or parasitize them in this way, said Hoelmer, calling it "part of the balance of nature."

In a quarantine lab in Newark, Delaware, Hoelmer has been evaluating the pros and cons of allowing Trissolcus out into the open in the U.S. It's certainly a cost-effective approach.

"Once introduced, the wasps will spread and reproduce all by themselves without the need to continually reintroduce them," he says.

And these wasps will not hurt humans. "Entomologists already know from extensive research worldwide that Trissolcus wasps only attack and develop in stinkbug eggs," Hoelmer says. "There is no possibility of them biting or stinging animals or humans or feeding on plants or otherwise becoming a pest themselves."

But there is a potential downside: the chance the wasp could go after one or more of North America's native stinkbugs and other insects.

"We do not want to cause harm to nontarget species," Hoelmer says. "That's why the host range of the Asian Trissolcus is being studied in the Newark laboratory before a request is made to release it."

Ultimately, the USDA's Animal and Plant Health Inspection Service will decide whether or not to introduce the wasp. If it does, the new natural enemy could be let loose as early as next year.

Do you have stinkbugs in your area? Have they invaded your home this winter? Or your garden last summer? How do you combat them? Share your sightings and stories in the comments.