Can wasps squash the stink bug plague?

Apr 28, 2011
Originally published on April 26, 2011 12:01 am

Home is where the heart is. It's also probably where a lot of stink bugs are right now, crawling out from cracks and crevices. They were introduced into Allentown, Pa., from Asia in the 1990s and have been spreading ever since, reaching seemingly plaguelike proportions in the mid-Atlantic states. But an experiment is under way to reintroduce the stink bug to its mortal enemy: a parasitic Asian wasp.

The shield-shaped brown marmorated stink bugs descended on the mid-Atlantic region with the fury of a plague last year. If you try to crush them or vacuum them up, they release a smell like cilantro and burning rubber.

But for Bob Black, who runs Catoctin Mountain Orchard in Thurmont, Md., they're more than just a nuisance. It's about money.

"This thing is going to put a big chapter in my book of life. I mean, I've never had anything affect me like this," he says.

Just like many other farmers across the region, Black saw a lot of his crops decimated by marmorated stink bugs. They take their long needle-like mouthpiece and stick it into the flesh of fruits and vegetables, leaving them bruised and disfigured.

"One of our late [apple] varieties — Pink Lady — we had 50 percent damage on that," he says. "I can handle a few percent, but gets up to 25 percent, 50 percent — that's pretty devastating to me."

And as Black discovered, his usual pesticides didn't really do much.

"This one can actually play in it and eat it, and it won't even kill it — that's how tough this insect is," he says.

And this year, the stink bug invasion will probably be worse.

"We're going to hear a collective wail up and down the East Coast as hordes of these things come out of people's attics and find their way outdoors," says Mike Raup, an entomologist at the University of Maryland.

"They're now found in more than 30 states, as far west as Washington and California; as far south as Florida they've been detected," he says. "But right here in the mid-Atlantic region — this is ground zero for the brown marmorated stink bug."

He says at the core, the problem is pretty basic: When they escaped Asia, they simply arrived here without their natural enemies.

Invading The Invader

A hundred miles away in Newark, Del., that is exactly what scientists are studying at a U.S. Department of Agriculture insect lab. Outside a red door marked "Quarantine," entomologists Kim Hoelmer and Kathy Tatman are suiting up.

Behind the door are a myriad of insects being evaluated to see if they can fight invasive foreign pests that have gone wild in North America. The corridors of the complex are bathed in dark red light, which minimizes insect flight movement.

"Because most insects can't see red, this looks like a dark room to them," Hoelmer says.

Everything is designed to prevent escape, including the building's air and water systems.

Tatman pulls out tray after tray of little vials and petri dishes from modules whose temperature, light and humidity are precisely controlled. It's an insect growth chamber. Inside the vials, rafts of tiny, pearly green orbs sit on leaves. They're stink bug eggs.

"This is a typical example of a fresh brown marmorated stink bug egg mass — 25 to 30 eggs," Hoelmer says. "We're exposing them to female Trissolcus wasps."

The tiny black dots are zipping around in the jars. Just 2 millimeters long, the parasitoid Trissolcus wasps, from China, Japan and Korea, don't look like much more than gnats. They don't bite or sting, and they feed on nectar, but in Asia, they are the natural nemesis of the brown marmorated stink bug.

"These small wasps will deposit their eggs inside the stink bug eggs. Then the parasite egg hatches, and the immature feeds on the inside of the stink bug egg," Hoelmer says. In a few weeks, out pops a new wasp, and no stink bug. Hoelmer says these wasps are extremely specialized.

"If they can't find stink bugs or stink bug eggs to lay their own eggs in, they'll die. They can't survive on anything else," Hoelmer says.

Weeding The Bad From The Good

There are almost 300 types of stink bugs in the United States, and a lot of them are helpful because they eat other pests. So Hoelmer needs to know if these wasps would ever go after other stink bugs, including stink bugs that are closely related to the brown marmorated stink bugs. That's what he's testing in the vials in his lab.

"If they don't attack any of the close relatives, they won't be as likely to attack more distant ones," he says.

It will take three years before he's satisfied that the wasps don't pose a risk. Hoelmer points to examples where this has worked before — gypsy moths were controlled by an introduced fungus, and white flies in California were cut down by other parasitic wasps.

Back at Catoctin Mountain Orchard, Bob Black can't wait.

"Using the wasp will hopefully be our answer. I mean, we've had other things — drought, other issues — but this insect is one of the toughest things that we're going to have to work on," he says.

Until then, seven states are asking the Environmental Protection Agency to relax pesticide regulations. And researchers are looking at pheromones, traps and naturally repellent landscape plants — none of which are considered fully effective. Copyright 2011 WAMU-FM. To see more, visit http://wamu.org.

Transcript

STEVE INSKEEP, host:

Now we have the latest coverage on a plague of stink bugs. Stink bugs look like brown shields with legs. They are native to Asia but showed up in the United States, in the mid-Atlantic region, in the 1990s. And they have now spread to 30 states. But as Sabri Ben-Achour, from member station WAMU, reports, help may be on the way.

SABRI BEN-ACHOUR: By now, it almost seems like everyone in the mid-Atlantic knows these invaders.

Ms. MARION BERHARDT(ph): They're everywhere in the house.

Mr. CHARLES BLACK: In the couch, in clothing.

BEN-ACHOUR: The brown marmorated stink bug.

Mr. FABI MERADIAN(ph): During the daytime, when they swarm, they all come. You know, it was all black on my walls.

BEN-ACHOUR: That's Marion Berhardt, Charles Black and Fabi Meradian.

If you try to crush a stink bug, it gives off a smell like cilantro and burning rubber - pretty annoying in your home. But for farmers like Bob Black, it's about money.

Mr. BOB BLACK (Co-owner, Catoctin Mountain Orchard): This thing is really going to put a big chapter in my book of life. I've never had anything affect me like this.

BEN-ACHOUR: Black is out checking his stink bug traps at his orchard in Thurmont, Maryland. Like a lot of mid-Atlantic farmers, he's seen some of his crops decimated by marmorated stink bugs. They take their long, needle-like mouthpiece and stick it into the flesh of fruits and vegetables, leaving them bruised and disfigured.

Mr. BLACK: One of my late varieties Pink Lady, which a lot of people like we had up to 50 percent damage on that. I can handle a few percent. But you know, it gets up to 25 to 50 percent - that's pretty devastating for me.

BEN-ACHOUR: And this year will probably be worse. Mike Raup is an entomologist at the University of Maryland.

Dr. MIKE RAUP (Entomology, University of Maryland): We're going to hear a collective wail up and down the East Coast as hordes of these things come out of people's attics and try to find their way back outdoors.

BEN-ACHOUR: He says the problem is pretty basic.

Dr. RAUP: When they escaped Asia, they simply arrived here without their natural enemies.

BEN-ACHOUR: A natural enemy. Well, that's exactly what a U.S. Department of Agriculture insect lab has in Newark, Delaware. Outside a red door marked quarantine, entomologist Kim Hoelmer is suiting up.

(Soundbite of zipping)

And taking me down a series of dark, glowing red corridors.

Mr. KIM HOELMER (Research Entomologist, Agricultural Research Service, USDA): You see that all the light is red to minimize insect flight movement - because most insects can't see red. This looks like a dark room to them.

BEN-ACHOUR: Hoelmer takes out try after tray of vials and petri dishes. Inside, rafts of tiny, pearly green orbs sit on leaves. They're stink bug eggs.

Mr. HOELMER: This is a typical example of a fresh brown marmorated stink bug egg mass. And we're exposing them to female Trissolcus wasps.

BEN-ACHOUR: Is that what's crawling around in there right now?

Mr. HOELMER: That's what's crawling around in the vial right now.

BEN-ACHOUR: Parasitoid Trissolcus wasps, from China, Japan and Korea. Just two millimeters long, they don't look like much more than gnats. They don't bite or sting. But Hoelmer tells me that in Asia, they are the mortal nemesis of the brown marmorated stink bug.

Mr. HOELMER: These small wasps will deposit their eggs inside the stink bug eggs. And then the parasite egg hatches, and its immature stage feeds on the inside of the stink bug egg.

BEN-ACHOUR: In a few weeks, out pops a new wasp and no stink bug. Hoelmer says these wasps are extremely specialized.

Mr. HOELMER: If they can't find stink bugs eggs to lay their own eggs in, they'll die. They can't survive on anything else.

BEN-ACHOUR: But there are almost 300 types of stink bugs in the U.S., and a lot of them are helpful because they eat other pests. So Hoelmer needs to know: Will these wasps ever go after them?

Mr. HOELMER: If they won't attack any of the close relatives, they will not be as likely to attack any of the more distant ones.

BEN-ACHOUR: Using one species to control another actually can work, but there have also been some spectacular failures. That's why Hoelmer will spend three more years studying these wasps before he's satisfied they won't solve one problem but cause another.

For NPR News, I'm Sabri Ben-Achour in Washington, D.C. Transcript provided by NPR, Copyright National Public Radio.