BLACKVILLE, S.C. - Kudzu - the "plant that ate the South" - has finally met a pest that's just as voracious. Trouble is, the so-called "kudzu bug" is also fond of another East Asian transplant that we happen to like, and that is big money for American farmers.

Soybeans.

"When this insect is feeding on kudzu, it's beneficial," Clemson University entomologist Jeremy Greene says as he stands in a field swarming with the brown, pea-sized critters. "When it's feeding on soybeans, it's a pest."

Like kudzu, which was introduced to the South from Japan in the late 19th century as a fodder and a way to stem erosion on the region's worn-out farmlands, this insect is native to the Far East. And like the invasive vine, which "Deliverance" author James Dickey famously deemed "a vegetable form of cancer," the kudzu bug is running rampant.

Megacopta cribrari, as this member of the stinkbug family is known in scientific circles, was first identified near Atlanta in late October 2009. Since then, it has spread to most of Georgia and North Carolina, all of South Carolina, and several counties in Alabama.

And it shows no signs of stopping.

Kudzu and soybeans are both legumes. The bug - also known as the bean plataspid - breeds and feeds in the kudzu patches until soybean planting time, then crosses over to continue the moveable feast, says Tracie Jenkins, a plant geneticist at the University of Georgia.

On a recent sunny day, Greene and doctoral student Nick Seiter visited the 10-acre test field at Clemson's Edisto Research & Education Center in Blackville, about 42 miles east of Augusta, Ga.

Starting in the middle of the field, Seiter walks down a row, sweeping a canvas net back and forth through the bean plants as he goes. Bugs cling to his pants and shirt, dotting his face like moles.

"I feel like I'm wearing a bee beard over here," he says. "It tickles."

At row's end, Seiter pushes his hand up through the net. Bugs cascade over the edge and pool on the sandy soil at his feet.

The writhing pile makes a fizzing sound like a freshly opened soda.

"Wow. It's a couple of inches thick," Greene says. "That's just shy of a standard sample that we use to evaluate soybean insects ... and we're looking at a couple of thousand bugs, easy."

The bugs secrete a caustic substance that smells like a cross between a commercial cleanser and an industrial lubricant. Greene says it's unclear whether this is a defensive device, a way of locating each other in a field, or serves some other purpose.

Whatever it's for, the secretions are potent enough to etch the bottoms of the plastic tubs he uses to ship samples to colleagues - and to stain the skin on Seiter's blistered right palm a pale orange that can't be washed off.

"Self tanner," he quips.

These insects are what entomologists call "true bugs," meaning they have needle-like mouth parts that they use to suck on the plant. So rather than feeding on the pods or leaves, as corn ear worms and common stinkbugs do, kudzu bugs attack the stems and leaf petioles, literally draining the life out of the soybeans.

"It's reducing the ability of the plant to produce or to send photosynthate ... the food that the plant makes from the sun, to the fruit, to the seed," says Greene. "So we're going to have ... a reduced number of pods per plant, reduced number of seed per pod, and reduced seed size as well - all the above," he says. "It's not showy in terms of the damage that it does to the plant ... but it's going to cause yield loss."

University of Georgia researchers have recorded losses as high as 23 percent in untreated fields.

"If you add up all our insect damage put together of different pests on soybeans, it probably would total maybe in an average year maybe a 5 percent yield loss," says North Carolina State University pest specialist Jack Bacheler, who has been warily watching the bug's spread through his state. "And sometimes, with agricultural crops like soybeans, 20 bushels an acre at $10 to $13 could be the difference between profit and loss."

One thing that concerns Bacheler and others is the bug's hardiness.

Jenkins says they may be able to respond to temperature and other environmental changes by turning a gene or genes on or off, making them particularly adaptable. They've been found on the windows of Atlanta skyscrapers, from the mountains to the coast.

"And these are pretty resilient little suckers," she says. "They can get on your car, and you can be going 60, 70, 80 miles an hour down the road, and then you stop, and they're still there. And they're alive. So they can take a pretty good lot of abuse."

Studies of climate data in the bug's native land are not encouraging.

"I think it's going to be able to dwell anywhere in the United States that we grow soybeans," says Greene. "So that should be concerning for some of the states that produce millions of acres of soybeans."

That seems to be where they're headed.

In 2010, Georgia produced 6.8 million bushels of soybeans, South Carolina 10.5 million and North Carolina more than 40 million, according to the American Soybean Association.

Jenkins says there have been unconfirmed sightings in Tennessee, which produced 44 million bushels of soybeans last year.

From there, it's just a hop, skip and a jump to states like Illinois and Iowa, where production is measured in the hundreds of millions of bushels.

"They're moving north and west," Jenkins says. "And I think they'll keep going."

Especially without an effective way to control them, says Bacheler.

"Its opportunities to spread seem to be unlimited right now," he says.

Researchers are experimenting with a tiny Asian wasp that lays its eggs inside the kudzu bug eggs. So far, the wasp doesn't seem to have any effect on native insects, Greene says.

Jenkins is trying to pinpoint the country of origin by studying the DNA of a bacterium, or endosymbiont, that lives in the bug's gut. She is comparing DNA from the U.S. bugs with samples sent to her from India, Japan and China.

The samples she's analyzed from the various states have all so far been traced back to the same maternal line - meaning this infestation could have begun with a single gravid or egg-bearing female that hitched a ride here on a plant or in someone's luggage.

Jenkins is hoping a weapon might emerge from her DNA analysis.

"If there's a gene that's allowing it to adapt really well, if it has the insect gene, then I might be able to pull that out and use it against it," she says.

For now, farmers are having to rely on chemicals. So far, the results have been mixed, at best.

Insecticides that work on other stinkbugs have shown promise. But a couple of days after an application, the fields are re-infested.

"We basically spray, we get kill on what we touch with the spray, and then we get decent activity for a couple of days," says Greene. "And then it's pretty much gone."

"The problem with this insect is its sheer numbers," says Bacheler. "It's not that this thing can't be controlled. But it's probably going to be costly to do so."

Greene says the bug is still too new for experts to have come up with the most effective spraying regimen. He hopes data from this season's tests will help solve the problem.

Farmers like Jack Richardson here in Blackville are counting on it.

He has been farming for about 30 years and has about 200 acres of soybeans under cultivation. He buys some of his chemicals from a dealer in Georgia, but a year's more experience hasn't imparted any special wisdom.

"He says, 'If you get too nervous, spray 'em,"' says Richardson, standing waist-deep in a field speckled with bugs. "Well, I've sprayed 'em twice, and it doesn't seem to kill 'em."

Rumbling across the field in his sprayer, Richardson stares at the bugs clinging to the windshield and sighs.

"We don't need any new pests," he says. "We've got enough now."

Allen G. Breed is a Raleigh, N.C.-based national writer for The Associated Press. He can be reached at features(at)ap