Soybeans. “When this insect is feeding on kudzu, it’s beneficial,” Clemson University entomologist Jeremy Greene said. “When it’s feeding on soybeans, it’s a pest.”

Like kudzu, which was introduced to the US South from Japan in the late 19th century as a way to fight erosion on the region’s worn-out farmlands, this insect is native to the Far East. And like the invasive vine, 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 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 feast, said Tracie Jenkins, a plant geneticist at the University of Georgia.

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

One thing that concerns researchers is the bug’s hardiness. Jenkins said 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.

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 going.

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

From there, it’s not far 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.

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 US 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.

“The problem with this insect is its sheer numbers,” said North Carolina State University pest specialist Jack Bacheler. “It’s not that this thing can’t be controlled. But it’s probably going to be costly to do so.”