Researchers focus on attacking, killing dreaded stink bug

By JASON SHOUGH

Columbus Dispatch

COLUMBUS

Kim Hoelmer stood beneath a tree in eastern China a year ago and studied its leaves.

He scanned a section as sunlight passed through the foliage, revealing the backlit image of the first thing he was looking for — an egg mass laid by a brown marmorated stink bug.

Hoelmer pulled the leaf down for a closer inspection and spotted the second thing he had hoped to see — evidence that a particular parasitic wasp had been there, too.

Bingo.

The scientist collected the eggs and returned to his lab at the U.S. Department of Agriculture, where he hopes to turn the wasp into a weapon to stop the stink bug.

The invasive species was first identified in Allentown, Pa., in 1998, but researchers there think it had been around for at least a couple of years. It hit Ohio in 2007 and now is in 33 states, including every state east of the Mississippi River and along the Pacific coast.

The bug, they say, probably hitched a ride on containers from Asia, where it damages fruit and soybeans from China to Japan.

The emerald ash borer arrived in much the same manner from China and has left in its wake millions of dead trees.

Where it is found, the brown marmorated stink bug, which has no natural predators here, outnumbers native stink bugs 10 to 1. And they eat at least 100 different plants. Last summer, the stink bug damaged 20 percent to 100 percent of the fruit crops in some areas of Maryland and West Virginia, according to government entomologists.

In Asia, however, the bug is kept in check by a wasp in the genus Trissolcus. This wasp preys exclusively on the eggs of the brown marmorated stink bug. It simply injects its own eggs into the stink bugs’ eggs. Within days, wasp larva hatch and feed on the developing stink bugs.

Hoelmer is studying the Trissolcus in hopes of one day setting the wasp loose on the brown marmorated stink bug in the U.S.

“Our approach is to introduce a permanent solution,” said Hoelmer, who works in the agency’s Beneficial Insects Introduction Research Unit.

Right now, it might be the only thing that works. Commonly used pesticides have had little effect on the bug.

Hoelmer and his team are testing four species of Trissolcus wasps at the University of Delaware.

Finding a way to stop stink bugs is a growing concern. Entomologists worry that the insect is breeding faster than it did when it first arrived, from one generation every year to two or even three a year, said Ron Hammond, an entomologist at Ohio State University.

Hammond, like others, is wary of introducing new species.

“You have to be really careful whenever you release something like this. You don’t want to cause more harm than what the stink bugs do,” Hammond said. “We don’t want to introduce a natural enemy of the brown marmorated stink bug who will attack all stink bugs here. We want it to be precise.”

The method is known as “classical biological control” and has been employed in the United States since 1888 to control more than 100 invasive species, said Jian Duan, a USDA scientist.