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Scientists around the United States are studying a natural enemy of the brown marmorated stinkbug that has been imported from China with the hope that it might help keep the pest in check in this country.

The parasitic wasp Trissolcus halyomorphae was collected in the fall of 2011 by U.S. Department of Agriculture scientists in China, where it was found emerging from brown marmorated stinkbug eggs. The species was not known before. It was imported into a USDA rearing facility in Delaware and is being held in quarantine until scientists determine if it would safe to release as a potential biocontrol.

A concern with the import of exotic biocontrol agents is that they might attack native species, so research is focusing on how the wasp reacts to nontarget stinkbug species, some of which are beneficial.

Christopher Hedstrom, graduate research assistant with Oregon State University,  is working with the new parasite at the university’s USDA-approved quarantine facility in Corvallis.

First, the scientists determined that the parasite does attack and kill eggs of the brown marmorated stinkbug (Halyomorpha halys). Now, they are exposing the parasite to eggs of stinkbug species that are native to Oregon and the Pacific Northwest to find out if it attacks them, too. Initially, no-choice tests are conducted, which involve putting a ­parasite in a vial with the egg of one species to see if it attacks. If it does, more tests are conducted where the parasite is exposed to multiple species, to study its preferences.

Hedstrom said he and his colleagues are about halfway through screening native stinkbugs for their vulnerability to the wasp. If their study proves that the parasite only attacks the brown marmorated stinkbug and is not a threat to other species, the next challenge will be to find out if the parasite can survive in West Coast conditions. Because of differences in climate, such as temperature and rainfall, imported natural enemies often fail to become established.

The Oregon Department of Agriculture has received funding from the USDA to conduct the studies. It is hoped that, if all goes well, the parasite could be reared in insectaries and released into the natural environment at about the same time that brown marmorated stinkbug populations take off in the Pacific Northwest, perhaps in two or three years’ time, in an attempt to avoid the kind of damage that the East Coast has experienced. The bug has been in Portland since 2004 and recently spread to agricultural areas in Oregon, including the Willamette Valley and Hood River.

Helmuth Rogg, manager of the Oregon Department of Agriculture’s insect pest ­prevention and management program, stressed in a press release that the brown marmorated stinkbug has proven a difficult pest to control, so there are big hopes for ­biological control.

“On a pest risk scale of one to ten, I would say the  brown marmorated stinkbug is a 15,” he said. “Hopefully, time is on our side, and we can avoid the big outbreak we’ve seen in eastern states. Biological control can help.”

Scientists in Florida and Michigan are also screening the same parasite against native stinkbugs in those regions and will share their results before any decision is made about rearing the wasp in large enough numbers to release into the environment, the ­Department of Agriculture said.