NC State University News ServicesCampus Box 7504Raleigh, NC 27695-7504919/515-3470[email protected]www.ncsu.edu/news.html
Media Contacts:Dr. Fred Hain, 919/515-3804 or [email protected]Kevin Potter, NC State News Services, 919/515-3470 or [email protected]
June 6, 2001
NC State Scientist Battles Insect Threatening Hemlock Forests
FOR IMMEDIATE RELEASE
A tiny Asian insect currently decimating hemlock forests in the northeastern United States has appeared in North Carolina near the Great Smoky Mountains National Park.
A forest entomologist at North Carolina State University is looking for ways to stall the advance of the aphid-like hemlock woody adelgid, an exotic insect that defoliates an ecologically and aesthetically important tree species in the Southern Appalachians.
Dr. Fred Hain, NC State professor of entomology and forestry, explains that the pinhead-sized insects could wreak even greater environmental damage than the closely related balsam woody adelgid, which has ravaged Fraser fir populations in the high Appalachians in recent decades.
"Eastern hemlock is an important streamside species. If you lose that shade along the streams, I'm not sure what's going to replace it," Hain said. "The hemlock woody adelgid situation is particularly pessimistic because the hemlock does not reproduce as prolifically as the Fraser fir does. That's really bad news for the hemlocks."
It could also be bad news for forest life that depends on hemlocks. Fish and other aquatic life could suffer if hemlocks die off in great numbers because more direct sunlight would reach streams, increasing water temperature. And hemlock provides cover to several bird species.
The hemlock woody adelgid, which has the scientific name Adelges tsugae, feeds entirely on the new growth at the base of hemlock needles, killing a tree in as little as three to four years. The insects form fluffy, cotton-like puffs on infested hemlock trees.
The East Asian species was accidentally transported to the eastern United States in the 1950s. Initially, it was a problem mostly in ornamental hemlock trees, until about 15 years ago -- after a severe storm may have blown the insects into hemlock forests in the Northeast and in the Appalachians. Since then, the adelgid has killed millions of trees from Massachusetts to Virginia.
First reported in North Carolina in 1995, hemlock woody adelgid has been documented in most of the mountainous counties that border Virginia. For the first time this year, it was found at several Graham County sites near Great Smoky Mountains National Park and at a Yancey County site near Mt. Mitchell. One of the locations is also close to Joyce Kilmer Memorial Wilderness Area, which is home to several hemlock trees that are 400 to 600 years old.
Individual trees can be treated with insecticidal soaps and horticultural oils to control the hemlock woody adelgids. But such an approach isn't practical on a landscape scale, including at Great Smoky Mountains National Park, where eastern hemlock (Tsuga canadensis) covers an estimated 3,820 acres, or 1 percent of the park. Much of that area is old growth forest that contains hemlock trees more than 400 years old.
As an alternative, Hain and other scientists are studying whether insect predators might keep the adelgid under control. Recently, Hain and an NC State graduate student, Matt Wallace, found that native insects are not likely to do the job alone, since the adelgids "hibernate" during the summer months when those predator species are active. Additionally, many of the predators are generalists that prefer feeding on alternate food sources.
Hain and other entomologists are hoping the Japanese ladybird beetle (Pseudosymnus tsugae) might prove more successful. About the size of a poppy seed, the beetle feeds exclusively on the hemlock woody adelgid, even during the adelgid's hibernation stage. Research has established that releasing the ladybird beetle near adelgid infestations doesn't pose a threat to native insect species.
"It seems to have all the characteristics to be a good natural predator for the hemlock woody adelgid," Hain said.
Two years ago, scientists released 10,000 ladybird beetles at North Carolina's Hanging Rock State Park. While they haven't yet impacted the adelgid population there, Hain has begun to raise ladybird beetles in an NC State lab for future releases in the North Carolina mountains.
He notes that other predators -- including native Southeastern insects and species from the Pacific Northwest, where the adelgid has not caused major problems -- also might be necessary to control the spread of the pest. "We don't think this one predator is going to do it all," he explained. "We think it's a complex of predators that might be useful in controlling the hemlock woody adelgid."
Hain hopes to study isolated stands of hemlock trees that have lived as long as seven or eight years after being infested. These sites may have characteristics that will allow scientists to predict where the hemlocks are likely to live the longest after an infestation. It is in such stands that predator releases are more likely to be successful since the predator will have more time to affect the adelgid population. In addition, some hemlocks, either native or from outside the eastern United States, may be resistant to the adelgid; such hemlocks eventually might be planted on sites where the insect has wiped out the existing hemlock trees.
"Is the survival of those trees site-specific -- because of where the trees are located -- or is there something genetic that allows them to resist the hemlock woody adelgid?" he asked. "If so, we can try to breed resistant strains and establish a natural balance among pest, predators and host, similar to the balance in Asia and western North America."
Hain adds that it's important to recognize that there is no current solution to the hemlock woody adelgid problem: Extensive research efforts will be necessary to bring the pest under control. "Hopefully, that can be done before we lose all the old-growth hemlock," he said. "However, the resources required to support this research effort are not readily available."
- potter -
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