Photograph: Hemlock mortality at Linville Gorge. Photograph credit: CAMCORE.

A pile of cottony-speckled logs sits prominently against the back wall of entomologist Dr. Fred Hain’s research lab in NC State University’s College of Agriculture and Life Sciences. The logs are samples of a history of devastation for North Carolina’s Fraser fir, a native tree popular for its beauty both in the forest and as the state’s best-selling Christmas tree. On the bark of the logs are live colonies of balsam woolly adelgid, an exotic insect from Europe that nearly eliminated the Fraser fir forests in the 1950s and ’60s and that continues to threaten North Carolina’s multi-million dollar Christmas tree industry.

The balsam woolly adelgid (BWA) has threatened Fraser firs since the 1960s, when large populations of Frasers at Mount Mitchell began dying as a result of BWA infestations. At that time, the US Forest Service treated the pest by deploying natural enemies and pesticide sprays. Unfortunately, neither proved effective, and BWA populations spread throughout the southern Appalachian forests. In 1995, North Carolina forests became host to another enemy: the hemlock woolly adelgid (HWA), a serious pest of hemlocks that now threatens hemlocks along the east coast and into the Midwest.

Frustrated by the ineffectiveness of biological and chemical controls, Hain initiated the Partnership for Threatened Forests along with long-time colleague Dr. John Frampton of NC State’s Department of Forestry and staff members from CAMCORE, the university’s international cooperative for gene conservation and tree improvement. The goal of the partnership is to breed Fraser firs and hemlocks that can survive an adelgid infestation.

The woolly adelgids are tiny black insects that grow white, waxy threads on the outside of their bodies, giving them a “woolly” appearance. The nymphs insert their mouthparts into the bark of the tree and stay there until death. Hain has spent the past several years collecting adelgid-covered Fraser fir logs and observing how the tree responds to the insect’s attack. Pointing at the reddish markings on the rim of the trunk on one of his logs, he explains that Fraser firs succumb to the adelgid because they overreact to the attack.

“When you cut a tree down, instead of looking whitish, it has a reddish color,” he explains. “It acts as if it’s being attacked by a much bigger insect. The adelgid is feeding on the bark, but the tree’s response is going into the xylem. The tree is attempting to isolate a wound by producing a chemical around the wound site, and it becomes impermeable tissue. It can’t translocate fluids.” Christmas tree growers spend hundreds of dollars treating for balsam woolly adelgid. Although an infested Fraser fir will take years to die, the top of the tree reacts almost immediately—the distinct terminal branch at the top of the tree is bent over. As a result, the tree is not marketable.

Hain and Frampton intend to breed a BWA-resistant Fraser fir and an HWA-resistant hemlock. The idea began several years ago as they observed Asian firs in Europe covered in woolly masses of adelgids, but still thriving. Hain hopes to discover how each tree’s genetics plays a role in how it reacts to a BWA infestation. To find out, Hain and entomology graduate student Leslie Newton use a “suspended log method,” hanging an adelgid-infested log horizontally above planted seedlings from various Fraser fir and hemlock populations. As the adelgids begin to multiply, Hain and Newton look for differences in the population on one seedling versus another. Hain hopes to find resistant seedlings from existing North Carolina trees that will foster a new adelgid resistant breed. CAMCORE – which stands for Central America and Mexico Coniferous Resources — has been providing hemlock seeds for the project.

“I wanted to look at the whole picture,” Hain says. “These pests are introduced, and in the rest of the world they are not a problem. Why is that? Biological control may be part of the answer, but it’s not the whole answer. The tree has to tolerate the insect in time for the natural enemies to work. Right now they can’t tolerate it.” In addition to CAMCORE’s hemlock conservation specialists, Hain has welcomed anyone into the partnership who is working on either of the adelgid species.

“As we continue to talk about BWA and HWA, we’re including anyone in the partnership who works on host resistance in hemlocks or firs,” Hain says. “Others are interested, including a number of people throughout the eastern seaboard. The next step is to generate money.”

With federal funding in flux, Hain is seeking donations by private philanthropists. He hopes that some of the foundations that threw thousands of dollars into rearing facilities for biological control will become interested in funding resistance breeding. While young Fraser firs in the North Carolina mountains will not feel the effects of the BWA for the next several years, Hain and his partners know that the fading hemlock forests and frustrated Christmas tree growers have a much more immediate need. So as they continue to search for new funding sources, the logs in Hain’s lab serve as a reminder that the research can’t stop.

Written by: Rosemary Hallberg, Communication Specialist, Southern Region IPM Center, 919-513-8182 or rhallberg@sripmc.org

Photograph: Hemlock mortality at Linville Gorge. Photograph credit: CAMCORE.