If you’ve visited Clingmans Dome, Newfound Gap, or driven along U.S. 441 on a clear day, odds are you’ve seen patches of dead Eastern hemlocks and wondered how they met their demise. Most of these trees were killed (and are being killed) by a non-native insect called the Hemlock Woolly Adelgid (HWA). The HWA is tiny; a magnifying glass can be used to see it up close. That’s when you realize something so small has irreversibly impacted more than 90,000 acres of protected land.
Living off the sap at the base of the Eastern hemlock’s needles, the HWA prevents the tree from absorbing vital nutrients. This causes its needles to change die and fall off. Without these needles, the tree loses its resilience in harsh weather and ultimately starves. The HWA’s presence is easily identified by a protective white, waxy coating it creates on the undersides of hemlock branches.
The loss of the Eastern hemlock means the loss of our park’s the only shade-tolerant conifer. Hemlocks can grow in 5 percent sunlight; their continued success provides shade for other plants and moderates stream temperature and flow. These trees also serve as homes to some neo-tropical birds and many other species. Without them, the park is losing shade along creeks, which is threatening the survival of some trout and damaging the lives of birds. The loss of such a significant tree could have serious and unpredictable consequences for our entire forest ecosystem.
After DNA testing of the HWA, entomologists determined its area of origin – Osaka, Japan – and observe how native plants there combat the presence of HWA. They discovered that in Japan and the U.S. Pacific Northwest, the HWA has natural predators that prevented it from destroying the native hemlocks. That predator, Laricobius nigrinus or “Larry” for short, has been used in the Smokies as a biocontrol since 2002; however, bringing Larry to the park is no easy task.
First, Larry must be ordered specially from the Pacific Northwest or Southern Japan to be reared in East Tennessee. The beetle is high-maintenance, requiring more than five different temperature settings over the course of its growth. Once Larry is ready to be placed on a living Hemlock tree, he has a few more obstacles to overcome. Unfairly advantaged, the HWA can reproduce parthenogenically, meaning it doesn’t need a partner to reproduce. The female HWA can get pregnant on her own and will usually lay between 30-60 eggs at a time. Once the eggs are laid, Larry will feast on them, slowly removing the HWAs from the hemlock.
Great Smoky Mountains Association has for years funded HWA control methods, including the establishment of predatory beetles, foliar spray treatments and systemic spray treatments.