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The prospects for one of the mountains’ most beautiful trees look better than they did a decade back.
“The beetles are doing their job,” says Carrie Jubb, insect mass rearing supervisor for Virginia Tech’s Department of Entomology, as she scans the needles of an Eastern hemlock. Jubb, Tom McAvoy, research entomologist for the department, and I are standing in a hemlock grove at the university’s Kentland Farm test forest, near Blacksburg, Virginia.
Jubb’s praise for a creature about the size of a large period is well justified and shows that the labor of her, McAvoy and others in Tech’s Department of Entomology has been well worth the time and effort. For the dead creatures that we are examining are the infamous hemlock woolly adelgids (HWA) that have ravished the Blue Ridge’s hemlocks for several decades now.
Some backstory is required. In the early 1950s, the HWA was first detected in Richmond, Virginia although it is quite likely this Asian invasive insect had been present in our region before then. At first, its spread was slow as two decades passed before the creature appeared somewhere else—Rocky Mount, Virginia.
“But then the HWA just took off,” says McAvoy. “Once it arrived in the Blue Ridge Mountains in the 1980s, the adelgid went north first, then headed south, especially devastating the hemlocks in the Smoky Mountains. In parts of the Blue Ridge, 100 percent of the hemlocks have died, in others, 20 to over 90 percent have died.”
It is the female of the species that does the damage to Eastern and Carolina hemlocks, the two species that live in our region. The insects suck the tree’s life-giving sap, and in the process hide themselves and their eggs in white woolly masses on the needles. The trees typically decline in health for a few years after that, but then rebound by sending out new growth. It is then that the HWA returns in force, this time often causing the tree to critically weaken even more.
“After a few cycles of that,” continues McAvoy, “many trees die. Some may take four or five years to succumb, others 20, and some do not die, especially if they live in the open and have good soil and receive lots of sunlight. Trees that live further north and at higher elevations often have the best chance of survival. But global warming is changing that as temperatures will increase even faster in the northern latitudes, causing HWA to spread even faster and survive at a greater rate.”
Which brings us to why Jubb has lauded an insect, because the creature that has killed the HWA on that Eastern hemlock is Loricobius nigrinus, a beetle native to the west coast. For over 15 years as part of a U.S. Forest Service grant, Tech entomologists (Jubb and McAvoy among them) have travelled to west coast mountains to gather L. nigrinus, rear them and their offspring in a university lab, then ship these predators to various national forest home offices across our region. Of course, this entire process began only after Tech entomologists and others determined that releasing L. nigrinus would not cause harm to any native species.
Next, Jubb shows me a hemlock branch that has been enveloped in a bag so that the L. nigrinus could not reach the HWA feasting on the tree. Of course, that bag contains a healthy colony of HWA and the woolly nurseries within are vibrant and alive, whereas the branches where the beetle has become established show “dried disturbed wool,” proof that the invasive adelgids have expired.
After leaving Kentland Farm, we drive to Tech’s insectary where the L. nigrinus are being raised along with another predatory beetle, the close relative L. osakensis from Japan. Of course, before this beetle species could be released, it had to go through the same rigorous vetting process that L. nigrinus did in order to make sure that no native species would be harmed.
Jubb next shows me the bottles where the adult females lay their eggs, and, also, the nursery containers where the young live and eventually drop into an attached bottle below so that the offspring can spend the summer in soil. One can’t help but be impressed by what Virginia Tech has devised in its battle against the HWA.
“The hemlock is a keystone species in a climax forest,” says McAvoy. “The tree supports a suite of species from native brook trout to salamanders to songbirds such as the blackburnian warbler and blue-headed vireo. It’s imperative that we do everything we can to save it.”
Earlier, Scott Salom, professor of entomology at Tech, had told me that to save our region’s hemlocks a three-prong approach is needed: biological (predatory beetles), chemical, and silvicultural. So several weeks later, I head for the New River Gorge National River in Fayette County, West Virginia, where National Park Service biologist John Perez and many others labor to stop the advance of the HWA. Perez tells me that so far the NPS has used the Imidacloprid insecticide to treat an incredible 17,982 trees with about 25 percent of those being trees that received additional treatments. Trees need to be retreated periodically, especially if an infestation occurs.
“At the New River, Gauley River, and Bluestone River Gorges, hemlocks are often a major component of the few remaining old-growth forests in the parks, with some trees approaching 400 years old,” he says. “Hemlocks are known to harbor two species of birds dependent on hemlock forests: the Acadian flycatcher and black-throated green warbler.
“The dense shade provided by hemlocks helps maintain the micro-climates of globally rare cold-cove forests. Hemlock forested riparian zones help maintain the cool mountain streams so important to native brook trout populations.”
Interestingly, this insecticide is a neonicotinoid, which is based on the natural insecticide nicotine found in tobacco plants. So the same substance which can cause such damage to human health can, in its synthetic form, be extremely toxic to the HWA. Perez says the insecticide is released into the soil and can be effective in controlling the adelgids for up to seven years. The cost to treat a 12-inch diameter tree is about $24.
Since the mid-2000s, the NPS has also been deploying L. nigrinus as a biological control against the HWA.
“Our monitoring of this predatory beetle and its effects on maintaining healthy hemlocks is encouraging,” continues Perez. “We continue to release them into the park. We are hopeful that biological controls can provide a long-term cure, but they are not available commercially.”
The biologist emphasizes that the NPS is very concerned about the use of insecticides in riparian zones and has a $250,000 research project with West Virginia University to study the effects of insecticides on soil macroinvertebrates, salamanders, and benthic (creatures that live on the bottom) aquatic organisms.
After our discussion at park headquarters, Perez and I head for a trail where a stand of hemlocks appears near the pathway’s starting point. The biologist explains that staff selected this stand to be treated so that visitors could easily learn first-hand about the danger the HWA presents and what the NPS is doing about the threat. He also shows me an information display among the trees. Next, he walks over to a particular tree.
“We’ve been monitoring this hemlock since 2006,” he says. “It wouldn’t be so healthy without the treatments. It’s obviously more than held its own. That’s absolutely a victory.” . . .
. . . END OF PREVIEW
The story above is a preview from our Sept./Oct. 2018 issue. For the rest of the story, subscribe today or log in to the digital edition with your active digital subscription.
