Tiny bugs may help save hemlocks from extinction
Twenty years ago, hikers making their way up the Cascade Falls trail in Giles County, Va., were shaded by massive old-growth hemlock trees that sprouted from the banks of Little Stony Creek. The evergreens not only cooled the forest air, they provided shade to the native brook trout and a place for songbirds to nest.
But during the last two decades, the hemlocks were cut down as an invasive insect, the hemlock woolly adelgid, infected and killed the evergreen trees that are a cornerstone of the forest ecosystem. The same scenario played out in woods from Vermont to Georgia as the hemlock woolly adelgid and its signature fluffy white masses expanded their deadly range and threatened to change the composition of forests across the eastern United States.
Scott Salom isn’t going to sit by and watch that happen.
Salom, a professor of entomology in the College of Agriculture and Life Sciences, has worked for years to develop ways to combat the woolly adelgid and save the trees.
In 2013, he and his team of researchers released one of the hemlock woolly adelgid’s predators from its native habitat in Japan into the woods in Virginia and West Virginia. If all goes as planned, the beetle will be another tool that resource managers will have to save the treasured trees.
“We don’t want to lose the hemlocks, and we have to explore every avenue we can to save them,” Salom said. “This is a battle we feel compelled to take on.”
The Laricobius osakensis beetle was discovered in Japan in 2005, where it was feasting on the hemlock woolly adelgid and keeping its population in check. Salom obtained a permit from the U.S. Department of Agriculture to bring the beetles to Virginia Tech, where they were under quarantine for six years. During that time, he did a series of tests to ensure that the beetle wouldn’t harm other native species and would indeed go after the hemlock woolly adelgid.
In 2010, Salom got approval to release the beetles. In fall 2012, his team placed 500 into two sites where the adelgids were wreaking havoc. In 2013, 6,000 beetles were released at five additional sites, adding Maryland and Pennsylvania to the state lists.
Since then, Katlin Mooneyham, an entomology graduate student from Wilmington, N.C., has been making trips to the field, where she is sampling the trees to see how many of the beetles survived. She then takes them back to the Virginia Tech insectary, where she works with others to rear the next generation of beetle larvae that will then be released back into the wild. The insectary has the capability of producing about 25,000 beetles a year.
So far, the project is succeeding in that the beetles are adapting to the new climate and reproducing on their own in the wild.
But this one beetle is not going to be the salvation of all hemlocks, Salom said. It’s one of many tools under development that when used in concert with others may help save the trees.
In 2003, Salom released another type of beetle from the western United States into the forests of Virginia. Since the program’s inception, more than 200,000 of those beetles have been put into the wild. He is also working with other researchers to develop chemical treatments used in conjunction with the predator beetles that they hope will help the trees fight off adelgid infestations.
As a keystone species of the ecosystem, hemlocks play a large role in how the forests function. They provide shade and cool the woods, create habitat for birds and bugs, and influence what other plants will grow nearby.
“What we lose is a beautiful ecosystem that can’t be replaced,” Salom said of the potential loss of hemlocks. “Once we lose this tree, there are no other trees that can replace it.”
- For more information on this topic, contact Zeke Barlow or 540-231-5417.
Professor Scott Salom talks about his efforts to stop the invasive woolly adelgid from destroying the hemlocks.
Eastern hemlocks: At a glance
- Can live for up to 800 years, but most remaining old-growth trees are more than 300 years old
- Grows up to 150 feet tall
- State tree of Pennsylvania
- Called “Redwood of the East”
- Bark historically used to tan leather
- Wood is sometimes used for railroad ties but generally thought of as too knotty for timber use
- Needles can be made into a tea
About the wooly adelgid
- Kills hemlocks when it feeds on the needles, disrupting the tree’s nutrient flow and causing the tree to starve to death in three to five years
- Originally from Japan, where native beetles keep it in check
- Came to eastern U.S. in the early 20th century
- Spreads via birds and wind and as a hitchhiker on ornamental plants
- Is responsible for killing more than 80 percent of the hemlocks in the Shenandoah National Park
- “Wool” is a protective coating for the insect, which feeds on the nutrient storage cells at the base of the hemlock needles