Could ‘Herd Immunity’ Save Ash Trees From Beetle In Allegheny National Forest?
Researchers have a new plan to tackle the emerald ash borer in the Allegheny National Forest.
Native to China and eastern Asia, the pesky beetle first appeared North America in 2002, and in the forest in 2013. It’s been killing trees ever since. Emerald ash borer larvae feed just beneath the bark of ash trees, cutting off the trees’ circulatory systems so they can no longer transport water or nutrients.
Researchers want to see if treating only a portion of the trees in a particular area with insecticide can protect other trees nearby.
“That’s kind of like herd immunity for humans with vaccines,” said Kathleen Knight, a research ecologist with the USDA Forest Service’s Northern Research Station. “When you have people being vaccinated against a disease, in some people either the vaccine doesn’t work or they don’t get vaccinated, but they’re still protected because everyone else around them is vaccinated and can’t get the disease.”
She said contractors will drill a hole into the base of certain ash trees to inject the insecticide. The trees then absorb the liquid up through their trunks and canopies.
Researchers want to pinpoint what percentage of trees in an area need to be treated to provide immunity to the rest. They have secured federal grant money to fund the first year of this three-year project, which is a collaboration between the Northern Research Station, the Allegheny National Forest, and Washington & Jefferson College.
Knight said the grant ensures the researchers can finish work already underway. The trees, for example, are already marked and ready to be injected with insecticide.
“We’ll go to every tree and check it out to see how healthy the canopy of the tree is, if it’s exhibiting any of the symptoms of emerald ash borer,” she said.
Those symptoms include branches that have lost their leaves, and small D-shaped holes in the trunk, formed when adult emerald ash borers exit the tree.
Knight said researchers elsewhere in the country are taking a similar “herd immunity” approach to protecting ash trees in parks and on the street.
“It will be really interesting with people testing this concept of herd immunity in multiple environments whether we see the same thing, or whether we see different things happening in different kinds of environments,” she said.
It’s important ash trees stay healthy because they serve a variety of functions, Knight said. Various ash tree species can help wetland drainage and mitigate flooding. Their wood is also harvested for commercial purposes, like baseball bats, and it’s used by some Native American tribes for basket weaving.