ADDISON COUNTY — With the invasive emerald ash borer knocking at the door, Vermont’s ash tree population is in grave danger of being wiped out.
But if scientists and forest workers can identify the insect early enough, the profitable hardwoods might still have a fighting chance — by using the paralyzing powers of a native wasp to serve as an early warning system.
During its larval stage, the emerald ash borer burrows into the circulatory system of a tree — known as the xylem and phloem — cutting off the tree’s vital flow of water and nutrients.
The emerald ash borer isn't the only threat to Vermont's ash population. This illness-prone tree is in present danger of catching a case of the ash yellows.
“The trees are essentially dying of drought stress. They can no longer transport what they need to function as a living organism,” said Addison County Forester Chris Olson, who is all too familiar with the emerald ash borer.
Growing up in Detroit, Olson first witnessed Dutch elm disease kill off the elm trees in his neighborhood. Then, in 2002, he saw the emerald ash borer move in from Asia, taking out all the ash trees that were planted in place of the elms.
“Forty years later they cut down all of the ash trees in the same neighborhoods,” he said. “This foolishness occurred twice in my life, first with the elm trees and second with the ash trees ... It’s wise, I think, to diversify a little bit, and they didn’t.”
Although a variety of trees thrive in Vermont, the economic impact of losing just this one could be huge.
Ash accounts for 6 percent of the state’s total saw timber — harvested second only to sugar maple — said Trish Hanson, the state forest protection entomologist. According to numbers from the U.S. Forest Service, ash accounts for almost 7.5 percent of trees in Addison County that have a diameter greater than one inch.
For the moment, the emerald ash borer has not been identified in Vermont. But it’s close by.
“We have emerald ash borer in Montreal and just outside of it, which is about 30 miles away, and we have it down in the Hudson Valley in the Kingston area about 50 miles to the southwest,” said Barbara Burns, Forest Health Program Manager for the state.
The problem with the emerald ash borer is that it proliferates rapidly. For that reason, Olson explained that it’s imperative to identify the ash borer as soon as it enters the state. Once it’s identified, it must be quarantined.
The only way to do that, said Olson, is by cutting down trees.
Large, triangular, purple traps with a sticky surface hang from ash trees across the state. In the northern half of Vermont, an emerald ash borer traps hangs in about every two square miles. Scientists are checking the sticky traps to see if the ash borer has arrived.
But there’s another way to reveal the arrival of the dreaded ash borer — by working with the native wasp known as cerceris fumipennis.
During its two-month life, the wasp preys on beetles like the emerald ash borer. When the wasp finds its prey, it stuns the victim with a paralytic serum. The predator then drags its paralyzed victim back to its underground nest, where wasp larvae feed on the beetle. When the larvae and wasps have had their fill, they discard the carcass by the entrance of their anthill-like nest.
By using this method of “biosurveillance” — monitoring the wasps in July and August — experts hope to discover the arrival of the emerald ash borer.
“The ash borer does not feed low on a tree where humans might be looking, it feeds high in the tree 40 feet above the ground, which is exactly where the cerceris wasp hunts them,” said Olson. “The wasp then brings the ash borer down to ground level to feed its young (located in underground nests at) ball fields, soccer fields, parking areas and agricultural lanes along corn fields. So it’s much easier to find the ash borer there than to look for them in the top of a 60-foot tall ash tree.”
The idea is to keep an watchful eye on the entrance of the nest. Although it might look like similar stinging wasps, the cerceris cannot harm a person.
“One could monitor the cerceris as they go in or after they’ve discarded the carcasses,” said Olson. “So long as a shortstop doesn’t run it over.”
WHAT PEOPLE CAN DO
This summer, Olson has been going around from field to field to let Little Leaguers and other young sports players know what to watch out for. Rather than running over the carcass of an emerald ash borer, Olson hopes that a shortstop will one day stop, inspect the insect and say, “Hey! I found one!”
“If you’re aware of the fact that the wasp does discard emerald ash borer carcasses, you might actually find one,” said Olson. “There are people who have seen this wasp before, but just don’t realize it. So the question is can people be a little bit attentive to see what the wasp is feeding on?”
Hanson is also working with citizens across the state to monitor the insects, and she’s eager to find more people who are willing to help. Volunteers regularly inspect cerceris nests and collect beetle carcasses. The volunteers freeze the carcasses in a bag and when they have 50, send them to the state’s Forest Biology Lab.
People can also inspect ash trees near their house. Hanson said to look for “s-shaped larval feeding galleries that weave back and forth across the grain of the wood.”
Burns, the Forest Health Program Manager, also said that there is one excellent preventative measure: Don’t bring firewood into Vermont from out of state.
“The emerald ash borer spreads quickly, and the fastest way that it spreads is on firewood,” she said. “When people move firewood, it can go 65 miles an hour down the interstate.”
Since the emerald ash borer has only been present in the U.S. for a little less than 10 years, Scientists are still grappling with how to control it.
“If some of this research is successful, maybe we won’t see the devastating impacts seen elsewhere,” said Burns. “The most important thing right now is to stall for time. Right at the moment, emerald ash borer is a tree killer, so we’re really suggesting communities prepare for it.”