Inside the battle against emerald ash borer

How parasitic wasps are deployed to combat invasive pest in the Adirondacks

By Gwendolyn Craig

When Reed Middendorf gets a box of live wasps delivered to his apartment in Saranac Lake, all other work stops.

A seasonal terrestrial invasive plant assistant with the Adirondack Park Invasive Plant Program, Middendorf has less than 24 hours to rush the wasps to woodlands in Johnsburg in Warren County. The insects would not survive long in a package and they have a mission in the wild.

Middendorf’s made the trip several times this summer. One July day, shortly after storms and tornadoes ravaged the region, he drove his truck through a gated dirt driveway until he came upon a white colonial home overlooking the hills and valleys of the Siamese Ponds Wilderness.

Karl Kurka emerged from the front door wearing a bucket hat with a drawstring. He inquired about the weather. He’d lost power and had no cell service.

Middendorf was his source for news—and for wasps.

Kurka, a retired environmental program manager for the City of Sacramento, Calif., owns about 40 acres of woods and wetlands in the Adirondack Park. Ash trees represent 10% of his forest, he estimates. He had read about the emerald ash borer found nearby in Chestertown in 2020, the first discovery of the invasive insect that kills ash trees in the Adirondack Park. 

One day he noticed his ash trees in the driveway looked sick. On closer inspection he could see the notorious D-shaped holes the invasive insect makes as an adult exiting the tree.

“I was really pretty upset about it,” Kurka said.

Kurka volunteered his property to be part of a nationwide experiment underway using biological controls, in this case, parasitic wasps, to combat these ash-killing, wood-boring beetles. It is a long-term method federal, state and Indigenous leaders hope will curb the emerald ash borer’s population growth and allow more ash trees to survive.

“It’s still a big pest,” said Jian Duan, a research entomologist with the U.S. Department of Agriculture’s Agricultural Research Service in Delaware. 

But emerging data show the parasitic wasps can fight the borers and help protect the trees, he said.

About the emerald ash borer

About as long as a penny, the emerald ash borer is a metallic green insect native to Asia. It likely arrived in the United States in the 1990s in wood-packing material but wasn’t discovered until 2002 in southeast Michigan.

The insect lays eggs under the bark of ash trees. After a few weeks, cream-colored grubs emerge. They munch on the inner bark of the tree, poop and shimmy, creating the tell-tale serpentine galleries one can see when peeling back the bark of an infected tree.

The larvae will pupate and become the metallic green adults, chewing their way through the bark and escaping through a D-shaped hole.

Besides the exit holes and serpentine galleries, infected ash trees display dying branches, thinning crowns and lighter colored bark. The weakened tree may shoot new leafy branches at its base in an attempt to stay alive. Woodpeckers may also be attracted to the tree and its invaders. Most infected ash trees will die in two to four years.

 Emerald ash borer has been documented in 36 states, Washington D.C. and five Canadian provinces. 

Ash trees make up about 7% of New York’s forestland and even a lower percentage in the Adirondacks. The trees are mostly used in urban areas to provide shade and greenery along sidewalks and cityscapes. But the Adirondack Park Invasive Plant Program has kept track of some beautiful stands, iconic to the park’s lowlands. 

The U.S. Forest Service considers ash an important component to northern hardwood forests and losing them causes food and habitat loss for a variety of wildlife, soil erosion, shade loss and other important services the tree provides. They are also culturally significant to the Haudenosaunee, and have been used to make baskets, baseball bats and furniture. 

The beetle was first discovered in New York in 2009 and in the Adirondacks in 2020. There are only two counties where emerald ash borer has not been documented—Lewis and Hamilton, though Jason Denham, forester with the state Department of Environmental Conservation, said it could very well be there.

What could be helping keep emerald ash borer out of those counties, Denham said, is a relatively smaller number of ash trees.

But, he warned, “adults are perfectly capable of making that flight,” from other infested counties.

Essex County had most recently been on the short list with Hamilton and Lewis until July, when interns with the Essex County Soil and Water Conservation District noticed D-shaped holes in ash trees on a trail in the Beaver Bend Nature Preserve in Westport. They set up traps and were able to catch a few of the invasive beetles.

In Akwesasne, north of the park, environmental officials with the St. Regis Mohawk Tribe found emerald ash borer there in 2016. The insect invasion has been particularly devastating to the tribe, as their traditional pack and artistry baskets are made with black ash.

Finding solutions

At first, the federal government led an attempt to eradicate emerald ash borer, decimating infected trees and enforcing strict firewood transportation regulations. But it became clear the insects had spread too far and wide.

In 2003, USDA researchers began exploring the ash borer’s native ranges including in northeast China, the Russian far east, Japan and South Korea to search for natural enemies, Duan said.

They found various kinds of parasitic wasps. Some attack the emerald ash borer’s eggs, while others attack its larvae. The wasps are stingerless and do not harm humans. What appears to be stingers on their bottoms are actually ovipositors, mechanisms to lay their eggs.

The process for such research and study is complicated.

It takes one to two years of planning, said Duan, who assisted on explorations in China and Russia. Special authorization is needed from both the USDA Animal and Plant Health Inspection Service and the counterpart country. The ash borer is not considered a pest in these countries, Duan said, and is trickier to find.

Duan said a counterpart in China or Russia will assist researchers by artificially stressing an ash tree. It’s an approximately year-long process of attracting the ash borer to lay its eggs and hope its natural enemies will arrive before U.S. researchers can come and collect these parasitic wasps.

Biocontrols go through a rigorous environmental assessment and not all are approved for release, Duan said.

When vetting one of the parasitic wasps to control emerald ash borer, however, the U.S. Environmental Protection Agency provided comments with concerns about post-release monitoring. One of the wasps that attacks ash borer eggs could potentially impact other wood-boring insects if emerald ash borer is not present, USDA’s assessment found.

In response to EPA’s concerns and that risk, USDA’s Animal and Plant Health Inspection Service determined the benefits outweighed the risks. If there were extensive impacts to other species, the USDA noted, it would not issue any more releases or permits for that species.

In 2007, the federal government authorized three Chinese parasitic wasps for release in Michigan, where the USDA rears them.

The USDA added to its arsenal a Russian parasitic wasp in 2015. Duan and a colleague discovered this wasp in 2012 in a suburb of Vladivostok. It became an important player due to its longer ovipositor, giving it the ability to deposit its eggs in older, thicker-barked ash trees and its ability to withstand colder temperatures.

At that time, there was better collaboration with Russia and China, Duan said, but policies have changed amid political tensions. The Russian wasps released today are the progeny of those 200 wasp cocoons Duan brought back a dozen years ago

More than 8.5 million wasps have been raised in Michigan since 2007, with releases in 32 states and four Canadian provinces. In 2023 alone, the USDA distributed more than 486,000 wasps and expected to distribute the same number this year.

The emerald ash borer biocontrol program costs about $6 million annually, the USDA Animal and Plant Health Inspection Service said. And it does not appear the wasp-rearing program can be scaled up to include outside labs, at least not anytime soon.

“The space, personnel, and materials all are costly,” a spokesperson for the service said. “We are not yet at the stage where we can efficiently have outside labs rearing these biocontrol wasps in numbers sufficient enough to sustain programmatic releases.”

Biocontrols in the park

Ash borer fighters are not the first kind of biocontrol used in the Adirondack Park. The state has used predator beetles and flies to control invasive hemlock woolly adelgid and another kind of beetle to manage purple loosestrife, among others.

Denham, with the DEC, said there have been two dozen release sites of parasitic wasps targeting emerald ash borer across the state.  

The Johnsburg location is the first in the Adirondacks.

The Adirondack Park Invasive Plant Program, part of The Nature Conservancy, gets about a day’s notice when the parasitic wasps will be shipped overnight. The program released wasps in 2023 and this year and will conduct monitoring next year to see if the wasp populations are surviving.

A wasp release may sound like a climactic event. One might picture a swarm flying into the air or surrounding an ash tree.

But during the July release the Explorer attended, the tiny, flying bugs were reluctant to leave their vials and Middendorf had to coax them out by tapping the sides. Others were invisible, hidden inside a piece of ash log that Middendorf tied to an infected tree to emerge later.

On this outing, Middendorf released 112 of the Russian parasitic wasps and 220 Chinese parasitic wasps that deposit their eggs in ash borer larvae. Both wasps are known to survive in colder climates.

The St. Regis Mohawk Tribe has released three parasitic wasp species to combat emerald ash borer over the last several years in the Akwesasne region of northern Franklin County and St. Lawrence County, said Jessica Raspitha, assistant director of the tribe’s environmental division.

Their control efforts are focused on the black ash stands, though white and green ash also populate the area. The Mohawks’ three-pronged approach for tackling the problem consists of selective removal of certain trees to allow for new generations of black ash to grow, some pesticide injections and parasitic wasps.

Future

This spring, tribal inspectors peeled back the bark on four infected ash trees to look for evidence of the parasitic wasps. They didn’t find any. Raspitha said it’s too soon to say if the wasps are working. She and her colleagues are working with the USDA on further studies to see if any wasps are reproducing on site.

The Adirondack Park Invasive Plant Program will be surveying next year to see if their two years of releases have taken up residence. The USDA considers the wasps “established” if they are found at least two years after release. Researchers are recovering the wasps in nearly a dozen or more states, depending on the species.

Two release sites in New York—in Dutchess County in acreage owned by Bard College, and in private forestland in Columbia County— are part of longer-term studies for monitoring the establishment by Duan and his colleague. So far, the wasps are thriving there.

Duan said two of the parasitic wasp species’ populations are very prominent in Michigan where the experiment first began.

But the most time-consuming test will be whether ash trees can regenerate and recover, he added. It’s a test that will take decades, but he is hopeful.

So are Kurka and Middendorf. They’re rooting for the 8,267 Warren County wasps released since last year. 

Kurka lived in Tennessee for a time and saw the devastation hemlock woolly adelgid caused on the area’s giant eastern hemlock trees. It was “heartbreaking,” he said. It isn’t practical to spray pesticides on each individual tree, Kurka said, and he knew some sort of biocontrol would be necessary.

“I hate to say it, but this is just a teaspoon in the ocean,” Kurka said, looking out at his property and into the neighboring forest preserve. “There are huge ash trees back there and all along Route 8. You see up and down the trees are dying everywhere. It’s just a matter of time.” 

Top photo: Tammara Van Ryn, formerly of the Adirondack Park Invasive Plant Program, peels away bark from an ash tree to show the invasive emerald ash borer damage on Aug. 19, 2020 in Warren County. Photo by Gwendolyn Craig