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Flies could avert hemlock threat in New York

July 13, 2015
By SHAUN KITTLE ( , Lake Placid News

Mark Whitmore, a forest entomologist for Cornell Cooperative Extension, took a trip to Great Smoky Mountain National Park and saw the devastation firsthand.

Before him stood hundreds of acres of hemlock trees, all dead.

The trees there had been impressive in size. They can grow more than 150 feet tall on trunks measuring 6 feet in diameter. Some exceeded 500 years old, according to the National Park Service.

Article Photos

White woolly patches on hemlock needles are a sign of infestation by hemlock wooly adelgid, a small insect that has wiped out hemlocks in other parts of the U.S. and is spreading in New York. It hasn’t yet been found in the Adirondacks.
(Photo provided)

That all changed in 2002, when an invasive insect called hemlock woolly adelgid was discovered in the park.

The prolific insect feeds on hemlocks and relocates by hitching a ride on the wind or on birds' feet. It has killed 80 percent of the hemlocks along the Blue Ridge Parkway and Shenandoah National Park, where it's lived since the late 1980s. It looks like the Great Smokies are on track for a similar fate, and that's what has Whitmore concerned - what happens when the insect makes its Adirondack debut?

"It's happening in the Catskills, too," Whitmore said. "I was just in an area in Tannersville called Twilight Park, an area where an ancient community of hemlocks is. There are hemlocks there over 4 feet in diameter, and they're all dying."

The insect's telltale white, woolly masses, which appear near the base of a hemlock's needles, have been found south of Albany. That's close enough for Whitmore, who said New York state needs to manage the insect before it becomes an epidemic.

He thinks he's found a way to do it.

"The strain of hemlock woolly adelgid that we have on the East Coast is native to Japan, but interestingly enough, it's also native to the Pacific Northwest," Whitmore said. "In the Pacific Northwest there are over 20 different predators that feed on it."

One of those predators is a silver fly. Whitmore said that insect also lives here, but for some reason the eastern variety doesn't prey on hemlock woolly adelgid.

Whitmore led a research team that included representatives of the University of Vermont, the U.S. Forest Service and Oregon State University, and released silver flies along the shore of Skaneateles Lake on June 25.

If the silver flies become established and begin reproducing, Whitmore said his team will start working on developing techniques to release them on a larger scale.

"The silver fly is the second most abundant predator of the adelgid in the Pacific Northwest," Whitmore said. "This is the first time we've used it on the East Coast."

Silver flies aren't the first biological control Whitmore has released against adelgids. In 2009, his team released 900 Laricobius nigrinus beetles into a stand of adelgid-infested hemlocks on Cornell Plantations land near Lansing and at two sites on Seneca Lake. He hopes the beetle and fly species are enough to exploit all the potential habitats the adelgids could live in.

"What I'm trying to do with the beetles, and hopefully with the fly, is get it going across the state and engage volunteers and professionals to monitor these locations so we can keep track of prey, or hemlock woolly adelgid, abundance," Whitmore said. "Hopefully, after we've introduced these predators, we can collect their progeny and spread them around further. Basically, we need to build up these predator populations around the state before hemlock woolly adelgid populations get to the Adirondacks."

Whitmore said scientists initially thought cold Adirondack winters would be the best defense against the insect, but so far, frigid temperatures aren't having the desired devastating effect. Even when the cold does put a dent in a population, as the last two winters did, adelgids produce two generations of females annually, each of which can produce 100 offspring. With those numbers, it doesn't take long for the population to snap back.

"That's why I think the Adirondacks really are threatened," Whitmore said. "All you need to do is look around at the number of hemlocks in the Adirondacks, and people should be very concerned."

Hemlock woolly adelgids use their long mouth parts to draw nutrients from eastern hemlock, western hemlock and Carolina hemlock trees. It does this by penetrating the bark, usually at the base of a needle.

A hemlock responds to the insect intrusion by blocking off its own circulation, essentially creating a dam that stops the flow of water and nutrients to the insect. That also stops the flow of water and nutrients to the needles, causing them to die. After several years of this, the tree dies, too.

With cold enough winters, it could take as many as 10 years for an infested tree in the Adirondacks to die.

Eastern hemlocks are a "foundation species" in the Adirondacks, which is an ecologist's way of saying the tree helps create favorable conditions for other species. Some birds exclusively use hemlocks for nesting and food, and the shade they provide along stream banks creates critical habitat for cold-water-loving animals like brook trout.

In the Adirondacks, the Nature Conservancy's Adirondack Park Invasive Plant Program recently teamed up with the Adirondack Mountain Club to lead a backcountry monitoring workshop to teach people how to identify the insect. The first workshop was held in March at the Adirondak Loj near Lake Placid. The next is scheduled for Aug. 29 in Lake George.

Early detection is "really vital," said APIPP coordinator Brendan Quirion. "There have been instances in other places in the state where Mark (Whitmore) has found the first branch of a hemlock tree that became invaded, and he was able to effectively eradicate that infestation because it was so early."

Quirion said an infected tree can be treated using chemicals to prevent the insect from spreading further, but those treatments aren't realistic when it comes to handling large infestations. That's where biocontrols come in.

About 10 years ago, the black-margined loosestrife beetle was released in the Adirondacks to combat an invasive plant called purple loosestrife.

"That beetle has been in the Adirondacks for 10 to 15 years, and we're seeing widespread decline in purple loosestrife now, with no off-target impact to the species in the surrounding habitat," Quirion said. "The decades' worth of research that has to go into developing the biocontrol to make sure it's selective to the species that you're trying to get rid of, in this case the hemlock woolly adelgid, really makes the case that Whitmore's team is going to develop something that's very effective."



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