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A tiny fly could help save Eastern hemlock forests.

Byline: Diane Dietz The Register-Guard

CORVALLIS - Oregon State University researchers have found a species of fly that might come to the rescue of millions of ailing hemlock trees in 17 Eastern U.S. states.

The grain-sized "silver fly" that researchers have found in forests from Corvallis to Seattle could be the predator to stop an aphidlike insect that's sucking the life out of most East Coast hemlock trees.

"Hemlocks are being killed at a very high rate," OSU entomologist Darrell Ross said. "It seems to be threatening the species' existence."

The woolly adelgid has chewed its way up the crest of the Appalachian Mountains from the Carolinas to Canada.

The tree deaths are so alarming to people on the East Coast that when Ross and his research partner and wife, University of Vermont entomologist Kimberly Wallin, released preliminary results on the fly, insect experts and foresters beat a path to their doorways.

The researchers' work has been noted in Entomology Today and The Washington Post in recent days.

"It's a very good time for us with the research and the obvious interest," Ross said.

The hemlock woolly adelgid is a poppyseed-sized invasive insect that hitched a ride from southern Japan - probably on an ornamental hemlock tree - and landed in Richmond, Va., in 1951. Scientists traced the bug's continent- hopping journey based on its present location and genetic code, Ross said.

Each insect is mobile briefly after it hatches, and soon finds a cozy spot at the base of a hemlock needle.

"They insert their mouth parts - which are very long, sucking mouthparts - into the tree and then they never move again."

As a mass of adelgid draws nutrients from a tree, the blue-green color fades, the crown thins and the needles fall off. The process takes a year or two in the south and as many as seven years in the north, where the insects are periodically slowed by hard freezes.

Ross has walked Eastern forests where the adelgid have grazed.

"It's very disturbing to me as a biologist to understand we've done this," he said. "We brought this thing here - and we're seeing these things die. Where once there were deep green trees, there's nothing but gray."

Commerce spreads bugs

In the past two decades, the movement of invasive species has increased rapidly with container ship and jet plane commerce, Ross said.

The volume is so great, it's impossible for governments to inspect and treat all the cargo for invasive hitchhikers.

"It's never perfect. Things slip through," Ross said.

The results on forests can be devastating.

A century ago, a pathogen - or blight - traveled from China to New York City on some nursery stock and wiped out a continent's worth of huge, majestic American Chestnut trees, Ross said.

The Emerald ash borer, a beetle that came from Asia - probably on a wooden packing crate - got a toehold in Michigan in 2002 and is wiping out the ash tree as it travels west.

"It's going to spread and find its way to Oregon and everywhere that ash (trees) occur," Ross said.

So far, the beetle has gotten as far as Wyoming, according to government- sponsored tracking.

The mountain pine beetle that's ravaging millions of acres of lodgepole pines across the West didn't come from another land, however. It's a native. But human activity paved the way for its spread, Ross said.

Blame that on fire suppression, mono culture and uniformly aged stands. "That's a different way we can screw things up, to put it very bluntly," Ross said.

Early trials encouraging

To save the Eastern hemlock, researchers have tried insecticides and predatory beetles.

The former isn't practical because of the cost, Ross said. Using predatory beetles to feed on the adelgid has, so far, shown limited success.

Meanwhile, some researchers are trying to preserve the tree species by taking seeds to South America and growing trees there to maintain a genetic base until a foil for the insect is found, Ross said.

OSU got the idea of enlisting the silver fly in the fight to save the hemlock after an OSU master's degree student found that the flies were plentiful in Northwest hemlock trees.

Adelgid don't kill trees here because the bugs and the trees evolved together, Ross said. The trees developed resistance - and parasites and pathogens arose to feed on the adelgid and keep the population in check.

When the silver fly is in its larval stage, it's a small yellow maggot, also with sucking mouth parts.

"They just move through those adelgid egg masses, feeding on those eggs," Ross said.

In May and June, Wallin tested the Northwest silver fly on infested branches in New York and Tennessee.

"They mated. They laid their eggs. The offspring developed all the way to adult stages, and they developed in very high numbers," Ross said.

The U.S. Forest Service has supported Ross' and Wallin's research for more than a decade under its Hemlock Woody Adelgid Initiative.

Ross didn't immediately have a specific figure for the amount of grants they've received.

In the coming year, Ross at OSU and Wallin in Vermont will enlist graduate students into studies to discover more about the flies, such as understanding their basic biology, figuring out whether they can survive East Coast winters, how much adelgid a single fly could eat, how many would be needed to clean up a forest of hemlock, and techniques for rearing generations of flies in the laboratory.

"I don't want to go too far out on a limb," Ross said, "but we're hopeful that these will help provide a solution to problems in the East. The early results are very, very encouraging."

Follow Diane on Twitter @diane_dietz. Email


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Title Annotation:Forestry
Publication:The Register-Guard (Eugene, OR)
Date:Jul 10, 2015
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