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TOPIC: Chamaemyiidae flies could aid hemlocks
http://groups.google.com/group/entstrees/browse_thread/thread/da9a5ccad664ac27?hl=en
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== 1 of 1 ==
Date: Fri, Mar 14 2008 6:03 am
From: "Valdmets, Lisa (MED US)"




Tiny fly could aid the mighty hemlock


Scientists look at natural way to combat pest that is destroying
majestic trees in eastern U.S


from News and Observer, Raleigh; Wade Rawlins, Staff Writer


A tiny, exotic pest that is devastating forests of hemlock trees from
the Carolinas to Maine has so far confounded scientists' efforts to
check the destruction.

But forestry researchers at Oregon State University may have found a new
weapon in the battle to save the giant evergreens in the eastern United
States. They have identified two species of flies that are natural
enemies of the hemlock woolly adelgid in the Pacific Northwest. The
flies could be introduced to prey on the adelgid in the East after
further testing.

Since the mid-1990s, the U.S. Forest Service has conducted mass releases
in Appalachian states of several types of insects that eat adelgids,
including more than 1.5 million Asian ladybird beetles. Despite the
efforts, the infestation has continued spreading.

"We're losing just thousands of trees every year because of this pest,"
said Brad Onken, forest entomologist with the U.S. Forest Service in
Morgantown, W.Va. "We don't have the natural enemy complex out here to
keep it in check."

The eastern hemlock, known as the redwood of the East, grows to be a
forest giant and can live up to 500 years. But tens of thousands of
hemlocks in the eastern United States now bear the telltale signs of
infestation -- cottony white adelgid egg sacs clinging to branches. The
bare gray trunks of dead hemlocks are visible on mountainsides.

The adelgid, a native of Asia, was accidentally imported on nursery
stock to the eastern United States in the 1950s. It is an aphid-like
insect that sucks the juices from hemlock tree needles. Trees typically
die within four to 10 years of infestation.

The hemlocks' loss threatens drastic changes to Appalachian forests,
where the trees provide deep shade to keep mountain streams cool for
trout and offer food and shelter for nearly 90 species of birds.

The adelgid has been present in Western states much longer, scientists
say, and a larger number of natural predators prey on it, so it isn't
causing the same problems. In addition, western hemlocks, which grow
from northern California to southeastern Alaska, appear to have greater
natural resistance. The western hemlock is related to the eastern
hemlock, but it is a different species.

Two contenders

Darrell Ross, a scientist at Oregon State, said two species of
Chamaemyiidae flies, a tiny silvery insect that feasts only on adelgids,
offer good potential as natural predators to throw into the fight
against the adelgids. The flies were identified through research funded
by the U.S. Forest Service.

"They are as strong a candidate as some of the beetles that have been
looked at and released," Ross said, noting that further testing will be
needed before they would be released. "If things go well, it will pan
out and contribute to efforts to control the hemlock woolly adelgid."

The researchers noted that flies within the same family have been used
to control pests in Hawaii and Chile. The researchers' work appears in
the April issue of Environmental Entomology, a peer-reviewed scientific
journal.

Scientists are trying to find insects that prey exclusively on the
adelgid to reduce the chances they will wreak unintended havoc if
introduced. The search has taken scientists to the Pacific Northwest and
to Japan and China, where the adelgid has lived much longer than in the
eastern United States.

'Still searching'

"We're by all means still searching and looking," said Rusty Rhea, an
entomologist with the U.S. Forest Service Forest Health Protection unit
in Asheville. "We're looking at these flies and trying to evaluate what
kind of role they might have."