Native Species Step Up
to Fight Ash Parasite
Scientists Make Headway in
Curbing Scourge With Some
Woodpeckers, Wasps
Caroline Porter;onlinewsj.com
When the emerald ash borer showed
up in the U.S. about a decade ago,
the native ecosystem didn't put up
much of a fight against the Asian
beetle—and the invader quickly
munched its way through ash trees
from Minnesota to New Hampshire,
causing destruction that will cost
billions of dollars to repair.
Now, however, scientists have found
three reliable native allies in their fight
against the scourge: Certain woodpeckers,
nuthatches and parasitic wasps have
developed a taste for the beetles. In
conjunction with natural predators
imported from the borers' original home
in China and chemical treatments, the
native species are helping curtail the
pest after years of destruction.
For just those trees in urban areas, cities
are looking at the death of about 17 million
trees by 2019 with a replacement cost of
$11 billion by 2019, according to Robert
Venette, a research biologist with the Forest
Service. In natural areas and cities, the
beetle has killed tens of millions of trees.
In Michigan, the current estimate is well
over 50 million.
Fighting Battles in the Forest
2002, the emerald ash borer—
a half-inch-long bug with a green
metallic sheen on its wings and
a reddish stomach—is believed
to have hitched a ride in packing
materials from China. While
researchers hustled to gain control
over the invasive beetle, which
burrows under trees' bark and
cuts off their nutrient supply,
for years they showed little
success. They shipped Chinese
wasps to the U.S. to prey on the
beetle, deployed numerous traps
and mounted a national awareness
campaign for homeowners to adopt
and treat trees in their neighborhoods.
Yet the ash borer thrived in its new
home amid a dearth of predators native
to the U.S."We found very few natural
insects attacking the emerald ash borer
in Michigan," said Leah Bauer, an insect
researcher with the U.S. Forest Service,
part of the U.S. Department of Agriculture.
"In China, there are three insect species
that eat the beetle. It is their biological
control."
But now the native parasitic wasps,
red-bellied woodpeckers and white-
breasted nuthatches are giving scientists
new hope that they can at least slow the
destruction of ash trees with the help of
chemical treatments and the Chinese wasps
that were imported and are now being
reared in the U.S. The USDA "is working
very hard to put these little enemies [the
Chinese wasps] out there to become
established and help control the emerald
ash borer," said Ms. Bauer.
Native parasitic wasps have discovered
that the beetles make excellent hosts for
their eggs. After the eggs hatch, the larvae
snack on the ash borers. "They were like,
'Hey, wow, look at this new giant buffet
for us.' Now folks looking at the emerald
ash borer are taking notice," said Therese
Poland, who studies insects with the U.S.
Forest Service in East Lansing, Mich.
"Parasitic wasps may be most important
in combination with woodpeckers as natural
enemies become more relevant to fighting
the bugs," said Deb McCullough, a professor
of forest insects at Michigan State University.
"They play a really valuable role."
Red-bellied woodpeckers, which feast on the
ash borers' larvae, are experiencing a
population boom due to the new food supply,
according to a report this month by the U.S.
Forest Service and Cornell University.
White-breasted nuthatches are also
experiencing a population increase,
according to the report.
The woodpeckers also lead scientists to ash
infestations, which can be otherwise difficult
to spot. That is also helping the fight against
the borer.
On a recent day, Ms. Bauer used woodpecker
markings on ash trees to set up traps intended
to monitor the number of specially raised
Asian wasps in a forest south of Lansing
."They have a way of finding these trees
and really do a number on them. They
just pepper the bark."
Still, many scientists agree that the emerald
ash borer maintains the upper hand. "We
have just seen the tip of the iceberg," said
Andrew Liebhold, an insect researcher with
the Forest Service and co-author of the
report. "In Detroit, there are a lot of dead
trees everywhere. We're going to see that
in every Eastern city in the next 20 to 30
years. It's kind of a horrific thing."
For homeowner Kate Simons in Cicero,
N.Y., an influx of woodpeckers seemed
to indicate the arrival of the invasive beetle
in her area. While she's not bothered by
the woodpeckers' noise, she is concerned
about the financial burden of tree treatment
for the borers, which is recommended in
areas prone to infestation.
She plans to cut down the ash tree in her
backyard that would otherwise cost about
$300 to treat every year or two. "It's not
that I don't like trees," said the 41-year-
old paralegal. "I can't justify the cost."
No comments:
Post a Comment