This is the VOA Special
English Agriculture Report.
A beetle invasion in the United States has killed at least twenty million
ash trees. The invasion of the
emerald ash borer was first discovered near Detroit, Michigan, in 2002. Experts
believe the small green insects arrived in the 1990s in shipments of goods from
China.
The emerald ash borer has destroyed trees in the Midwest and as
far east in the United States as Maryland. The insects have also spread as far
north as Ontario, Canada.
Ash trees are popular. They grow well in heavy clay soils, and they can
survive ice storms well. They produce many leaves, so they provide shade
protection from the sun. And in the fall the leaves turn a beautiful gold and
purple.
Ash trees can resist many diseases. But they cannot resist the emerald ash
borer. It lays eggs on the bark. Then the young larvae drill into and feed on the inner bark. This
harms the ability of the tree to transport water and nutrients.
The insect is attacking tree farms and can also spread when logs and firewood
are transported.
The United States Department of Agriculture is working to save the ash tree.
So are agriculture departments and university extensions in a number of states.
In some places, farmers are using "detection trees." These have an area where
bark has been cut away. The area circles the tree and is called a girdle. The
girdling process weakens the trees. It makes them easier targets for borers, and
shows if the insects are nearby.
Efforts to stop the spread of the emerald ash borer include cutting down
affected trees. A tree farmer in Maryland, for example, recently faced the loss
of hundreds of trees.
There are worries that the ash tree might disappear unless the invasion is
controlled. To prepare for such a possibility, a government laboratory is
collecting seeds from ash trees.
David Burgdorf works in East Lansing, Michigan, for the Natural Resources
Conservation Service; the service is part of the United States Department of
Agriculture. He is asking people to send in ash seeds. The laboratory examines
and x-rays the seeds to make sure there are no living borer embryos.
The best seeds are then sent for storage in a seed bank in Fort Collins,
Colorado. There, they are dried and frozen at the National Center for Genetic
Resources Preservation. Should the seeds ever be needed, the hope is that
scientists might someday develop an ash tree that could resist the little green
attackers.
And that's the VOA Special English Agriculture Report, written by Jerilyn
Watson. I'm Steve Ember.
ash tree :
白蠟樹(shù)（這種樹(shù)的木材堅(jiān)硬有彈性，用于制作家具、工具柄、運(yùn)動(dòng)器材如板球拍等）
larvae :
幼蟲
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（來(lái)源:VOA 英語(yǔ)點(diǎn)津姍姍編輯）
