They are part of our forests, parks, yards, and city streets. Or at least they have
been. But ash trees are now under serious threat from an invasive beetle called the
emerald ash borer (Agrilus planipennis). It is native to Eastern Russia, northern China,
Japan, and Korea. The adults are bright green with somewhat darker wings. They infest
all types of ash trees. The adults feed on the ash leaves but cause little defoliation. They
lay their eggs between the bark crevices. Under the bark is a layer of tissue called the
phloem. Beneath that is the cambium and under that is the xylem. The larvae chew
through the inner bark, phloem, cambium, and outer xylem to create long serpentine
galleries. This disrupts the nutrient and water flow, which starves the tree. In the fall
they excavate chambers and overwinter in the outer bark. In the spring the adults chew
a D-shaped exit hole.
According to http://www.emeraldashborer.info, the beetle is found in over 30 states
and 5 Canadian provinces. It has caused quarantines in multilple states, cost millions in
removal, and killed millions of trees in North America.
Gwen Kozlowski, the Education Coordinator for the University of Vermont
Extension, said that 99% of infested trees will die. Ecosystems will adapt and change,
but there will still be a “significant effect.” She also said that woodpeckers and the
cerceris wap have been preying on the larve, but it has not been enough to make dent in
the population.
There are two primary control methods for the emerald ash borer. One is
insecticide and the other is the release of parasitoid wasps that prey on them in their
native range. In 2007, three of these were released in southern Michigan. One, Oobius
agrili, feeds on the eggs and the other two, Tetrastichus planipennisi and Spathius agrili
feed on the larvae. In 2015 a fourth one, Spathius galinae, was approved because S.
agrili did not establish in northern regions. According to http://www.nrs.fs.fed.us, there have
been “encouraging results,” with reductions in emerald ash borer populations being
correlated with wasp releases. Kozlowski said Vermont was considering releasing
these wasps in the next two years.
In addition, Kozlowski said insecticide is also being used to counter the spread
in North America, though that takes a yearly application and can be costly. She also said
this is only effective if the infestation is within 10-15 miles. She said the insecticide has
proved effective, though there are always some risks.
Kozlowski said the long term plan is to slow the spread as eradication is not
considered a realistic option at this point. States were formerly getting federal funding
to combat the emerald ash borer, but that funding has decreased. If people see a tree
they think is infested, it should be reported to Vermont Invasives or, if not in Vermont,
the appropriate state agency.
COMING IN TWO WEEKS: HOW TO IDENTIFY BOTH ASH TREES AND SIGNS OF
INFESTATION
The Nature Journal 