June 2012 - Outbreak
of borers on oaks
East Texas foresters are receiving
numerous calls about insects killing their oak trees.
I have also been getting calls and e-mails about this.
I am seeing a lot of activity from metallic or
flat-headed wood borers on recently dead and dying oak
trees (and other trees). These borers are
basically scavengers on dying and recently dead trees.
With large trees, the beetles may be only attacking
parts of the tree that are dying or recently dead.
These beetles initially infest the cambium and then bore
into the wood. In order for them to successfully
infest the cambium, the cambium cannot be healthy.
That is why treating for the beetles to prevent
additional attacks is “after the fact” and does little
if any good. The borers are there because the
trees have other problems and the other problems relate
back to lack of water. These borers are NOT
killing the trees.
The borers are the insect family
Buprestidae and the genus Chrysobothris. They have
a bronze metallic underside and the wings (elytra) on
top are a gray to black color. When they spread
their wings to fly, they reveal a bright metallic green
color on the top of their back (abdomen). The
drought of 2011 has caused tremendous problems for trees
and various fungi and insects are responding to the
drought-stressed trees. The metallic wood borers
you are seeing are a part of this complex of insects and
fungi. Chrysobothris is a large genus that
contains at least 134 species in North America.
Here is a link to information about
one of the common Chrysobothris species. It has a
large list of hosts including oaks, even though its
common name is flat-headed apple tree borer.
Below are two photos I took of
various Chrysobothris in the collection at the Forest
Health office in Lufkin.
In the photo above you can see the
bronze metalic color on the underside of the beetles,
their gray to black wing covers (elytr), and the exposed
green back (abdomen) of one of the beetles that lost its
elytra. These beetles came from an emerald ash
borer trap, but they are also common on dying oak trees.
In the above photo is Chrysobothris
shawnee. You can easily see the green color under
the wings as well as the gray to black color pattern on
the top of the wing covers (elytra).
I hope this information will be
H. A. (Joe) Pase III, CF
Regional Forest Health Coordinator
Texas Forest Service