A recent survey of damage caused by various wood borers to three species
in the white oak group revealed an estimated annual loss in the South
exceeding 20 million dollars. One of the more important borers
responsible for this damage is the white oak borer.
[Illustration: Adult white oak borer.]
Usually the white oak borer attacks oaks one to eight inches in
diameter. The damage, like that of other hardwood borers, is the result
of larval feeding in the wood. Galleries up to one-half inch in diameter
extend upward through the sapwood into the heartwood. The white oak
borer takes three to four years to complete one generation. The mated
adult female beetle lays her eggs singly in the inner bark through a
small oval niche chewed through the outer bark. After about three weeks
the eggs hatch and the larvae immediately bore into the sapwood. Later
they bore upward into the heartwood. The boring frass ejected out of the
entrance is evidence of an active infestation. Pupation occurs behind a
plug of excelsior-like frass at the upper end of the gallery in the
heartwood. In about three weeks, adults emerge by boring separate and
perfectly round holes through the wood and bark. In the South, adults
generally emerge in May and June and feed for a short time on oak leaves
and the tender bark of twigs before the females lay their eggs.
Woodpeckers may destroy up to 25 percent of the larvae during the winter
months, but this and the small toll taken by insect predators and
parasites are not sufficient to keep the white oak borer population low
enough to avoid serious economic loss.
[Illustration: Entrance and emergence holes in white oak.]