Locust Borer
Contact: Eric Day, Manager, Insect Identification Laboratory
August 1996
Locust Borer
Coleoptera: Cerambycidae, Megacyllene robiniae
Plants Attacked
Black locust
Description of Damage
Larvae tunnel in trunk and larger
branches of live trees. Most damaging on younger trees during
dry seasons. They attack healthy young trees boring into the
heart and sapwood of stems and branches. Young larvae feeding in
the spring cause bleeding at the site of the injury. Wet spots
are present on the bark.
Identification
Adult overall color is black with yellow
markings. Most characteristic mark is the W-shaped yellow mark
on the first pair of wings. Adults prominent in fall feeding on
goldenrod pollen.
Life History
Very small larvae pass the winter in the inner
bark of the host. In early spring they begin development moving
into the sap and heart woods. Maturity is obtained about
midsummer and a pupal cell is excavated. The adults emerge about
the first of September. They are extremely active and may be
found actively feeding on goldenrod and associated plants. As
with the Painted hickory borer feeding is required for
oviposition. The eggs are laid in cracks and crevices of the
bark, they hatch and the young larvae bore into the inner bark
next to the sapwood before the approach of cold weather.
Control
Heavily infested trees should be destroyed. Locust
borers can be controlled by applying a drenching spray in early
September or late August. One application may protect the trees
for two or three years. Applications applied in early spring
also may be effective in killing larvae before they tunnel into
the wood. High dilution rates are required; see V.P.I.
recommendations.
Remarks
Older trees are not damaged and younger trees 6 inches
in diameter and over are seldom bothered.