Locust Borer Virginia State University Extension	Locust borer larvae tunnel into sapwood Virginia State University Extension

Scientific Name: 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.

Remarks

Older trees are not damaged and younger trees 6 inches in diameter and over are seldom bothered. 

Prepared by: Eric Day and D. Ames Herbert, Department of Entomology, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061-0319.

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