Locust Borer Damage in Black Locust Trees
A wood-boring beetle that targets black locust trees, tunneling through sapwood and heartwood in a pattern that can weaken and eventually kill the tree.
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What the Locust Borer Targets and How to Identify It
The locust borer is so named because its primary target is black locust trees. Mature larvae are about 25 mm long and white with dark heads. Adult beetles are about 18 mm long, black with bright yellow bands across the thorax and wing covers — the third band on the wings forms a distinctive 'w' shape.
Life Cycle Through the Year
Adult beetles emerge in late summer and early fall and are commonly found on goldenrod flowers. In fall, they lay eggs in cracks, crevices, and bark wounds on black locust trees. Newly hatched larvae immediately bore into the tree and spend the winter in the inner bark, then tunnel through sapwood and heartwood during spring and summer. The species completes one generation per year.
Signs of an Active Infestation
By spring, entrances to the larval tunnels are marked by sap oozing from the tree and granular exudate pushed out by the larvae — both good visual cues that a tree is under attack.
Long-Term Damage to Black Locust Trees
Larval tunneling can honeycomb the wood, weakening the tree structurally and leaving it vulnerable to windthrow. Borer damage also opens the door to heart rot fungus (Fomes rimosus), which further weakens and can eventually kill an infested black locust.
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Tree Risk Assessment
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Borer Control
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