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Locust Borer

Adult Locust Borer

About Locust Borer

Lives on black locust.  Mature larvae are 25 mm long and white with dark heads.  Adult beetles are about 18mm long and black with bright yellow bands across the thorax and wing covers.  The third band on the wings forms a "w" design.

Beetles emerge in late summer and early fall and are commonly seen on goldenrod flowers.  In the fall they deposit eggs in cracks, crevices, and bark wounds.  Newly hatched larvae immediately bore into the tree and overwinter in the inner bark.  Larvae tunnel in the sapwood and heartwood throughout the following spring and summer.  There is one generation per year.

By spring, entrances to the larval tunnels are marked by sap oozing from the tree and granular exudate pushed out by the larvae.  Larval mines can literally honeycomb both sapwood and heartwood, weakening the tree and making it subject to windthrow.  Borer damage also provides an opening for infection by heart rot fungus.  This fungus weakens and can kill black locust.

To Control

Spray trees with lindane either in late summer or early fall or when buds expand in spring to kill young larvae.  Stressed trees and trees growing on poor sites are most susceptible to attack. Avoid planting this shallow rooted tree where soil conditions are unfavorable, or where the roots will be moisture stressed.