Ornamental & Turf Insect Note Logo


James R. Baker, Extension Entomologist Emeritus

CAUTION: This information was developed for North Carolina and may not apply to other areas.

LOCUST BORER, Megacyllene robiniae (Forster), Cerambycidae, COLEOPTERA

adult beetleLocust borers are black, long-horned beetles with bright yellow bands across the body. The legs and antennae are reddish yellow. These beetles are about 3.4 inch long. There is no description of the eggs, but the immature stage is a plump, white grub with six tiny legs near the head. The grubs grow to about 1 inch long.



Locust borers are found throughout the United States, and black locust is the only host tree. Locust borers damage black locust by boring into the inner bark and later into the heart wood. Heavily infested trees break apart due to extensive tunnels in the heart wood. Trees growing on poor sites are especially susceptible to locust borer infestations.

drawing of adult and larva

Adult locust borers feed on pollen and are often common on the flowers of goldenrod in August and September. Females lay eggs in crevices of the bark and around wounds. Newly hatched larvae tunnel into the inner bark where they spend the winter. Growth resumes in the spring and the grubs begin to tunnel into the heart wood . The larvae maintain openings to the outside through which they push granular frass (waste products). There is one generation per year. Locust borers tend to attack black locust trees that are young or under stress. Healthy, dominant trees are often unaffected.


  1. Spray trunks and larger limbs with a pesticide from the table below. The first application should be made about mid August and a second 2 or 3 weeks later. Insecticides are generally not very effective, however.
  2. If the borers are already inside a tree, fumigate using aromatic solvent such as fingernail polish remover. Put the solvent into an oiler or some device that will squirt the solvent into the grub holes. After fumigation, sealing the tunnels with wax or putty helps to hold in the fumes.
  3. Remove and destroy badly infested trees in late fall or early spring.
  4. Select a good site for black locust trees and keep them healthy.
  5. Do not allow livestock to graze in locust plantings.

Pesticide  (Trade Name)  Formulation
permethrin (Astro)

Locust borer not specifically mentioned on label. See label for sites and application information. Not currently labelled for nursery use. Use other permethrin product.

imidacloprid (Merit & others) Imidacloprid has been found helpful in reducing impact of other longhorned beetles. It can be applied as a soil drench at the base of the tree or possibly as a trunk injection. (Imicide)
chlorpyrifos (Dursban Pro, Pageant) Not for use on or near residential. 22.2% emulsifiable concentrate
50% wettable powder or water soluble granular

* Home owners may find permethrin containing products available in stores. Check label for "borer" recommendations.

Useful Link for Biological Information:

USDA Forest Service Leaflet

Other Resources

For assistance with a specific problem, contact your local North Carolina Cooperative Extension Service personnel.

Published by North Carolina Cooperative Extension Service Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University at Raleigh, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.
© 2001 NC Cooperative Extension Service
Prepared by: James R. Baker Extension Entomologist. Adult photo USDA Clemson.

May 1994 (Revised)

Web page last reviewed January, 2011 by the webperson.