Habitat and Life Cycle: The brightly colored adults appear when goldenrod (Solidago sp.) is in bloom, generally mid-August through October here in the midwest. I took photos of this specimen feeding on goldenrod pollen in the midst of a large mown field, hundreds of yards from trees of any variety, and so it's obvious to me the beetles will range far from their host plants in search of food. Females start laying eggs in the early afternoon and continue until dusk, August - October. Eggs are laid under the bark, around pruning wounds and wind breakage and in cracks in the bark - rarely where they can be easily detected. About a week later, the eggs hatch and small white larvae bore into the inner bark, where they make a small hibernation cell and overwinter. In the spring, the larvae bore into the woody part of the tree, eventually enlarging their tunnels until they are 3-4 inches long and 1/4 inch in diameter. By mid-July, most of the larvae begin the pupal stage, which lasts about 2 weeks. The mature adult beetles emerge through the holes made by the larvae.

Mature larvae are white, about 1 inch (2.5 cm) long and one-quarter of an inch (0.6 cm) in diameter. Newly formed pupae are creamy white and about three-quarters of an inch (1.9 cm) long. Both the larval and pupal stages are spent within the tree and are not readily seen.  [1]
 

Control
Black locust shade trees or lawn specimens can be protected from borers by spraying the trunks and the larger limbs with a lindane emulsion. To prepare small amounts of the spray, add 2 tablespoons (30 ml) of a 20-percent emulsifiable concentrate to 1 gallon (3.8 1) of water. For larger amounts, add 3 pints (1.42 1) of the concentrate to 50 gallons (190 1) of water. In the spring at the time the buds are opening, spray trunks and limbs until wet. Repeat the application in 10 to 14 days. This treatment kills active young larvae that are enlarging their galleries just under the bark.

The same lindane spray also may be applied in late summer to protect the trees from newly hatched larvae attempting to penetrate the bark. Spraying may be done anytime from late August through September, since the female beetles continue to lay eggs during this period.

Spraying with chemicals is not considered practical for the protection of black locust in a forest. Severely injured forest stands can be regenerated by clearcutting during the dormant period. The sprouts that follow clearcutting should be thinned by removing all but the most vigorous in each group. This procedure has resulted in a good second crop of trees with very light subsequent injury.

Moderately to lightly injured stands on medium-to-good sites benefit from thinning. In such stands, injury is confined mainly to overtopped, intermediate, or decadent trees. Removal of these trees should reduce the borer population and thereby help protect the more desirable trees.

Borer injury is usually less serious when black locust is grown with other tree species. Mixed stands usually produce denser shade and more leaf litter than do pure stands of locust. Trees are more vigorous when nutrients from decomposed leaf litter are available. In pure locust stands, the addition of several inches of hardwood leaves results in accelerated growth for several years after the treatment and should reduce chances of serious borer damage.

Old black locust trees with dying tops serve as brood trees for the borer. Removing these trees from the vicinity of planting areas should be helpful in reducing damage to the young planted trees. These large brood trees should be cut during the dormant period and either peeled or burned to destroy the borer larvae. [1]

References
1. Jimmy R. Galford, Entomologist, Northeastern Forest Experiment Station, Forest Service, U.S. Department of Agriculture,
Forest Insect & Disease Leaflet 71, The Locust Borer