If you’re driving along the highway in July or August, you may notice clumps of trees with brown leaves that look dried, dead, or scorched. This is likely the handiwork of the locust leafminer, Odontota dorsalis, a small beetle that feeds on black locust, a common roadside tree in South Carolina.
Adult locust leafminer beetles are small, flat, about ¼ inch long, and “elongate” in shape; they look sort of like lightning bugs. The head is black, and the wings are orange with a broad black stripe down the center that widens towards the rear. Larvae are a creamy-yellow color, flat, and slightly longer than adults. In South Carolina, locust leafminers have two generations. The adult beetles overwinter in bark crevices and leaf litter under the trees. They emerge in the spring and begin to feed on the new leaves. The adult beetles lay eggs on the undersides of leaves. As larvae emerge from eggs, they start feeding between the top and bottom leaf layers creating mines (tunnels. The larvae pupate in these mines, emerge as adults around July, and repeat the cycle. Locust leafminers prefer black locust but also use honey locust, apple, beech, birch, cherry, elm, oak, and hawthorn trees as host trees.
Locust leafminer infestations occur nearly every year, and larval and adult feeding commonly leads to late-season browning and defoliation in their host trees. While this damage can look alarming, infested trees rarely die. If you are concerned about a favorite locust tree in your landscape, providing adequate water during the summer months can help trees withstand the stress of defoliation. For more information on tree care, see HGIC 1037, Tree Maintenance.