The Asian longhorned beetle, or ALB, is an invasive insect that feeds on a wide variety of trees in the United States, eventually killing them. The beetle is native to China and the Korean Peninsula and is in the wood-boring beetle family Cerambycidae. Adult beetles are large, distinctive-looking insects measuring 1 to 1.5 inches in length with long antennae. Their bodies are black with small white spots, and their antennae are banded in black and white. Checking your trees regularly for this insect and looking for the damage it causes and reporting any sightings can help prevent the spread of the beetle.
Adult females chew depressions into the bark of various hardwood tree species. They lay an egg—about the size of a rice grain—under the bark at each site. (Females can lay up to 90 eggs in their lifetime.) Within 2 weeks, the egg hatches, and the white larva bores into the tree, feeding on the living tissue that carries nutrients and the layer responsible for new growth under the bark. After several weeks, the larva tunnels into the woody tree tissue, where it continues to feed and develop over the winter. Larvae molt and can go through as many as 13 growth phases. As the larvae feed, they form tunnels or galleries in tree trunks and branches. Sawdust-like material, called frass, from the insect’s burrowing can be found at the trunk and branch bases of infested trees.
Over the course of a year, beetle larvae develop into adults. The pupal stage lasts 13 to 24 days. After adult beetles emerge from the pupae, they chew their way out of the tree, leaving round exit holes approximately three-eighths of an inch in diameter. Once they have exited a tree, they feed on its leaves and bark for 10 to 14 days before mating and laying eggs.
Because ALB can overwinter in multiple life stages, adults emerge at different times. This results in their feeding, mating, and laying eggs throughout the summer and fall. While adult beetle activity is most obvious during the summer and early fall, adults have been seen from April to December. Adult beetles can fly for 400 yards or more to search for a host tree or mate. However, they usually remain on the tree from which they emerged, resulting in infestation by future generations.
Signs of ALB start to show about 3 to 4 years after infestation, with tree death occurring in 10 to 15 years depending on the tree’s overall health and site conditions. Infested trees do not recover, nor do they regenerate. Foresters have observed ALB-related tree deaths in every affected state.
Collectively, the tree species the insect favors are called ALB host trees. In the United States, known ALB host trees include all species of the following 12 genera:
Golden raintree (Koelreuteria)
London planetree/sycamore (Platanus)
Mountain ash (Sorbus)