Wood-boring insects damage woody plants by burrowing through the plant's vascular tissue, in the worst cases eventually interfering so drastically with the plant's ability to transport nutrients that the plant dies. Many different types and species of insects cause this kind of damage, and individual species often prey on a specific species of host plant.
Long-horned beetles are so named because the adult insects, some of which may be up to 2 inches long, have extremely long antennae. Adults typically feed on pollen, leaves or new shoots of plants and usually don't cause any serious damage. Their grub-like larvae, which are commonly called round-headed borers, can be a serious threat to trees, however.
Adult long-horned beetles typically lay their eggs in cracks in tree bark, and after the eggs hatch, the larvae tunnel under the bark to feed. Larvae are often active only in the summer or fall, but some species have long life cycles and remain in the tree for years before emerging as adults. The cottonwood borer, for example, takes approximately two years to mature from egg to adult.
Common long-horned beetle species include the locust borer, the cottonwood borer, the red oak borer and the poplar borer.
Adult metallic beetles typically have an iridescent sheen, and some species are bright blue or green in color. Both adult beetles and their larvae have flattened body segments behind their heads, and they are commonly referred to as flat-headed borers. These beetles usually complete their life cycles within a single year.
Common metallic beetle species include the flat-headed apple tree borer and the bronze birch borer.
Clearwing borers are not beetles, but rather moths. The wings of adults are not scaled like most other moths, and they resemble small wasps. They do not sting, however, and they feed on nectar and do not injure plants. Their larvae are pale-colored, hairless caterpillars, and like the larvae of other borers, they can cause serious damage to host plants. Like metallic beetles, clearwing borers usually complete their life cycles in one year.
Serious pest species of clearwing borers include the dogwood borer, the lilac borer, the peachtree borer and the banded ash borer.
Other Borer Types
Several other types of insects burrow into woody plants and can be a threat in the garden. Carpenter worms bore into vascular tissue just under a tree's bark, but they also tunnel deep into a tree's heartwood; they have a long life cycle and can take up to three years to develop into adults. Some weevils, bark beetles and horntail wasps also attack woody plants in a similar fashion.