Bougainvilleas are popular plants due to their colourful tropical flowers and low maintenance requirements. The vines are vigorous growers that seem to thrive on neglect and are rarely bothered by pests or disease. The most common insects that affect them are aphids and cabbage loopers. Insect borers typically only affect plants that are stressed or weakened by other factors. Since bougainvilleas are very hardy, it is extremely rare that they are infected by wood-boring insects, but it does happen.
Flat-headed borers in their adult stage are metallic-coloured beetles in shades of green, copper, blue, or bronze. These boat-shaped beetles are flat and have short antennae. As larvae they are legless, with wide, flattened bodies. When the larvae bore into bark or sapwood, they create an oval or flattened hole. These borers infect plants that are already weakened or stressed in some way, so if your bougainvillea is a healthy plant, flat-headed borers will be unlikely to attack it.
Adult weevils are black and look like beetles but have a long snout (similar in appearance to an elephant's trunk or anteater's snout). This snout contains the weevil's mouthparts, which are capable of chewing rough bark and wood. Weevil larvae are cream-coloured and have no legs. The larvae do not tunnel like other boring insects, but rather feed beneath the bark in hollow cavities. Weevils may cause extensive damage to plants. There are several species of weevils that attack the roots or bases of woody shrubs and ornamentals such as bougainvillea.
There are several different species of wood-boring caterpillars. Moths are the adult stage of the caterpillar, and are rarely seen except at night. The caterpillars have legs--both true legs and "false legs," which are actually rows of tiny hooks. There are many species of caterpillars within this group, but the one most likely to infect bougainvillea is the American plum borer, which affects a variety of woody plants. The American plum borer invades the plant through wounded or damaged branches and may cause extensive damage.
Round-headed borers are also referred to as long-horned beetles due to their long antennae, which may occasionally be longer than the insect's body. The larvae of these borers usually have three small pairs of legs, though some species may be legless. The larvae tunnel into the heartwood of a tree or shrub and create a round or oval-shaped hole in the plant. Unless you have a large bougainvillea with heartwood, it is unlikely that these insects will infect your plant as the larvae live in heartwood. Most species of round-headed borers only attack weak or damaged plants, so if your bougainvillea is healthy there is little chance of round-headed borers infesting it.