WOOD BORER
Wood-Boring Beetles
Revised by Richard M. Houseman
Division of Plant Sciences
There are several types of beetles that damage wood used for construction.
They are commonly placed into three main groups: powderpost beetles, round-headed borers and flat-headed borers.
These three groups include beetles from five scientific families: Lyctidae, Bostrichidae, Anobiidae, Cerambycidae and Buprestidae (Figure 1).
Most species are less than 6mm (1/4 inch) long, but a few reach 25 mm (1 inch) in length.
figure 1.
Wood-damaging beetles:
adults, top, and larvae, bottom. Left to right: Lyctid, Bostrichid, Anobiid, Cerambycid (old house borer), Buprestid.
damage
Wood infested with wood-boring beetles has numerous "shot holes" in the surface. Small pieces of sawdust (frass) produced by the larvae as they tunnel may sift from the holes when the wood is bumped or disturbed.
Cutting into the infested wood often reveals many tunnels filled with frass.
Characteristics of the frass and the tunnel system vary between different wood-boring beetle species.
Subflooring, hardwood flooring, interior trim, joists, sills and especially beams are subject to attack.
Other wood products, such as hardwood furniture, implement handles and ladders, may also be attacked. Log houses are especially vulnerable.
Vacation or recreation structures are also more prone to beetle attack because they often have higher moisture content in the wood due to intermittent heating or poor ventilation.
The amount of damage caused by wood-boring beetles will vary based on the species of beetle and their unique feeding and egg-laying preferences.
Damage weakens structural timbers and results primarily from the feeding activities of the beetle larvae.
Life history
The stages in the life cycle of wood-boring beetles are illustrated in Figure 2. Young beetle larvae hatch from eggs, burrow into wood, and begin feeding.
The larvae of different wood-boring beetle species differ in size and shape (Figure 1), but most larvae are yellowish white with dark mandibles (jaws). The strong jaws enable the larvae to construct tunnels as they feed on starch and other compounds within the wood.
Wood-damaging beetle larvae often go unnoticed because they feed beneath the surface of the wood and their tunnels are not visible. Feeding tunnels vary in size and shape according to species, and can be distinguished from other types of insect damage (e.g., termites, carpenter ants).
The time required for the larvae to complete their development varies from a few months to several years, depending on the species and the availability of food and moisture in the wood.
figure 2.
Wood-damaging beetles
spend most of their life cycle in the larval stage, in which the damage occurs.
When beetle larvae have completed their development inside the wood, they pupate.
The pupal stage is an inactive developmental period. The pupae eventually change into adult beetles that bore holes to the outside of the wood. The size and shape of these exit holes vary between species.
Soon after emerging from the wood, adult beetles mate and the newly mated females search for suitable sources of wood in which to lay their eggs.
The female often tastes the wood to determine whether suitable levels of starch and moisture exist. Some groups of beetles prefer hardwoods while others prefer softwoods.
Most wood-boring species lay eggs only on wood before it is seasoned and processed, but a few species will lay eggs on seasoned lumber.
Source: Extension, University of Missouri
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