The common name powderpost beetle loosely applies to three
closely related beetle families: Lyctidae, Anobiidae, and Bostrichidae. Powderpost beetles breed in dead wood, as well as dried and cured lumber. It is their larvae's feeding that reduces wood to what scientists call frass - a fine powder or a mass of small pellets.
Damage by powderpost beetles occurs in a wide variety of wood products - floors, molding, paneling, crates, furniture, antiques, tool handles, gunstocks, etc. Damage usually is not evident until adults cut holes and emerge; then the powder becomes visible. Where damage is extreme, wood is converted to a mass of powder or pellets held together by a thin outer surface penetrated by numerous exit holes. Damage this severe usually indicates that several generations of beetles have re-infested the same piece of wood.
Lyctids are the true powderpost beetles. Larval feeding within wood produces a frass as fine as face powder, which will stream from the exit holes at the slightest jar or tremor. The appearance of powder does not necessarily indicate an active infestation. Remove the wood and examine it closely to confirm the presence of live insects. You may not see adult beetles; however, they're attracted to light and may appear on windows or sills. Have them identified by an expert. There are many look-alike beetles such as bark beetles from fireplace wood. Lyctids attack only large-pored hardwoods such as oak, ash, hickory, myrtle, and mahogany. Bamboo is also subject to attack.
Adult lyctids (Figure 3) are flattened, slender, colored dark brown to nearly black, and generally 3 to 6 mm long (1/10 to 1/5 inch). Mature larvae are C-shaped and slightly hairy with three pairs of small spine-like legs immediately behind the head. Larval body color is yellowish-white and the head is tan to brown. Females mate after emerging from wood and lay most of their eggs the first week. Eggs are deposited within pores of wood or in cracks and crevices.
Upon hatching, larvae begin feeding on and tunneling into the wood. After the larval feeding is complete, pupation occurs just below the wood surface. Adults emerge by chewing a small circular hole 2 to 3 mm in diameter through the remaining wood. The complete life cycle (from egg to adult) ordinarily requires 9 to 12 months; under favorable conditions, it may be reduced to only 6 or 7 months. Under adverse conditions, the life cycle may be prolonged up to 2 to 4 years or longer.
Two lyctid species that are common powderpost beetles in Oregon and the Pacific Northwest are Lyctus planicollis (LeConte) and Lyctus brunneus (Stephens). The latter species frequently is found in furniture made from bamboo.
Anobiid powderpost beetles attack sapwood but only rarely heartwood. Unlike the lyctids, anobiids reduce wood to pellets, instead of a fine powder. Adults range from 3 to 7 mm long, and their slender, cylindrical bodies generally are reddish-brown to nearly black. In most anobiid species, the head is bent downwards, and the eyes are not visible when viewed from above. The larvae, similar to lyctid larvae, are C-shaped and nearly white except for a darkened head capsule. The life cycle of anobiids may require 2 to 3 years for completion depending on the prevailing temperature and condition of the wood. Adult exit holes are round and range from 1.6 to 3 mm in diameter. An important member of this family is the native powderpost beetle, Hadrobregmus gibbicollis (LeConte). This beetle is most abundant along the coast, where it commonly attacks unpainted Douglas fir timber in barns and bridges and the basement timbers of dwellings. Greatest damage usually is confined to the lower portion of structures. The frass of anobiids is tightly packed in the galleries (feeding areas). It is not powdery but composed largely of tiny fecal pellets that give the frass a slightly gritty feel. Once the sapwood is consumed, infestations may die out. If there are large numbers of exit holes and frass is bright and light-colored like freshly sawed wood, the beetle infestation is old and active. In the Pacific Northwest, anobiid powderpost beetles are most common in unheated or infrequently heated buildings. They do best in wood with a moisture content above 14 percent. Coastal second homes, wooden shelters or buildings in rest areas, bridges, etc. are all susceptible to attack.
Bostrichids are most abundant in the tropics, so they're not as important as the lyctids and anobiids in temperate regions (such as the Oregon and the Northwest).
However, some species do attack wood in the Pacific Northwest. Most bostrichids feed on the sapwood of hardwoods, but a few also attack conifers. Bostrichid adults typically are 3 to 6 mm long, with slender, cylindrical bodies. Their reddish-brown to black color is similar to other powderpost beetles. The head projects downward as in species of anobiids, and the eyes are not visible from above. The segment immediately behind the head often bears numerous short spines that produce a rasp-like appearance. The larvae are also C-shaped grubs; however, in this family, the segments immediately behind the head are much wider than the segments near the tail end. An exception to the general appearance of adults of this family is the "black polycaon beetle," Polycaon sfoufi i (LeConte). This coal-black bostrichid is 12 to 25 mm long, and its prominent head extends forward. The segment immediately behind the head does not have a spiny surface. The bostrichid life cycle is similar to that of other powderpost beetles, but its egg-depositing behavior is unique. Female beetles bore into wood and prepare "egg tunnels" instead of laying eggs in pores or cracks on the wood surface. The frass of bostrichids is meal-like and contains no pellets.
It is tightly packed in the galleries and does not sift out of the wood easily. Although they're found occasionally, the bostrichids are not considered a serious pest of structures in the Pacific Northwest. When problems occur, they originate in hard-woods shipped from other more susceptible parts of the country or from other countries. Many of the species do not infest wood after it has been seasoned, so damage is limited to that inflicted by the first generation. The black polycaon beetle attacks
any softwood and several hard-woods. It sometimes burrows into the softwood interior of certain multiple-ply veneers, and it produces damage that may not be noted until adult beetles bore through to the surface of panels that have been made into furniture. Dinoderus minufus (Farbicius), the bamboo powderpost beetle, is found in baskets, picture frames, furniture, and other bamboo material imported from the Orient.
Revised by Jack D. DeAngelis, Extension entomologist, Oregon State University.
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