Meet the (True) Powderpost Beetle

The beetles formerly known as lyctids (now family Bostrichidae, subfamily Lyctinae) are one of three powderpost beetle groups that infest and feed on wood, leaving galleries and damage. Anobiids and bostrichids are the other powderpost beetles.

Tiny round exit holes (1/32-1/16 inch or 0.6-1.5 mm diameter) made by emerging adults are characteristic of infested wood; even smaller holes may be left by parasitic wasps. Emergence holes made by adults of the other two powderpost beetle groups are slightly larger. The reddish-brown to black true powderpost beetles are only 1/32- to 1/4-inch (1-7 mm) long, elongated, flattened and have 11-segmented antennae with a two-segmented club.

As they feed and tunnel in galleries, the whitish, grub-like larvae produce a fine, powdery frass (digested wood) that feels smooth; larvae of the other two groups produce a coarser frass that feels gritty.

Frass is not tightly packed in tunnels but is easily jarred loose from exit holes. Mature larvae are about 1/4-inch (7 mm) long and pupate inside their galleries. The larvae require seasoned wood with a high starch content and wood moisture of at least 8 percent. Development time from egg to adult usually takes 9-12 months but may take up to four years, depending on moisture and other conditions.

* Modified from the Beetle Identification Guide by Nisus Corporation.

PEST POTENTIAL. True powderpost beetles typically infest seasoned hardwoods such as oak, hickory, ash, walnut, poplar, as well as some tropical hardwoods; some species attack bamboo. Eggs are laid in the wood usually while it is drying or stored. The wood can be used for building or brought into a structure. Infested sites include hardwood floors or stairs, wood paneling, trim pieces, built-in cabinets and furniture (especially imported).

Once adult beetles emerge from the wood in early spring, flour-like frass can be seen sifting from exit holes or on surfaces beneath infested wood. Adults may fly to lights or windows at night. Control depends on the extent of the infestation and potential for re-infestation and may require replacing infested wood, or surface treatment or injection of the wood with a borate or other product. Furniture items can be fumigated individually.

KEY POINTS. True powderpost beetles rarely successfully re-infest hardwoods inside a structure that is centrally heated with no moisture problems. They will not lay eggs in wood that is sealed. When conditions do allow these beetles to re-infest, the sapwood eventually can be reduced to powdery frass inside.

The authors are well-known industry consultants and co-owners of Pinto & Associates.