Powderpost beetles are small, reddish-brown insects that attack lumber and by their feeding activity reduce the wood to powder. Ongoing problems with true powderpost beetles (genus Lyctus) are moderately rare in Iowa, and chemical treatment is seldom necessary.
True powderpost beetles attack the sapwood of freshly cut hardwoods such as ash, hickory, oak, walnut and similar species. Adult powderpost beetles lay eggs in the open pores of the sapwood and the larvae burrow through the wood creating tunnels packed with fine, powder-like sawdust. After a few months to a year or longer (depending on the species) the larvae transform to adults and the new beetles emerge through small (1/16 inch) round holes in the wood surface. Damage is most severe in the sapwood portions of lumber though internal and surface damage may occur in heartwood. Varnished and cured lumber are not attacked, and soft woods such as pine, spruce and fir used for house framing, are not attacked.
Powderpost beetles are only active in wood with adequate moisture (from 8 - 32% moisture content) and starch (greater than 3%). Therefore, most powderpost beetle infestations naturally disappear within a few years as moisture and starch content decrease. Presence of the fine powder sifting from wood does not prove that powderpost beetles are still active within the wood, as sawdust continues to vibrate from exit holes long after the infestation has ceased.
An active infestation of powderpost beetles can be determined by finding adult beetles within the structure, observing fresh sawdust at exit holes, or by plugging all existing exit holes in a small area (app one square foot) and observing additional unplugged exit holes 6 to 12 months later. Thick latex paint is an easy way to plug exit holes in the surface of rough lumber. Otherwise, colored wood filler can be used.
If an active infestation is determined, your control options include discarding or replacing damaged wood or treating with an insecticide. Currently there are no insecticides available to homeowners for powderpost beetle control, so you should work with pest management professional. Existing finishes must be removed prior to insecticide application. Kiln drying kills larvae within infested lumber but reinfestation is possible. Vault or tarp fumigation of infested lumber or movable items is a possibility, but is usually not practical. Structural fumigation is also not practical and is rarely, if ever, done in Iowa.