Powderpost Beetles

Encyclopedia Article

Description of powderpost beetles

Powderpost beetles are small, reddish-brown insects that attack wood and by their feeding activity reduce the wood to powdery-fine sawdust. Lumber, furniture and other items made of wood can be weakened or destroyed by repeated attack over an extended period of time when conditions are suitable.  Powderpost beetle larvae feed inside the wood and create tunnels and galleries packed with powdery frass (excrement).  The surface of powderpost beetle-infested wood will be perforated with small (1/16 – 1/8th inch) round exit holes where the adult beetles emerged.

There are several kinds of powderpost beetles belonging to three different families of beetles; Lyctidae, Anobiidae and Bostrichidae).  Some types are specific as to the types of wood they infest - hardwood or softwood (conifer) - while others are general feeders.  Infestation and damage is dependent on species, age and moisture content of the wood and temperature and relative humidity.  Characteristics and preferences of the different families of powderpost beetles are presented in Table 1. 

Life cycle of powderpost beetles

All beetles have a complete life cycle of four stages: Egg > Larva > Pupa > Adult.  Female powderpost beetles lay their eggs in cracks, crevices, pores or previous exit holes of bare, unfinished wood.  Tiny larvae hatch from eggs, burrow into wood, and begin feeding.  Larvae feed on starch and other compounds within the wood as they tunnel forward.  The tunneling and development occur entirely below the wood surface and out of sight. Larvae continue to feed and grow, and at maturity burrow toward the surface and pupate.  The adult beetles emerge from the pupae, tunnel through the surface and leave the wood to mate, lay eggs and start the cycle over.  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 within the wood.

Damage caused by powderpost beetles

Homeowners are much more likely to see evidence of wood damage than the powderpost beetles themselves.  Typically, especially with the true powderpost beetles, homeowners will discover limited damage to hardwood flooring, cabinets, casings, and moldings by the presence of one or a few small exit holes on the wood surface and/or the powdery frass sifting from the holes.

Wood that is repeatedly attacked may become completely riddled with holes and galleries packed with the powdery frass held together by a thin outer shell of surface wood perforated with exit holes.  Extensive damage to the point of wood failure usually requires many generations of beetles reinfesting the same piece of wood.

Management of powderpost beetles

The first step in evaluating a powderpost beetle problem is to determine the extent of the infestation and whether the infestation is still active.  In new hardwood flooring and cabinets damage by true powderpost beetles may be localized in a very small number of isolated locations where sapwood was incorporated into the product.  Repair or refinishing rather than extensive treatment is all that will be warranted.

Since powderpost beetles are most active in wood with adequate moisture (from 15 - 32% moisture content) and starch (greater than 3%), infestations may naturally disappear over time or if the moisture content of the wood can be reduced.  Dehumidifiers, moisture barriers and increased ventilation can lower the humidity in buildings and crawl spaces.  Moisture caused by wood-to-ground contact van only be reduced by separating the wood from the ground.

Determining if a powderpost beetle infestation is active may require time and effort.  Techniques include 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.  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.

If an active infestation is determined, your control options include discarding or replacing damaged wood or treating with an insecticide. Treatment by an experienced pest management professional is recommended. Existing finishes must be removed prior to insecticide application. Boron-based insecticides (e.g., Bora-Care®, Tim-Bor®) will effectively control powderpost beetles when applied to bare wood surfaces.  Treatments that penetrate deeply into the wood will kill larvae and will prevent re-infestation.

Kiln drying kills larvae within infested lumber but is not practical for lumber in place.  Heat treatment of lumber, furniture or art pieces is effective in a heating chamber if the temperature can be held at 133 to 150 degrees F for 30 minutes to 4 hours. The heating chamber must be kept humid to avoid drying and cracking the wood.  Vault or tarp fumigation of infested lumber or movable items by certified professionals is a possibility, but is usually not practical. Structural fumigation is also not practical and is rarely, if ever, done in Iowa.

Table 1.  Adapted from "Wood-Boring Beetles," University of Missouri Extension publication # G 7422 by Richard M. Houseman.

Beetle Family

Adult Appearance

Wood Preferences

Damage

Lyctidae:

true powder-post beetles

Reddish brown to black; Somewhat flattened, head projecting forward; 1/8 to 1/4 inch long.

Sapwood of hardwoods (ring-porous hardwoods such as oak, hickory, ash; diffuse porous hardwoods such as walnut, pecan, poplar and wild cherry; tropical hardwoods such as Meranti/Lauan. Prefer newer lumber.

Will reinfest.

1/32 to 1/16 inch exit holes; Sapwood with cylindrical tunnels or reduced to fine powder that readily sifts out.

No pellets

Bostrichidae:

false powder-post beetles

Reddish brown to black; Cylindrical, head directed downward; thorax rough with small spines; 1/8 to 1/4 inch long.

Sapwood of hardwoods; occasionally attack softwoods.

Rarely reinfests.

3/32 to 9/32 inch exit holes; Sapwood with cylindrical tunnels packed with meal-like frass the rarely sifts out. Few, if any, pellets.

Anobiidae:

furniture beetles

Reddish brown to black; elongate and cylindrical; head directed downward and covered by hoodlike thorax; 1/8 to 1/4 inch long.

Hardwoods and softwoods; usually in sapwood or adjacent heartwood; Seasoned wood.  Slightly decayed wood with a high moisture content (14 – 30%) is preferred.

Will reinfest

1/16 to 1/8 inch exit holes; powdery frass contains elongate or bun-shaped pellets.

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