Powderpost beetles can be found in dead as well as dried and cured lumber. Damage occurs to many wood products such as rafters, joists, flooring, moulding, panelling, crating, furniture, antiques, tool handles, gun stocks, fishing poles and baskets. Sometimes homeowners hear rasping or ticking in the wood at night, notice a blistering appearance on the wood, see powdery frass piled below holes in the wood, find numerous round or oval exit holes at the wood surface, and even collect powderpost beetles around windows or lights. Mistakes are sometimes made determining if the infestation is active or non-active.
Powderpost beetle is a term used to describe several species of wood-boring insects. Adult Lyctids are flattened, slender, reddish-brown to black, varying from 0.7 to 3-mm long. The basal abdominal segment is long, and the antenna bears a club of only two segments. The head is visible from above. Mature larvae are C-shaped, slightly hairy with three pairs of spine-like legs, and yellowish-white with a brown head. The frass is fine flour or talc-like and loosely packed in tunnels. Large quantities often fall out at exit holes and cracks.
Adult Anobiids have slender, cylindrical bodies, are reddish-brown to nearly black and range from 1.5 to 3-mm long. In most species, the head is bent downward. The widest point of the thorax is slightly forward of the base, tapering backward and appearing as a rough, diamond-shaped outline. Larvae are C-shaped and nearly white except for a dark head. The frass is fine to coarse, pellet-shaped, usually a gritty quality and packed loosely in tunnels. There also is a small amount of frass around the exit holes.
Adult Bostrichids, 0.7 to 9-mm long, are cylindrical in most species, dark brown or black, with a roughened thorax. Antennae bear a club of three distinct segments. The head is usually not visible when viewed from above. Larvae are C-shaped; the body segments immediately behind the head capsule are much wider than the body segments at the rear. The frass is fine to coarse, tightly packed and tends to stick together.
LIFE CYCLE & HABITS
Lyctids attack only large-pored hardwoods such as oak, ash, hickory and mahogany. They attack “seasoned hardwood” and sapwood timbers found in woodwork molding, window and door frames, plywood, flooring, structural wood, furniture, tool handles and firewood. Pine and soft woods are not normally attacked. Adult beetles can emerge from wood stored in the home and infest structural wood or furniture. Lyctids rarely infest wood older than five years. Infestations usually result from wood that contained eggs or larvae when placed in the home. The wood could have been improperly dried or stored. Adult exit holes are round and 0.7 to 1.5-mm in diameter. Larvae cause the damage.
Anobiids may attack both hardwoods and softwoods, which means that infestations may be found in all the same places as Lyctid beetles as well as in structural timbers (beams, sills, joists, studs, subflooring, etc.). Maple, beech, popular and pine are especially susceptible to attack. Anobiids prefer to infest wood which is damp; therefore, infestations usually begin in moist, poorly-ventilated areas such as crawl spaces, basements, garages and utility sheds. Under favourable conditions of moisture and temperature, infestations may spread upwards into walls and upper levels of the structure, including furniture. Infestations may occur as a result of using infested lumber, or from beetles flying in from outdoors or being carried in on firewood. Infestations develop slowly, but wood can be reinfested year after year. Anobiids are called deathwatch beetles because in the past superstitious people believed the ticking one species makes foretold impending death in the household. Adult beetles make the sound during the mating season by tapping their heads on a hard surface. They attack seasoned softwood, hardwood, sapwood and heartwood found in woodwork, flooring, structural wood, furniture, tool handles and sometimes firewood. Exit holes are round and 1.5 and 3-mm in diameter.
Bostrichids are more abundant in the tropics. The bamboo powderpost beetle is found in baskets, picture frames, furniture and other imported bamboo material. These insects attack unseasoned and seasoned softwood, hardwood and sapwood, and are often found in dying trees or recently felled logs as well as seasoned lumber and wood products. Adults rarely reinfest wood. Adult exit holes are round and 2.3 to 7-mm in diameter. Both larvae and adults cause the damage.
Adult females lay eggs on or in the pores of bare, unfinished wood. Eggs hatch into tiny larvae that tunnel through the wood. Adults emerge one to five years later, usually April-July through holes cut to the wood surface by the larvae. Adults are short lived, active at night and may return to the same wood or go elsewhere, lay eggs and start a new life cycle. It is the damage that homeowners are more likely to see.
The length of the life cycle for Lyctids is three months to one year, for Anobiids one to three years and for Bostrichids about one year. Some wood-boring beetles complete the life cycle in a few months, while others live in wood 30 years before emerging.
The key to avoiding serious problems from powderpost beetles is early detection. Homeowners are much more likely to see damage than the beetles themselves. Since tunnelling and development of the larvae takes place entirely below the wood surface, the only signs of infestation are the emergence holes made by the adults and the powder-like frass sifting from the holes.
LYCTID OR ANOBIID BEETLES
Knowing how to differentiate Lyctid from Anobiid beetle damage is more than academic since Anobiids have a broader range of woods that they can potentially infest. Both Lyctid and Anobiids chew small, circular emergence holes in the surface of wood. Holes made by Lyctid beetles are about the diameter of a pinhead whereas exit holes made by Anobiids are slightly larger. One way to differentiate holes of the two species is to insert a “click-type” (refillable) ballpoint pen into the exit hole; only the tip of the ball will fit through a Lyctid beetle emergence holes. If the hole was made by an Anobiid, the tip of the pen will enter part way up the angled face of the point.
Another way to differentiate powderpost beetles is from the consistency of the powder (frass) that sifts out of the exit holes. Lyctid frass is extremely fine and feels like talc when rubbed between the fingers. Anobiid frass is also powder-like, but feels gritty.
Infestations sometimes die out on their own accord. Therefore, it is important to be able to determine whether the infestation is active or inactive. Active infestations will usually have powder the colour of fresh-cut wood sifting from the exit holes. In contrast to old, abandoned holes, new holes will not have taken on the weathered appearance of the surrounding wood. Powder streaming from recently opened holes may accumulate in small piles beneath the exit holes. If these piles of powder are covered with a film of dust or debris, the damage is old. Careful observation may be required to distinguish new powder from frass that has been dislodged from old larval galleries by vibrations.
One final means of confirming that an infestation is active is to mark or seal any existing exit holes. Use crayon or tape over the holes to see if more holes appear. Sweep up all powder, and recheck the wood for new holes and powder at a later date. Since most emergence occurs from April-July, it might be worthwhile to wait until the following spring to determine if new holes and fresh powder are present. This is especially true when attempting to make a determination during the fall or winter months.
Homeowners should know that there are various options for control. Selecting which is best depends on a number of factors including the severity of infestation, area being attacked, potential for reinfestation and treatment expense the customer is willing to bear. POWDERPOST BEETLES DAMAGE WOOD SLOWLY; thus, homeowners should not feel as though they must act immediately in order to preserve the structural integrity of their home. A “wait and see” approach is often desirable, especially when there is still doubt as to whether the infestation is active.
Most powderpost beetles are introduced into homes in lumber or finished wood products (e.g., furniture, paneling or flooring). Lumber which has been improperly stored or dried should not be used, particularly if beetle exit holes are present. Many of the most serious infestations arise from clients who used old lumber from a barn or woodpile behind their house to panel a room or build an addition.
Powderpost beetles will only lay their eggs on bare, unfinished wood. Wood which is painted, varnished, waxed or similarly sealed is generally safe from attack provided no unfinished surfaces are exposed. Bare wood can be protected from attack by painting or finishing exposed surfaces. Beetles emerging from finished articles such as furniture were usually in the wood before the finish was applied. (Note: beetles emerging from finished wood can, however, reinfest by laying eggs in their own exit holes; sealing the holes prevents this possibility).
Powderpost beetles, especially Anobiids, have specific moisture requirements for survival. Since wood moisture levels below 13 percent (during spring and summer) are generally unsuitable for anobiid development/reinfestation, it’s advisable to install a moisture barrier in the crawl space of infested buildings. Covering the soil with four to six mil polyethylene reduces movement of moisture into the substructure and reduces the threat of an infestation spreading upwards into walls and upper portions of the building. Most beetles do not develop in wood with a moisture content below 10 to 15 percent.
Another way to lower moisture content in damp crawl spaces is to increase ventilation. This can be accomplished by installing foundation vents (0.09 square metres of vent area per 13 square metres of crawl space). Moisture meters, used by some pest control operators, are useful tools for predicting the potential reinfestation in wood.
If the infestation appears to be localised (e.g., only a few holes in a board or sheet of paneling), simply replacing the board or sheet of paneling may solve the problem. If additional holes begin to appear in adjacent areas, additional action can then be taken.
KILN DRIED LUMBER
For new construction, use kiln-dried lumber (dried a minimum of eight hours at 54 to 60 degrees C and 80 percent relative humidity). Also, chromated copper arsenate (CCA) salts with trade names such as Wolmanized is an excellent wood preservative for wood in soil contact. The life of CCA treated wood is 40 years or more. This product is not available for homeowner application to wood since pressure application is essential. Treated wood has a slightly green cast and is often sold for use as landscape timbers and for fencing and deck construction.
Compounds available under trade names of Cuprinol are sold for homeowner application to wood. Penetration on wood surfaces is only about 3-mm and protection is much shorter than CCA treated wood.
A number of insecticides are labeled for surface treatment of bare, exposed wood. Spraying or brushing these materials onto infested wood creates a barrier that kills adult beetles as they chew out of wood, and newly-hatched larvae attempting to bore into wood. Homeowners may apply amorphous silica gel (Drione, Tri-Die) or borates (Bora-Care, Shell-Guard, Guardian). Labeled Restricted-Use Pesticides include chlorpyrifos (Dursban, Equity, Tenure), cyfluthrin (Tempo), cypermethrin (Demon TC), methyl bromide, permethrin (Dragnet, Flee), silica gel-pyrethrins (Tri-Die PT 230), and sulfuryl fluoride (Vikane). Formulations containing “borate” are especially effective against powderpost beetles in that they penetrate and kill beetles within the wood, as well as those entering or exiting the wood surface. Killing larvae within their tunnels is advantageous, especially where there is concern about marring the wood surface with additional emergence holes.
For borates to penetrate wood, the surface must be unfinished. Therefore, joists, sills, rafters, subflooring, studs, decking and siding are all excellent candidates for treatment. Although borates will not penetrate paint or varnish, they will penetrate wood surfaces previously treated with a water-repellent stain (e.g., wood siding, decks, or log homes), provided the water-repellency is broken down by pressure washing prior to treatment. An infested wood floor can likewise be treated with borates, but would first need to be sanded to remove the finish.
The two borate formulations registered for residual surface treatment of wood are Bora-Care® and Tim-bor®. Both formulations are virtually nontoxic, odorless, and remain effective for as long as 40 years. It is recommended that these products be applied by professional pest control operators. Homeowners, insisting on performing the application themselves, can obtain Bora-Care® through chemical distributors and lumber companies.
The two most recent borate formulations registered with the EPA for permanent treatment against wood-boring insects are SHELL-GUARD® and GUARDIAN®. One advantage that these products have is the use of essentially nontoxic propylene glycol and polyethylene glycol carriers. These carriers are not only very safe to users, but are very effective penetrating carriers.
GUARDIAN® is a highly concentrated paste that is applied as a bead from a caulking tube. GUARDIAN® can also be applied by direct injection into galleries or into drilled holes where insect populations are detected.
SHELL-GUARD® is a liquid formulated for a topical application using a sprayer or brush. Both products provide effective remedial and preventative treatment against most wood destroying organisms.
Both of these products are labeled for home use and can be easily and safely applied by the homeowner. (For further information on either SHELL-GUARD® or GUARDIAN®, contact PERMA-CHINK Systems at (800)548-1231 or (800)548-3554.
One final point to remember when applying borates or other liquid surface treatments is that the application will only control infestations which are accessible, i.e., wood that is exposed and can be reached for treatment. Infestations which have spread into walls or between floors are candidates for more drastic measures such as fumigation.
Fumigation is an expensive means of ridding a structure of powderpost beetles and should be considered a last resort. However, in the case of severe, widespread infestations, it may be the only option. Instances warranting structural fumigations are when infestations have spread into walls, between floors, and other areas where access or wood removal is impractical. The best way to avoid such problems is through early detection and implementation of one or more of the corrective actions mentioned above. Fumigation of a home will typically run upwards of $3,000 or more. After fumigating, there is no residual chemical left to prevent subsequent infestations.
Fumigation of infested furniture, antiques, and other manufactured articles can be done at a substantially lower cost by placing the items under tarps, in trailers, or in vaults that maintain gas concentrations at high levels. This service is offered by some pest control companies. Only the licensed, trained pest control operator or applicator can apply fumigants such as methyl bromide or sulfuryl fluoride (Vikane).
William F. Lyon
Keith L. Smith, Associate Vice President for Ag. Adm. and Director, OSU Extension.
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