Structure-infestingwood-boring beetles

L-17846-00

J. A. Jackman*

S everal kinds of beetles damage storedwood, structural timbers and other woodproducts. These beetles come from at least

12 families and vary greatly in size, wood prefer-ence, nature of damage and other habits. Thetunneling activities of larvae and emergence ofadults can weaken the structural strength ofwood and may destroy its appearance.

Proper identification of beetles or beetle dam-age is extremely important, because control mea-sures vary according to species. Preventing bee-tle infestations is desirable, but once infestationsare found, control measures are available.

Other insects attack and seriously damagewood. Their appearance and damage characteris-tics vary greatly. Refer to Extension publicationsB-6080, Subterranean Termites; L-1782, DrywoodTermites; L-1783, Carpenter Ants; and L-1826,Carpenter Bees, for more information.

DetectionThere are several indicators that wood-boring

beetles are present. Immature beetles tunnelingin wood produce an audible rasping or tickingsound while chewing which is most often heardduring quiet times at night. Another indicationmay be a blistering appearance on the woodcaused by larvae tunneling just below the woodsurface. While feeding, beetles often push pow-dery frass from holes they have constructed inthe infested wood. This frass is piled below theholes or in cracks in structures. The consistencyof the frass ranges from very fine to coarse,depending on the species. Exit or emergenceholes in the wood, created by the adult beetle,also may be seen. Occasionally, wood staining or

the obvious presence of adult beetles will benoted. As adult beetles emerge in confined struc-tures, they often are attracted to lights or win-dows and may accumulate at these locations.

IdentificationIf beetle larvae, adults or other evidence of an

infestation is discovered, obtain a correct identi-fication of the beetle family or species involved.Wood-boring beetles range in size from under aneighth of an inch to more than 2 inches. Many ofthem are dark colored, but some are metallicblues and greens striped with yellow or red. Ifonly adults are found, locate any emergenceholes or damaged wood which identifies theinfested area. Knowing the kind of wood, hard-wood or softwood, can be helpful in identifyingthe beetle species involved. Frequently, wood-boring beetles enter homes accidentally becausethey are attracted by lights, but these cases arealmost always nondamaging to property. Beetlesmay also emerge from infested wood broughtinto the house. Application of insecticides shouldbe avoided unless actual infestation and damageare found and determined to be a potentialthreat to the structure.*Professor and Extension Entomologist, The Texas A&M University

System.

Powderpost beetle tunneling.

Biology and habitsWood-boring beetles have four life stages: egg,

larva, pupa and adult. The eggs and pupae donot feed. Larvae, or grubs, are the main damag-ing stage, but in some species adults can damagewood. The majority of wood-boring beetles donot damage seasoned structural timbers or fin-ished wood products. However, if infested woodis used in construction, beetles can emerge fromfinished furniture or buildings. Most species areunlikely to reinfest structures or breed in thehome.

The length of the life cycle (egg to adult stage)of wood-boring beetles varies greatly. Some bee-tles complete a life cycle within a few months,while others have been known to live in wood aslarvae for 30 years before emerging as adults.This complicates detection and control because itis difficult to assess the time an infestation hasbeen present. The variation in biology for thesebeetles is outlined in Table 1. Emergence holes ofwood-boring beetles are usually round, but somespecies produce semicircular or oval holes.

The type and location of frass is also charac-teristic of various beetle groups. Notice whetherit is packed into the tunnels or extruded throughexit holes. Also, note the texture (powdery, pel-letized, coarse or shredded). All these character-istics can help identify beetles when no speci-men is available. A hand lens is often helpful todetermine the frass characteristics of wood-infesting beetles.

Often, various beetle groups can be recognizedand control measures planned based on knowl-edge of their wood preferences. Table 2 summa-rizes the types of wood attacked, the usual dam-age or emergence sites in buildings and reinfesta-tion capabilities. This table should help in plan-ning appropriate control measures. For instance,the powderpost beetles attack only seasonedhardwoods, and are serious pests when they do.Thus, powderpost beetles found in hardwoodfloors or furniture would not be expected toattack the softwood ( e.g., pine) timbers in ahome. On the other hand, deathwatch beetlescan attack both softwoods and hardwoods, andgenerally feed on seasoned wood. Other beetlegroups do not reinfest structural timbers, so con-trol may be unnecessary.

One of the most significant wood-infestingbeetles is the old house borer, which generallyattacks structural softwoods. Contrary to itsname, it is often a pest in newer homes builtwith infested wood. Wood that is improperlykiln-dried or treated, or stored too long is suscep-tible to attack. This insect will readily reinfeststructural timbers.

ADULT1 TO 35 DAYS

FLYING,MATING,EGG LAYING EGG

1 TO 4 WEEKSLAID ON OR

IN WOOD

PUPA1 TO 4 WEEKS CHANGE

FROM LARVA TOADULT OCCURS NEAR

WOOD SURFACE

LARVA11/2 MONTHS TO

12 YEARS FEEDINGWITHIN WOOD

Typical wood-boring beetle lif e cycle .

Powderpost lar va (3 - 5 mm)

Typical length of po wderpost beetle adults (4 - 6 mm)

Old house borer lar va

Typical length of old house borer adults (12 - 18 mm)

The majority of flatheaded borers, roundhead-ed wood borers, and bark beetles are foundshortly after a structure is built. Adults of thesespecies generally will emerge within a few yearsafter a building has been constructed. These bee-tles do not normally reinfest structural wood.There are a few exceptions, of course, such asthe old house borer which is a member of theroundheaded wood borer family.

Preven tionPrevention is the best way to avoid damage

caused by wood-destroying beetles. Several stan-dard procedures to eliminate or avoid these prob-lems are available.

Evaluate wood closely before purchase.Purchase only structural wood and wood trimthat has been properly kiln-dried or chemicallytreated. Proper kiln drying will eliminate any

infestation. However, infestations may still occurin wood which is stored after being kiln-dried.Commercially pressure-treated wood will resistinfestation for many years.

Powderpost beetle dama ge.

Table 1. Biological characteristics of wood-destroying beetles.Typical

Exit Hole Destructive Length ofGroup Diameter Shape Stage Life Cycle Types of Frass

Lyctidae 1/32 to 1/16 Round Larvae 3 mo. to 1 year Flour or talclike; readily(powderpost beetles) inch pours out of exit holes and

cracks.Anobidae 1/16 to 1/8 Round Larvae 1 to 3 years Fine to coarse; pellet shapes;(deathwatch beetles) inch usually a gritty quality. Loose

in tunnels; little at exit holes.Bostrichidae 1/8 to 3/8 Round Larvae Usually 1 year Fine to coarse; tightly packed;(false powderpost inch and Adult tends to stick together.beetles)Ptinidae 1/16 to 1/12 Round Larvae Several months Fine and powdery; fills larval(spider beetles) inch under favorable tunnels.

conditionsCurculionidae 1/32 to 1/16 Round Larvae Varies with Powdery or granular dusts(weevils, snout beetles) inch and Adult species packed in irregular tunnels.Buprestidae 1/32 to 1/2 Oval Larvae 1 to 30 years None at exit holes; coarse(flatheaded borers) inch powder in tunnels.Oedemeridae 1/4 inch Round Larvae Approximately Shredded and moist.(wharf borer) 1 yearCerambycidae(roundheaded borers)

1. old house borer 1/4 inch Oval Larvae 1 to 32 years Tunnels filled with powdery(normally 3 to 10) dust often formed in pellets.

2. flat oak borer 1/16 to 1/12 Slightly Larvae 1 to several Tunnels packed with fineinch Oval years flourlike dust and granules.

3. other roundheaded 1/8 to 1/2 Round Larvae Variable Coarse and fibery in tunnels.borers inch

Scolytide Less than Round Adult 2 mo. to 1 Little or none at exit holes.(bark beetles) 1/16 inch and Larvae year or more Very little or none in tunnels.Brentidae, Less than Round Larvae Unknown Galleries free of frass and Lymexylidae, and 1/32 to 1/8 (probably not stained.Tenebrionidae inch several years)(timber worms)

Carefully inspect antique furniture, pictureframes, bamboo products and other wood itemsbefore buying them. Consider any evidence offresh emergence holes, larval infestations andextruding frass to be an active infestation. Treatthese properly before placing them in your homeor in storage.

Employ moisture control methods, such asvapor barriers and insulation whenever possible.This will help prevent decay that can aggravatewood-boring beetle problems. Most wood-infest-ing beetles cannot develop in wood that has amoisture content below 10 to 15 percent.

Avoid other sources of infestation such asindoor storage of fireplace wood. Store fireplacewood as far from the home as possible, and onlybring in wood which will be used immediately.Adult beetles can emerge from wood temporarilystored in the home and infest structural wood orfurniture or become a nuisance.

Maintain a fresh coat of paint or varnish on allfurniture or exposed wood in your home. Mostwood-infesting beetle species will not reinfestwood that is painted, varnished, waxed, or hassome other type of finished surface. Obviously,much of the structural timber is always exposedand untreated by necessity.

Contr olThere are several options available for control-

ling wood-boring beetles. Identification of thebeetle or beetle group involved, the extent of thedamage, and an evaluation of the structural char-acteristics of the infested building are necessaryto properly plan any control efforts. Keep inmind that some beetle groups will not reinfeststructural timbers so control procedures are notneeded. Most control programs are limited totemperature treatment, replacing infested wood,spot treatment with residual insecticides or fumi-gation.

Small home furnishings, wooden artifacts orfurniture may be treated by freezing or heating.It is necessary to maintain the wooden items atapproximately 0 degrees F for several weeks toeliminate infestation, because many wood-boringbeetles are resistant to cold temperatures.Alternately, some control programs might beaimed at increasing temperatures to high levels(e.g., 140 to 150 degrees F for 2 to 4 hours).Extremely high temperatures probably aid inreducing beetle infestations in many attics. Be

aware that surface temperatures of wood seldomreflect the internal temperature. It is necessaryto hold the wood at the desired temperature foran extended time for the internal temperature toreach the desired level.

When an infestation is localized, replacinginfested wood is a viable option. Damaged struc-tural wood or furniture should be removed andreplaced whenever it is economically feasible.

Pesticide treatments for wood-boring beetlesare best done by pest control operators. A local-ized infestation may be treated by spraying orbrushing on residual insecticides. Proper treat-ments may be effective for 10 years or more.However, this only affects adults that emergefrom the wood or attempt to reinfest it. Larvaldevelopment beneath the wood surface oftencontinues. Also, surface treatments generally donot control infestations of deep-boring beetlessuch as the old house borer. Products containingchlorpyrifos, borate, permethrin, cypermethrinand cyfluthrin are registered for wood-boringbeetle control. Applications are typically made asa water emulsion applied twice, the second timebefore the first application dries completely.Applications to the unfinished wood surfaceswill allow some penetration into the wood.However, many types of wood finishes—paint,varnish, wax—do not permit insecticide penetra-tion, or could be damaged by chemical interac-tion. If warranted, finishes may have to beremoved before treatment.

Fumigation is the most reliable and effectivemethod of eliminating wood-boring beetles. Atoxic gas penetrates beneath the wood’s surfaceto kill the developmental stages of the beetle.However, fumigation will not leave any residualchemical on the wood surface to prevent subse-quent infestation. Because it is a costly, highlytechnical and hazardous process, fumigationmust be left to pest control operators experi-enced in this technique. Refer to Extension pub-lication L-1785, How to Select a Termite ControlService, for more information.

Insecticide label clearances are subject tochange and changes may have occurred sincethis publication was printed. The pesticide USERis always responsible for the effects of pesticideson his own plants or household goods as well asproblems caused by drift from his property toother property or plants. Always read and followcarefully the instructions on the container label.

Table 2. Attack sites of wood-destroying beetlesAdult Emergence

Wood Stage Sites & DamageTimbers Attacked Attacked in Buildings Reinfestation

Powderpost x x x x x x x x yesbeetlesDeathwatch x x x x x x x x x x * yesbeetlesFalse x x x x x x x x x x x rarelypowderpostbeetlesSpider beetles x x x x x x x noSnout beetles x x x x x x x x x x x yesFlatheaded x * x x x x x x * x x * x noborersWharf borers x x x x x yesRoundheadedborers1. Old house x x x x x x yes

borers2. Flat oak x x x x x x no

borers3. Other x x x x x x x x x x * x no

roundheadedborers

Bark beetles x ** x x x x x x * x x x noTimber x x x x x noworms

*Possible**Rarely

Previous version of this publication was written by J. A. Jackman and P. J. Hamman.

The information given herein is for educational purposes only. Reference to commercial products or tradenames is made with the understanding that no discrimination is intended and no endorsement by the TexasAgricultural Extension Service or the Texas Agricultural Experiment Station is implied.

Produced by Agricultural Communications,The Texas A&M University System

Extension publications can be found on the Web at:http://texaserc.tamu.edu

Educational programs of the Texas Agricultural Extension Service are open to all people without regard to race, color, sex, disability, religion, age or national origin.

Issued in furtherance of Cooperative Extension Work in Agriculture and Home Economics,Acts of Congress of May 8,1914,as amended,and June 30,1914,incooperation with the United States Department of Agriculture. Chester P. Fehlis, Deputy Director, Texas Agricultural Extension Service, The Texas A&MUniversity System.

5M,Revision