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Wood boring beetles fall into two major categories, those that infest only live trees or recently harvested wood and those that infest dry, seasoned wood. For all practical purposes, it is not necessary to treat wood for beetles such as round head borers, flat head borers, ambrosia beetles, or bark beetles since they will not re-infest dead wood. However, emergence holes on exterior surfaces should always be filled to prevent water from penetrating into the wood, causing decay.
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The most commonly encountered wood boring beetle infestation is caused by the anobiid beetle. Although often called a "powder-post" beetle, it is not a true a powder-post or lyctid beetle. One reason for its widespread presence is its ability to infest both hardwoods and softwoods. Since most modern construction uses spruce, pine, and fir softwood species, wood members such as floor joists, beams, sills, and studs are susceptible to attack by anobiid beetles. Most infestations start in crawl spaces or other moist areas then move to other sections of the home. Since most infestations develop rather slowly, damage is usually detected in homes older than ten years.
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Fine sawdust or frass coming out of small holes in the wood is typically the first sign of the presence of anobiid beetles. The frass has a gritty feel to it as opposed to the talcum powder consistency of lyctid beetle frass. One of the challenges when dealing with an anobiid beetle infestation is the determination of whether the infestation is active or old. A good method is to cover a six-inch area of suspect wood with one layer of masking tape in early to late spring. If after a couple of weeks there are no small holes in the masking tape the chances are that the infestation is old and inactive.
Treatments for anobiid beetles should always start with moisture control. Anobiid beetles prefer moist wood and high moisture levels shorten their life cycle and speed the development of the infestation.
The most effective chemical treatment is the application of borates such as Shell-Guard and Armor-Guard. These products make the wood toxic to the developing beetle larvae and prevent newly laid eggs from hatching. Usually it takes from two to three months to eliminate an anobiid beetle infestation. We recommend the use of Shell-Guard® for treating active infestations and Armor-Guard® for protecting un-infested wood from future attack.
The true powder-post or lyctid beetle attacks only hardwoods such as oak, ash, hickory, walnut, and mahogany. Infestations are most likely to occur in hardwood flooring and paneling. Other common infestation sites include bamboo furniture and trim and picture frames made from tropical hardwoods. Like anobiid beetles, the first sign of an infestation is usually fine talcum powder-like frass coming out of tiny round holes in the wood. Another indicator is the presence of small, elongated black beetles on windowsills and other surfaces.
Lyctid beetles are typically introduced into a home as eggs or larvae in firewood or in new molding that has been improperly stored or dried. They have a relatively short life cycle and an infestation can spread to unpainted wood surfaces within a year or two. The female lays her eggs in the pores of the wood and if these pores are filled with a paint or stain, the wood will not be susceptible to infestation.
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Treating for lyctid beetles is similar to treating an anobiid beetle infestation. Lyctid beetles are particularly sensitive to borates and both Armor-Guard and Shell-Guard will eliminate an existing infestation and protect the wood from future attack. However, an infestation of lyctid beetles often becomes evident after the infested wood has been coated with a finish. For example, infested wood flooring may show no signs of an infestation until a year or so after it has been installed and finished. In order to properly treat the floor with a borate it will be necessary to entirely remove the finish by coarse sanding. Once the floor has sanded and cleaned the borate (in this case we recommend Shell-Guard because of its penetrating ability) may be applied. Once dry, the floor may then be fine sanded and the finish reapplied.
Old House Borers
Old house borers present the greatest control challenge to the pest management professional. They are large insects with a life cycle that can extend to 10 or more years. The old house borer attacks only softwoods and the initial introduction typically occurs while lumber is being stored in a lumberyard. Although named the old house borer, the first emergence of these beetles in a home usually appears within five to seven years after construction.
The earliest indication of an old house borer infestation is usually the noise made by older larvae chewing in the wood. This can be very disconcerting to the homeowner, especially in the middle of the night when larvae are most active. The appearance of oval emergence holes is the next step in the process. The frass consists of fine powder and small tightly packed pellets. Like an anobiid beetle infestation, most structural damage is caused by water infiltrating into exterior emergence holes, thus promoting decay.
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Treating a home for old house borers takes some patience on the part of the homeowner. The only quick remedy is a structural fumigation. However, few homeowners are willing to bear the cost of fumigation or the inconvenience of leaving their home for a few days. Borate treatments work but they take time, sometimes lots of time before total control is achieved. It is not uncommon for old house borer activity to continue for up to a year and a half after a borate treatment.
Additional borate treatments will not speed the control process. Since older beetle larvae are large insects and at that stage of their lives eat little wood, their tolerance to borates is quite high. They will probably complete their life cycle and emerge as adult beetles. The presence of borate in the wood does two things; first it kills younger beetle larvae that are feeding in the wood, and second it prevents any old house borer eggs from hatching. Thus, the borate treatment interrupts the beetle's life cycle and eventually the infestation will end.
Armor-Guard and Shell-Guard
Both Armor-Guard and Shell-Guard are highly effective against wood boring beetles. We recommend using Shell-Guard for eliminating active infestations because the glycol components aid the penetration of the borate into the wood where the beetle larvae are most active. This results in quicker control. Areas that have been treated with Shell-Guard will also be protected against future infestations.
Armor-Guard is best used as a preventative measure since it typically stays near the surface where it prevents beetle eggs from hatching. For example, if an active infestation of anobiid beetles is found in a crawl space, we would recommend that Shell-Guard be applied to those areas where activity is noted and Armor-Guard be applied to the remainder of the crawl space as a precaution against future infestations.
For additional information on wood boring beetles refer to the FIELD GUIDE FOR THE MANAGEMENT OF STRUCTURE-INFESTING BEETLES by Stoy Hedges and Dr. Mark Lacey available from Pest Control Technology, Cleveland, Ohio.