By: Wizzie Brown
Several kinds of beetles tunnel through wood. When their larvae tunnel through structural wood, they can weaken it. The adults may also ruin the appearance of wood by creating holes in its surfaces.
Wood-boring beetles come from various insect families. They vary in size, damage and wood preference. Infestations can be managed, but it is critical to identify the beetles accurately because the management options vary by species.
Detecting an infestation
The presence of adult wood-boring beetles may or may not indicate an infestation. Adult beetles are attracted to lights, windows, and doorways where they may accumulate.
Several signs can indicate an infestation:
- The holes that beetles leave behind when they emerge from wood.
- The presence of powdery material called frass which is a mixture of wood fragments and excrement. This frass usually piles below the holes or collects in structural cracks. It can be very fine to coarse, depending on the beetle species.
- Stained wood or blistered wood surfaces caused by larvae tunneling just below the surface.
- Audible rasping or ticking sounds made by the larvae while chewing on wood.
Identify the beetle
Gather the following information to identify the beetle infesting your wood (Table 1):
- Note the color, size, and shape of the larva and/or adult.
- Determine whether the wood is hardwood of softwood.
- Note the size and shape of the exit holes.
- Examine the texture and location of the frass (Fig.1).
Some beetles re-infest wood, but most complete their development and lay their eggs in new wood.
Adult wood-boring beetles range from less than 1/8 inch to more than 2 inches long depending on the family. Many are dark colored; others are metallic blue or green, or yellow or red striped.
If you find adult beetles, look for holes or damaged wood to find the infested area. Wood-boring beetle larvae, or grubs, usually remain inside the wood. Larvae can be tiny to more than 2 inches long (Fig. 2). They are elongated, segmented, soft, fleshy, and white to cream colored. They have a distinct brownish, hardened head capsule. Grubs may be cylindrical or flattened.
The holes that wood-boring beetles make are usually round, but some species leave semicircular or oval holes. The shape and size of the hole can help identify the beetle species.
The texture and location of frass can indicate different types of beetles. Frass can be packed into the tunnels or extruded through exit holes. Whether it is powdery, pelletized, coarse, or shredded can help identify its source when no beetle specimen is available. A magnifying glass or microscope can help you examine frass more closely. Table 1 summarizes the characteristics of various wood-borer groups.
Beetles can be recognized and controlled based on whether they prefer soft or hardwood. Table 2 summarizes types of wood, the usual damage, the usual emergence sites, and the likelihood of reinfestation.
For example, lyctid powder post beetles (Family: Bostrichidae) attack only seasoned hardwoods. These beetles threaten hardwood floors, wood trim, or furniture but would not be expected to attack softwood such as pine framing in a home. Deathwatch beetles, on the other hand, feed on seasoned soft and hardwoods.
Sometimes wood-boring beetles are attracted by lights but do not infest wood. More often, beetle infestations come from using wood that is already infested during the construction of a house or from a piece of furniture.
Biology and habits of beetles
The life cycle of wood-boring beetles consists of egg, larva, pupa and adult. Only the larva and adult stages feed. Though adults of some species damage wood, the larvae do the most damage.
The length of the cycle from egg to adult of wood-boring beetles varies according to species and environmental conditions. Some beetles complete a life cycle within a few months; others can live in wood as larvae for up to 30 years before emerging as adults. This type of infestation is difficult to detect and control.
One of the most significant wood-infesting beetles is the old house borer (Fig. 3). As member of the roundheaded wood borer family, this beetle attacks softwoods by laying eggs in the crevices of freshly felled timber or wood in lumberyards (Fig. 4). It will reinfest and is often found in homes that have been built using infested wood.
You may not need to treat beetles that do not reinfest structural timbers, such as flatheaded borers, roundheaded wood borers, and bark beetles. These insects are found shortly after a structure is built. Adults of these species generally emerge within a few years after construction and normally do not reinfest seasoned structural wood.
Preventing beetle infestations and damage starts when trees are harvested. Bark should be removed from felled timber quickly to keep beetles from laying eggs there. Timber should be removed from the forest quickly and allowed to dry. Kiln drying will kill beetles, but they may reinfest the dried wood when it takes on moisture from the environment.
Most types of wood-boring beetles do not damage seasoned structural timbers or finished wood products that have been air or kiln dried to reduce moisture content. However, if infested wood is used in construction, beetles can emerge from structural timber, doors, flooring, molding, cabinetry, or paneling.
When you buy wood, inspect it for exit holes or other signs of infestation. Use structural wood and wood trim only if it has been properly kiln dried or chemically treated. Remember that beetles can still infest wood that is stored after being kiln-dried. Wood that is pressure treated with chemicals will resist infestation for many years.
Control moisture in your home to help avoid beetle infestations. Repair leaks and install vapor barriers, insulation, dehumidifiers and air conditioners. Most wood infesting beetles cannot develop in wood that contains less than 15 percent moisture. Low moisture will also help keep wood from rotting.
Keep a fresh coat of paint or varnish on all furniture or exposed wood in your home. Most beetle species will not infest wood with a finished surface.
Avoid bringing infested material into the home. Adult beetles can emerge from wood stored in the home and infest structural wood or unfinished furniture. Stack firewood well away from your home and never against its outer walls. Bring in only firewood that will be used immediately.
Inspect antique furniture, picture frames, bamboo products and other wooden items before buying them. Properly treat any item that has borer holes, larval infestations, or frass before placing it in your home or in storage.
After identifying the offending beetle, determine the extent of the damage and evaluate the structural characteristics of the infested item or building.
Beetle management options include replacing infested wood, killing the beetles with heat or cold, treating the wood surfaces with insecticides, or fumigating the structure. If the infestation is limited, remove or replace structural wood or furniture where economically feasible. Replacing infested wood keeps the infestation from spreading and eliminates visible damage.
Treat small home furnishings, wooden artifacts, or furniture by freezing or heating them. Maintain the infested wooden items at about 0 degrees F for at least 7 days to make sure that the beetles are killed. Some wood-boring beetles are resistant to cold temperatures and the length of exposure is important in killing these beetles.
To kill insects with heat, raise the internal temperature of wood to 140 to 150 degrees F for 2 to 4 hours. Wood that is more than 2 inches thick takes longer to reach the required internal temperature, so expect the treatment to take longer. The surface temperature of wood is usually higher than the internal temperature and high temperatures may damage certain items. In warm climates, the heat probably contributes to reduction of beetle infestations in attics.
Insecticides are another treatment option and should be applied by a licensed pest control operator. A localized infestation can be treated by spraying or brushing a residual insecticide on the wood surface.
Insecticides may remain on the surface or penetrate the surface of the wood. Those that stay near the surface affect only the adult beetles that emerge from the wood or that try to reinfest the wood. These insecticides will not eliminate larvae, which can continue to develop beneath the surface. Some beetles, such as the old house borer, can mate and produce eggs without leaving their larval tunnels.
Products with active ingredients containing beta-cyfluthrin, bifenthrin, cyfluthrin, cypermethrin, deltamethrin, fenvalerate, imidacloprid, and lambda-cyhalothrin can be used as surface treatments. These products do not penetrate wood very well and are used primarily to prevent rather than treat wood-boring beetle infestations.
Wood-penetrating treatments with water-soluble borate products such as Tim-Bor and Bora-Care work best when applied to wood before a home is completed. These are typically applied as an emulsion in two stages, the second application being made before the first one dries completely. These products penetrate the wood only partially.
Paint, varnish, wax, and other finishes prevent insecticides from penetrating wood. Outdoor wood is also a poor candidate for borate treatments because of leaching. Rain and humidity tend to draw out the soluble compounds and make them less effective over time.
Fumigation involves introducing a toxic gas into a structure, usually under a gas-proof tarp. The gas penetrates the wood and kills beetles at any stage of development. It does not prevent new beetles from infesting wood after treatment. This method is costly, technical, and hazardous; it must be performed by experienced pest control operators.
Wood can also be damaged by termites, carpenter ants, acrobat ants and carpenter bees. These insects and the damage they cause vary considerably. For more information on these insects, see these AgriLife Extension publications: Formosan Subterranean Termites (publication number E-367), Drywood Termites (E-366), Subterranean Termites (E-368), Carpenter Ants (E-412), Carpenter Bees (L-1826), and Managing Household Ant Pests (B-6183).
Always follow recommendations and instructions as printed on insecticide labels. The user is always responsible for insecticides on his own plants and property and problems caused by drift onto other properties.
The suggestions contained herein are based on insecticide labels and research conducted by the Texas AgriLife Extension Service and Texas AgriLife Research. The use of product names is not intended as an endorsement of the product or of a specific manufacturer, nor is there any implication that other formulations containing the same active chemical are not equally effective. Product names are included solely to aid readers in locating and identifying the insecticides suggested. Information given herein is for educational purposes only.
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