Wood Destroying Beetles

The Mississippi Valley, Gulf States, Eastern Seaboard and other areas of high humidity and temperate-to-seasonally-warm climates are most susceptible to wood boring beetles and their damage. In the western states subareas are the most prone to attack. California, Oregon and Washington are considered to be susceptible to a greater level of wood boring beetle infestations than is currently appreciated. As a consequence further emphasis should be placed on examination of crawl spaces in homes of western states, particularly those in close proximity to the ocean.

As our population increases along with the demand for lumber there has been a corresponding increase in the use of salvaged, second growth and imported timber. This activity has resulted in the development of more problems from wood destroying insects. Salvaged timber typically has more insect problems, fire and fungal damage and other pest infestations. When it is used in structures as low-grade lumber new challenges to the pest control operator develop.

Second growth timber is a result of replanting deforested areas and typically results in lumber, which is unusually palatable to these organisms partially due to high starch content. The heavy importation of timber and products such as antiques, bamboo furniture, cabinet facings and other items undoubtedly results in new and challenging species of wood destroying beetles.

Wood boring beetles fall into 2 broad categories. Namely those that reinfest wood and wood products and those that do not. Generally speaking beetles that do not reifest wood require bark to be present for egg laying. Those that reinfest can lay their eggs on wood with or without bark.

Beetles that typically reinfest

These insects are commonly referred to as the true and false powder post beetles.

Bostrichidae: Bostrichids-False powder post beetles, twig borers.

Anobiidae: Anobiids-False powder post beetles.

Lyctidae: Lyctids-Powder post beetles.

Bostrichidae - False Powder Post Beetles, Twig Borers

This is a fairly large group of beetles comprising of approximately 70 US species ranging in size from 1/8 to over 2 inches in length. Most are black in color, cylindrical in shape and have a short-clubbed antennae with 3 to 4 terminal segments (Figure 1). When viewed from a dorsal angle, the head is almost totally hidden by the hood-like thorax. The head is also inserted into the thorax and only partially visible from any angle. Most species possess pyramid shaped spines on the top of the prothorax (behind the head). These beetles typically infest dead wood in nature and are not considered pests. However, there is one species that is a stored product pest (Figure 1) and a few that are wood pests.

Bostrichid beetles differ from the other 2 families of beetles that commonly reinfest wood by the fact that the adults bore into wood forming tunnels for egg deposition. The other families lay their egg externally on the wood. With bostrichids oviposition (egg laying) occurs in the wood pores leading to these tunnels with hatching larvae boring throughout the wood thus forming tunnels of varying size. The larval stage of these beetles is typically C-shaped with a well-developed head capsule and no thoracic legs. Also the thoracic area is somewhat swollen (Figure 2). Pupation occurs near the surface and emerging adults eat their way to the surface leaving circular holes in the wood. These beetles are most abundant in the tropics and typically are not as important (as a group) of wood pests as the other 2 families in this category.

Lead Cable Borer

This is one of the more interesting of the bostrichid beetles (Figure 3). It is common along the Pacific Coast particularly in Northern California and southern Oregon. Outdoors it normally infests dead and seasoned oak and less commonly attacks acacia, eucalyptus, maple, California laurel and other hardwoods. Adult beetles can reinfest wood from which they emerge. These beetles are occasional pests of hardwood paneling and floors (Figure 4). They are also attracted to cork in wine bottles and can severely damage oak caskets that contain liquor or wine. There is only one generation per year and adults typically emerge in the summer months.

One of the more interesting facets of their biology is that this insect also bores into lead sheathing (Figure 5). Actually a number species of beetles and other insects bore into lead but this is the more common and notorious of the lot. We are not sure why this occurs but one author reports that the lead cable borer is greatly stimulated by heat. As a result they are drawn to the heat absorbed by lead and even asphalt roof. The main damage due to this activity occurs in the lead sheathing of telephone wire. The 2mm diameter holes produced by this activity allow moisture to enter and short-circuit the lines. Another common name is the short circuit beetles. Periodic inspection of telephone lines is frequent, especially in those areas of the Pacific Northwest that receive heavy rainfall (Figure 6).

Bamboo Borer

This beetle is indigenous to Asia but has been shipped all over the world with its primary host, bamboo. This is a small beetle with adults measuring approximately 1/8 inch in length (Figure 7).

In parts of Asia this beetle causes considerable damage to cut bamboo, one of the major materials used in home and furniture construction (Figure 8). It also is a stored product pest infesting drugs, grain, flour and spices. Even though it has undoubtedly been shipped to the United States in bamboo furniture an undetectable number of times, it has not becomes well established here and typically is not a major problem.

An additional problem with this insect in much of Asia is associated with the fine powdery frass that is expelled from the bamboo as the beetle larvae feed. The frass contains small bamboo fibers that are very abrasive. Since bamboo is used in roofing construction these fiber filter down onto inhabitants and cause considerable itching. Considering the number of people living in Asia and the extent that bamboo is used in home construction, this may be one of the major human maladies of the world.

Black Polycaon

This beetle does not have the hooded head that is characteristic of most bostrichids (Figure 9). It is also considerably larger (1/2 to 2 inch body length) than the other pest species.

This beetle occurs in the Pacific Coast states and Arizona. It readily attacks both hard and soft woods. As a pest it is most commonly found attacking the three-ply paneling used in making desks and other furniture. The larvae bore in the inner ply of soft wood and are not detected until the adults emerge eating their ways through the outer ply of hardwood. In doing so they leave circular emergence holes that are approximately 7 mm in diameter. They do not reinfest finished wood so in these cases initial infestations typically occurred prior to manufacturing the furniture. The entire life cycle takes about one year. Stacked plywood is also occasionally attacked.

Anobiidae - False Powder Post Beetles

Almost all anobiids are small measuring 5/16 inch or less in body length. Their shape is quite variable but can be distinguished from the bostrichids in that the head is not pulled into the thorax and is readily visible, but as with the bostrichids cannot be viewed from a dorsal angle as it is hooded by the thorax. Their antennal shape is quite variable but with most species that attack wood the last 3 segments are elongated (Figure 9). As with the bostricids the larval body is C-shaped, but unlike them it has well developed legs (Figure 10).

Of the 310 species of anobiids in the US the following are considered the most economically important.

Drug Store Beetle
Cigarette Beetle
Deathwatch Beetle
Furniture Beetle

Two of these species are stored product pests, namely the drugstore beetle and cigarette beetle (Figures 11). They infest any of a variety of dried processed foods and drugs. Unlike the wood infesting forms they have a relatively short life cycle.

The wood infesting forms of these beetles typically deposit their eggs in cracks and crevices in wood, in end cuts of lumber or in emergence holes of the adults. Uninfested lumber with paint or varnish is less susceptible to their attack. Their life cycles are quite long completing one generation every 2 years under ideal conditions but can be extended to 5 years under unfavorable conditions. They typically attack sapwood of both hard and soft wood with moisture content between 14 to 30 percent. There is also a preference of wood 10 years or older.

Deathwatch Beetles

There are a number of species of deathwatch beetles around the world. They get their names from the method of attracting the opposite sex for mating. When sexually mature either sex will tap its head against any available surface. This makes a faint ticking sound (like a watch) which alerts and attracts the opposite sex. An old English superstition is that this faint ticking is a sign of impending death. This sound was most frequently heard in rooms where someone was very sick and consequently where little noise was made to drown out the ticking.

The California deathwatch beetle (Figure 12) is the most common species along the Pacific Coast. The adults range in size from 2.5 to 5.5 mm in length with striated elytra and are humpback in appearance. This is the most destructive of the false powder post beetles in the US. As with other species it prefer old wood and does most of it damage in crawl spaces where high humidity exists.

Furniture Beetle

In the US this beetle is widely distributed but it has not nearly reached the status of its importance in Europe and New Zealand. For example in Germany and New Zealand it is reported to infest nearly every building that has been existence for over 15 years. It attacks structural timber, paneling, flooring and furniture. In these areas it is a major part of the structural pest control industry. Infestations appear to be closely dictated by environmental conditions since moderate temperatures are essential for its development. The furniture beetle only attacks well seasoned wood and will not attack wood where the bark is still present. According to one source it is rare for soft woods to be attacked until about 20 years and sapwood of oak about 60 years after it has been cut.

Lyctidae - Powder Post Beetles

Powder post beetles are relatively small (3 to 7 mm in length), dark brown to reddish-brown in color and possess an elongated body (Figure 13). These beetles can readily be distinguished from the other two families of beetles that reinfest wood by the presence of a two-segmented club forming the tip of the antennae (Figure 14).

Powder post beetles are relatively small (3 to 7 mm in length), dark brown to reddish-brown in color and possess an elongated body (Figure 13). These beetles can readily be distinguished from the other two families of beetles that reinfest wood by the presence of a two-segmented club forming the tip of the antennae (Figure 14).

In the United States there are 10 species of true powder post beetles of which 6 are of economic concern. In the continental US these pests are second only to the termites as far as insect destruction of lumbered wood but confine their damage to large pored hardwoods such as oak, hickory, ash and bamboo. These beetles attack any product made of these woods including hardwood flooring, furniture, toys, statues, gunstocks, axe handles and similar objects. These beetles can readily be distinguished from the other two families of beetles that reinfest wood by the presence of a two-segment club forming the tip of the antennae (Figure 15). Unfortunately signs of their damages is not visible until the adult emergence and completion of their life cycle (Figure 16).

Adult beetles are nocturnal and fly to lights, a behavior that may be useful in detecting an infestation. Their eggs are deposited in the pores of hardwood, which are exposed when the wood is cut or the female may open them herself. Finely sanded, painted, varnished or other finished wood is not normally suited for egg laying. Upon hatching the young larvae tunnel with the grain but eventual can take an irregular course. As they feed they pack their tunnels with the very fine powdery frass. The entire life cycle of powderpost beetles from deposition of the egg until emergence of the adult may be completed in as little as 6 months or may be extended to years under unfavorable conditions.

As with the other two families of beetles that reinfest wood, lyctid larvae are C-shaped; however, unlike bostrichid larvae but as with anobiids, lyctid larvae (Figure 17) possess well developed legs. However, the latter two can be separated by the fact that the legs of anobiid larvae have 3 segments and no terminal claw while those of a lyctid are 5 segmented with a claw at the end.

Three factors primarily determine the acceptability of hardwood to the attack of these beetles, namely pore size and starch and moisture content. The primary nutrient of wood to lyctids is starch, as they do not digest cellulose and other components. The starch content in lumber depends on the species of tree, season when the tree was cut and method by which it was dried. Lyctids attack new lumber as opposed to old since starch is lost with aging. Lyctid larvae can live in wood with a water content between 8 and 32 %. Green lumber contains around 50% water and is not accessible to attack by these beetles. Finally hardwood with large pores is preferred as wood with fine pores is not readily accessible for deposition of the eggs.

Prevention and Control of True and False Powder Post Beetles

In nature these beetle normally attack the branches and trunks of dead and dying trees. Since these are such small beetles and probably don’t fly that far from these natural sources of food, infestations in buildings, homes, furniture and other wooden products generally begin by infested wood being built into or brought into the structure or from nearby infested old wood. In many cases this may begin at the lumberyard or manufacturing location. Based on this sanitation becomes a very important if not the most important factor in preventing infestations. Since most of these beetles have a relatively long life cycle, the periodic elimination of susceptible scrap or excess wood is essential and quite effective.

At manufacturing locations or lumber yards where is wood stored for any length of time, periodic inspections are essential, especially since visible signs of damage are not detectable for months if not years following an initial infestation. Unused firewood or stored old lumber can lead to infestations in homes.

These beetles are typically not capable of infesting lumber that is finished with varnish, paint or even fine sanding in some cases. Such finishes should also include the end cuts. Once an infestation is established in a structure or other object, possible controls include the use of heat, fumigants and even toxic solutions in some cases.

Beetles that typically do not reinfest

The following families of wood boring beetles typically do not reinfest lumber. Normally speaking they require bark to be present for egg laying or oviposition. There are some exceptions to this rule but the following families are generally represented here.

Buprestidae: Metallic Wood Boring Beetles or Flat Headed Borers.
Cerambycidae: Longhorned Beetles or Round Headed Borers.
Scolytidae: Bark Beetles.
Scolytidae-Platypodidae: Ambrosia Beetles.

Buprestidae - Flat Headed Borers

Adults of this family can readily be recognized by their flattened and boat-shaped bodies and the fact that there is metallic coloration somewhere on the body (Figure 18 and 19). The shape of the larvae is very distinctive with a broadened and flattened thoracic area and no legs (Figure 20).

As previously indicated these beetles almost always (there are rare exceptions) require bark to be present for egg laying. In rare instances they can deposit their eggs on fire scared or freshly cut lumber or even more rarely old lumber. The larvae bore throughout the tree or in some species beneath the bark. These beetles normally attack trees that are either cut, disease, damaged by fire or in some other way have lost their vigor. Healthy trees have copious amounts of sap that serve as a defensive mechanism against beetle attack. In healthy trees sap tends to drown out hatching larvae. As a consequence wood boring beetles rarely deposit their eggs on the bark of healthy trees. However, when a tree is stressed its sap flow drops and beetles and other wood boring insects are readily attracted. Hatching larvae mine heartwood as well as sapwood. Their mines tend to be flattened taking on the shape of the enlarged larval thoracic area and are tightly packed with powdery frass, a characteristics which can be used to distinguish them from the mines of round headed borers. The mines of round-headed borers are circular in shape and are loosely filled with a mixture of fibrous and powdery material.

The life cycle of metallic wood-boring beetles is quite long requiring 1 to 3 years to complete development. However, if an infested tree is lumbered the cycle of any surviving larvae in the wood can be greatly extended. Lumber contains less moisture and nutrients than living or freshly cut trees. In extreme cases this cycle may be extended to 20 or more years.

On occasion adult buprestids do emerge from the walls and other wooden structures in the home. Invariably these are surviving larvae that have completed their development and "were built into the house". This is fairly rare since most lumber is kiln dried and any infesting larvae cannot survive this process.

Cerambycidae - Round Headed Borers

These beetles are also referred to as the long horned beetles (Figure 21 and 22). As this name implies most but not all adults have elongated antennae, which in some cases can be as long or longer than the entire length of the body. Most have an elongated cylindrical shaped body and are further characterized by the fact that the first antennal segment (where it attaches to the body) is at least 5 times longer than the second.

The larval stage is a legless and club-shaped grub (Figure 23). The term round headed borer refers to the cylindrical tunnel this larva leaves as it bores through wood. As with the metallic wood boring beetles these beetles rarely reinfest and typically require bark for oviposition. Their life cycle is very similar to that of the metallic wood boring beetles typically requiring several years to complete development in cut timber or stress trees. Again the cycle may be greatly extended once infested trees are lumbered.

New House Borer

One of the more common long horned beetles that is found completing its development in lumber from infested trees is the new house borer (Figure 24). This species is prevalent throughout most of the western United States and western Canada. It attacks pine and Douglas fir, especially in fire swept areas. When lumber from such trees is built into homes, the emergence holes of the adults may be found in hardwood flooring, linoleum, plaster, plasterboard or any other covering of the infested framing of the home. Although the entire life cycle of these beetles is around 2 years, the emergence of the adult beetles typically occurs within the first year of building. The apparent reason is that as the lumber dries out it does not support development and the infesting larvae do not survive.

In recent years infestations by this beetles and others that do not reinfest are on an increase. The apparent reason for this is that lumber costs are increasing and therefore the use of lesser grades of lumber in home construction are correspondingly on an increase. In the past fire damage trees (attractive to these beetles) were generally rejected for the production of lumber.

Old House Borer

One notable exceptions to the "rule" that "long horned beetles do not typically reinfest" is the old house borer (Figure 25). This beetle is spread throughout much of the eastern US to as far west as Texas. Reinfestation in homes is common and in some areas this can be a serious structural pest. As with the new house borer this species only attacks softwoods. Most damage from this beetle occurs in attic framing in the northeast and substructure along the mid-Atlantic coast. Fumigation is an effective treatment for this pest.

Eucalyptus borer

The eucalyptus longhorn borer, Phorocantha semipunctata, is a serious and destructive beetle pest of eucalyptus trees. Native to Australia, it has spread to eucalyptus cultivation areas on all continents. Until recently, California’s eucalyptus trees were considered virtually pest free. However, in 1984, the first North American record this beetle was detected in dying eucalyptus trees in Orange County. Since then, this pest has been detected in almost all southern California counties and is expected to occur wherever eucalyptus is grown.

Adult beetles are approximately one-inch in length and black and brown in color (Figure 25a). The larvae feed beneath the bark of eucalyptus trees, creating sawdust filled tunnel. Upon inspection circular exit holes 1/2 to 3/4 inches in diameter are readily visible. Lines of sap on the trunk may originate from these holes. Saplings may die within the first year after infestation due to trunk girdling and mature trees may die within 2 years of infestation. The movement of infested eucalyptus firewood spreads these beetles. Adult are strong fliers and may fly several miles from their emergence site to find suitable egg laying locations.

As far as is currently known, all eucalyptus species grown in California are susceptible. Previous research suggested that only stressed trees were attacked, but recent studies indicate that even healthy trees can become infested. They attacks freshly cut or fallen eucalyptus logs and branches as well as living trees.

There is no fail-safe method to prevent attack from these beetles. The best approach is to maintain trees in a vigorous condition and prevent dry season water stress with periodic deep irrigation. Eucalyptus firewood should be tightly covered with a tarp or plastic sheet for at least six months after cutting. This will prevent escape of emerging adults, which could attack surrounding trees and will prevent egg laying by free flying adults. Pruning branches and cutting firewood during winter and early spring when adults are not active also reduces the chances of spreading this pest.

Through a cooperative effort of the University of California, Riverside and Santa Barbara County, 2 nursery sites for the establishment of a non-native wasp parasite of the eucalyptus longhorn borer are being maintained in Goleta. These nursery sites are used to raise wasps for distribution to other infested sites. At this time, the distribution of these wasps is determined by staff. Hopefully, the wasp will establish itself, and not require further human assistance. Entomologists are optimistic regarding the potential success of this project.

Although field trials have not been conducted, chemical controls are not expected to be effective against eucalyptus longhorn borer because the larvae feeds inside the tree where it is protected from contact with control materials. Results of research trials using injected pesticides for control of similar wood boring pests on other trees have been discouraging, and there are no pesticides currently registered for trunk injection in eucalyptus trees. Contact and/or residual activity pesticides are not likely to be effective because the flight period of the adult eucalyptus longhorn borer, which begins in April and continues through the summer months, precludes targeting a narrow effective treatment window.

Asian Longhorn Beetle

Another beetle that attacks and is capable of killing living trees is the Asian longhorn beetle. This species is indigenous to Japan, Korea and China. In 1996 it was found killing trees in a few areas of New York. At that time federal agencies quickly attempted to eradicate it by killing and destroying all infested trees. A few years later it was discovered in 3 communities in the Chicago area. As a result new regulations have been implemented limiting the importation of solid wood packing materials from China.

This is a potentially serious pest to our shade and forest trees and anyone working in the pest control industry throughout the US should be aware of its existence and report any findings immediately to the USDA-APHIS authorities. The adults are approximately 1.25 inches in length and as with some other beetles of this family the antennae are 1.3 to 2.5 times longer than the body (males have longer antennae than the females) (Figure 25b). Additional characteristics include:

A shiny black body with about 29 white spots.
Antennae with alternating bands of black and white.
Legs that is bluish-white on the upper surface.

The infestation in New York was most serious in maple and horse chestnut. Other trees infested and killed in the US include poplar, ash, willow, elm, mulberry and black locust. Infestations start with the female chewing a funnel shaped hole in the bark and laying an egg in this depression. Hatching larvae subsequently feed under the bark potentially girdling and killing the tree (Figure). Healthy trees are susceptible to the attack of this pest.

Scolytidae - Bark Beetles and Ambrosia Beetles

These are relatively small (3 to 5 mm length), cylindrical robust beetles with a head that is partially or completely concealed when viewed from above (Figure 26). Their antennae are short with a 3 to 4 segmented terminal club that can be compacted in a tight ball.

The bark beetles are one of if not the most important of our forest pests. Huge numbers of these beetles are attracted to trees that are weakened by drought, forest fires, disease or merely by lack of sufficient light (under-story trees). In these conditions or even if a tree is merely cut its natural defense of sap flow is greatly reduced. Trees in this condition release chemical odors that attract these beetles. In addition once a beetle is attracted to a tree and begins to feed it releases an aggregation pheromone that is produced in its gut. This chemical attract other individuals of the same species which in turn release more pheromone and in time thousands of beetles are attracted to the weakened tree. This mass attack eventually kills the tree. This is a very effective means of finding susceptible trees. Healthy trees do not release chemical odor that are attractive to these beetles and even if a beetle were to fly to and attack a healthy tree it would be drowned by the sap flow prior to releasing the aggregation pheromone. The elm bark beetles is also a key vector of Dutch elm disease, a fungal disease that has killed many of the American elm trees in the United States.

Bark beetle only attack trees with bark and that have enough moisture content to sustain their survival. Once male and female beetles reach a susceptible tree they bore into the bark and form an elongated brood gallery (Figure 27) between the inner layer of the bark and the sapwood (outer surface of tree just under the bark). Depending on the species this gallery may be occupied by an adult male or female or in some species the male may have a harem of 2 to 4 females. After mating the female(s) deposits her eggs on both sides and at short even intervals along the elongated brood gallery or chamber. Once the larvae hatch they bore out from the brood gallery at a more or less right angle remaining between the bark and sapwood. Each species make characteristic engraving patterns in this area (Figure 27). The width of the larval galleries increases in as the larvae grow and continue to feed. These tunnels are frequently packed with their frass (Figure 28). Immediately prior to pupation the larvae form a pupation chambers at the end of their tunnel (Figure 28). Once the adults emerge from the pupae they eat their way to the outside through the bark leaving small circular emergence holes. In heavy infestation it almost look like someone shot the tree with buckshot; hence another common name-the shot hole borers.

Since these beetles cannot survive in seasoned wood or even in trees that have been cut for year or more, they are not a structural pest. However the pest control operator should be aware of their existence since the building of expensive-trendy log cabins is coming very popular especially in mountainous areas. It is very unlikely that these beetles would attack such an existing structure but built-in beetle infestations may cause some nuisance problems.

As with the bark beetles ambrosia beetles in this family typically do not reinfest but unlike the bark beetles they bore into and form galleries that extend several inches deep into weakened trees. These tunnels may be used for several generations provided sufficient moisture is present. Ambrosia beetles do not feed on wood but feed on a fungus that grows on the walls of their tunnels. These beetles are often referred to as wood stainers as the tunnel walls take on a black or brown color due to the fungi.

These beetles do not reinfest and cannot survive in seasoned wood and therefore are not a structural pest. However, since their galleries do extent deep into trees it is not uncommon to find seasoned wood or wood products that contain damage due to previous infestations. In this case all damage was done prior to the production of the lumber or manufacturing of the product. Damage due to these beetles can be readily recognized by the appearance of small round holes (approximately 1.5 cm in diameter) that are stained black or brown around their perimeter.