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By Walter Ebeling
Roundheaded Borer Species List
The family Cerambycidae includes many species of large, slender, woodboring beetles. The adults usually have very long antennae that may be much longer than the body, giving them the common name, "longhorned beetles." The 2 most important cerambycid pests of buildings, the newhouse borer and oldhouse borer, do not have particularly long antennae. All adult cerambycids have large, strong, toothed mandibles.
The larvae are somewhat cylindrical, and have a large and fairly cylindrical thorax, resulting in burrows of a similar shape in the infested wood, hence the name, "roundheaded borers." The larvae have small heads, but powerful mandibles. Larval legs are lacking or vestigial.
The newhouse borer is a cerambycid beetle found throughout most of the western United States and western Canada. It occurs in pines and firs, but particularly in Douglas fir ("Oregon pine" of lumbermen). It breeds in dead or dying trees, and is especially abundant in fire-swept areas, probably being attracted to the trees mainly during the first summer after a fire. When lumber from such trees is used for building houses, the emergence holes of the adults may appear in hardwood flooring, linoleum, plaster, plasterboard, or composition roofing.
Biology. The adult (figure 121) is a narrow, black beetle, 2 to 3 cm long. The larva is yellowish white, and is about 4 cm long when full grown. The female lays eggs in deep crevices of the bark.
Because the bark has been removed, the female does not oviposit in wood that has been converted into lumber. Therefore, there is no danger of reinfestation from beetles that have emerged (Wood, 1964). In trees, the larvae initially tunnel at the juncture of sapwood and bark. Later, they tunnel entirely in the sapwood, and finally move into the heartwood. They always pack their tunnels tightly with fibrous frass. If 2 pieces of recently cut lumber are in contact with each other, the larvae sometimes tunnel from one piece into the other. In isolated pieces of lumber, the larvae occasionally bore to the surface, plug the hole, and continue tunneling in the interior. The fullgrown larvae construct large pupal cells, and when the adults bore their way out of the wood, they make clean-cut oval holes at the surface about 6 mm in diameter. These are easily distinguished from the circular holes made by emerging woodwasps. Also, surrounding each emergence hole of the newhouse borer there is usually an accumulation of long drillings that looks like a pile of cigarette tobacco.
Duration of Infestation. Although it takes at least 2 years for the newhouse borer to complete its life cycle, the appearance of adults in a house may occur within a few months after construction is completed, and rarely after 1 year. The reason appears to be that as the wood dries out, it becomes unsuitable for larval development. Only those larvae that are nearly full grown are able to survive and reach maturity under these dry conditions (Eaton, 1959).
Types of Lumber Infested and Extent of Infestation. Apparently, the most commonly infested lumber is Douglas-fir subflooring. Any material, such as hardwood flooring or other floor covering on the infested lumber, may be perforated in order to provide an escape route for the emerging adult. Eaton and Lyon (1955) once found 1 to 8 (average 4) visible emergence holes per house in a tract in which there was some evidence that the Douglas-fir subflooring had come from a fire-killed stand of timber. The beetles sometimes emerged from infested wood framing in the walls or ceilings of buildings, or from sheathing. In one building, 34 exit holes were counted in the plaster. The infestations are never extensive enough to cause serious mechanical weaknesses in a structure. Nevertheless, the holes, just as those caused by woodwasps, may be causes of consternation and worry for the homeowner.
The incidence of infestation by such insects as the newhouse borer and woodwasps has increased in recent years. This is because of the increased demand for wood, which has made it profitable to cut timber that in past times would have been rejected, particularly since this kind of timber can be obtained at little or no cost. It is perfectly sound for structural purposes. Air-drying of the lumber for over 1 year, or kiln-drying, would solve the problem, and the complete use of such timber would result in a greater utilization of our natural resources.
Western lumber destined for eastern markets is generally kiln-dried because removal of water decreases its weight. Beetles and other insects are killed by the process. Lumber harvested in the West which is to be used on the West Coast is often air-seasoned for just a few weeks. To allow a long period for air-seasoning and storage would likely cause the death of most wood-infesting insects, but increase the cost of production.
Control of the Newhouse Borer
Wood (1964) pointed out that radiographic techniques were available, so that the presence and extent of woodborer infestations in finished lumber could be determined. It may be desirable to use this technique before investing in an expensive control measure, such as fumigation. Fumigation with methyl bromide gas has been successful in the United States and Europe for the control of the oldhouse borer, Hylotrupes bajulus, which has habits similar to those of the newhouse borer and does similar damage. Therefore, it is reasonable to suppose that methyl bromide can be successfully used against the latter species.
Infestation of a building by newhouse borers is seldom, if ever, sufficiently severe to justify the ,great expense of fumigation. Filling of exit holes or repair of damaged areas after the adults have emerged is the most economical solution. In any case, by the time the infestation has been detected it is often too late for any measures aimed at the destruction of the insects themselves.
The oldhouse borer apparently originated in northern Europe, where it has been found in 40 to 50% of the houses in some surveys. It has spread from there to many parts of the world, including most of the states of the Atlantic seaboard and in various other areas as far west as Minnesota and Texas. An August mean temperature of about 73 �F (23 �C) is an important factor favoring the development of the oldhouse borer, and might be a useful criterion in predicting the future distribution of the beetle in North America (Anonymous, 1967c). There are well-documented records of the oldhouse borer having been transported to new areas in infested wooden boxes and packing cases. From France, the insect was transported to England in pine flooring, and to Australia, in the pine framing of prefabricated houses (NPCA, 1965). Thus, while this serious pest has not yet been established in the western United States, there is no reason to believe it could not be accidentally introduced.
Unlike the newhouse borer, the oldhouse borer can be present in old houses as well as new ones and, most importantly, can reinfest timbers from which it emerges. It can thus cause great structural damage.
Korting (1962) stated that lumber in houses 60 years and more of age was less subject to infestation than in new houses. Moreover, adult female beetles in the older houses are smaller and have fewer progeny. Patton (1931) reported that, in Denmark, roofs of timber covered with metals more than 20 years were most subject to attack. Houghton (1939) stated that in the United States, H. bajulus was most likely to attack attic and roof timbers, but infested framing and flooring also. In Norway, H. bajulus was found mainly in attics, and only in districts of the highest mean temperatures and the longest periods of relatively high temperatures during the summer (Knudsen, 1967). In Massachusetts, houses that are centuries old, some of historic interest, are being infested. Sometimes the infestations are so severe that the occupants of infested houses hear "gnawing" or "clicking" sounds that are caused by the beetles (Becker, 1954). Like the newhouse borer, the oldhouse borer attacks only softwoods, feeding mainly on the sapwood, but the adults may bore through other types of wood or plaster in order to emerge.
Whereas both Arhopalus productus and Hylotrupes bajulus can be introduced into a building in infested lumber at the time of construction, of the 2 beetles only H. bajulus can infest the building after construction. At least in the United States, it is strictly a structural pest, and has not been found in logs and stumps (Snyder, 1955a), presumably because it is an introduced species that has not yet become established in nature. [Another species, H. ligneus (F.), has been found damaging rustic furniture in cabins (Thompson, 1932).] Although infestation by H. bajulus can occur wherever susceptible wood is present, in the United States the majority of infestations are said to be in attic framing in the northeastern area and in the substructure along the mid-Atlantic Coast (NPCA, 1965).
Description. The adult females of
Hylotrupes bajulus may reach a length of 2.5 cm, but the males are only about half as long. The adults are slightly flattened, grayish black to very dark brownish black, with many gray or yellowish-gray hairs on the head and anterior part of the body. However, these may be rubbed off on older specimens. Two elevated black, shiny knobs on the prothorax give the dorsum an appearance like a face with a pair of eyes (figure 122). About a third of the way posterior on the elytra, and centrally located, there are 2 grayish, transverse marks.
The full-grown larva (figure 122) is grayish white, from 2 to 4 cm long, has a broad thorax, and tapers posteriorly. There are deep folds between the abdominal segments, and there is a deep groove running lengthwise in the center of the prothorax. There are 3 black ocelli in a row on each side of the very small head, but a hand lens is required to see them. The stout, very dark jaws are relatively prominent. The pupa is about the size of the adult, and is at first creamy-white and then becomes light brown.
About 150 to 200 white to grayish-white, spindleshaped eggs about 2 mm long are laid in checks, cracks, crevices, or irregularities of the wood. Stacks of lumber are said to be excellent oviposition sites. It takes 2 or 3 weeks for the eggs to hatch. The larvae feed in the dry sapwood from 2 to 10 years (usually 3 to 5) until the sapwood is completely destroyed. They fill their mines loosely with frass composed of tiny pellets and fine, powdery material. The frass occupies a greater volume than the wood from which it was produced, and this causes the surface of the infested wood to have a blistered or rippled appearance (Hickin, 1963a). A rhythmic rasping or chewing sound made by the larvae may be the first indication of their presence, for their tunnels seldom break through to the surface, even though the interior may be severely mined.
Life Cycle. The adults may remain in the tunnels prepared by the larvae for 7 to 10 months before emerging, but then live for only a brief period. They appear in the summer, and oviposition takes place at that time. In the United States, the period required for the life cycle of the oldhouse borer may be from 3 to 5 years in the southern states, whereas northward from the latitude of Washington, D.C., an additional 2 to 3 years may be required. Most of the period is spent in the larval stage, for the egg and pupal stages each last only about 2 weeks, and the adults live 8 to 16 days. The majority of adults fly in June and July. Adult beetles often emerge from attic timbers a year or two earlier than from basement wood in the same building, because of the higher attic temperatures (Patton, 1931; Craighead, 1950; St. George et al., 1957; Hickin, 1963a; McIntyre and St. George, 1961).
Signs of Infestation
There are a number of indications when oldhouse borers are active in a building. In the early stages of an infestation, the rasping or ticking sounds made by the larvae while boring may be heard, or a blistering of the wood when the larva works close to the surface may be seen. If the wood surface is probed where tunneling is suspected, the larvae or their powdery borings may be located. Only after the buildings are at least 3 to 5 years old in the southern states, or 5 or more years old northward from the latitude of Washington, D.C., will the emerging adults, or their 7-mm, broadly oval emergence holes, be evident (McIntyre and St. George, 1961).
Relation of Protein Content to Susceptibility of Wood to Attack
Becker (1963) determined that a minimum of 0.2% of protein was required, in the softwoods investigated, to support an oldhouse borer population. From that point, larval development increased in direct proportion to an increase in protein content. The suitability of the wood for the development of larvae decreased as it aged, probably because of a change in the nutritive value of proteins during storage, a decrease in vitamin content, and other chemical or structural changes in the wood. The suitability of the wood for larval development could be fully restored by the addition of protein and vitamin B. Nevertheless, as just stated, some very old buildings are being severely attacked. The older the building, the greater the chance that it may have an infestation, despite the decreasing nutritional value of the wood.
During the first stages of decay, wood infected by wood-destroying fungi, such as Lenzites, shows an increase in protein content and becomes more favorable for larval development. Likewise, pine wood contains more protein than spruce, and in areas of Europe where pine is widely used in construction, oldhouse borer infestations are more frequent and severe than in areas where spruce predominates. A reduction in quantity and quality of protein and a loss of vitamin B can be quickly accomplished by artificially applied gamma radiation. This suggests a new approach to the protection of wood from attack by the oldhouse borer (Becker, 1963).
Larvae of the oldhouse borer were unable to develop in 4 commonly used types of fiberboard, whereas termites (Reticulitermes, Heterotermes, Coptotermes, and Kalotermes) were able to attack and destroy them, and chemical preservatives were required to protect them from termite attack (Becker, 1969b).
Control of the Oldhouse Borer
In both Europe and the United States, fumigation of infested buildings is considered to be an effective treatment for Hylotrupes bajulus infestations (Rasmussen, 1967; McIntyre and St. George, 1961), but of course fumigation leaves no protective residue. Methyl bromide at 3 lb, or HCN gas at 2 lb per 1,000 cu ft (1.36 or 0.91 kg per 28 cu m) has been used satisfactorily (St. George et al., 1957). Fumigation must be done only by qualified pest control operators. Borer larvae can be killed by applying 2% chlordane in deodorized kerosene to the infested wood with a brush or, for larger areas, a sprayer, applying the liquid at the rate of 1.5 pt per cu ft (0.71 L per 28 cu dm) of wood treated. For example, one would apply 1.5 pt to 12 linear ft of a 2 x 6-in roof rafter, or 18 linear ft of a 2 x 4-in. stud, or 12 sq ft of subflooring. [Metric equivalents: 0.71 1 per 28 cu dm; 0.71 L to 3.65 linear m of a 5 x 15-cm roof rafter; 5.5 linear m of a 5 x 10- cm stud; about 1.10 sq m of subflooring.] Wood absorbs kerosene solutions when it is dry and the temperature is at least 80 �F (27 �C). For spot treatments, 0.50% lindane may be used instead of the chlordane solution. If the infested wood does not at first absorb the required quantity of toxic solution, the treatment must be reapplied until the necessary quantity has been absorbed. The solution will not penetrate properly if the wood has been painted, varnished, or waxed. Unlike fumigation, treatment with toxic solutions is not only a control but also a preventive (Mclntyre and St. George, 1961).
In South Africa, similar solutions have been applied on infested timbers, but lumber used to replace timbers structurally damaged by Hylotrupes bajulus was impregnated with a preservative such as copper naphthenate or zinc naphthenate, preferably applied by vacuum pressure (Durr, 1956).
The pentachlorophenol emulsion Woodtreat-TC, which has been used successfully against subterranean and drywood termites in structural timbers, may also be effective against newhouse and oldhouse borers (Ebeling, 1968).
Other Cerambycids
Any insect that infests old, weakened, or fire- or insect-killed trees is likely to be incorporated into buildings constructed from lumber obtained from such trees if it is not kiln-dried. Among such insects are many species of cerambycids besides those already discussed.
One of the most conspicuous and best-known species found in lumber is Ergates spiculatus (LeConte) (figure 123, A), a large, slender beetle, 4.5 to 6 cm long, reddish brown, with head and thorax darker than the elytra. The lateral margin of the prothorax is armed with a few large and many small, sharp spines. The adults are often attracted to lights. The creamy-white larvae are 5 to 7 cm long. According to Linsley (1962), E.spiculatus "not only attacks the wood of recently killed or felled trees, but also fallen logs, stumps, and power and telephone poles," and "has often ruined fire-killed Douglas fir before salvage operations could begin." This species occurs throughout western North America.
Another cerambycid, the black pine sawyer, Monochamus scutellatus (Say) (figure 123, B), is 1.6 to 3 cm long and shining bronzy black, with a white scutellum, coarsely punctured, a large median "tooth" on each side of the prothorax, and very long antennae, often twice the length of the body. It is widely distributed in the coniferous forests of North America, and is especially abundant in timber following burns (Chamberlin, 1949). The spotted pine sawyer, Monochamus maculosus Haldeman, may reach a length of 3 cm or more, with antennae 2.5 times the length of the body. These beetles are brown, with bluish-gray dorsal spots. The prothorax has a prominent median tooth on each side. The larvae are very destructive to both heartwood and sapwood of dying, fire-scorched, and recently felled pines in the western states. The black timberman, Monochamus oregonensis (LeConte), ranges from British Columbia to southern California and east into the Rocky Mountain states, sometimes causing losses to fir logs exceeding 10 to 20% if they are left in the woods a few months. This species is 2.5 to 4 cm long, and has a cylindrical, deeply and coarsely punctured body. The color is uniformly black, sometimes with a bronzy reflection, and the scutellum is white. Silvery-white spots are sometimes scattered over the elytra and on the thorax and antennae (Chamberlin, 1949).
The banded alder borer, Rosalia funebris Motschulsky, is one of the best-known and most attractive of the Pacific Coast cerambycids. It is 2.5 to 4 cm long, marked with black and white as shown in figure 123, C, and has very long antennae that are annulated with black and white. It breeds in ash, alder, and California laurel and, east of the Sierra Nevada, generally in willow. According to Doane et al. (1936), this species is responsible for the hollowing-out of the trunks of many of the larger laurel trees in California. It is mentioned here mainly because of its conspicuous and striking appearance, resulting in many requests for identification. However, during periods of very high temperatures, the beetles are attracted to recently painted dwellings after the paint has become dry, apparently attracted to certain volatilized ketones from the paint. They are present on some buildings in such large numbers as to be a definite nuisance (Chemsak and Linsley, 1971; Essig, 1943).
A common eastern species on hickory, locust, and ash, often attracting attention in resort areas, is the fourspotted longhorn, Eburia quadrigeminata (Say) (figure 123, D). It is 1.5 to 2.5 cm long, light brown to tan, and easily recognized because of the 2 pairs of elevated, ivory-colored swellings on, and the 2 spines at the tip of, each elytron. The life cycle usually requires 2 years, but this species has also been found emerging from flooring, sills, and other wood members 10 to 15 years after the materials were installed (Chamberlin, 1949).
The nautical borer, Xylotrechus nauticus (Mannerheim) (figure 124), is a western species, 8 to 15 mm long, and varies in color from grayish brown to nearly black. It has 3 transverse, zigzag white lines on the elytra, and rather short antennae for a cerambycid. The larva is robust in form, and may attain a length of 18 mm. In California, the larvae may be found in live oak, black oak, and sometimes in eucalyptus and madrone, or in walnut or stone-fruit trees in orchards. It is most frequently encountered in the home emerging from firewood cut from such trees.
Various species of Neoclytus likewise commonly emerge from firewood and are found in homes. This genus is characterized by the many transverse carinae (elevated ridges) on the disk of the pronotum. The antennae are relatively short, as in Xylotrechus, but are more or less clubbed, and the legs are long. Unlike the larvae of Xylotrechus, which have no legs, those of Neoclytus have small legs composed of at least 2 segments (Linsley, 1964). Probably the most common species of Neoclytus on the Pacific Coast is N. conjunctus (LeConte). It has either white or yellow markings on a black background. The pronotum is broadly rounded, the elytral apices are rounded, ancl the head, thorax, and abdomen are hairy (figure 125). It breeds in Oregon ash, various white oaks, madrone, manzanita, eucalyptus, pear, and apple (Doane el al., 1936; Linsley, 1964). Any of these trees cut for lumber should be utilized promptly, otherwise the larvae of N. conjunctus will render the wood useless for anything but firewood. Even the value of the infested timber as firewood is reduced because of the honeycombing of the wood by these beetles. Cordwood should be piled and covered with brush, for shaded wood is not attractive to the beetles (Chamberlin, 1949).
In the eastern United States, 2 species of Neoclytus that emerge from firewood and are sometimes found in houses are N. acuminatus (F.) and N. caprea (Say). Neoclytus acuminauts is 6.5 to 18 min long, reddish brown, with 4 yellow bands across the elytra, and long, reddish legs. It attacks unseasoned wood with bark remaining, and frequently causes serious losses of ash, hickory, and oak logs left exposed during the flights of these insects (Craighead, 1950). Neoclytus caprea is 12 to 15 mm long, deep purple, with 3 yellow bands across the elytra and 3 narrow, yellow bands across the prothorax (Sweetman, 1965). This species sometimes destroys an entire winter clut of ash logs, honeycombing the sapwood with tunnels that are tightly packed with granular frass (Craigheah, 1950).
This insect, which resembles a cerambycid, is found throughout much of the United States and Canada, particularly in coastal areas, along lake shores, and along major inland waterways. The larvae niay be found in moist timbers, such as wharf timbers, foundation pilings under buildings, in damp cellars or crawl spaces, in wood around leaky faucets, in buried wood, or in any wood that is damp or soggy, and particularly if it is decayed. In England, it has been found in timbers of many barges and wooden-hulled ships sailing in the region of the Thames estuary. In London, the adults have been seen by the "tens of thousands, running over the pavements of the Strand" without their origin being discovered (Hickin, 1963a).
It is not known if wharf borer larvae damage sound wood. They are pests primarily because the adults may suddenly emerge in a building in large numbers and gather around windows, doors, or other sources of light, and thereby become nuisances.
Description. The slender adult is about 10 mm long, and is brown to reddish yellow above, with the tips of the elytra, the eyes, sides of the thorax, legs, and ventral parts generally blackish. There are 3 raised, longitudinal lines on each elytron. The body is covered with a yellow pubescence. The antennae are about half as long as the body (Balch, 1937; Hickin, 1963a). The full-grown larvae are about 3 times longer than the adults, cream-colored, with brown mouthparts, and mandibles that are almost black at the tips. Besides 3 pairs of true legs on the thorax, they have prolegs on the third and fourth abdominal segments. Their legs are larger than those of other wood-boring larvae.
   
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