Description. Water is conducted from damp ground through strands of mycelium comprising the rhizomorph, which is rootlike in appearance (figure 102, bottom). The rhizomorph varies in color from white to brown to brownish black, depending on its age, and varies from 3 mm to as much as 5 or 8 cm in thickness. The water-conducting strands can extend for 30 ft (9 m) or more across the surface of concrete, brick, or other impenetrable material and upward to the second or third floor of a building, spreading out into flattened veins embedded in sheets of mycelium. Over this entire area, the wood is moistened by the fungus and made susceptible to decay, even though it would otherwise be too dry.
The wood is moist while the fungus is alive, and in a cross section of infested timber, progress of the fungus is indicated by a dark stain (figure 102, top). The common name, "dry rot," presumably derives from the appearance of the wood after the fungus is dead. The severely decayed wood is brown, and breaks up into irregular chunks resulting from shrinkage cracks both across and in the direction of the wood fiber (figure 102, bottom). Sheets of white mycelium can often be seen in the cracks. Owing to the extraction of cellulose by the fungal hyphae, the wood becomes very light in weight and loses its structural strength. The dry material has a distinct odor where the more succulent fruiting bodies occur, reminding one investigator of "drying slippery-elm bark" or of certain of the fleshy Hydnums (fungi) when they are dried out (Humphrey, 1923). The fruiting bodies can reactivate the infection if the wood becomes damp again.
Paperlike, fanshaped sheets of mycelium that appear on wood in damp places are often the first indications of decay. Masses of mycelium may protrude along the bottoms of baseboards or where timbers are joined. Leathery, crustlike sporophores are produced annually. They vary in color, from orange through olivaceous to deep purplish black, depending on their age and location, and all these colors may be represented in order from the margin to the center of a single fructification (Boyce, 1961).
Type of Wood Attacked and Rate of Destruction
It happens that the rough frame lumber most commonly attacked by dry-rot fungus is coniferous, but Humphrey (1923) pointed out that the fungus is an omnivorous saprophyte that can attack and destroy almost any of the commercial woods of the United States, even such reputedly highly durable ones as cedar, cypress, juniper, sequoia (redwood), catalpa, greenheart, black locust, sassafras, white oak, black walnut, and black cherry, all of which are severely attacked and sometimes completely destroyed.
Rapidity of Destruction
Another important characteristic of Poria incrassata is the rapidity with which it can destroy structures. A frame house in Florida suffered severe loss in 3 years, and in 5 years about 25% of the house was visibly affected. A 3-year-old house in Kentucky suffered severely from decay of subfloor timbers, flooring, and casings. In another house in Louisiana, much of the front wall and 750 sq ft (69 sq m) of flooring had to be replaced within 3 years after construction. In a store in that state, heart cypress paneling laid over a brick wall lasted only 6 months (Humphrey, 1923).
The same kind of decay as produced by Poria incrassata is produced by the teardrop fungus, Merulius lacrymans, which occasionally causes much damage to structural timbers in the northern part of the United States and in Canada. The 2 rots cannot be distinguished unless sporophores are present. In Europe, where P. incrassata does not occur, M. lacrymans is the "dry-rot fungus," and is very important.
A considerable amount of what has been said about P. incrassata pertains also to M. lacrymans, including the rhizomorph and its water-conducting capacity. The specific name lacrymans, which means "weeping," refers to the characteristic the fungus shows in active growth under damp conditions, when innumerable globules of water are seen, "which sparkle in the light of a torch like a large number of teardrops" (Hickin 1963c).
The mycelium of the teardrop fungus grows rapidly, and is snowy white, but where the edge of an expanse of mycelium comes into contact with drier air or is exposed to light, it becomes bright yellow (Hickin, 1963c). When the mycelium of the closely related Poria incrassata grows through the cracks in the floor into a lighted room, the mycelium turns orange in color, and this color change has been likewise observed in partially lighted basements (Humphrey, 1923)
The prodigality of nature is indicated by the estimate that 1 sq m of a sporophore of M. lacrymans will produce over 50 million spores per minute over a period of many days, and that other wood-decay fungi have been found to be even more fruitful.
Many species of decay fungi attack buildings. In New York state, Poria incrassata is not known to occur, but in an extensive survey, 11 other species of Poria were found attacking wooded buildings, resulting in 22.8% of the incidence of decay. In the same family of fungi (Polyporaceae) Lenzites saepiaria made up 12.4% of the total and, in the family Hydnaceae, Odontia spathulata was found with about the same frequency (12.8%,) (Silverborg, 1953). The latter species produces a white, stringy rot, unlike the brown, cubical type associated with the other common building-decay fungi. In the foregoing investigation, Lenzites trabea was found in 4.6% of the instances of decay. This fungus came prominently to the attention of entomologists in the early 1960's, when an extract from L. trabea rotted wood was found to be an attractant to termites (Esenther et al., 1961). It was later discovered that this extract induced trail-following by the eastern subterranean termite, Reticulitermes flavipes, similar to that induced by a trail-marking pheromone secreted by the sternal gland of this insect (Smythe and Coppel, 1966a). Trail-marking substances isolated and purified from R. viriginicus and from wood infested with L. trabea were found to be identical (Matsumura et al., 1969).
Wood may be attacked by molds, which are superficial fungi, generally green, yellowish green, red, or black, depending on the species. Molds do not damage wood and can be easily scraped off, but they indicate that conditions are right for the growth of decay-producing fungi and that corrective measures should be taken.
Wood is also affected by sap-stain or blue-stain fungi. They penetrate more deeply than molds, but do not significantly weaken the wood. The fungi are usually bluish, and cannot be scraped off wood like molds. They do no damage unless they occur where they may be considered to be unsightly, but like the molds, they indicate that conditions are favorable for the growth of the more destructive decay fungi (Anonymous, 1963).
All that is required for the control of a waterconducting decay fungus such as Poria incrassata is to break the connection between the source of water and the infected structural wood member. The source of water should be eliminated, if possible, and the water-conducting rhizomorphs should be removed. The wood will then dry out and the fungus will die. Replacement of the infected wood member is required only if the wood is too weak to support its load. Verrall (1968) advised against dependence on surface applications of wood preservatives, or on such supposedly decay-resistant woods as redwood, as controls against fungi that are "water-conductors."
Wood used in construction should not have a moisture content of more than 20%. Depending on the atmospheric conditions in the area in which it is dried, air-dried wood may have a moisture content between 6 and 24%, whereas kiln-dried wood has a content of from 6 to 12% Wood that is not pressure-treated with a wood preservative should not be allowed to contact the soil. The caulking around windows, doors, bathtubs, and sinks should be maintained to prevent accumulation of water in walls. Paint decreases penetration of water into wood except at joints between the wood members (Amburgey, 1972).
In many homes, condensation of moisture within insulated walls and floors favors wood decay. Warm, moist air passing into walls comes in contact with wood members with temperatures below the dew point of the air, resulting in deposit of excess water. Measures that may be taken to reduce or prevent condensation vary in different geographical regions, and are discussed in chapter 10, under "Sources of Moisture in Buildings."
The damage caused by these 3 families of beetles can be identified as follows: The true powderpost beetles (Lyctidae) loosely fill their galleries with very fine powder, similar in appearance to face powder; the false powderpost beetles (Bostrichidae) tightly pack their galleries with a coarser boring dust, often containing small wood fragments; and the deathwatch beetles (Anobiidae) fill their galleries with small pellets. The frass in the galleries of the bostrichids and anobiids is not only coarser than that of the lyctids, but tends to stick together. Although all these beetles have sometimes been collectively referred to as "powderpost beetles," in a more definitive sense the term should apply only to the lyctids, for their larvae are the only ones that produce a fine, powderlike dust in their galleries.
The homeowner often asks whether the damage he sees lias been caused by termites or beetles. Damage to wood caused by lyctids, bostrichids, and anobiids is likely to be first noticed when the round emergence holes of the adults are seen or the beetles are found on infested wood, such as windowsills.
Probing or tapping the infested area of the wood will usually reveal one of the types of frass described above. In the United States, the fine powder of the lyctid beetles is most often encountered. In the wood structure of the building, beetle infestations occur most often in hardwood cabinets and flooring. On the other hand, the presence of subterranean termites usually first comes to the attention of the homeowner when he sees blisters or dark stains in flooring or other wood or where the paper-thin surface covering the infested wood is crushed, as when furniture is moved about.
When the structural damage is caused by termites, there are no exit holes in the vicinity, and their irregular tunnels are not filled with powder. Drywood termite tunnels may hold many pellets, but the pellets are larger than those produced by deathwatch beetles (anobiids), are characteristically sculptured, and are blunt at each end (figure 83, this chapter). The presence of drywood termites usually comes to the attention of the occupants of a building when the pellets are pushed out of occasional "kickout" holes in wood members, such as the frames of doors or windows or exposed timbers.
There can be no confusion between the typical appearance of termite workers and the worm-like larvae of beetles. The winged reproductives of termites are often seen during their brief, fluttering flights. After they have landed and are crawling about, they are often mistaken for "winged ants."
On the other hand, all of the adult lyctid and anobiid beetles are strong fliers and are attracted to light. They may, therefore, often be discovered at or near windows when an infestation occurs in a room. Even experienced ento- mologists often mistake the furniture beetle, Anobium punctatum, for a fly, since in flight .it closely resembles the latter, even to the extent of flying around light bulbs (Hickin, 1963a).
Lyctids are small beetles ranging from 2 to 7.5 mm in length. They are reddish, various shades of brown, or black; have a prominent head not covered by the prothorax; short, 11-segmented antennae, each with a 2-segmented terminal club and tibiae with distinct spurs (figure 103).
To distinguish between species of Lyctidae, a description of certain features of the elytra is generally utilized. The interspace (figure 103) is the surface between striae; a stria is a longitudinally depressed line or furrow, frequently punctured, extending from the base to the apex of the elytra; and a carinula (diminutive of carina) is a keel-like ridge.
Lyctids are cosmopolitan, each geographical region having indigenous as well as established introduced species. Of the 66 known species, 10 occur in the continental United States and 6 of these are common and important as pests. In the United States, species of Lyctus and Trogoxylon are widely distributed. Species of Minthea and Lyctoxylon are often intercepted in wood products in maritime ports of entry. Representative species of these 4 genera are shown in figure 104. In this country, lyctids are second only to termites in their destructiveness to wood and wood products, but confine their attacks to large-pored hardwoods such as oak, ash, hickory, mahogany, and bamboo. Powderpost beetles may be found in hardwood flooring, hardwood timbers, plywood, and wood articles such as crating, furniture, antiques, tool handles, spokes of wheels, gunstocks, etc., causing millions of dollars' worth of damage every year
The damage the beetles cause consists of reducing sound wood to fine powder, and is usually not evident until the emergence holes of the adults are seen (Gerberg, 1957b).
Lyctids are generally brought into buildings in wood that contains their eggs or larvae. Lumber should be examined for signs of infestation. Once in a home, hardwood items are usually finished with paint, varnish, shellac, sealer, or wax, which treatments prevent oviposition by adult beetles.
If the adults' emergence holes are found in such finished items, it may usually be assumed that the infestation began before the finish was applied. From an economic standpoint, the 2 most important lyctid species in the United States are Lyctus planicollis and Trogoxylon parallelopipedum.
The genus Minthea is characterized by the erect, flattened hairs along the denticulate lateral margins of the pronotum (figure 104, C). The elytra have 6 or 7 rows of erect, flattened, whitish hairs, usually separated by a row of fine, reclining hairs. The adults are 2 to 3 mm long. The terminal segments of the antennae are slightly longer than the preceding ones, and the lateral margins of the pronotum bear about 19 flattened hairs. This species is found throughout tropical regions. It has been intercepted in quarantine in the United States in wooden articles, and even in such products as ivory nuts (Phytelephas macrocarpa; Palmaceae) and dried roots of Derris elliptica (Legtiminosae) (Gerberg, 1957a, b).
This genus can be readily distinguished by the elongate antennal club: both segments are longer than broad, and the terminal segment is narrower than the preceding one (figure 104, D). The beetles are 1.5 to 2 mm long. The species is apparently distributed throughout the Orient, but may have become established in Panama. It is often intercepted in quarantine in the United States, usually in bamboo (Gerberg, 1957a).
The Life Cycle of Lyctid Beetles
Adult lyctids mate soon after they emerge from infested wood. Oviposition begins 2 or 3 days later, and continues for a week or two, most of the eggs being laid within the first 7 or 8 days. The female has a long, flexible ovipositor that she inserts deeply into the pores of hardwoods, laying 1 or several eggs in each pore. Investigators generally report that the female places her eggs only in the spring in wood vessels or pores. These are exposed when the wood is cut, or may be opened by the beetle herself. Cymorek (1965) observed that Lyctus brunneus and Lyctus africanus Lesne did not restrict their oviposition to the vessels of the wood, but also oviposited in all kinds of cracks and crevices. He also found that both species could oviposit and develop in corn and wheat grains in the laboratory.
From 15 to 20 eggs per female have been reported for L. linearis and 17 to 21 for L. brunneus. The lyctid egg is about 1 mm long, translucent white, and cylindrical, with rounded ends, and bears a threadlike process at the anterior end (figure 107). Eggs are never deposited in polished, waxed, varnished, or painted surfaces (Gerberg, 1957a).
The incubation period can range from 1 to 3 weeks, depending on temperature. The emerging larva is white, straight-bodied, and bears a pair of small spines at the rear. After the first molt, the larva assumes a curved form. The young larva usually tunnels with the grain of the wood, but later takes an irregular course, sometimes intersecting its earlier track or the tunnels of other larvae. The tunnels are packed with a fine, powderlike dust. The larvae do not penetrate to the surface but, like termites, leave a thin, unbroken surface layer. Outdoors, the larvae grow chiefly during spring and summer, but in heated rooms they can develop continuously.
A mature larva is usually less than 5 mm long, curved, and enlarged at the thorax. Its antennae are 3-segmented and have an accessory appendage. The abdomen bears 8 spiracles, and the most posterior pair is 6 times larger than the others (figure 108). The legs are distinct, 3-segmentcd, and unclawed. In contrast to lyctid larvae, the larvae of anobiids do not have an enlarged posterior spiracle and they have 5-segmented legs, with the terminal segment clawed (figure 108). The mature lyctid larva bores to a point near the surface of the wood and builds a pupal chamber (figure 105). The pupal period lasts from 12 days to a month. After metamorphosis, the adult chews its way to ttie surface, forms an exit hole 2 or 3 mm in diameter, and generally pushes some of the fine dust out of the hole when emerging (figure 109). Small piles of the dust are common near new emergence holes. Although the larva confines its burrowing to sapwood, if the adult has no other way of emerging, it can bore its way through heartwood, softwood, asbestos, lead sheeting, or plaster (Tooke, 1949).
Adult lyctids conceal themselves in cracks and holes in the wood during the day, but they become active at night, fly readily, and are positively phototactic (Gerberg, 1957b). Indoors, they may be seen crawling on floors, windowsills, furniture, and other surfaces.
The life cycle, from egg-laying to emergence of adults, ordinarily requires 9 to 12 months, but under exceptionally favorable conditions of high temperature and high starch content of wood, that period may be reduced to only 6 or 7 months. Two generations a year are not uncommon in the southern United States, but under adverse conditions of temperature and nutrients, the life cycle may be prolonged to 2.5 to 4 years, or longer (Gerbera, 1957a, b). Development of Lyctus brunneus was greatly prolonged in compressed oak sapwood when compared with the same wood before compression (Cymorek, 1967). There can be a great difference in the length of the life cycle of different species; the average for Trogoxylon parallelopipedum, for example, being 3 to 4 months compared with 9 to 12 months for Lyctus planicollis (Gerbera, 1957a).
Wright (1960) investigated the life cycle of L. planicollis in a laboratory under uniformly high temperature (31 °± 3 °C av. 88 °F) and at 85 ± 5% relative humidity. He reared the beetles on red-oak wood chips or wood flour. The mean incubation period for eggs was 8.2 days. The mean length of the larval stage was not determined, but some larvae remained alive as long as 42 days. A prepupal stage, not recorded earlier, lasted from 2 to 5 days. The mean pupal period was 8.1 days. The mean length of adult males was 3.5 mm and of adult females, 3.7 mm. The 2 sexes occurred in approximately equal numbers. The mean adult life of males was 33.1 days and of females, 35.1 days. Adult beetles lived about 2 weeks after emergance from the wood. The number of eggs deposited per female ranged from 18 to 122, with a mean of 51.4.
Factors Affecting Lyctid Infestation
Starch Content of Wood. Lyctid beetles primarily infest the sapwood of hardwoods. Ash, hickory, maple, and oak are preferred, but many other hardwoods are sometimes damaged. Bamboo, which is a grass, not a hardwood, is readily attacked in the Orient, frequently by Lyctus brunneus. Their chief source of food is starch, and whatever sugar and protein may be present; they do not digest cell walls, for the larvae cannot digest cellulose, hemicellulose, lignin, or pentosans - these pass through the intestine undigested. Lyctids will not oviposit in sapwood with a starch content of less than 30% and the greater the concentration of starch, the better they thrive.
The starch content of lumber depends on the tree species, the season the tree is cut, and the method by which the lumber is dried. Lyctids prefer recently dried rather than old wood because the starch content of lumber decreases as it is converted to lignin in the long process of natural seasoning.
Water Content of Wood. A definite range of water content is also necessary. Lyctids can live in wood with a water content of between 8 and 32%. Since the water content of green wood is commonly about 50% and can be even higher, it is obvious why attack by powderpost beetles is generally confined to partially or wholly seasoned wood (Christian, 1940a, b; 1941; Tooke, 1949). The moisture content of seasoned wood in the United States is said to average between 12 and 15%. The greatest lyctid beetle activity is found in wood with a moisture content of from 10 to 20% (NPCA, 1961).
Pore Diameter in Wood. The diameters of the pores or vessels in the wood can be a limiting factor, for they must be large enough to allow insertion of the ovipositor, otherwise oviposition cannot take place. The average size of the ovipositor of Lyctus brunneus is 0.078 mm; of L. linearis, 0.083 mm; and of L. planicollis, 0.076 mm (Parkin, 1934). Hardwoods with pores or vessels with diameters greater than these dimensions are subject to infestation. Softwoods or conifers do not have pores, usually have a low starch content, and generally are immune to infestation.
Natural Enemies. Natural enemies of lyctus beetles are common in infested lumber in millyards (Snyder, 1926; Christian, 1941). Among 6 species taken from an infested piece of wood, Christian found 2 predaceous clerids, Tarsostenzis univittatus (Rossi) and Monophylla terminata (Say), as well as 4 parasitic Hymenoptera, Monolexis fuscicornis Foerster [=M. lycti (Cresson)], Sclerodermus macrogaster Ashmead, Heterospilus n. sp., and Ecphylus n. sp.
The Lyctidae and Anobiidae do not contain large-sized species, whereas the bostrichids have a considerable number of them. The most striking example is the palm borer, Dinapate wrightlii Horn, that is 4 to 5.5 cm long and infests native fan palms in California deserts and Baja California.
The bostrichids differ from the other 2 families mentioned in that the adults bore into the wood, preparing "egg tunnels" instead of ovipositing in surface cracks or pores. The female oviposits in pores leading from the tunnels. The larvae also bore tunnels. Thus, the bostrichids' tunnels vary greatly in size and shape. Like the lyctids, bostrichids can continue to breed in a piece of wood as long as it affords adequate sustenance. However, some species attack and breed in both hardwoods and softwoods.
The bostrichids are most abundant in the tropics, and are not so important as the lyctids and anobiids in temperate regions. Several species mine dead, seasoned, or cured hardwoods or hardwood furniture. Some species of Amphicerus and Polycaon burrow into the small twigs of living fruit trees, usually at the crotch or bud axil, but are usually not abundant enough to cause serious damage.
Although Polycaon stoutii is generally reported in the literature as occurring in furniture, particularly veneer furniture, Mallis (1969) stated that it would also attack cured hardwoods in the lumberyard and buildings in mountainous areas. Pest control operators have captured and obtained identification of adults emerging from hardwood flooring over a subfloor of Douglas fir, the beetles having originated in the fir.
Description. The leadcable borer (figures 111, 112) is 5 to 6 mm long, cylindrical, brown or reddish brown to black (usually black), with reddish mouthparts, legs, and antennae. The antennae are 8-segmented, with the 3 terminal segments much enlarged, and most of the head is concealed from above by the hoodlike pronotum, as is generally the case with the bostrichids. The prothorax has many tubercles on the anterior half, and the elytra have deep, linear punctures.
Life Cycle. The life cycle of the leadcable borer was investigated in great detail by Burke et al. (1922). The female bores an egg gallery, beginning at any place where leverage can be obtained, such as a knot, scar, bark scale, crevice, or between 2 pieces of wood. After the gallery reaches a depth of some 8 mm, it turns abruptly and runs parallel to the surface and across the grain of the wood for approximately 6 cm. Mating usually takes place when the tunnel has reached about the length of the female. The eggs are deposited in pores at a distance of 1 to 2.5 mm from the gallery - a single egg in each pore. The female apparently stops at any suitable pore to oviposit as she goes back and forth to throw out the borings. Some eggs are found so close to the gallery entrance that it appears the female can also back down into the gallery to oviposit.
The dull-white or cream-colored egg is very elongate, averaging 2.1 mm in length, including the stem, and 0.14 mm in width. It hatches in about 3 weeks. The larva mines parallel with the grain of the wood, packing its borings behind it, and becoming full grown (figure 112) after 6 molts and in a period of about 9 months. By the time it is ready to pupate, it has mined out a gallery 50 to 60 cm long. No distinct pupal cell is made. The prepupal larval skin gradually becomes transparent, and the pupa (figure 111) can be seen within for abouit 6 days before the skin is shed. The pupal stage lasts about 14 days, and the adult remains in the wood for a month to 6 weeks, hardening and maturing and becoming darker brown and finally black. The adult then eats its way out of the outer wood and bark. After emerging, the males live from 10 to 18 days and the females 30 to 44 days, provided they have access to wood; otherwise, both sexes die in 5 to 7 days. There is 1 generation a year. Adult beetles may be seen from the middle of April to the last of September, but they are most common in July and August.
Types of Damage. The usual damage to wood is a complete riddling caused by the egg galleries of the adults and the larval tunnels packed with a meal-like frass, leaving nothing but the bark and enough solid wood to hold the tunnels together (Burke et al., 1922).
The leadcable borer derived its name from its ability to bore through the lead sheathing of aerial telephone cables, making holes 2.5 mm wide. Much damage and great losses occur when moisture enters the cables, causing short circuits. According to Linsley (1943b), the adults appear to be greatly stimulated by heat, and sometimes bore into lead or asphalt roofing materials because of high temperatures. Such attacks, as well as attacks on lead cables, can be precipitated by forest fires, particularly in oak, where the beetles may occur in large numbers.
Various species of beetles that bore into lead and other metals include other bostrichids, as well as certain anobiids, lyctids, ptinids, buprestids, cerambycids, anthribids, bruchids, curculionids, dermestids, and tenebrionids. Insects of other orders that can do the same are termites; woodwasps (Siricidae); certain carpenter moths (Cossidae) (Burke et al., 1922; Chamberlin, 1949); and some species of carpenter bees (Xylocopa) (H. Scott, 1932; Middlekauff, 1960).
In May and June, 1972, many houses in 2 new residential tracts in Fresno, California, were infested with leadcable borers. Adult beetles emerged from the acoustic layers of the ceilings and from the wall plaster - as many as 50 beetles in 1 house - leaving holes about 2 mm in diameter. The probable sources of the beetles were piles of heavily infested fig prunings in an orchard situated between the 2 tracts. Scobicia declivis was reared from portions of dried fig branches taken from these piles. Also reared was another bostrichid, Amphicerus cornutus (Pallas), siniilar to S. declivis in superficial appearance but much larger (11 to 13 mm long). The leadcable borer had not been recorded before from the fig. The beetles probably entered the attics via the attic vents or by crawling beneath shingles. With none of their favored wood species to attack, they tried to escape from the attics by crawling down through holes made in the ceiling plates for electrical conduits. The conduits were in the corners of the rooms, and the beetles' emergence holes in the plaster were likewise always found in these corners. The infestations ceased after the piles of fig prunings were burned (Ebeling and Reierson, 1973b).
Probably the most common bostrichid in the eastern United States is the redshouldered shothole borer, Xylobiops basilaris (Say), which can attack practically any freshly cut and partially seasoned hardwood, and has been found attacking partially seasoned pecan lumber. It principally attacks the wood of hickory and persimmon, although it has been found in elm and other species. It has been found in lumber shipped to England (Craighead, 1950). St. George (1970) considers X. basilarus to be the only powderpost beetle in the eastern states that seriously damages wood products such as log cabins, rustic bridges, or wood used in the manufacture of rustic furniture, rustic fences, arbors, and wooden tool handles. Sometimes this beetle causes a 50% loss in these wood products. In the usual manner of bostrichid beetles, the adult bores in from the outside and down through the bark of freshly cut wood. It mines a tunnel in the wood for a short distance, following the annual rings, and this serves as an egg tunnel. Most of the larval boring is in the sapwood, which is ultimately destroyed (Chamberlin, 1949; St. George, 1970).
In the Midwest, Scobicia bidentata (Horn) is commonly found in the freshly cut wood and lumber of many hardwood species.
The bamboo borer, Dinoderus minutus (F.) (figure 113), is a cylindrical brown beetle, 3 to 4 mm long, which is indigenous to Asia but is now cosmopolitan in distribution. It attacks bamboo furniture, poles, and ornaments, as well as drugs, spices, stored grain, and flour. Powder sifting from cracks in bamboo and adult beetles found in buildings after emerging from bamboo articles are usually the first indications of infestation. It is particularly destructive in the West Indies (Plank, 1948).
Heterobostrychus aequalis (Waterhouse) is occasionally found in wood products imported from the Orient. The specimen shown in figure 114 was taken from imported mahogany furniture. This appears to be the most common of the larger bostrichids in India and parts of southeast Asia, where it bores into packing cases, boxes, plywood, furniture, and lumber, reducing the wood to a powder to a depth of 2 or 3 in. (5 or 7.5 cm) in severe infestations. In January, 1967, H. aequalis was found in oak lumber in Fort Lauderdale, Florida, and infestations were later found in Florida in lumberyards in the Fort Lauderdale and Miami areas and in an oak hammock near Hallandale (Woodruff, 1967). The species is now believed to be well established in Florida in scattered and localized areas (R. E. Woodruff, correspondence).
Heterobostrychus aequalis is 6 to 13 mm long, and reddish brown to brownish black. The anterior half of the strongly convex pronotum has broad, toothlike, marginal projections. The elytra are nearly tubular in shape back to the somewhat excavated apical declivity, which in the males has 2 incurved, hooklike projections. The surface of the elytra has deep punctures arranged in fairly distinct rows (Woodruff, 1967).
There are about 260 species of anobiids in the United States, the majority of which feed on dead wood. However, 2 species, the cigarette beetle (Lasioderma serricorne) and the drugstore beetle (Stegobium paniceum) are important pests of stored food products. Anobiids are widely distributed, and in some parts of the world, for example in Europe and New Zealand, they are much more important than in the United States. They attack mostly sapwood, but can extend their attacks into heartwood, and they attack both hardwoods and softwoods.
Anobiids range from 1.1 to 8 mm in length, and are highly variable in body form, ranging from narrow and elongate to nearly circular from the dorsal aspect. When viewed from above, the hoodlike or "bellshaped" pronotum usually conceals the head, as in the case of the Bostrichidae and Ptinidae, but is unlike that of the true powder-post beetles (Lyctidae), in which the head is not hidden when viewed from above. The last 3 segments of the antennae are usually lengthened and broadened, or simply lengthened, but in some species the antennae are either serrate (sawtoothed) or pectinate (combshaped). (The antennal clubs of lyctus have only 2 segments.) The tibiae lack the spurs found on the tibiae of the lyctids and bostrichds. The tarsi are 5-segmented, with divaricate (widely separated) claws.
Illustrations of some of the anobiids that have been recorded as pests in the United States are shown in figure 115.
In the United States, the furniture beetle is widely distributed, but has nowhere attained the importance it has in Europe. It is fairly common in the East, but not along the Pacific Coast, where infestations are usually isolated in imported furnitlire. The species is confined to the temperate regions of the world, and is not likely to become a pest in tropical regions except at high altitudes where the climate may be suitable for its development.
Even in temperate regions where it is well established, the incidence of infestation and the parts of a building infested can be greatly influenced by differences in climate within a small area. Thus, in Norway A. punctatum was found as frequently in attics as in cellars near the coast where summer temperatures were low, whereas relative frequency of infestation in attics decreased with increasing distance from the coast because of increasing summer temperatures, affecting attics more than cellars (Knudsen, 1967).
The furniture beetle attacks only well-seasoned lumber, provided the surface offers ovipositional sites, and it attacks wood only if the bark is removed. Exit holes of this species are never seen in the bark (Hickin, 1963a, b). Oviposition is greatly reduced on normally favored wood if it is finely sandpapered, painted, or varnished, all of which eliminate oviposition sites (Kelsey et al., 1945). According to Hickin (1949), it is rare for softwood to be attacked until about 20 years, and the sapwood of oak about 60 years, after it has been cut. However, exit holes have been found in birch plywood as little as 5 or 6 years after being cut.
Description. The furniture beetle (figure 115, A) is 4 to 6 mm long, cylindrical, reddish brown to dark brown, with longitudinal rows of pits on the elytra. These punctures are clearly visible through the fine, yellowish hairs that cover the beetle. As in all anobiids, the head is not visible from above; this distinguishes adult anobiids from the lyctids. The head has a prominent frontal protuberance, and the antennae are 11-segmented with the last 3 segments enlarged so that the 3 together are longer than the first 8 segments combined (White, 1962).
The grayish-white larva is about 6 mm long. Spinules occur on the first 7 abdominal segments, and are absent on the last 3 segments. On the first 6 segments, the bands (transverse markings) have 2 rows of spinules, and on the seventh segment the band has only a single row. A tubular projection or air tube on each spiracle is about equal to the length of the spiracle itself, and is longer than the projections on the spiracles of other common anobiid larvae. As stated earlier, anobiid larvae differ from lyctid larvae in not having a greatly enlarged posterior spiracle and in leaving 5-segmented legs, the terminal segment with a claw (figure 108). The tunnels formed by the larvae, mostly along with the grain of the wood, are loosely filled with frass. The frass consists of cigar- shaped pellets composed of minute fragments of the chewed wood. In severe infestations, large amounts of frass may be forced out of old exit holes, but "powdering" does not occur to the same extent as with lyctid beetles (Hickin, 1963a).
Life Cycle. Adults emerge in the spring from pupal cells just below the surface of the wood. They mate soon after emergence, and a day later the female lays her eggs in a crack or crevice in the wood (figure 116), in rough end-grain, rough-sawed timber, unplaned wood where the grain is open, or just inside old emergence holes (Hickin, 1963a, b). The eggs are easily seen with the unaided eye, appearing like groups of "oval pearls," but are often slightly deformed when forced into creviccs during deposition (Hickin, 1963). The average number of eggs laid has been reported to be 18 by Kelsey et al. (1945), 28 by Hickin (1963a) and, in the laboratory, 54.8 by Spiller (1964). The eggs ordinarily hatch in 6 to 10 days. Spiller (1949) observed either no hatching or impaired hatching at relative humidities below 60%.
Outdoors, the larvae require about a year for development, and will pupate for 2 to 3 weeks in a cell just below the surface of the wood. Indoors, the life cycle may require 2 to 3 years or more; this may result in a staggering of generations, so that all stages may be found in the wood at any one time. The longer indoor developmental period is presumed to be the resut of a lower moisture content of the wood (N. E. Hickin, correspondence)
Wood must be partially predigested by fungi before the deathwatch beetle can utilize it. In nature, it attacks several hardwood species. Indoors, it infests hardwood timber that was at some time infected with fungi. In England, where so many buildings are constructed of oak, this is the principal timber infested. The timbers most likely to be attacked are those soaked by rain or that are in poorly ventilated locations. Infestation always originates in hardwood, but can extend into adjacent softwood. Heavy furniture is often infested, particularly if made of oak or chestnut. Deathwatch beetles can also attack books (Fisher, 1937; Hickin, 1963a). In the United States, X. rufovillosum is much less important as a pest than it is in Europe. It is common in certain parts of eastern North America, but not along the Pacific Coast (Linsley, 1943b).
Description. The deathwatch beetle adult (figure 115, B) is about 7 mm long, dark grayish brown, with a pattern of yellowish, scalelike hairs on the pronotum and elytra; if the elytra are old and worn, the beetle may appear more reddish and shining (Hickin, 1963b). Xestobium rufovillosum does not have longitudinal rows of small pits on the elytra, such as are present in the furniture beetle, Anobium punctatum. The antennae are 11-segmented, but much shorter than those of A. punctatum, and the last 3 segments are somewhat enlarged and as long as the preceding 5 combined (White, 1962). Circular emergence holes of the deathwatch beetle are about 3 mm in diameter - about twice as large as those of the furniture beetle. The frass consists of relatively large lenticular or "bunshaped" pellets, characteristic of the species (Parkin, 1933).
The creamy-white larva of the deathwatch beetle is the largest of the anobiid larvae, being up to 11 mm long. The head is yellowish, and the mandibles are nearly black. The eyes consist of 2 black spots on each side of the head, compared with 1 black spot in A. punctatum larvae. Spinules occur dorsally on the first 8 abdominal segments, and laterally and ventrally on the ninth and tenth segments. Unlike the spiracles of A. punctatum, those of X. rufovillosum have a very short, tubular projection or air tube (Parkin, 1933).
Life Cycle. In England, where the deathwatch beetle has been investigated extensively, the adults begin to appear in April and May, and their tapping noise is then commonly heard. Unlike the furniture beetle, the adults may remain in their pupal cells until the following spring. They mate soon after emergence, and then die in a few weeks.
The female lays her eggs in small clusters, usually of 3 or 4, on rough surfaces, in cracks, or just inside the emergence holes. When first laid, the eggs are sticky and adhere together. They are whitish, oval, smooth throughout, and about twice as large as those of the furniture beetle. Usually, 40 to 60 eggs are laid, but up to 201 have been recorded. They hatch in 2 or 3 weeks. Under favorable conditions of food and temperature, the deathwatch beetle may go through its life cycle in a year, but this period may be prolonged to as much as 10 years. Outdoors, in oak infected with fungi, the life cycle has varied in duration from 3 to 7 years, and indoors it is believed to average about 4.5 years (Hickin, 1963a).
The eastern deathwatch beetle, Hemicoelus carinatus (Say) (=Hadrobregmus) (figure 115, C), is reddish brown to blackish brown, and is 3.4 to 6.8 mm long. The antennae are 10-segmented, with the last 3 segments (club) as long as or longer than the pronotum in the male, but shorter than the pronotum in the female. It is widely distributed in eastern North America, and has been recorded from ash, basswood, maple, beech, and elm, and in sills, joists, beams, and flooring. The larvae often cause much damage (Payne, 1936; Linsley, 1943b; Craighead, 1950; Wright, 1959). Payne called attention to the fact that the damage caused by H. carinatus resembled that caused by lyctid beetles in hardwoods, except that the emergence holes were a little larger and the frass was somewhat coarser.
The Cailifornia deathwatch beetle, Hemicoelus gibbicollis (LeConte) (=Hadrobregmus) (figure 117), is similar in appearance to the eastern species, but has 11-segmented antennae, and the pronotum is distinctly narrower than the base of the wing covers, whereas in Hemicoellis carinatus they are about the same width. Linsley (1943b) stated that the California deathwatch beetle bred in old, well-seasoned Douglas-fir studs, joists, and supporting timbers along the Pacific Coast, and was especially common in basement timbers of buildings 20 years old or more figure 118). Hatch (1946) found serious damage from this species to the weathered boards of spruce in the flooring of a porch. In the areas where it occurred, Linsley considered H. gibbicollis to be the most serious pest among the powderpost beetles in the broad sense of the term.
Ernobius mollis (L.) appears somewhat like a large Anobium punctatum. The short, golden hairs of the newly emerged adult produce a light shade of golden brown, but when some of the hairs are lost, the beetle becomes more uniformly brown. The elytra are less horny, and lack the longitudinal rows of pits characteristic of A. punctatum. Ernobius mollis oviposits only in softwoods, and then only when the bark is attached. Hickin (1963a) found that when the bark was stripped off, the infestation rapidly died out. In the United States, however, E. mollis occasionally does much damage to pine and spruce flooring (Craighead, 1950).
White (1962) listed 7 species of Ernobius occurring in the eastern United States, including E. granulatus LeConte. This species has unusually large eyes. It is 2.3 to 4.3 mm long, reddish brown, with elytra yellowish apically, appendages and abdomen yellowish brown, and with a very fine, short, yellow pubescence. The last 3 antennal segments are very long. Ernobius granulatus has been recorded from many eastern states.
Despite the usual propensity of anobiids to attack old, seasoned wood, some species can destroy weakened shoots of young pine trees, and are scavengers in the cones of conifers. In California, the species most commonly involved is Ernobius punctulatus (LeConte). The beetles are most abundant where dead pine branches have been allowed to accumulate (Doane et al., 1936).
Priobium sericeum (Say) (= Trypopitys) (figure 115, D) is 4.9 to 6.2 mm long, with the head deeply retracted within the prothorax. It is reddish brown to brown, covered with a short, yellowish pubescence. Antennal segments 3 to 7 are distinctly serrate, 8 to 10 are somewhat serrate, and segment 11 is rather narrow and elongate. The combined length of the last 3 segments of the antennae equals the combined length of the 5 or 6 preceding ones (White, 1962). This species is occasionally found in flooring, sills, and in buildings in the eastern states.
In southern California, Priobium punctatum (LeConte) (= Trypopitys), a species closely resembling the furniture beetle, Anobium punctatum, has been found on oak door casings and flooring and in maple wainscoting. This species has also been found in Monterey cypress and pine (Doane et al., 1936).
Ptilinus ruficornis Say (figure 115, E) is 2.8 to 4.8 mm long. The male is completely black, or black with light-brown elytra. The female is bright reddish brown to dark reddish black, with the pronotum bright reddish brown. Both sexes have reddish-brown to reddish-yellow appendages. The antennae of the female are distinctly serrate, whereas those of the male are actually branched, with each branch, on segments 5 to 10, nearly or quite as long as the combined length of segments 1 to 10. The pronotum of both sexes is roughened anteriorly, but particularly so in the female. This species infests beech, maple, oak, sycamore, mesquite, and other hardwoods, and is a rather common and injurious pest of woodwork and of stored wood products (Craighead, 1950). In California, another species, Ptilinus basalis LeConte, along with the bostrichid Scobicia declivis, attacks California laurel (Umbellularia californica) so readily that laurel has had to be nearly abandoned for interior finishing, for which this very beautiful wood is well suited (Doane et al., 1936).
Xyletinus peltatus (Harris)(figure 115, F) is 3.4 to 6.3 mm long, reddish brown to brown, with a fine, short, yellowish pubescence. Its eyes are large, those of the male separated by about 2 times, and those of the female about 3.3 times, the width of the eye as seen from the front. The 11-segmented antennae are moderately serrate, and the last 3 segments are slightly enlarged. The elytra are finely, not deeply, striate (furrowed), with the interval between striae feebly convex (White, 1962).
Xyletinus peltatus is widely distributed throughout the eastern states, and is the most frequently collected species of the genus (Wright, 1959; White, 1962). Williams (1973) considered it to be the most common anobiid in the southeastern states. It often does great damage to cellar joists and flooring in damp buildings, particularly when they are unoccupied or closed up. This species appears to require moist conditions and associated fungi. When conditions are optimum, it can attack both softwoods and hardwoods so severely that complete structural failure will occur. However, it has been known to manifest distinct preferences for certain wood species. Williams (1973) gave an example of such a preference in lumber stored in an old earthen-floor barn infested with X. peltatus. The wood species were yellow poplar, cypress, and western pine. The cypress and western pine were not infested, but radiographed sample boards of yellow poplar contained an average of 72 larvae per sq ft (929 sq cm), and yellow-poplar molding contained about twice that number.
An extremely important phase of prevention is sanitation. In nature, beetles breed in old and dried wood, such as dead branches and limbs of trees, and material of this kind should be burned if it exists near piles of lumber. The same may be said of old lumber and other materials that are subject to infestation. Storage areas should be inspected periodically. Infested lumber should be burned, and pallets, stacking sticks, stakes, platforms, and shelves should be protected against attack. Paraffin wax, varnish, shellac, and paint will fill the pores in which lyctid beetles lay their eggs, and thereby prevent infestation. Infestation by lyctid beetles can be avoided merely by using only softwoods for the pallets, stacking sticks, etc. However, oak is preferred, despite its susceptibility to attack, because it is stronger, more durable, and does not shatter or splinter so easily as coniferous woods.
Firewood stacked outdoors is frequently a source of beetles that can infest structural wood after the firewood has been carried into the house. Other woodborers that may not be able to infest seasoned wood, but are nevertheless nuisances and sources of anxiety when found crawling or flying about in the home, can also emerge from firewood.
Green lumber can be protected against powder-post beetles by submerging it in an insecticidal cold-water emulsion. Similar protection for seasoned wood can be obtained with a solution of insecticide and deodorized kerosene. Insecticides that have proved to be effective in this connection are 5% toxaphene, 2% chlordane, 0.5% dieldrin, and 0.5% lindane. Immersion for 3 minutes gives protection for at least 3 years. A 5-minute dip in 5% pentachlorophenol in a light fuel-oil base is also said to be effective, and this same compound, added to the insecticide emulsions or solutions just mentioned, acts as a fungicide. Protection for 1 season can be obtained with only a 10-second immersion in these insecticides or a 15-second dip in a 5% borax solution heated to 180 °F (82 °C). Following any of these treatments, the treated lumber or wood products can be painted or varished after a reasonable drying period (NPCA, 1961).
Some homeowners would certainly not want to have insecticide-treated lumber used for such articles as kitchen cabinets and baby cribs. A concentration of 0.3% dieldrin or aldrin added as an emulsifiable concentrate to glue prepared for plywood manufacture has been found to provide good protection of plywood against Anobium punctatum in New Zealand (Harrow et al., 1970).
All stages of lyctid beetles can be killed by heat in kilns. In table 3, the periods of exposure of wood of various thicknesses that are required to check damage by powderpost beetles at different temperatures and relative humidities are given. The required periods of exposure increase with increasing thickness of the wood, decreasing temperature, and decreasing relative humidity (St.George, 1970).
The type of treatment selected for control of powderpost beetles will depend on a number of circumstances, among them the size of the infested area. If the infestation is localized, the application of a toxic solution to the infested wood surface or a liquid gas volatilized under a tarpaulin may be considered. Infested furniture can be fumigated in a gastight fumatorium. For the treatment of a large infested area, such as an entire house, tent fumigation, such as practiced for dry-wood termite control, may be the only practical procedure. Even if one finds only a few beetles, believed to be a localized infestation, a complete fumigation of the entire structure is the most reliable way to control the infestation. It is often difficult to locate incipient infestations. However, even with complete fumigation of a building, incomplete control of lyctid beetles occurs in about 10% of the treatments.
Toxic Solutions
For treatment of raw hardwood flooring, unfinished paneling, or structural timbers already infested with powderpost beetles, 2% chlordane or 5% lindane, dissolved in a moderately volatile light oil such as deodorzed kerosene, have been successful when sprayed or painted on the wood at 1 gal per 100 sq ft (4 L per 9 sq m) of surface or until the wood can no longer absorb the liquid. (Solutions of 5% DDT and 0.5% dieldrin are no longer registered for this purpose.) On finished wood, the entire sur face should be treated evenly with a coarse, fan-type spray, but not to the point of runoff puddling. Repeated applicationsmay be necessary to obtain absorption of the reccommended quantity. Each successive application should be made after the preceding one has been absorbed, but before the surface is completely dry. Unless the treatment is applied to thew ground floor, care should be exercised to avoid staining the ceiling and walls below the treated floor. Treated floors should not be walked on, and no objects should be placed on any treated surface for at least 24 hours. Since the treatment can destroy wood finishes, it is advisable to treat a small, ionconspicuous area for preliminary observation before treating infested finished wood. Damaged surfaces must be resanded, refinished, and rewaxed. Sanding, of course, can also be done before treatment, particularly if the floor happens to need it. A few beetles may occasionally emerge after treatment, but the toxic residue will prevent reinfestation. When parquet or block flooring is bound to concrete slab by adhesive, the oil carriers for insecticides can deteriorate the adhesives. In such cases, the entire building should be fumigated.
Smith (1968) was able to prevent infestation of ash lumber by Lyctus powderpost beetles during air-drying, which commonly requires 3 to 18 months. Ash is highly susceptible to infestation. Boards were dipped in lindane emulsions of various concentrations for 10-second periods and then stood on end in a rack to dry for 1 hour. Twenty boards, 1.2 m long and 10 to 20 cm wide, were used for each lindane concentration. The boards were then placed in stacks, with 1.5-cm pine spacers between them to keep them apart. About 12 months after treatment, the boards were exposed to infestation by introducing infested boards from laboratory-reared colonies. All surfaces were examined annually. With 0.06% lindane emulsion, the number of Lyctus beetle holes varied from none the first year to 6.5 the third year, compared with 22 and 295, respectively, in the untreated controls. At 0.25% concentration of lindane, no holes were found during the 3-year period. Since the normal storage period was not longer than 18 months, Smith concluded that a 10-second dip in 0.06% lindane emulsion was adequate for protecting lumber from Lyctus beetles during air-drying. A 25% increase in lindane concentration sufficed for protection against ambrosia beetles, which are discussed later.
For the treatment of timbers such as those used in log cabins, rustic bridges, rustic furniture, and the like, a 0.5% lindane solution in petroleum oil, sprayed onto the surface of the bark or wood, is effective for the control of bark beetles or borers that have only recently attacked and have not penetrated deeper than the outer surface of the wood. Wood that has been attacked for a longer period should be soaked for at least 5 minutes.
Toxic Solutions for Anobiid Beetles
Anobiid infestations usually begin in crawl spaces, particularly if the soil is wet, for the wood then contains more moisture, favoring infestation. Fortunately, the infestation spreads slowly. Control is least difficult and least expensive when the beetles are still confined to the substructure and before they have spread upward into the walls (Williams, 1973). Extensive research was done by Spink et al. (1966) at Louisiana State University on the control of the anobiid Xyletinus peltatus. The external signs of infestation by this beetle were entrance holes less than 1.6 mm in diameter and exit holes about 3 mm in diameter. The number of holes might exceed 200 per sq ft (929 sq cm). Dieldrin at 1% and chlordane at 2% concentrations, in either water or kerosene, gave complete control when applied with a 1-gal (4-L) compression sprayer to the inner sides of 2 joists and the subflooring between them. The liquids were sprayed back and forth over the infested wood until no more liquid was absorbed. There were 4 replications of each treatment. Pretreatment and post-treatment evaluations were based on the number of pellets falling from the infested areas. The tests were stopped after a year.
Another test was made in 6 houses. Dieldrin at 0.15% and 1% and chlordane at 1% and 20% concentrations in water or kerosene were applied to subfloor wood members infested with Xyletinus peltatus. The liquids were applied with a motorized 15-gal (57-L) sprayer, with pressure held to a minimum. The spray was applied in a solid, cone-type pattern, using a No. 5 nozzle disk with a 2-mm aperture. The sprays were applied back and forth over the wood until the timbers were saturated. Approximately 4 gal (15 L) of kerosene solution or 4.5 gal (17 L) of water solution were required for treating 100 sq ft (9 sq m) of infested wood surface. No spreaders or stickers were added to the spray liquids because the tests were made to determine whether sprays as used for termite control and applied with similar equipment, but with reduced pressure, could control anobiid beetles. Evaluations of efficacy were made as in earlier tests, and no further evidence of infestation was seen after any of the treatments.
When the beetle larvae bore into wood, they fill their entrance holes with frass. Tests with water-soluble dye have shown that the frass acts as a wick to carry the insecticide deeply into the wood.
Fumigation for Powderpost Beetles
Methyl bromide fumigation for drywood termites was discussed under the heading "Fumigation." Fumigation for powderpost beetles can be done in the same way, but instead of a concentration of 2 lb per 1,000 cu ft (0.91 kg per 28 cu m) of building space, 3 lb (1.36 kg) is generally recommended for a 24-hour period, provided the temperature is over 60 °F (16 °C), the space being fumigated is properly sealed, and a minimum of 0.5 lb per 1,000 cu ft (0.23 kg per 28 cu m) of gas remains at the end of the 24-hour period of fumigation. Under some circumstances, a higher initial dosage or additional gas sometime during the fumigation period may be required. Methyl bromide fumigation should be done only by a licensed and experienced operator.
Movable items such as furniture can be fumigated in vaults or fumatoriums designed for this purpose. Some pest control firms have such facilities (figure 119). Because of tighter sealing and controllable temperature, either the dosage or exposure can be decreased below that which is required for effective building fumigation. For vault fumigation with methyl bromide, the usual relationships of dosage and period of exposure are, per 1,000 cu ft (28 cu m): 1 lb (0.45 kg) for 24 hours, 3 lb (1.36 kg) for 8 hours, or 9 lb (4.08 kg) for 3 hours. When it is possible to provide partial vacuum, dosage or time can be even further decreased (NPCA, 1961).
Beetle-infested timbers may also be placed in a pile, covered with a tarpaulin, and fumigated with methyl bromide at the rate of 4 lb per 1,000 cu ft (1.82 kg per 28 cu m) of air space. The gas should be confined for about 72 hours. Methyl bromide is an odorless gas and deadly poisonous if inhaled (St. George, 1970).
Sulfuryl fluoride (Vikane), often used for fumigation of drywood termites, is not recommended for control of lyctid beetles because of its relatively low efficacy against the eggs. About 10 times the dosage used in drywood termite fumigation is required to kill lyctid eggs.
An aluminized, neoprene, portable, gastight fumigation tent, with walls and floor continuous, and supported by a collapsible tubular metal pipe frame (figure 120) was developed in England for on-the-spot fumigation of small commodities. It is 7 ft wide, 7 ft high, and 9 ft deep (about 2 m and 2.75 m) and has a 300-cu ft (8.4-cu m) capacity. It has 2 types of gastight seals for the front opening: an industrial metal zipper or a pressuretight channel that completely seals all edges of the flexible flap opening. A 10-in. (25-cm) fan is operated in the tent for a period of 3 minutes, immediately after the fumigant is introduced, to thoroughly distribute the gas (Burns Brown and Heseltine, 1964). A metering device is supplied with the tent that delivers the entire contents of a 1-lb (0.45-kg) can of methyl bromide, supplying a concentration that is the equivalent of a little over 3 lb per 1,000 cu ft (1.36 kg per 28 cu m). As stated above, in vault fumigation the period of exposure for this concentration of methyl bromide is normally 8 hours.
If a lower rate of dosage is required for the commodity fumigated, a shorter exposure period should be utilized, rather than using less gas.
Fumigation is very expensive, and when an infestation of powderpost beetles is known to be confined to a section of hardwood flooring, a localized treatment may be appropriate. S.T.D., proprietary 15.17% solution of the liquid fumigant ethylene dibromide and 4.03% chlordane, in deodorized kerosene, may be mopped evenly over the infested area, using just enough to wet it without leaving puddles. On upper floors, care must be taken to avoid using so much liquid that some of it will stain the ceiling below. The treated area is covered with a polyethylene tarpaulin, the edges of which are taped down to the dry floor surrounding the wet area, and the tarp is left in place for 24 hours. It is then removed, and the windows are opened to allow for complete ventilation.
Occupants are kept out of the room(s) being fumigated during this 24-hour period and the additional period required to completely remove the gas (Ehmann, 1961; NPCA, 1961). Repeated treatments may be required, but pest control operators in the Los Angeles area advise us that the surprisingly few "callbacks" after localized treatment for powderpost beetles indicate to them that their treatments are generally successful. Such pest control operators usually offer a 1-year guarantee on their work.
In another form of localized treatment for powderpost beetles, some pest control operators place a tarpaulin over infested areas, such as hard wood wall cabinets, and release methyl bromide under the tarp.
The localized treatment with ethylene dibromide, when properly performed, usually will not harm a varnished floor surface but will dissolve the wax coating.
In cases where parquet or block flooring is laid directly on a slab to which it is bound by adhesive, the liquid fumigant should be applied in a pan under the tarp so that the ethylene dibromide will contact the floor only as a gas and not as a liquid; otherwise, the adhesive under the floor may be dissolved. Plywood is more difficult to penetrate with a gas because of the glue layers, and increased dosages and extremely careful application techniques are required to ensure good results.
The homeowner may decide to consider removal and destruction of infested wood as an alternative to fumigation (NPCA, 1961).
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.
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.
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).
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.
The winding tunnels made by the larvae tend to have approximately the same shape as their thoraxes - about 3 times broader than high. In this respect, the tunnels frequently can be distinguished from the more nearly rounded tunnels of most of the roundheaded borers of the family Cerambycidae. The life cycle of most buprestids usually requires only 1 or 2 years, and is therefore ordinarily completed before the lumber is used, but with several species found in structural lumber, development can continue for a much longer period. Their tunnels, packed with frass, are often seen in softwood lumber, especially in that from trees salvaged after forest fires, windstorms, or bark beetle infestations.
In recent years, buprestid beetle damage to "grapestake" fences has come to our attention. Damaged fences can sometimes be found throughout a newly developed residential tract. If the wood becomes wet, the frass within the burrows expands and extrudes through the oval burrows. This may lead observers to believe that active burrowing is taking place. The wood for such fences was cut from trees that had been infested, but it cannot become reinfested. Buprestid beetles are long-lived, but probably very few of the insects remain in the wood to cause further damage.
Life Cycle and Habits. The golden buprestid prefers Douglas fir, but will also attack several species of pine, spruce, and fir, and is occasionally found in western red cedar. The adults generally oviposit on trees, with the bark still on them, that are dying or have been lightning-struck, fire-scorched, or recently felled. They are particularly attracted to resinous wood. They usually, but not necessarily, oviposit on the bark. They can also oviposit on fire scars, in cracks of freshly sawed lumber, and less frequently on older, dry, or partially dried structural lumber. It is believed possible, but probably rare, for beetles emerging from a building to reinfest it. Upon hatching, the larvae bore into the tree, their winding tunnels continuously increasing in size as the larvae grow during the 2 to 4 years required for their development. They readily mine heartwood as well as sapwood. The tunnels are broadly oval, reach a width of about 10 mm, and vary in length from 1 to 5 m. The tunnels are packed with powdery borings, which aids in distinguishing them from the tunnels of cerambycid (roundheaded borer) larvae that are packed with a loose mixture of fibrous and powdery material (Every and Rudinsky, 1962).
The longevity of the larvae of B. aurulenta in furniture and in lumber used in construction is amazing, some having been recorded as living 15 to 20 years (Every and Rudinsky, 1962) and even up to 40 to 50 years or more (NPCA, 1964b). Linsley (1943c) believed that in the many records of such longevity, the chance that the beetles oviposited long after the structures were built was very remote. For one thing, this species, like oiher buprestids, mates and oviposits in the bright sunshine of midday, and is not likely to be ovipositing within a building. Also, in some of the instances of prolonged larval life, the beetles were found in linoleum-covered flooring or boring in kitchen cabinets. As further evidence for infestations originating during construction, an adult emerged from a dresser in Germany, where the species does not occur, 13 years after the dresscr was manufactured, partially from wood of American origin.
Pupation takes place in oval pupal chambers near the surface of the wood. The adults eat their way out of the wood, leaving the typical oval buprestid exit hole. In nature, adults emerge most frequently in spring and early summer, but inside buildings they emerge most frequently between late fall and late spring. The adults live 3 to 5 months (Every and Rudinsky, 1962).
Control of the Golden Buprestid
Infestations of the golden buprestid are not likely to occur in lumber cut from logs removed from the forest soon after they were felled, and which were healthy when cut. The beetles cannot survive in kiln-dried lumber. The insect can survive in air-seasoned 1-in. (2.5-cm) boards, but it is most often reported from 2-in. (5-cm) tongued and grooved Douglas-fir subflooring. Lumber to which bark is still attached is more likely to be infested than bark-free lumber. Wood preservatives will discourage oviposition to some extent (Every and Rudinsky, 1962). Exit holes can be plugged and damaged surfaces can be refinished. Infestations are only occasionally severe enough to cause serious structural weakness.
Among scolytids, only 1 sex selects the individual host tree in which mating and oviposition take place. In Dendroctonus, a monogamous genus, the female excavates the entrance tunnel, and in Ips, a polygamous genus, this is done by the male (Wood, 1970).
Bark beetles tunnel through the bark and then between the bark and the sapwood, often scoring the surface of the latter. The adults excavate brood galleries and lay their eggs in tiny niches at intervals along the sides of these galleries. In some species, the brood galleries may be constructed by a single mated pair of beetles; in others, the male may have a harem of 2 or more females, each of which excavates a brood gallery. Fine, brownish-white, sawdustlike frass is pushed out of the entrances of the burrows by the beetles. The larvae bore out on either side of the egg tunnel, but remain between the wood and the bark, making patterns and engravings that are characteristic for each species (figure 128). The larval tunnels are filled with frass, and become larger as the larvae increase in size. Pupation takes place at the end of the tunnel, and the adults bore out through the bark. The exit holes may be so numerous that the tree appears as if it had been riddled with birdshot.
When the bark is pulled away, the engravings are revealed, but the galleries do not penetrate deeply into the wood. In log cabins, rustic wood furniture, or rustic bridges, the engravings are revealed when loose bark falls off. However, before the bark falls off, the frass (the same color as the underbark), which is made up of small, granular, gritty particles, may fall through cracks in the bark. Adult beetles may emerge from exit holes in the bark for as long as a year after the tree is killed. In structures built of infested logs, they may be found at windows where they are attracted by light. They cannot reinfest the dry bark from which they have emerged (St. George, 1970).
Some species of Dendroctonus attack weak, dead, or dying trees, but others seem to prefer normal, healthy trees. Infested trees can be detected because of their fading foliage, the presence of pitch tubes with reddish boring dust on the trunk, or loose dust in the crevices of the bark. Egg tunnels and larval tunnels can be seen between the bark and wood (Hopkins, 1909; Chamberlin, 1918, 1925, 1939; Doane et al., 1936; Keen, 1938; St. George, 1970).
This beetle attacks principally pondcrosa pines, and occasionally, in very destructive epidemics, any trees with trunks over 6 in. (15 cm) in diameter.
The principal species of Ips are the California fivespined ips, I. confusus (LeConte), in the West, and the pine engraver, I. pini (Say), in the eastern United States and Canada.
The adults are reddish brown to pitch-black, 4 to 4.5 mm long, and have 5 pairs of spines on the margin of the elytral cavity (figure 130). The male makes the "nuptial chamber," and then is joined by 1 to 5 (usually 3) females. Each constructs an egg gallery, and the galleries radiate longitudinally from the central nuptial chamber, with 1 to 5 from each chamber. A gallery typically has 3 branches in the form of a "Y" (figure 128, bottom), mostly in the inner bark and only slightly scoring the outer sapwood. Twenty-five to 50 eggs are laid in each egg gallery. The larvae mine directly away from the main galleries, leaving the mines behind them filled with frass and excrement. Pupation takes place at the ends of the larval mines in cells formed in the inner bark. There are 3 to 5 generations produced d
