TERMITES

byWalter Ebeling  

• Termite Pests
• Western Subterranean Termite, Reticulitermes hesperus Banks (Rhinotermitidae)
• Formosan Termite, Coptotermes formosanus Shiraki
• Western Drywood Termite, Incisitermes minor (Hagen) (Kalotermitidae)
• Southeastern Drywood Termite, Incisitermes snyderi (Light)
• Desert Drywood Termite, Marginitermes hubbardi (Banks)
• Powderpost Termite, Cryptotermes brevis (Walker)
• Pacific Dampwood Termite, Zootermopsis angusticollis (Hagen) (Hodotermitidae)
• Nevada Dampwood Termite, Zootermopsis nevadensis
• Zootermopsis laticeps (Banks)
• Desert Dampwood Termite, Paraneotermes simplicicornis (Banks) (Kalotermitidae)
• Florida Dampwood Termite, Prorhinotermes simplex (Hagen) (Rhinotermitidae)
• Family Termitidae
• Control of Subterranean Termites
• Control of Drywood Termites
• Control of Dampwood Termites

Termites are social insects of the order Isoptera. They live in colonies comprising winged and wingless reproductive forms and numerous wingless sterile workers, nymphs, and soldiers. Despite the fact that social insects account for only a small percentage of the structural pests, 2 groups of social insects, termites and ants, are among the first 3 in importance. The other group, the cockroaches, comprises ancient insects from which the termites are believed to have descended.

Termites feed on wood, and throughout a large area of the world they are the most destructive insects to wood structures. This is a measure of the importance of their natural role in nature - breaking down and returning to the soil and atmosphere the enormous tonnage of dead and fallen trees and other cellulosic material that is continuouslv accumulating on the earth's surface. They are important pests of agricultural crops, forest nursery seedlings, and range grasses, and also damage an enormous amount of stored food and household furniture and commodities, including even most plastics (Snyder, 1935, 1955b; Harris, 1961; Ebeling, 1968). Damage from termites plus the cost of controlling them probably amounts to approximately a half billion dollars per year in the United States alone (Ebeling, 1968). Our knowledge of the history of South America would probably have been much more complete if it had not been for termites, for they are said to have eaten most of the books more than a century old (Howse, 1970).

Termites are found in tropical, subtropical, and in most temperate climatic zones. They are increasing their range and density northward, being favored by the accelerated urbanization incident to the "population explosion," particularly in areas where central heating of buildings affords them a particularly favorable environment for the establishment of colonies.

Much has been written about termites, yet until recently the largest and most comprehensive work, particularly on termite biology, was a book titled Termites and Termite Control. It was edited by C. A. Kofoid, and published by the University of California Press in 1934 (partially revised in 1965), and includes the contributions of 35 experts on termite biology, taxonomy, and control. In 1969 and 1970, a treatise of 2 volumes, titled Biology of Termites and edited by Kumar Krishna and Frances M. Weesner, was published. Twenty-five scientists contributed to this exhaustive treatise, which covered many aspects of termite biology, systematics, distribution, behavior, social organization, and control. Termites- Their Recognition and Control, by Harris, published in 1961; and Termites-A World Problem, by Hickin, published in 1971, are books on the distribution, classification, economic importance, and control of termites, as well as wood-preservation procedures, written from a world standpoint. An excellent popular book on termites was written by Howse (1970).

The lower termites (e.g., drywood and damp-wood termites) can be easily collected and then cultured and observed under glass. The higher termites are more difficult to culture, but successful techniques for culturing have been developed for certain species in all families, and have been described by Becker (1969a). An observable termite colony should be a fascinating subject for classroom demonstration.

Climatic Limitations

Although termites were able to extend their range to approximately the 50 �F (100 �C) annual mean isotherm north and south of the equator, only time will tell how much farther they may be able to go because of the improved microclimate afforded them by heated buildings.

In Wisconsin, the approximate northern limit for the eastern subterranean termite, Reticulitermes flavipes, coincides with an annual minimum isotherm of -30 �C (-22 �F). Upward movements of termites from the soil cease near zero C, and they overwinter primarily at a soil depth of from 3 to over 4 ft (1 to 1.5 m). In this way, the insects can escape adverse weather conditions, such as dryness or low temperature. It appears that the most adverse effect of winter is to confine them to a zone below an adequate source of food, which is usually near the ground surface. The survival of termites in cold climates depends on their ability to repopulate during the warm season (Esenther, 1969).

The situation in Wisconsin is probably typical of all areas in which subterranean termites are extending their range into colder regions. Esenther (1969) points out that only "man-oriented" colonies have been found in Wisconsin. He believes that they were introduced originally on infested lumber and spread mainly through new colony formation facilitated by their subterranean tunneling. Unlike the situation in the warmer southern parts of the range of the species, dissemination by flight must be relatively insignificant in the north. The rate of development of an incipient colony in the north is too slow, and therefore the termites are not likely to survive the rigors of the first winter to form alates. Thus, reproduction is by neotenic individuals, those which attain sexual maturity without attaining the alate (winged) form.

Becker (1970a, b) has observed differences between Reticulitermes flavipes in Wisconsin and Hamburg, Germany, when compared with what he considers to be bioecological races of that species in South Carolina and Hallein, Austria. The northern forms were the most active gallery builders, and demonstrated daily rhythms of activity that were lacking in the southern forms.

Biology and Colony Formation

Termites are relatively primitive from an evolutionary standpoint, but their social organization is the most complex among the insects. Along with the ants and the more highly organized bees and wasps, they belong to the truly social or eusocial insects. The common traits of eusocial insects are: (1) cooperative caring for the young, (2) a division of labor in which more or less sterile individuals work on behalf of fecund individuals, and (3) an overlap of at least 2 generations in life stages so that during some period of their life, the offspring can assist their parents. Species of insects lacking all these traits are called solitary. There are also many species among the wasps and bees that are in various stages of sociality between solitary and eusocial (Wilson, 1971).

A society can be developed only if its members are long-lived. This in turn depends on an adequate and continuous food supply. Termites solved this problem by acquiring the ability to use wood-cellulose as food. The principal termite pests in the United States are in the families Rhinotermitidae and Kalotermitidae, the members of which depend on protozoa (mastigophoran flagellates) in their hindguts to break down cellulose. Termites do not possess these protozoa when they are born; they must obtain them by proctodeal feeding, that is, feeding upon liquid intestinal content taken from the anal aperture of an older termite. Every time the termite molts, the lining of the hindgut is shed, along with the entire body cuticle, and the protozoa are lost. Refaunation takes place by proctodeal feeding (Andrew, 1930; Honigberg, 1970).

In some areas of the world, termites belong primarily to the family Termitidae. The termitids are responsible for most of the earthen termite mounds, some as much as 10 meters in height, which form a characteristic feature of many landscapes of the African and Asian tropics. These termites have no intestinal fauna of the types that can aid in digestion. They may consume grass, leaves, humus, the manure of herbivorous animals, and decaying wood. The Macrotermitinae have spongelike fungus combs in their nests. They are constructed of chewed wood and feces, and are built up to fit the chambers of the nest. These termites feed on fungus (Termitomyces) in the combs. The function of the fungus in digestion appears to be mainly the breakdown of lignin, but probably other factors are supplied, such as nitrogenous materials and vitamins (Sands, 1969). Thus, termites have an abundant, continuous food supply, and this, coupled with their longevity, the potential immortality of the colony, and their ability to care for their eggs and young and protect the colony against natural enemies and the elements, allows for the development of enormous numbers of individuals. For example, in a large colony of the moundbuilding termite Nasutitermes exitiosus (Hill) in Australia, 11.05 kg of termites were removed, representing 2.5 million insects, of which about 87% were of the wood-destroying worker caste (Gay and Wetherly, 1970). Such enormous numbers of termites result in a great capacity for destruction of wood structures, with no seasonal letup in tropical areas. Most of the foregoing factors also favor another social insect, the ant, as a successful and persistent pest of man. Ants may not have as constant a food supply, at least not in nature, but they can store foods in their well-protected nests.

Termites live what is known as a "cryptobiotic" mode of life. They live in enclosed passageways, either entirely in the wood in which they feed or partly within the wood and partly within soil. At certain times of the year, depending on the species, a certain percentage of the colony develops wings and changes from the whitish color of the nymphs to the distinctive dark or black color of the winged reproductives (alates). The latter fly off to form new colonies.

The alates are the members of the colony most likely to be seen by the homeowner. They are the potential kings and queens. The homeowner often confuses alates with "winged ants." The abdomen of the termite is broadly joined to the thorax, while the thorax and abdomen of the ant are joined by a narrow petiole or "waist" (figure 66). The termite has straight, beadlike antennae, while those of the ant are elbowed. Unlike the castes they left behind, the termite alates are heavily pigmented. The fore- and hindwings of the alate termite are approximately equal in length, and usually extend from 25 to 33% of their length beyond the end of the abdomen when folded. The hindwings of the alate ant are much shorter than the forewings, and the folded wings rarely extend beyond the end of the abdomen (figure 67).

After the flight of the alates, their wings break off near the base. Males and females pair off and begin a small excavation for a new nest. Subterranean termites (Rhinotermitidae), for example, may excavate their nest in wood found after digging into the ground, or between a piece of wood and damp ground, or in a crevice in wood on damp ground. (Galleries eventually extend deeply into the ground.) The pair then mate, and the first eggs are laid. The egg-laying capacity of the queen increases as she grows older. Queens of some moundbuilding tropical termites can lay as many as a thousand eggs per day for as long as 25 years.

Several years may pass before all castes are present in a new colony. The complete colony consists of the primary pair of reproductives (royal pair) and three castes: (1) the workers, which feed on wood or fungi and, by regurgitation and excretion, provide food for the young and the other castes; (2) the soldiers, which in the United States are usually large-headed individuals with massive jaws that guard the nest entrances and the royal pair; and (3) usually 2 kinds of supplementary or substitute reproductives known as neotenics. These may be either lightly pigmented and with short wing pads (brachypterous) or very lightly pigmented and without wing pads (Krishna, 1969).

Chemicals that are secreted to the outside of the bodies of insects for caste regulation, attraction, communication, trail-marking, etc., are called pheromones. A colony of social insects (termites, ants, wasps, or bees) maintains its social cohesiveness primarily through the utilization of such chemicals. They are produced in specialized tissues known as exocrine glands. In response to specific stimuli, these glands evacuate their contents into the environment (Blum, 1970).

Termites continually groom one another by means of their mouthparts to obtain desired secretions or exudates containing pheromones. Among the pheromones they obtain in this manner are some that are believed to inhibit the formation of additional members of the sex or caste from which the hormones are obtained, thus serving as a regulatory mechanism to prevent a disproportionate ratio of males, females, and soldiers in a colony (Luscher, 1956a, b, 1961; Weesner, 1956). Luscher (1961) stated that the queen can inhibit sexual development of other potential reproductives, even if her abdomen is covered with varnish, thus covering all integumental glands and the genital opening, but that inhibition is no longer possible if the anus is blocked. He concluded that the inhibitor substance must be given off with the excrement.

There is considerable evidence that the "royal pheromone" that prevents Kalotermes flavicollis (F.) from undergoing the final molt is produced by the mandibular glands of the sexual forms. In 20 trials, when one of these glands from a primary sexual female was implanted in the abdominal cavity of a nymph shortly before the final molt, adult differentiation was blocked or inhibited, depending on how close to the final molt the nymph was at the time of implant (LeBrun, 1972).

Reproductives can also stimulate the development of a caste. For example, when a group of nymphs of Kalotermes flavicollis is separated from soldiers, some will differentiate into soldiers. The number of soldiers produced is much greater when reproductives are present. The effect of reproductives on soldier production was graded as follows: pair of reproductives (king and queen) > 2 queens = 1 queen = 2 kings > 1 king (Springhetti, 1970). Miller (1969) pointed out that, among the lower termites (all families but Termitidae), there is no evidence that the various castes are genetically different; their caste destinies are the expression of social and environmental factors. Even "workers" can become sexuals, and in laboratory colonies have been able to reconstitute all castes of the colony when they were sufficiently numerous.

The role of pheromones in the structure and formation of termite colonies, particularly when the order Isoptera as a whole is considered, is extremely varied and complex. The amazing extent to which an understanding of the role of pheromones has already developed from the pooled results of world-wide investigations is concisely discussed by Howse (1970). No doubt an even broader understanding will result from current investigations.

Supplementary reproductives (neotenics) are required for rapid increase in numbers of termites in a colony. When groups of workers and nymphs of the western subterranean termite, Reticulitermes hesperus, were separated from the mother colony, they formed a new colony in 6 to 8 weeks, utilizing supplementary queens developed from some of the short-winged nymphs found in every large colony (in addtion to the nymphs that develop into the alates that leave the colony). A supplementary queen can produce more eggs (60 to 80) in a day at the height of egg-laying than the primary queen in the first 2 years of the colony's development (Pickens, 1934a).

Trail-Marking Substances

It has long been known that termites follow "odor trails." The odor trails may serve varied purposes. It has been observed, for example, that breaks in the nest structitre of Zootermopsis stimulate the laying of trails to the breaks so as to recruit workers for repair work. The intensity of the stimulus the workers receive from the odor trails determines the number recruited (Stuart, 1967). This primitive trail-laying mechanism was apparently adapted secondarily for foraging purposes. The trail-marking pheromone may at the same time be a food attractant (Smythe et al., 1967a, b; Ritter and Coenen-Saraber, 1969), and in this capacity it offers some potential as a possible means of termite control. The pheromone is secreted by the sternal glands of the workers and soldiers of all termite families (Luscher and Muller, 1960; Stuart, 1961, 1963, 1964, 1969; Noirot and Noirot-Timoth�e, 1965; Mosconi-Bernardini and Vecchi, 1966; Smythe and Coppel, 1966b; Stuart and Satir, 1968; Moore, 1969; Noirot, 1969; Howse, 1970; Mertins et al., 1971). One such gland is situated on each of the third, fourth, and fifth sternites in the primitive Mastotermes of Australia's Northern Territory, on the fourth sternite of Stolotermes, Porotermes, and Hodotermes, and at the base of the fifth sternite (figure 68) on all other termites. In the sternal gland, there appears to be no duct associated with the glandular cells. The pheromone is probably secreted by the cells, and passes through the fine pores of the cuticle, collecting in a reservoir formed by the overlapping sternal plate of the preceding segment (figure 68). Possibly, the extent to which the aperture at the posterior end of this reservoir is opened is regulated by the pressure exerted by the abdomen as it is pressed against the ground (Stuart, 1969).

Extracts of the trail-marking pheromone from either Reticulitermes flavipes or R. virginicus were attractive to both these species and to R. hesperus, but not to the dampwood termite, Zootermopsis angusticollis (Smythe and Coppel, 1966b). Several synthetic analogs of the trail-marking pheromone of R. viginicus have been prepared, and the molecular structures to which these compounds owe their pheromone-mimicking characteristic have been identified (Tai et al., 1971).

Insect pheromones are generally rather species-specific. Therefore, it is of special interest that 6 subterranean termite species (Reticulitermes flavipes, R. virginicus, R. hesperus, R. tibialis, Coptotermes formosanus, and Leucotermes speratus [the latter from Japan]) all responded to 4 trail- marking pheromone analogs (Matsumura et al., 1972). The nonspecificity of these compounds would be advantageous in any attempt to use them as lures for trapping purposes in a control program. Two of the pheromone analogs have been found to be easily synthesized (Tai et al., 1971).

There are many other nonpheromone substances, some found in nature and some artificially produced, that have effects similar to those caused by pheromones. For example, wood rotted by the fungus Lenzites trabea produces an attractant for Reticulitermes flavipes as well as other species of Reticulitermes and Coptotermes. The fungus induces trail-following by termites similar to that induced by the trail-marking pheromone secreted by the sternal glands of these insects (Esenther et at., 1961; Esenther and Coppel, 1964; Allen et al., 1964b; Smythe et al., 1965, 1967a, 1967b; Esenther, 1969). Column chromatography of the unsaponifiable lipids from pine wood on which L. trabea was cultured yielded 2 well-separated fractions that were highly active in choice tests and in a trail-following test with Reticulitermes lucifugus (Rossi). The unsaponifiable lipids of the workers yielded only a single active fraction, but it corresponded to one of the fractions obtained from the wood (Ritter and Coenen-Saraber, 1969).

The attractance of 8 compounds formed in wood by wood-rotting fungi (Basidiomycetes) was tested, using 5 termite species as test insects. Five compounds were generally attractive, and 3 deterred termites or had no attraction. Acids were usually attractive, but aldehydes were attractive in only a few cases (Becker, 1964). Many organic compounds have been found to be attractive to R. flavipes (Watanabe and Casida, 1963).

A trail-marking scent for Nasutitermes exitiosus (Hill) was isolated and identified by B. P. Moore in Australia (Anonymous, 1967d), and was found to be an unsaturated diterpenoid hydrocarbon; only 10-8 gram was required to lay 10 m of trail. Other species of Nasutitermes followed the trail, but distantly related species did not. Because diterpenoid compounds occur in certain essential oils, Moore searched for possible attractants in vegetation. He found a substance in the oil from the Western Australian sandalwood, Eucarya spicata, which attracted Nasutitermes.

At the United States Forest Service's Wood Products Insect Laboratory in Gulfport, Mississippi, it was observed that Reticulitermes flavipes followed marks made by a certain ballpoint pen with blue ink, but other available ballpoint pens did not have this effect. This phenomenon was thoroughly investigated by Becker and Mannesmann (1968). In their investigation, they used 55 termite species from 21 genera of 4 families. They found 3 ballpoint inks that served as trail-markers for many termite species, and 3 others that attracted fewer species. Figure 69 shows workers of R. lucifugus following a spiral line made with a ballpoint pen with ink containing a glycol compound. The termites tend to follow a tangent to the curve, and must make repeated corrections in their direction of movement. The inks were less effective for Mastotermes and species of Kalotermitidae than for species of Rhinotermitidae and Termitidae. Nine glycol compounds, including some used in ink for ballpoint pens, proved to be trail-marking substances of varying degrees of efficacy. Diethylene glycol monoethylether and diethylene glycol monobutylether were very effective for almost all termite species, including Kalotermitidae. Also, some of the decomposition products (aldehydes and acids) produced when wood was attacked by Basidiomycetes were found to be attractants and trail-markers. Reticulitermes lucifugus is unable to react to scent trails if its antennae are partially amputated unless at least 8 segments are retained.

The possibility of practical utilization of termite attractants in wood baits is discussed under "Termite Baits" latter in this chapter.

Termite Pests

• Western Subterranean Termite, Reticulitermes hesperus Banks (Rhinotermitidae)
• Formosan Termite, Coptotermes formosanus Shiraki
• Western Drywood Termite, Incisitermes minor (Hagen) (Kalotermitidae)
• Southeastern Drywood Termite, Incisitermes snyderi (Light)
• Desert Drywood Termite, Marginitermes hubbardi (Banks)
• Powderpost Termite, Cryptotermes brevis (Walker)
• Pacific Dampwood Termite, Zootermopsis angusticollis (Hagen) (Hodotermitidae)
• Nevada Dampwood Termite, Zootermopsis nevadensis
• Zootermopsis laticeps (Banks)
• Desert Dampwood Termite, Paraneotermes simplicicornis (Banks) (Kalotermitidae)
• Florida Dampwood Termite, Prorhinotermes simplex (Hagen) (Rhinotermitidae)

Western Subterranean Termite, Reticulitermes hesperus Banks (Rhinotermitidae)

This is the principal subterranean termite in California. It ranges from British Columbia south to western Mexico and east to Idaho and Nevada. Winged reproductives (alates) are dark brown to brownish black, and have brownish-gray wings (plate I, 1 2,3; figure 70). Including the wings, they are 8 to 9 mm long, and the body, without the wings, is about 5 mm long. If a piece of termite-infested wood is opened in the winter or spring in southern California, the alates may be seen, already darkly pigmented, waiting for a warm, sunny day after a rain to emerge from the nest and fly away. The percentage of alates increases with increasing age of the colony. All other members of the colony except the queen are whitish in color. Densely packed in the termite nests are hundreds of workers and a smaller number of soldiers and supplementary reproductives (neotenics) (figure 70). The queen is always the center of considerable activity by other castes that are feeding, grooming, and guarding her and carrying away and caring for her eggs (plate I,1;2,3 figure 71). The best way to see this is to break open a piece of infested wood that has long lain on or beneath damp ground. Nests in soil may be as deep as 6 or 7 meters below the surface.

The term "workers" is retained because of common usage, although there is reason to believe that termites in the family Rhinotermitidae, in which Reticulitermes is one of the genera, have no definitive workers. Weesner (1965) stated that in Reticulitermes those forms that had generally been considered to be workers might instead be "fairly size-stable individuals functioning as workers, but still capable of molting and differentiating into slightly larger individuals, soldiers, or alates." True workers exist in the family Termitidae.

Colony Development

The growth of a colony from the primary pair of reproductives is slow. Only a few eggs are laid the first year, and they require an average of over 50 days to hatch. The first 2 instars require only 14 to 18 days each. The second and third instars require 1 and 2 months, respectively, and the fifth instar may be the dominant one, and last for as long as 2 years. In sufficiently large colonies that have a large amount of fraternal feeding (trophallaxis), large, well-matured workers and reproductive nymphs of the sixth instar may develop. There may be a seventh instar of still larger workers, and in this instar the perfect reproductive stage is attained in the reproductive caste. Even under the most highly favorable conditions, flights of alates cannot be expected before the third or fourth year. Later, the supplementary reproductives can be expected to greatly accentuate the growth of the colony, and tens of thousands of individuals can develop. (Pickens, 1934a).

The question is often asked as to how many years are required for a newly constructed building to show the first signs of subterranean termite infestation. If the infestation started from a primary pair of reproductives, at least 3 or 4 years would pass before even a few swarmers could be seen, even if the building became infested at the time of construction. Evidence of structural damage should not appear for an even longer period. On the other hand, if the building were built over or close to a strong existing colony, perhaps located in a buried stump or roots, substantial damage from termites could be noticeable within a year.

Shelter Tubes

When condtions of food, moisture, and temperature are satisfactory, subterranean termites can live without any contact with the ground, although this is rare. In most areas, the ground serves as a protection against extremes of surface temperatures, as well as being a moisture reservoir. Subterranean termites are known to change the depth of their nests in the soil to accommodate to changing temperature or moisture requirements.

Subterranean termites in the United States generally span the distance between the ground and the first wood members of the substructure of a building by working their way up through intervening wood or by building "shelter tubes" over concrete foundation walls. Intermittent sections of shelter tubes can also be seen on structural wood members. Periodically, the workers must return via the shelter tubes to their galleries in moist soil to regain moisture through their cuticles to replenish what was lost in the relativeldry wood where they have been feeding.

The tubes do not conduct moist air to the areas of termite activity, as is often recorded in the literature. A humidity sensor, inserted into termite galleries in joists only 18 in. (45 cm) above-ground and directly connected to the ground by shelter tubes, showed that the humidity was identical with that of the atmosphere surrounding the joists (Ebeling, 1968). However, the protection that the shelter tubes provide against air movement probably helps to preserve the termites' moisture to some extent. Likewise, shelter tubes are not built to keep out light, for termites have no aversion to light if they are protected, as in termitaria under glass. The principal function of shelter tubes appears to be protection against natural enemies, especially ants.

The worker termites build shelter tubes from particles of sand or earth, or minute particles of wood, or both, coating them with a gluelike substance that they secrete. Fecal material is also used as a cement. (For Zootermopsis, excrement is likely to be the principal construction material.) The particles may be tightly packed, or they may adhere so loosely as to form a coarse filigree. The western subterranean termite uses at least 4 types of shelter tubes. Usually, all types can be seen in the crawl space under an infested house on a "raised foundation."

Utility or Working Tubes. These form runways through which termites feeding on the wood above the foundations can return periodically to the moist atmosphere of their subterranean galleries in order to replenish lost body moisture. These tubes are wide, flattened, and usually extend from the soil to the wooden construction above it (figure 72, A).

If the tubes are broken as rapidly as they are repaired by termites, and if the insects have no other sheltered passageways through which to return to their nests, and if there is no source of moisture other than the damp soil below, those termites above the broken portions of the tubes will perish.

Exploratory or Migratory Tubes. These (figure 72, B) are similar to utility tubes, but are not so strong, usually do not reach the wood above, and have small exit holes. Figure 73 shows one of these tubes being constructed by a worker termite.

Suspended or Drop Tubes. These are utility tubes, built downward from a wood member to the ground. They are lighter colored than the other types of tubes because they contain more wood fiber (figure 72, C). At the top of the figure, note the 2 egg sacs of the western black widow spider attached beneath the subflooring.

Three types of shelter tubes are shown in figure 74: A, a utility tube against the concrete foundation; B, a utility tube reaching from soil to subfloor, but not attached to the foundation; and C, a suspended or drop tube. Note the much lighter color of the latter. Also, note the block of wood, 1), which was left lying on the ground and became infested with subterranean termites.

Swarming Tubes. These are constructed at swarming time to provide for the exit of alates. They usually extend aboveground about 4 to 8 in. (10 to 20 cm), but under particularly favorable circumstances may extend considerably farther, and may reach wood members of the substructure. Swarming tubes are often found around or beneath floor furnaces or in other warm places.

Formation and Defense of Galleries in Wood

Subterranean termites primarily attack the soft spring growth of the infested wood, in contrast to drywood termites and other nonsubterranean species which burrow indiscriminately across and with the grain of the wood, excavating broad pockets or chambers connected by tunnels (figure 75). Termites tend to feed in a structural wood member until only the harder wood portions and a fragile outer shell remain (figure 76).

The workers of subterranean termites have strong mandibles (figure 77), very large in relation to the size of the head. They are able to tear up and consume wood, but do not eat all the wood chewed out of a gallery. They transport some of it to the rear, and may pile it into a natural cavity in wood or soil, or into a large, unused gallery; much of it is mixed with fecal plaster and packed along the walls of the gallery. Workers also sustain the other castes by oral or anal feeding, care for the eggs, feed the very young nymphs (larvae), queens, kings, and soldiers, and in fact, they perform all the duties of the colony except for reproduction and defense. The solders (plate I, 3; figure 70, E) are responsible for defense. Thrusting their large heads and powerful jaws into breaks in the gallery system, they can defend it against the ant, the termite's worst enemy. Only in case of major destruction of the gallery system is the termite in danger from insect predators. After swarming, the alates are, of course, easy prey for predatory insects and birds.

The First Signs of Infestation

In California, the rainy season is in late fall, winter, and early spring. During this period, flights of subterranean termites take place on warm, sunny days after a rain. (Flights during this period can also be initiated by heavy irrigation or sprinkling in the vicinity of a house). The alates may be the first indication of infestation observed by the homeowner, and it is important that he be able to distinguish them from winged ants (figure 66 and 67) and from the alates of the drywood termite, Incisitermes minor. The total length of the alates of the drywood termite is 11 to 12 mm (about a fourth longer than that of the subterranean termites), the body is dark brown, and the head and thorax are reddish.

Another common indication of the presence of subterranean termites is the occurrence of dark areas or blisters in flooring. One can easily crush these areas with a knife or screwdriver. Shelter tubes may be seen in the crawl space. Sometimes, the distinctive sound of the soldiers may be heard. If they are disturbed, as by a knock on an infested wall, floor, or subfloor wood member, the soldiers jerk their bodes and heads violently up and down and produce an audible tapping as the head capsule strikes the roof or floor of their gallery.

Possible Extent of Damage

Subterranean termites may infest the "mud-sill," usually the first structural wood member encountered on their way up from their subterranean galleries. If the sill is of termite-resistant wood or has been chemically treated, the termites generally build their shelter tubes over this wood member, and attack support structures that rest on the mudsill (girders, joists, and cripples), as well as adjacent wood structures, such as flooring and studding (figure 78, left). These wood members may be hollowed out by the termite feeding. Shelter tubes, constructed of earth, bits of wood, and excrement, extend up into the infested timbers (figure 78, right), and are among the definite indications of subterranean termite infestation. The infested timber becomes hollowed out to the extent that it is vulnerable to ants and other predators, and the termites must construct shelter tubes to protect themselves from their attacks.

Other Indigenous Species of Subterranean Termites

Another species of Reticulitermes, R. tibialis Banks, may be found in some inland areas, such as the San Joaquin and Sacramento valleys and certain high deserts in California, and in general the inland areas of the Pacific Coast eastward to the Rocky Mountain region and Texas. The alates can be distinguished from those of R. hesperus by their pale, almost whitish, wings, with brownish veins in the forearea,as compared with the dark wings of R. hesperus (Weesner, 1965). The head of the soldier of R. tibialis is short, broad, and dark, compared with the long, narrow, and pale head of the solider of R. hesperus (Pickens, 1934b). Where these species overlap in distribution, R. hesperus prefers cool, shady, moist places, while R. tibialis requires open, sunny, drier locations. The 2 species are equally able to damage wood structures.

In the deserts of Arizona, southeastern California, and Mexico another subterranean termite, Heterotermes aureus (Snyder), occurs which can be very destructive, although much of its damage is probably attributed to species of Reticulitermes. The alates, which are nocturnal fliers, can be distinguished from those of Reticulitermes by their pale color. The soldiers of the 2 species are difficult to distinguish.

In the East, Reticulitermes flavipes (Kollar) is the most important termite pest. It extends along the Atlantic Coast north to Maine, and occurs to some extent in Canada, generally up to the line where the average annual minimum temperature does not fall below -20 �F. It extends southward throughout the eastern and midwestern states to the Gulf and into Mexico and Guatemala. It is the most common and widely distributed termite in North America, but does not occur in the western United States. It is similar in appearance to R. hesperus, but is somewhat smaller, and it has similar habits (Smith and Johnston, 1962; Weesner, 1965).

At its western limits, R. flavipes overlaps the range of R. tibialis; in the Great Lakes region, its range meets that of R. arenicola Goellner; and to the south it overlaps the range of R. virginicus (Banks) and R. hageni Banks. It can be distinguished from these species on the basis of size or color of body and wings, color of tibia, location of ocelli, or a combination of these features (Weesner, 1965).

Formosan Termite, Coptotermes formosanus Shiraki

Species of Coptotermes, present throughout the tropics, have an even greater capacity for destruction than Reticulitermes. The Formosan termite, a subterranean species, long very destructive in Hawaii, was reported from Houston, Texas, in 1965, and the known infestations were apparently exterminated. The following year, it was again found in Houston, as well as in Galveston and in several areas in Louisiana (Krishna, 1966), and it appeared to have become firmly established in the United States. It has since been found in incipient infestations in other states, including California.

All infestations noted have been in harbor cities, initially in boats, ships, dredges, piers, and floating drydocks, indicating that this species came to the United States aboard ship. It will probably eventually have the same range of distribution in latitude in this country as it has in other areas of the world.

The Formosan termite is a more vigorous and aggressive species than the indigenous North American subterranean termites, indicated by more extensive tube and tunnel building, the rapidity with which a new food source is located and attacked, and the greater variety of materials attacked. Coptotermes formosanus was compared with 2 indigenous termite species of the eastern United States. It ate more and survived better than Reticulitermes flavipes, which in turn ate more and survived better than R. virginicus (Smythe and Carter, 1970). Coptotermes formosanus was found to be much more aggressive in tunnel building than R. flavipes and R. virginicus. This characteristic, coupled with its greater tolerance to the currently used soil insecticides (aldrin, chlordane, dieldrin, and heptachlor) results in its being more difficult to control. Coptotermes formosanus could penetrate 5 cm of soil containing 500 ppm of insecticide, whereas Reticulitermes could not. This is near the recommended concentration for chlordane, and double the concentration recommended for aldrin, dieldrin, and heptachlor. (See table 1, chapter 2.) Pending the completion of field investigations recently in progress, the dosages currently prescribed for soil treatment directed against our native termite species should be increased when treating for C. formosanus (Beal and Smith, 1971).

The most obvious characteristics that distingtush the Formosan termite from native species of subterranean termites are its larger size and pale yellow body color, the oval shape of the head of the soldier (figure 79, 80) compared with the rectangular head of the Reticulitermes soldier (plate I, 3; figure 70, E), and the hairy wings compared with the absence of hairs on the wings of most of the native species.

The habits of the Formosan termite are similar to those of native subterranean termites. They make nests in wood in or on the ground, in hollows they have excavated from tree stumps or posts, or in the hollow spaces in the walls, floors, or attics of buildings. Earthen shelter tubes are built over objects the termites cannot penetrate, such as concrete or pressure-treated wood, although they can penetrate through cracks in the surface of the treated wood to reach interior portions that have not been treated chemically.

The enormous area covered by some Formosan termite gallery systems was revealed by an excavation of such a system in Louisiana in an earth-fill known to be only 10 years old (King and Spink, 1969). The galleries of a single colony totaled about 1,900 ft (580 m) in length, and covered about 1.4 acre (0.57 ha). The galleries ranged from 5 to 117 cm in depth, but in some areas they are known to extend down to a depth of 3 m. The primary nest (figure 81) of the gallery system was found 48 cm below the soil surface. The nest was 53 cm wide and 48 cm high, and was built of carton, a mixture of soil and masticated wood that had been cemented together by the saliva and excrement of the termites. The same kind of material lined the galleries.

The nest was encased in a 7-mm layer of cemented sand, and rested on a layer of cemented carton and sand. Small cavities separated by thin walls of the carton were found throughout the nest. In the center of the nest were 6 physogastric supplementary queens, about 14 mm long, and in near-by cavities were several batches of eggs. In the outer layers of the nest, soldiers were the dominant form, but workers became more numerous toward the center.

The primary king and queen, along with workers and soldiers, were found in a small piece of cypress wood. The gravid queen was 17.5 mm long and 4.5 mm wide at the broadest part of the abdomen. From the nest, galleries extended to adjacent small pieces of wood.

As with other subterranean termites, if only a portion of a Formosan termite colony is destroyed, even if that portion includes the queen (figure 79), supplementary reproductives will develop from individuals in the isolated group.

Warm, sultry evenings, especially following rain, are favorable for extensive flights. The flights usually begin before sundown and end before midnight. Alates of Coptotermes formosanus are strongly attracted to lights. Indigenous subterranean termites (Reticulitermes spp.) fly only during the day.