Termites belong to the insect order Isoptera. The term "Isoptera" is Latin and means "same wing," which refers to the similarity in size of the front and hind wings of the reproductive forms.
Most species of termites have microscopic, one-celled animals, called protozoa, within their intestines that convert wood cellulose into sugar, allowing termites to feed on wood or paper. Termites have a highly developed insect social structure, living in large colonies in the soil or in chambers carved in dead or, sometimes, living wood colonies are composed of castes, specialized forms of individuals that include soldiers, reproductives, and, in some species, workers. These pests cause serious damage to wooden structures and posts and may also attack stored food, household furniture, and even plastics.
Termites are sometimes confused with winged forms of ants, which also leave their underground nests in large numbers to establish new colonies and swarm in a manner similar to reproductive stages of termites. However, ants and termites can be distinguished by checking three features their antennae, wings, and waist.
Subterranean termites require moist environments. To satisfy this need, they usually nest in or near the soil and maintain some connection with the soil through tunnels in wood or through shelter tubes that they construct. Much of the damage they cause occurs in foundation and structural support wood.
The Western Subteranean termite (Reticulitermes Hesperus) is the most destructive of all termites found in California. Colonies include reproductive, worker, and soldier castes. Reproductive winged forms of subterranean termites are dark brown to brownish black, with brownish gray wings. On warm, sunny days following fall or sometimes spring rains, swarms of reproductives may sometimes be seen. Soldiers are wingless with white bodies and pale yellow heads. Their long, narrow heads have no eyes. Workers are slightly smaller than reproductives, wingless, and have a shorter head than soldiers; they are colored similar to soldiers.
Drywood termites infest dry, undecayed wood, including structural lumber as well as dead limbs of native trees and shade and orchard trees, utility poles, posts, and lumber in storage. From these areas, winged reproductives seasonally migrate to nearby buildings and other structures usually on sunny days during fall months. Drywood termites are the most typical termite in southern California, but also occur along most coastal regions, the central valley, and southern desert.Drywood termites have a low moisture requirement and can tolerate dry conditions for prolonged periods. They remain entirely above ground and do not connect their nests to the soil, but piles of their fecal pellets, which are distinctive in appearance, may be a clue to their presence. The fecal pellets are elongate (about 0.03 inch or 0.8 mm long) with rounded ends and have six flattened or roundly depressed surfaces separated by six longitudinal ridges. Winged adults of western drywood termites (Incisitermes minor) are dark brown with smoky black wings and have a reddish brown head and thorax; wing veins are black. These insects are noticeably larger than subterranean termites. Winged forms of the desert drywood termite, Marginitermes hubbardi, are pale. Soldiers of this species have a clublike third antennal segment that is almost as long as all the succeeding segments combined, easily distinguishing them from other species.
Dampwood termites nest in wood buried in the ground, although contact with the ground is not necessary when infested wood is high in moisture. Because of their high moisture requirements, dampwood termites most often are found in cool, humid areas along the coast and are typical pests of beach houses. The Nevada dampwood termite (Zootermopsis nevadensis), however, occurs in the higher, drier mountainous areas of the Sierra where it is an occasional pest of mountain cabins and other forest structures; it also occurs along the northern California coast.
Dampwood termites produce distinctive fecal pellets that are rounded at both ends, elongate, but lacking clear longitudinal ridges common to drywood termite pellets; flattened sides are noticeable. Winged reproductives typically swarm between July and October, but it is not unusual to see them at other times of the year.
Pacific dampwood termites (Zootermopsis angusticollis)are the largest of the termites occurring in California. Winged reproductives are dark brown with brown wings. Soldiers have a flattened brown or yellowish brown head with elongated black or dark brown mandibles. Nymphs are cream-colored with a characteristic spotted abdominal pattern caused by food in their intestines. Nevada dampwood termites (Zootermopsis nevadensis) are slightly smaller and darker than the Pacific species; reproductives are about 3/4 inch (18 mm) long.
Most termite species swarm in late summer or fall, although subterranean termites may also swarm in spring. An infestation begins when a mated pair finds suitable nesting site near or in wood and constructs a small chamber, which they enter and seal. Soon afterward, the female begins egg laying, and both the king and queen feed the young on predigested food until they are able to feed themselves. Once workers and nymphs are produced, the king and queen are fed by the workers and cease feeding on wood. Termites go through incomplete metamorphosis with egg, nymph, and adult stages. Nymphs resemble adults but are smaller. Adult termites may be soldiers, workers or reproductives; only the reproductives have wings. Soldiers have greatly enlarged heads and mandibles which they use to defend their colonies. Workers, the most numerous caste in colonies of many termite species, are responsible for constructing living chambers and tunnels and foraging for food. They also groom and feed one another and other colony members. More primative termite species such as the drywood termites, which do not have a worker caste, have these functions carried out by immature soldiers. Workers of the more advanced species probably evolved from this soldier caste. Reproductives are long-lived queens and kings that are winged during their early adult life but lose their wings after dispersing from their original colony.
Termites are the most destructive wood-destroying pest in the nation. At least 1 percent of the housing units in the United States require treatment each year for the control of termites. Utility poles, lumber, and other wooden structures may also be damaged by termites. Signs of infestation include swarming of winged forms in fall, winter and spring, and evidence of tunneling in wood. Darkening or blistering of wooden members is another indication of an infestation; wood in damaged areas is typically thin and easily punctured with a knife or screwdriver.
Successful termite management requires many special skills, including a working knowledge of building construction. In most cases it is advisable to hire a professional pest control company to carry out the control program. However, some understanding of termite biology and identification can help a homeowner detect problems and work with professionals. Management techniques vary depending on the species causing an infestation. Also, more than one species of termite can infest a building at the same time, which influences your control approach. Subterranean, and less frequently, dampwood termites can have nests at or near ground level, so control methods for these can be similar. However, drywood termites nest above ground, therefore the approach for eliminating them is unique.
Before beginning a control program, thoroughly inspect the building to obtain information about the infestation. Verify that there are termites, identify them, and locate the extent of their infestation and damage. Look for conditions within and around the building that promote termite attack, such as excessive moisture or wood in contact with the soil.
Use an integrated program to manage termites. Combine methods such as modifying habitats, excluding termites from the building by physical and chemical means, and using mechanical and chemical methods to destroy existing colonies.
Building design may contribute to termite invasion. Keep all substructure wood at least 12 inches above the soil beneath the building. Identify and correct other structural deficiencies that attract or promote termite infestations. Keep attic and foundation areas well ventilated and dry. Use screening over attic vents and seal other openings, such as knotholes and cracks, to discourage the entry of winged drywood termites. Although screening of foundation vents or sealing other openings into the substructure helps block the entry of termites, these procedures may interfere with adequate ventilation and increase moisture problems, especially if a very fine mesh is used in the screening.
Termite-resistant wood and other building materials may aid in reducing damage. Chemical treatment of structural wood used in foundations and other wood in contact with soil helps protect against termite damage in areas where building designs must be altered or concrete cannot be used. Inspect utility and service boxes attached to the building to see that they are sealed and do not provide shelter or a point of entry for termites. Reduce chances of infestation by removing or protecting any wood in contact with the soil. Inspect porches and other structural or foundation wood for signs of termites. Look for and remove limbs and tree stumps, stored lumber, untreated fence posts, and buried scrap wood near the structure that may attract termites.Recent research has proved the effectiveness of foundation sand barriers for subterranean termite control. Sand with particle sizes in the range of 10 to 16 mesh is used to replace soil around the foundation of a building and sometimes in the crawl space. Subterranean termites are unable to construct their tunnels through the sand and therefore cannot invade wooden structures resting on the foundation.
Controlling Drywood Termites
Drywood termite colonies are usually small, making it possible at times to control them by removing and replacing damaged wood. However, more than one colony may exist in a structure. Destroy damaged and infested wood promptly, preferably by burning if this is allowed. Otherwise, transport the material to a sanitary disposal site. Other control methods that may be used by pest control professionals include freezing with liquid nitrogen, electrical treatment, fumigation, or spot treatment of galleries by injecting them with insecticides. The use of heat is another means of controlling drywood termites that shows promise and may reduce or eliminate the need for insecticides. A comprehensive study on the advantages and disadvantages of each method has been completed and results will be forthcoming.
Controlling Subterranean and Dampwood Termites
Subterranean and dampwood termites cannot be properly controlled by fumigation, heat treatment, freezing, or termite electrocutor devices because the reproductives and nymphs are concentrated in nests near or below ground level in structures, out of reach of these control methods. For subterranean termites, whenever possible, destroy shelter tubes to interrupt access to wooden substructures and to open colonies to attack from natural enemies such as ants. For dampwood termites, if infestations are small, destroy accessible nests by removing infested wood. Spot-treat subterranean and dampwood termite nest areas with a liquid formulation of a long-lasting insecticide. Removing excess moisture from wood will also destroy dampwood termite nests. If colonies are numerous or inaccessible, hire a pest control professional to apply soil drenches of a long-lasting (3 to 7 years) liquid insecticide directly under the building or injected through the foundation or beneath concrete slabs.
When insecticides are selected, it is important to choose the least toxic material, yet one that will still be effective. Confine insecticide use to areas where termites are detected and to inaccessible areas. Chlorinated hydrocarbon insecticides, such as chlordane, have been used extensively for subterranean termite control because of their long persistence–30 years or more in the soil. Persistence and suspicions of health-related problems, however, have caused chlordane to be removed from the market. Pyrethroid and organophosphate insecticides, usually considered short-lived, are now being developed that will persist in soil for nearly 10 years. Foundations and structural wood can be protected by injecting insecticides into the soil beneath structures by horizontal or vertical drilling and rodding.
Special hazards are involved with applying insecticides to the soil around and under buildings and termite control should be carried out by a licensed professional. Soil-applied insecticides must not leach through the soil profile to contaminate ground water. The mobility of insecticides in the soil is a chemical property that is influenced by soil type, weather, and application techniques. Applications in the wrong place can cause insecticide contamination of heating ducts, radiant heat pipes, or plumbing used for water or sewage under the treated building.
Experimental efforts have been made to control soil-dwelling termites using biological control agents, including use of argentine ants and nematodes. However, these methods are not yet effective enough to be recommended.
IPM Education and Publications, Statewide IPM project University of California DANR Compiled from: Marer, Patrick. 1991. Residential, Industrial, and Institutional Pest Control. 1991. Univ. Calif. Agric. Nat. Resources Publication 3334. Oakland. Editor: B. Ohlendorf Technical Editor: M. L. Flint.
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