Subterranean Termites: This termites species typically dwells in the soil and work through it to reach wood above ground. In the United States, the vast majority of loss is caused by subterranean species.
The soil provides several advantages that make it suitable as the dwelling for subterranean termites. It serves as a source of moisture that protects termites against drying out, shields termites from predators, and is used as a building material for shelter tubes above ground. Termites can excavate passageways through the soil to reach food sources. If moisture is available from another source, subterranean termites may not require connection to the soil. Isolated aboveground infestations can occur in homes where subterranean termites have access to water from condensation, leaking roofs, pipes, or other sources.
Distribution of Subterranean Termites In all areas of the United States, subterranean termites are the most widespread and the most damaging of the three types. They are found in every State except Alaska. Drywood termites cause significant damage in localized areas, but are limited in distribution to the Atlantic coastal States south of Virginia, the entire State of Florida, the Gulf Coast, along the Mexican border, and along the Pacific Coast to just north of San Francisco.
Most of the termite damage in the United States is caused by native termite species. Infestations in buildings, especially in the Northern States, have become more common with the general adoption of central heating units; heated basements also increase termite activity around structures. The construction of suburban homes in forested areas also has increased the termite problem. Changes in building practices and the use of certain construction materials increase the likelihood of termite infestations. Because of this, termites have become a problem in areas where they were formerly of little economic importance.
The Formosan subterranean termite, an introduced species, was detected in Hawaii around 1850 and has since become a pest of considerable importance on the major islands. This termite was first reported in the continental United States in several port cities along the Gulf Coast in the 1960s, but it is not yet generally distributed. It was found in Florida in 1980, and since then it has been found in isolated parts of Alabama, Mississippi, Texas, Tennessee, Georgia, North Carolina, and South Carolina. It is of great importance in localized areas, such as New Orleans. These termites are larger, feed more quickly, and are more aggressive than native species, and they also occur in larger colonies.
In addition, they are less dependent upon ground contact than the native subterranean termites and often can nest in walls. Currently there are no data suggesting long-range movement of this species on its own on the mainland. Its movement has resulted largely from human transportation of wood products (especially railroad ties for landscaping). This is an important fact to consider when transporting wood materials from areas where the Formosan subterranean termite is known to occur.
Biological and Physical Characteristics of the Subterranean Termite Colony
Termites are social insects that live in highly organized colonies. Each colony is composed of “castes” of individuals that have different physical features or behavioral roles, or both. Three types of individuals make up the termite caste system: workers, soldiers, and reproductives (which may or may not be winged). Other intermediate forms are also present, but are rarely observed by the homeowner or pest management professional. One can identify termite species by noting physical characteristics of the soldiers and reproductives.
Physical characteristics distinguish the different termite castes. Worker termites are wingless, soft bodied, and white or yellow-white. They are found in the greatest numbers in a subterranean termite colony and are the ones most frequently seen when infested wood is examined. The duties of these reproductively undeveloped individuals are to care for the eggs and young, feed and clean other termites, forage for food, and construct and repair shelter tubes and other workings. This is the caste that actually eats the wood. Soldiers have larger, brownish heads and longer mouthparts than workers. They guard the colony and defend against predators. Reproductives), or sexual adults, have black or yellow-brown bodies. They have two pairs of long, whitish, translucent wings of equal size at the time when they disperse from the colony, but they shed their wings soon after flight. With increased age, the body of a functioning female reproductive may become greatly expanded with developing eggs and will attain a size several times that of workers.
Ants are often mistaken for termites, but readily visible characteristics differentiate the two very different insects. Ants, when winged, have two pairs of transparent wings of unequal size; termites have two pairs of equal-sized wings. Also, the region of the body behind the wings is “pinched” in ants but broader in termites. The antennae of ants are elbowed, while those of termites are straight and beadlike. These and other distinguishing features are pictured in figure 5. Additionally, ants generally have harder bodies than termites. Termite workers are almost always soft bodied and white to yellow (sometimes caramel colored), but rarely red, dark brown or black like ants. Finally, subterranean termites are almost never seen foraging out in the open.
A subterranean termite colony is self-perpetuating. When the colony is composed of a large number of individuals, a small percentage of workers develop into winged reproductives that then fly in swarms to establish new colonies. Most winged reproductives perish during the flight because of predators such as birds, bats, lizards, or other insects. The time of day and year when flights occur varies with the species of termite and its geographic location. Flights often occur during the first warm days of spring after a rain (therefore earlier in the year in the South than in the North), but they can occur at any time of the year. In buildings with heated basements, termites occasionally fly during winter.
Males and females in the flights are referred to as kings and queens, respectively. They shed their wings after the flight, and each pair excavates a cell in or near wood in the ground and mate. Most subterranean species in the United States lay fewer than 100 eggs during the first year, but egg laying increases with time.
Depending on species, a colony more than 5 or 6 years old may contain from several thousand to over a million termites and produce winged reproductives each year. In some situations, a few workers may develop into reproductives and supplement the egg laying of the original queen.
Materials Damaged by Subterranean Termites
The principal food of subterranean termites is cellulose obtained from wood and other plant tissues. Termites feed on the wooden portions of buildings, utility poles, fence posts, or other wood products. They can also damage paper, fiberboard, and various types of fabrics derived from cotton and other plants. They occasionally are found in living plants and sometimes in puffball mushrooms. As termites search for food, they can damage many noncellulose materials, including plastics, rubber, and even thin metal, although these do not serve as food sources.
Conditions Favoring Subterranean Termite Infestation
Understanding the biological requirements and conditions that favor termite activities better prepares one to inspect buildings and identify potential problem areas. An important consideration is the termite’s dependency on moisture. Their high moisture requirements increase the likelihood that they will maintain contact with the soil or locate near areas where water collects (such as air conditioning condensers, drains, condensation from pipes, etc.), or both.
Subterranean termites become more abundant in moist, warm soil containing a large supply of food. Such conditions often are found beneath buildings where there is inadequate water drainage, or poor ventilation, or where scraps of lumber, form boards, grade stakes, stumps, or roots are left in the soil.
Once termites locate such an area, they can move into buildings in a variety of ways. Termites invade most buildings through wood close to or in contact with the soil, particularly at porches, steps, terraces, fences, or planters. Termites can easily enter small cracks or voids in foundations (including the center of cinder blocks) and concrete floors to reach wood that does not touch the soil. As with all insects, termite activity and development depend on temperature. When soil is kept warm throughout the year, as it is when basements are heated, termite activity is increased and prolonged. Such a “thermal shadow” exists in most structure types and may be increased by heating units, steam pipes, or electrical conduits near the soil.
Termites may eliminate their contact with the soil when an aboveground moisture source is available. Damp wood near sinks, toilets, and leaking pipes or wood kept moist by runoff water, as from the roof or gutters, is a prime location for termites.
Detection of Damage Caused by Subterranean Termites
Early detection of termite infestations and subsequent control measures should enable homeowners to protect their dwellings. A relatively simple, but careful, inspection of one’s home may reveal previously undetected signs of termite activity.
Termite damage to wood often is not noticeable on the surface. This is because workers avoid exposure to air by constructing galleries within the materials they attack. Severely damaged wood may have a hollow sound when tapped. Prodding with a screwdriver is a simple way to determine the soundness of a suspected piece of wood. The exterior surface must be stripped away in order to see the extent of damage. Extensive tunnels that run along the grain are signs that subterranean termites have attacked the wood. These galleries are often covered with yellow-brown or gray specks of excrement and soil. Occasionally, termites completely honeycomb wooden timbers, leaving little more than a wooden shell. Subterranean termites do not reduce the wood to a powdery mass or push wood particles to the outside, as do many other woodboring insects (such as beetles and carpenter ants).
In exposed areas, termites must protect themselves from the drying effects of air. Thus, earthen shelter tubes constructed over the surface of foundation walls are typical signs of termite infestation. These tubes are usually about 1/4 to 1/2 inch wide, and termites use them as passageways between the wood and the soil. To determine if an infestation is active, break a section of the tube and watch for termites. If you do not see any termites, then check back in several days to see if the termites repair the damaged tubes or build new ones.
Most subterranean termite species found in the United States do not construct a clearly defined nest. The Formosan subterranean termite, however, often builds “carton” nests within walls. The carton nest is a honeycombed mass composed of chewed wood, saliva, and feces that retains water and protects the termites from predators. Although occupied carton nests are relatively moist and pliable, abandoned nests dry and harden to a concrete-like consistency.
Large numbers of winged termites swarming from the soil or wood are often the most obvious sign of a nearby termite colony. Although flights may not be observed, discarded wings on the floor beneath doors or at windowsills suggest that winged termites have either emerged within a building and have been unable to escape, or have emerged nearby. Winged reproductives are produced by well-established colonies, often containing at least several thousand members, and colonies of hundreds of thousands are common.
Control of Subterranean Termites in Existing Buildings
Ridding existing structures of termites and making them resistant to future infestations are major problems in termite control. Generally, buildings become infested because little or no attention was given during construction to the preventive measures that would have made the structures resistant to termites. It is in such buildings that termites cause heavy losses each year.
Observe the same principles that are recommended for the prevention of infestations in new buildings when controlling termites in existing buildings. That is, eliminate conditions favoring the development of termite colonies in the soil and permitting passage of termites to wood within the structure. Subterranean termites in the wooden parts of a building will die if they are unable to maintain contact with the soil or other sources of moisture.
Regardless of previous preventive measures, wooden structures should be inspected periodically for evidence of active infestation. If no preconstruction measures were employed, the structure should be inspected more frequently. Under certain circumstances, termites may breach even the best physical barriers, and even insecticides may be ineffective in stopping termites. The continuity of the termite barrier may be broken, and maintenance or repair personnel may leave a condition that favors termite infestation after working underneath or around the structure.
A homeowner can inadvertently disturb the treated soil or place wood on the soil against or under the building. If not cautious, the homeowner may overlook vegetation that has grown over or through the chemical barriers, providing access for termites. Settlement cracks may occur in the foundation walls or concrete slabs and allow termite entrance.
With proper inspection, very little termite damage should result before discovery. Termites typically work slowly and can be detected and controlled before causing structural weakness to the timbers. Although extreme haste is not required, once an infestation is discovered, treatment should be applied within a few months.
Sanitation and structural control measures should be given consideration in the control of existing infestations. In addition to chemical treatments, the following control measures should be used:
- Remove all wood, including form boards and other debris containing cellulose, from underneath and adjacent to buildings.
- Remove exterior wooden structures, such as trellises, that connect the ground with the woodwork of the house. Any wood remaining in contact with the soil should be treated with preservative.
- Replace heavily damaged (structurally weakened) sills, joists, flooring, etc., with sound wood. Where possible, remove all soil within 18 inches (46 cm) of floor joists and 12 inches (30 cm) of girders.
- ill voids, cracks, or expansion joints in concrete or masonry with cement or roofing- grade coal-tar pitch.
- Provide adequate drainage.
- Provide access for inspection of vulnerable areas.
Another way to treat under slabs is to drill horizontally through exterior foundation walls to the soil just beneath the slab and inject the chemical in the holes. This method is complicated, requires special equipment, and should be performed only by a professional. Extreme caution should be taken to prevent drilling into plumbing, electrical conduits, or heating ducts that may be imbedded in concrete. injection of termiticides into these areas must be avoided. Always treat along the outside of the foundation.
- Basement construction-Treat the soil along the outside walls of basements.
- Raised porches, terraces, and entrance slabs-Termite infestations frequently occur at porches, terraces, and entrance slabs. The most satisfactory way to control infestations at these locations is to excavate the soil adjacent to the foundation wall, remove all wood debris, and apply a chemical to the soil as recommended. Place an access panel over the foundation opening to permit inspection. Alternatively, holes may be drilled either through the adjacent foundation wall from within the crawlspace or basement, or through the entrance slab at intervals no larger than 12 inches (30 cm). Chemicals should be injected to form a continuous barrier.
- Buildings with wells, cisterns, sump pumps, French drains, or irrigation systems- Although most termiticides are not very soluble in water once they have dried to the soil, during application the chemical can be washed or blown into a well, cistern, or drainage system. Where wells are located close to or within foundation walls, care must be taken to avoid contamination of the well or cistern. If the label allows, the treated backfill method may be used. The soil around the well or cistern is removed onto a heavy plastic sheet or into a wheelbarrow. The termiticide formulation is applied at a rate equivalent to 4 gallons (15 liters) of diluted chemical to 10 linear feet (3 m) of trench for each foot (30 cm) of depth. The termiticide is thoroughly mixed into the soil and the soil is replaced into the trench.
Some termiticide producers caution against using their product near sump pumps and French drains. A termiticide may usually be applied near a sump pump if the water level in the pit is not rising. The soil around French drains usually may be treated if the soil is dry. For sump pumps and French drains, the treated backfill method may be used if desired. Do not apply a termiticide if precipitation is likely, and do not use irrigation systems until the termiticide has had time to dry.
Several termite bait applications have become popular in recent years. Baiting technology relies on certain biological principles. Termites, being social insects, are known to feed each other, and termites foraging on a treated substance (paper, cardboard, etc.) can transfer a portion of the active ingredient to nestmates. The idea is that not all termites need to encounter the bait itself to be killed. Some baits may be purchased and used by homeowners, others need to be installed and monitored by licensed professionals. Baits are applied in the same manner regardless of construction type.
Most currently available baits employ the placement of untreated monitor stations around or near a structure. The placement is determined by the manufacturer’s instructions. Here, the termite presence may be detected before the termites enter a structure. Most monitoring stations consist of a plastic tube with holes or slits cut to allow termite entry. Within the station is a food source, often wood, paper, or cellulose powder. The stations are monitored on a schedule and, once termites are detected in the monitoring stations, the toxic bait is added. The bait may or may not be in the same form as the monitoring material. The stations continue to be monitored and new bait added until termite activity stops for a specified amount of time, such as 1 year. Once this happens, the bait station is removed and replaced with a new monitoring station.
The active ingredients of some baits are insect growth regulators that interrupt important processes in the insect’s life, such as the shedding of skin. As a result, they are usually specific to insects with few effects on noninsect life. However, because they interfere only with certain stages, it may take weeks, months, or even years to control an infestation.
Other baits use metabolic poisons, which affect a specific point in the termites’ energy cycle. Baits may be used alone, or in conjunction with chemical treatments. Care should be taken to ensure that chemicals do not contaminate the monitoring/ bait stations. Such contamination may cause the termites to avoid the monitoring station, allowing them to go undetected. Also, care should be taken when using lawn care and landscaping pesticides in areas where bait monitoring stations may be present.
Because most homeowners cannot afford to use both chemical and bait treatments, the question arises as to which technology is preferable. This will depend on the homeowner’s preferences.
The many variations in construction prevent a detailed discussion of exact procedures for chemical treatment in all situations. In applying treatments, however, remember that the purpose is to establish a chemical barrier between termites in the soil and wood in the structure or to reestablish the barrier if it has been broken. It is best to have this work done by a professional. Some procedures for treatment of existing buildings are as follows:
- Crawlspace construction-Buildings with crawlspaces usually can be treated easily and effectively. The procedures recommended for pretreatment can also be used for termite control in existing buildings.
- Slab-on-ground construction-Termite infestations in buildings with this type of foundation present serious control problems. It is difficult to form an effective chemical barrier in the soil beneath such floors. One way to treat under a slab is to drill a series of vertical holes about 0.5 inch (1.2 cm) in diameter through the slab and into the soil beneath, particularly at the base of partition walls and other points where the termites may be entering. In most cases, holes should be no more than 12 inches (30 cm) apart. Because a complete barrier is necessary for the treatment to be effective, the chemical injected into each hole must meet with that injected in adjacent holes. The advantage of vertical drilling is that the chemical will flood and cover the surface of the soil.
Other Insects That Damage Wood in Buildings
Other insects attack wood in buildings, and their damage may be mistaken for that caused by subterranean termites. The insects most commonly involved are drywood termites, wood-destroying beetles, carpenter ants, and carpenter bees.
The work of these insects differs from that of subterranean termites in that the wood they attack is converted either to compressed pellets, powder, or shredded fibers. In contrast, subterranean termites leave small, grayish-brown specks of excrement in excavated areas. Subterranean termite galleries follow the grain of the wood, whereas the tunnels of most of the other insects mentioned usually cut across the grain.
Risk Factors for Termite Problems-A Checklist
Any items checked “yes” below should receive special attention at inspections and be checked more frequently. If possible, the problem should be corrected.
Are there . . .
- Cracks in concrete foundation?
- Posts in concrete?
- Earth-filled porches?
- Form boards left in place after construction?
- Leaking pipes or faucets?
- Shrubs near air vents?
- Wood debris underneath or around the house?
- Low foundation walls or footings?
- Brick veneer covering foundation? If bond fails, termites have hidden access.
- Flower planters near foundation walls?
- Wooden forms around drains?
- Porch steps in contact with the ground? Obstructions around heating unit? Paper collars around pipes?
- Trellises? Do they touch the soil?
- Rigid board insulation, stucco, or siding that extends all the way to the soil?
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Content source: U.S. Department of Agriculture:
Original & Complete FDA Article
Tags: Subterranean Termites Prevention and Control, subterranean termites, subterranean termite control, subterranean termite prevention
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