. Drywood TermitesDrywood 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 most prevalent in southern California (including the desert areas), but also occur along most coastal regions and in the Central Valley. 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. Piles of their fecal pellets, which are distinctive in appearance, may be a clue to their presence. The fecal pellets are elongate (about 3/100 inch long) with rounded ends and have six flattened or roundly depressed surfaces separated by six longitudinal ridges. They vary considerably in color, but appear granular and salt and pepperlike in color and appearance. 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. LIFE CYCLEMost termite species swarm in late summer or fall, although spring swarms are not uncommon for subterranean and drywood termites. New kings and queens are winged during their early adult life but lose their wings after dispersing from their original colony. An infestation begins when a mated pair finds a 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. Most species of termites have microscopic, one-celled animals called protozoa within their intestines that help in converting wood (cellulose) into food for the colony. 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 and are the most numerous stage in the colony PreventionBuilding design may contribute to termite invasion. Keep all substructural wood at least 12 inches above the soil beneath the building. Identify and correct other structural deficiencies that attract or promote termite infestations. Stucco siding that reaches the ground promotes 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. 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 tree stumps, stored lumber, untreated fence posts, and buried scrap wood near the structure that may attract termites. Consult your local city building codes before beginning repairs or modifications. 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. Stainless steel screening may also be available soon as a physical barrier for subterranean termites. Use only "exterior grade" pressure-treated lumber for areas that are exposed to weather; otherwise the chemical in the lumber may leach from the wood. All topical treatments, especially borates, that will be exposed to weather, must also have a sealer coat to prevent leaching into the soil following rain. Because they contain pesticides, disposal of treated lumber requires special handling. For more information on proper disposal of treated lumber, contact your local Household Hazardous Waste Collection site. For the site nearest you, call 1-800-253-2687. Controlling Drywood TermitesTreatments for this pest include whole-structure applications of fumigants or heat and localized or spot treatments of chemicals or treatments that use heat, freezing, microwaves, or electricity. Techniques to prevent infestations of this species include the use of chemicals, pressure-treated wood, barriers, and resistant woods.
Insecticides. Insecticides are applied to the soil either in drenches or by injection. Special hazards are involved with applying insecticides to the soil around and under buildings and a licensed professional does these procedures best. 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. Soil type, weather, and application techniques influence the mobility of insecticides in the soil; soil-applied insecticides must not leach through the soil profile to contaminate groundwater. In the past, chlorinated hydrocarbon insecticides (e.g., chlordane) and organophosphates (chlorpyrifos) were extensively used for termite control but many of these materials have been phased out because of health and environmental concerns. Active ingredients in currently available termiticides can be broadly classified as repellent or nonrepellent. Pyrethroids, such as permethrin and cypermethrin (Dragnet and Demon), are considered to be repellent. This means that the termites are able to detect the insecticide, which basically serves as a barrier, and they are repelled by it without receiving a dose that will kill them. Therefore, when using these materials it is important to make sure there are no gaps or breaches in the barrier. Also, any adjoining structures must be monitored to ensure that the repelled termites don't infest them. Recently introduced chemicals (imidacloprid and fipronil) are now available that are less toxic to humans and other mammals than the older insecticides but highly toxic to insects. Both of these insecticides are also nonrepellent to termites and have been shown to be effective in killing termites at low dosage rates under California's climatic conditions. Generally, the most effective insecticides are only available to licensed structural pest control operators. COMPILED FROMLewis, V. R. July 1997. Pest Notes: Drywood Termites. Oakland: Univ. Calif. Agric. Nat. Res. Publ. 7440. REFERENCESPotter, M. F. 1997. Termites. In A. Mallis, ed. Handbook of Pest Control, 8th ed. Cleveland: Franzak & Foster Co. Scheffrahn, R. H., N.-Y. Su and P. Busey. 1997. Laboratory and field evaluations of selected chemical treatments for control of drywood termites (Isoptera: Kalotermitidae). J. Econ. Entomol. 90: 492-502. Online ReferencesCalifornia:
CAL Termite Web page, http://www.cnr.berkeley.edu/lewis International:
UNEP/FAO/Global IPM Facility Workshop on Termite Biology and Management, http://www.chem.unep.ch/pops/pdf/termrpt.pdf. Author (revision): V. R. Lewis, Insect Biology, UC Berkeley
Editor: B. Ohlendorf
Technical Editor: M. L. Flint
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