Drywood Termites unlike subterranean termites, live in non-decayed wood having, require little moisture and they never need any contact with the soil. In some regions, eg. California or around the Caribbean, they are the most important termite pests.

In California, the most important species of drywood termites is the Western Drywood Termite, Incisitermes minor (Kalotermitidae). It is found under natural conditions as far north as Mendocino County and the Sacramento Valley. It is abundant in coastal regions, and extends eastward into Arizona in peripheral desert regions, in mountain canyons, and along stream beds. Colonies of this species have been transported to, and at least temporarily established in, various parts of the United States. Drywood termites are very amenable to accidental distribution because they may infest commonly transported articles, such as boxes, crates, and furniture, can tolerate low moisture conditions for long periods, and the colony is often small, infesting only a small volume of wood, and can therefore be readily transported for long distances.

In southern California, homes in new residential tracts tend to become infested by drywood termites sooner and in greater numbers than by subterranean termites. Most often, drywood termites infest these homes as alates originating in older buildings in near-by areas. However, infested telephone poles, posts, and piles of lumber or firewood can also be sources of further infestation.

Infestation Signs

The first evidences of drywood termite infestation are usually piles of brownish fecal pellets below "kickout" holes or chinks and cracks in the infested wood, particularly where outer walls of the wood member have become excessively thin from prolonged infestation. The pellets are elongate, averaging about 0.85 mm in length, with rounded ends, and with 6 flattened or roundly depressed surfaces. Longitudinal ridges occur at the angles between the 6 surfaces. The shape of the fecal pellet is the result of pressure exerted by 6 plates of rectal epithelium and 6 rectal grooves. Another indication of the insects' presence may be the flight of alates during warm, sunny days in the fall months. The drywood termite alates are dark brown, and has smoky-black wings with black veins. It may be distinguished from the alate of the western subterranean termite by its larger size (about 11 to 12 mm long) and by the fact that it has a reddish-brown head and thorax, while the subterranean termite is black throughout

Drywood termites generally enter houses through attic vents or shingled roofs but, particularly in hot, dry localities, they are often found in the substructure, where they may have entered via the foundation vents. They attack rafters, ridgepoles, and sheathing in the attic, window frames and sills, door and window jambs, doorsills and, in the substructure, mainly the floor joists and adjoining structural timbers. They may also infest wooden furniture or other wooden materials within the home.

Most kalotermitids can live in dry wood and do not require shelter tubes leading to the ground, they can damage wooden furniture, even if it is moved about frequently. This, plus the ability of a colony to exist in a very small piece of wood, results in kalotermitids and another nonsubterranean termite species being easily dispersed from one area to another. They often appear in areas far removed from regions in which they are indigenous, and it is then urgent that such localized infestations be eradicated.

Biology

After a flight of winged reproductives and subsequent breaking off of their wings, a mated pair of drywood termites will select a place to enter wood. About 90% of the infestations begin in some crack in the wood or in wood joints. The termites may also be in lumber used for construction. In southern California in the fall months, particularly in October, piles of lumber in lumberyards are often attacked by large swarms of drywood termite alates. The entrance holes of the primary pairs may be numerous, and are easily seen. After finding suitable p[iece of wood alate pairs work together to make a hole, and then seal themselves in. The hole serves as the entrance to the "royal cells," and is about 10 cm deep. The "royal pair" enlarge the hole, and the queen lays her first eggs. Generally, 2 to 5 nymphs hatch from the first eggs and begin an enlargement of the burrow. The nymphs perform the duties of the worker caste of the higher termites. The queen then lays more eggs in the advanced part of the main passage of the burrow.

Toward the end of the second year, after the colonizing pair has entered the wood, the colony generally consists of the primary king and queen, one soldier, and a dozen or more nymphs. By this time, the abdomen of the queen has become broader and longer, and she can lay a greater number of eggs. From late spring to late fall, the primary queen lays from 1 to 12 eggs each day for 7 to 10 days, ceases egg-laying for a month or more, and then resumes at the same rate as before.

The time required for Incisitermes minor to develop from egg to alate or soldier is believed to be more than 1 year. It has been estimated that a colony 15 years old might contain a primary king and queen, 1 or more supplementary reproductives, 120 soldiers, and 2,600 nymphs. Thus, the colonies are small compared with those of the subterranean termites, which may contain millions of individuals.

The relatively small colonies result in correspondingly less rapid and less severe damage to buildings than that which is caused by most subterranean termites, but proliferation of colonies in a building can result in extensive infestation.

Other Species of Drywood Termites

Southeastern Drywood Termites, Incisitermes snyderi ranges from South Carolina to Florida and west to eastern Texas. It is lighter in color than I. minor, and is not so severe a pest, but does similar damage. Its flights occur in May or June at nightfall.

Desert Drywood Termites, Marginitermes hubbardi replaces Incisitermes minor at lower elevations and in more arid regions of the deserts of southeastern California, in Arizona, and in northwestern Mexico. The alates are yellow to light brown and, including wings, are about 13 mm long. They may be distinguished from the alates of most other drywood termites of the areas by their very pale coloration, round ocelli, and by the third antennal segment, which is not longer than the second or fourth. In the soldier, the third antennal segment is clublike and is almost as long as all the succeeding segments combined, making identification easy. The alates emerge at night, usually just after a rain, and tend to collect at lights by the thousands. This species readily invades buildings, and is sometimes very abundant in favorable locations. Its damaging potential may increase as cities and suburbs extend into desert regions where it can exist in large cacti and in trees. It is very destructive to poles, posts, floors, ceilings, window and door frames and sills, furniture, boxcars, and other wooden objects in coastal or low-lying towns of the west coast of Mexico. It is much more common in wooden structures than in wood occurring in nature.

Powderpost Termites, Cryptotermes brevis was accidentally introduced into the United States, and is well established in Hawaii, Florida, and parts of Louisiana. It has not been recorded in any natural habitat, but only in man-made structures. It is widely distributed throughout tropical and semitropical areas of the world (Bahamas, Cuba, Hawaii, Honduras, Philippines, and South Africa). Like other drywood termites, powderpost termites can thrive in very dry wood, and need no connections with the ground. They can attack buildings, but are particularly noted for their severe damage to floors, woodwork, furniture, and small wooden objects. The alates of Cryptotermes brevis are 10 to 11 mm in total length, and their wing membranes are colorless, with brownish veins. The caste that most conspicuously distinguishes this species is the soldier. The head is mostly black, almost as broad as long, and high in front. The strongly truncated head is distinctly concave, and is rough in front.

Control of Drywood Termites

Although the following control recommendations are based on experience with Western Drywood Termites in California, they should also apply for the most part to the control of Powderpost Termites, for the behavior of the 2 species is similar. In either case, control differs greatly from that used for subterranean termites, because procedures employed for preventing access of subterranean termites to the wooden members of the foundation are not applicable. Conversely, fumigation of the building as practiced in drywood termite control is of little value against subterranean termites, for although subterranean termites that happen to be aboveground are killed, a large part of the colony, including the reproductive forms, is in the ground and is not affected.

Inspection

In most of California and in many southern states, a complete termite inspection includes, besides the inspection of the subarea for either subterranean or drywood termites, the inspection of the attic for drywood termites. Infestations of drywood termites may be revealed by fecal pellets that have dropped from "kickout" holes in infested wood members. The pellets may be in conical piles if they have dropped only a short distance, or they may be scattered if they have fallen from a greater distance, as from a ridgepole, rafter, or sheathing, to the floor of the attic. If infested wood is broken open, pellets may tumble out of galleries and pockets in the wood in large numbers. Fecal pellets that are seen in an attic may have been pushed up from below to the tops of ceiling joists and plates, but usually they have fallen from wood members above the place in which they are found.

Sometimes, holes ("royal cells") made by the primary pairs of reproductives can be seen. They are about 2 mm in diameter, and proceed straight into the wood at right angles to the surface. Such holes are usually sealed with wood fragments, and a small festoon of frass can often be seen hanging from them.

The attics of flatroofed houses may occasionally be too narrow for a man to crawl into, or they may not be accessible. In such cases, a termite operator indicates in his report what sections of the attic were inaccessible, and may recommend that an access be cut. He is not held accountable for control of termites in inaccessible areas of the attic. If the house is to be fumigated, the termites in such areas will be killed anyway.

In coastal areas, drywood termites are not found in subfloor areas as often as in attics. In areas of very high summer temperatures, as in the San Joaquin Valley of California, they are usually found only in subfloor areas, and not in attics.

Drywood termites are frequently found in window frames, sills, and internal trim. Pellets are usually seen there by the homeowner if an infestation is present. The window frames and sills are often so completely eaten out that they collapse and have to be replaced.

Treatment Methods

Control methods for drywood termites depend primarily on the extent of infestation. If the infestation is sufficiently localized and does not appear to extend into the walls, inaccessible parts of the attic, etc., treatment may be different from that used if it is widespread and partly inaccessible. In the latter case, fumigation is the only practicable procedure. Otherwise, the "drill-and-treat" method of control may be employed.

The "Drill-and-Treat" Method (Localized Treatment)

Termite galleries are located by probing suspected timbers with a screwdriver, ice pick, or other sharp instrument. Quarter-inch (7-mm) holes are then drilled into the infested wood members at about 1-ft (30-cm) intervals to provide access to the galleries, then a liquid insecticide is injected into the wood.

Fumigation

Fumigation is universally recognized as the most effective treatment for drywood termites. Frame houses must be covered with a gastight tarpaulin, usually of 7-oz nylon coated with rubber, neoprene, or plastic. Stucco structres with flat roofs are generally sealed with a special gastight paper over outer doors, windows, vents, and wherever the fumigator believes a satisfactory seal can be obtained without the labor of tarping. Fumigating should be done only by licensed pest control operators.

The procedures for house fumigation for drywood termites were first developed with HCN or methyl bromide, and the treatment was first shown to be effective against Incisitermes minor. HCN was soon discontinued for house fumigation because of the fire hazard. Sulfuryl fluoride was found to have many advantages as started being used instead of the HCN.
Sulfuryl fluoride is more penetrating and effective against both Incisitermes minor and Cryptotermes brevis than methyl bromide, and has the added advantage that it is not necessary to remove any furnishings containing foam rubber from the house.

One of the great inconveniences of fumigation is that the occupants of a building, including pets and plants, must stay out for a day or two. The gas must remain in the building for an extended period to be effective, and the building must be thoroughly aerated afterward.

If the entire building is not to be fumigated, and some furniture or other movable wooden objects are infested with drywood termites or powderpost beetles, the articles may be taken to a fumatorium for treatment. Some pest control operators and, in California, the County Agricultural Commissioners' offices (County Departments of Agriculture) have fumatoria.

Residual Protection

The localized treatment method provides residual protection only for the limited areas treated, and fumigation provides none whatever. The average rates of reinfestation following localized treatment are about 60% and for fumigation under 20% in the first year. One of the suggested solutions to this problem has been the pressure treatment of all framing lumber. The increased cost of construction has been estimated to be about 2%. The necessity for treating cut ends, notches, and bored holes at the time of construction to prevent points for termite entry makes the pressure treatment of all framing lumber an impractical procedure, in the opinions of many people. Some investigators have advocated brushcoating the lumber or spraying the rough framing of houses or the accessible wood of finished buildings with wood preservatives or boric acid.