Cryptotermes brevis
(powderpost termite)

C. brevis is the most widely and frequently introduced termite in the world. Within the genus Cryptotermes, it is also the most important, invasive, and widespread of pest species. Other invasive congenerics include C. cynocephalus, C. domesticus, C. dudleyi and C. havilandi (Edwards and Mill, 1986). Endemic species of Cryptotermes, e.g. C. primus in Australia and C. bengalensis in India, may also colonize structural wood (Edwards and Mill, 1986). The majority of Cryptotermes species are not structural pests because they have higher moisture requirements and other ecological restrictions.

C. brevis is the most widespread drywood termite in the tropics and subtropics worldwide. Humans have probably imported C. brevis to every corner of the world, because it may infest the smallest of woody or cellulosic objects. Hong Kong is the only locality in Asia where this termite has been reported. Either C. brevis has gone unreported in the rest of Asia, or Asia is the single subtropical/tropical region in the world where this species is uncommon. Unlikely sites of introduction and isolated establishment include such temperate locations as England (Hickin, 1961), Ontario, Canada (Myles, 1995), Wisconsin, USA (Gay, 1967), and Alaska, USA (RH Scheffrahn, University of Florida, USA, and MI Haverty, USA Forest Service, Albany, California, USA, personal communication, 2004). In addition to records in the distribution table of this datasheet, C. brevis is present in Anguilla, Antiga and Barbuda (RH Scheffrahn, University of Florida, USA, personal communication, 2004) and Azores, Portugal (TG Myles, University of Toronto, Canada, personal communication, 2004).

Although described from specimens collected in Jamaica in 1853 and now occurring on all inhabited islands of the West Indies, C. brevis is not indigenous to the islands of that region. This species only infests structural lumber, therefore its origin remains unknown, but is likely endemic to an obscure location on the neotropical mainland, possibly coastal Peru or northern Chile (J Krecek, University of Florida, USA, personal communication, 2004). Another clue to the endemic locality of C. brevis may be the occurrence of C. darwini, a species that closely resembles C. brevis. C. darwini occurs in standing dead trees and branches of the Galapagos Islands (Light, 1935), and like C. brevis, has no arolium between the pretarsal claws (Bacchus, 1987).

Tropical Asia remains the only region in which C. brevis is not widely dispersed. All other tropical and subtropical regions are now home to C. brevis to some degree because of the free movement of infested goods. Colonies of C. brevis are typically not associated with plant products or agricultural commodities, and therefore, are often bypassed by quarantine inspections or other exotic pest prevention programmes. Quarantine/eradication programmes in South Africa (Coaton and Sheasby, 1979) and Australia (Heather, 1971; Peters, 1990a) have not been successful for eradication, but they have substantially diminished the spread and damage caused by C. brevis. Because of the cryptic nature of their colonies, especially small incipient infestations, it is probably impossible to eradicate C. brevis once it becomes established in a new locality.

C. brevis is exclusively synanthropic. As an example of this dependence on wood in human habitats, of the approximately 6000 drywood termite samples collected from dead trees, shrubs, stumps, and other woody growth in the West Indies, where C. brevis is common in structures, none contained C. brevis (RH Scheffrahn, University of Florida, personal communication, 2004). This pattern of occurrence is characteristic for this species worldwide. The discovery of C. brevis in a woodland locality on Oahu, Hawaii, USA (Scheffrahn at al., 2000) is one of two known non-structural infestations of C. brevis. The other is a colony that was collected from a dead tree in Lima, Peru (J Krecek, University of Florida, USA, personal communication, 2004). As a general rule, if wood is exposed to rainfall or hot direct sunlight, it will not be successfully colonized by C. brevis.

C. brevis has been observed infesting the sapwood and heartwood of both softwoods and hardwoods of many wood species. It feeds on sound dry lumber, furniture, and structural wood that is protected from precipitation (RH Scheffrahn, University of Florida, personal communication, 2004). Although several studies have shown various levels of resistance or non-preference to certain woods or heartwood extracts to feeding pseudergates (Scheffrahn, 1991), none have directly dealt with host wood preferences of newly flown reproductives. It is the choice of these future kings and queens of the colony that ultimately dictates the species and form of wood in which the colony will live. Suggesting that alates show wood preference, Boone (1966) reported that inspection of a museum display in Hawaii, USA of 79 native Hawaiian woods found C. brevis damage on 25 species.

Genetics

Luykx and Syren (1979) reported that diploid mitotic chromosome number in C. brevis is 37 for males and 36 for females. The diploid chromosome complement consists almost entirely of acrocentrics and telocentrics, but has one metacentric that forms the central element in a chain of three chromosomes during meiosis.

Physiology and Phenology

Drywood termites rely on symbiotic flagellated protists (Kirby, 1941) for digestion of the cellulose in wood fibres into available carbohydrates. A drywood termite has a specialised rectum for water absorption. Rectal papillae remove essentially all moisture from the faeces, which is then expelled as a dry pellet. Cuticular hydrocarbons and a heavy cuticular cement layer may also play a role in the desiccation resistance of C. brevis (Collins, 1969). Haverty et al. (2000) reported that at least half of the hydrocarbons of C. brevis are olefins. Breznak et al. (1973) found that reproductives of C. brevis were capable of nitrogen fixation, an element that is very limited in wood.

Reproductive Biology

Each year, a proportion of pseudergates in a mature colony moults, via the nymphal stage, into winged reproductives also known as alates. The alates leave the colony during a series of dispersal flights over a period of several weeks. This is the only time when colony members leave the confines of their excavated wood galleries and is often the first sign of a structural infestation. Alates of C. brevis fly between dusk and dawn during the spring, most typically in May and November in the northern and southern hemispheres, respectively, with a smaller flight sometimes occurring in the autumn. In Key West, Florida, USA, Minnick (1973) reported peak flights in late May and early June at approximately 30 minutes after sunrise and 80 minutes after sunset. The alates are attracted to lights, thus drawing them to structures. After a brief flight, the alates land and almost instantaneously shed their wings and segregate into male/female pairs (Minnick, 1973). The male follows the female in tandem as they inspect wood surfaces for defects such as cracks, crevices, knots, or nail holes, which are the preferred foci for nuptial chamber sites. Once the pair selects the chamber site, its opening is sealed with liquid faeces. Copulation takes place within the nuptial chamber. During the first 6 months, the initial batch of eggs hatches into larvae. In the second or third year, the first soldier may appear along with additional brood. A colony matures in no less than 5 years, at which time it produces its first crop of alates. Colony growth is slow (McMahan, 1962). Colonies can live over 10 years and contain over 1000 members. As a result of recolonizing the same wood member, numerous colonies may live in close proximity and are thought to share gallery systems. Twenty colonies (as counted by number of pairs of primary reproductives) have been recorded from a single wooden door.

In a colony foundation study, Scheffrahn et al. (1998) used paired Picea sp. blocks as a C. brevis colonization platform. The preferred colonization site was the crevice between the two blocks followed by the bottom surface that formed a crevice with the metal substrate. The tops and exterior of the block pairs were least preferred for nuptial chamber construction. They further observed that lone heterosexual pairs headed 52% of colonies containing live termites. Of incipient colonies containing brood, 80% were headed by lone heterosexual pairs, 16% had additional dealates (alate that has shed its wings) occupying chambers with a heterosexual couple, and 4% lost one or both founding reproductives. The broods in 4-month-old C. brevis colonies were small, with the number of eggs and/or larvae being three or fewer, whereas the 6-month-old colonies contained a higher proportion of larvae over eggs than in the 4-month-old colonies. McMahan (1962) reported a mean of approximately one egg and three to five larvae or pseudergates (>third-instar) from 4- to 6-month-old C. brevis colonies composed of laboratory-paired dealates placed inside prepared termitaria.

Using larger attic simulation modules, Scheffrahn et al. (2001a) found that C. brevis constructed almost all nuptial chambers in crevices forming the junctures between boards. They found that two types of nuptial chambers were usually encountered, those that were empty and those that contained live or dead dealates. The empty protochambers mostly consisted of small surface excavations 0.5-1 mm deep and a few millimetres wide. Chambers containing live dealates and especially live brood were larger and deeper; up to 21 mm wide and 8 mm deep. These chambers also usually contained pellets, although in some cases the pellets had been expelled outside.

Environmental Requirements

Based on meteorological data from C. brevis localities in Africa, Williams (1976) estimated that this species thrives in climates of higher desiccation, lower wood moisture content (10-12%), and lower minimum average temperatures (7°C) than Cryptotermes dudleyi or Cryptotermes havilandi. Collins (1969) reported that C. brevis had the greatest desiccation tolerance and lowest weight loss among eight kalotermitid species exposed to 0-4% relative humidity (RH) and 35°C. Woodrow and Grace (1999) reported that microclimates associated with C. brevis in Hawaii, USA were fairly uniform with an overall mean wood-core temperature of 24°C. The highest wood-core temperature was 43°C and the lowest was 14°C. Ambient RH was more variable than temperature with values varying as much as 55% RH during a single month. Monthly mean RH was as high as 75% and ranged from 98% to 27%. In the laboratory, Steward (1983) found that C. brevis was able to reproduce quickly with adults or neotenic reproductives at moderate or low humidities (90 and 60-70% RH, respectively), whereas three other Cryptotermes species preferred higher humidities (85-95% RH).

Although ants may opportunistically invade C. brevis colonies, no species, genus, or family-specific predators or parasites are known for C. brevis. Numerous opportunistic but not obligatory predators, including ants, spiders, reptiles (anoles, geckos), amphibians (toads and frogs), birds, and bats will feed on imagos during dispersal flights.

The winged reproductives of Cryptotermes are difficult to differentiate by colour, size, or wing venation. However, the imago of C. brevis is unique among structure-infesting congeners in that the last tarsal segment, the pretarsus, lacks a fleshy pad, or arolium, between the claws. The course of the median vein, in both fore- and hind-wings, is variable in C. brevis. The median vein may run a typical route in which it contacts the costal margin near the mid-wing or it may be atypical for Cryptotermes by intersecting the costal margin far beyond the mid-wing or running to the wing margin without intersecting the costal margin (Scheffrahn et al., 1988). The wings of C. brevis, unlike many other structure-infesting drywood termites, have a prismatic sheen when light is reflected on the wing membrane. Among structure-infesting Cryptotermes, the soldier head capsule of C. brevis is conspicuously and deeply rugose over the entire surface of the frons and most of the vertex.

Like other drywood termites, C. brevis infestations can be detected by the presence of faecal pellets, often deposited in conical piles or circular patterns depending on the vertical distance from the 'kick-out' holes on the surface of infested wood. Alate dispersal flight or the wings they shed and leave behind are also signals of a nearby infestation. The infestation site or confirmation of a live infestation can be determined by a number of inspection techniques. The most common method is to probe suspected wood surfaces with a screwdriver or sharp tool to break the thin surface and expose the termites in their galleries. A number of non-destructive methods are being marketed that may prove useful for drywood termite inspections. More complete data have been published on acoustic emission detection (Scheffrahn et al., 1993, 1997a; Thoms, 2000). However, microwave, x-ray, infrared, metabolic gas, and canine detection methods also show promise (Quarles, 2004).

As with all termites, drywood termite species are social insects. Unlike subterranean termites, C. brevis and other drywood termites live entirely within the wood members they infest and obtain water adsorbed onto wood fibres and by metabolic processes. Drywood termites are generally larger and more cylindrical in body form compared to subterranean termites. Because their gallery systems are limited to and usually extend only a few metres within their home wood, drywood termites have proportionally shorter legs and move more slowly than their more distant-foraging subterranean counterparts. Characters shared with other termites include chewing mouthparts for feeding on wood, well-developed tarsal claws for gripping wood surfaces, moniliform (bead-like) antennae, and blindness except in the reproductive caste. C. brevis produces faecal pellets, 'kick-out' holes, and feeding damage that is identical to other drywood termite species. The size, colour, and shape of faecal pellets cannot be used to identify C. brevis. Structure-infesting Cryptotermes spp. can be differentiated from pest species of Incisitermes spp. in that soldiers of the former have phragmotic heads, whereas the latter have head capsules with long projecting mandibles.

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

Chemical Control

Chemical prevention involves the treatment of attics and wall voids with desiccating or toxic dusts that kill freshly flown reproductives as they contact treated surfaces while searching for nest sites. Borate dusts, silica dusts, and residual chemicals have been shown to impede nuptial chamber construction (Scheffrahn et al., 1998, 2001a). The application of preventative chemicals is best done during the framing phase of construction when all wood surfaces are accessible to treatment. Dealates (alates that have shed their wings) will not infest lumber that has been pressure-treated with chromated copper arsenate (CCA) wood preservatives (Scheffrahn et al., 1998).

Local or 'spot' treatments for drywood termite control include wood injection surface applications, microwave energy, electrocution, and wood replacement. Wood injection or 'drill-and-treat' applications use an insecticide that is injected into small holes drilled to intersect termite galleries (Scheffrahn et al., 1998). This is the simplest and most direct method of treatment. Recently, the non-repellent and slow-acting insecticides, fipronil, imidacloprid and thiamethoxam, have gained registration in the USA for intragallery injections for drywood termites. Spinosad showed good field efficacy against C. brevis in field trials (Scheffrahn and Thoms, 1999; Thoms, 2000), but this chemical has not been marketed for drywood termite control. Spray and foam applications of products containing boron salts must be applied to raw, uncoated wood surfaces. Because penetration depths of borate solutions and depth of drywood termite galleries vary, drill injection into infested wood should also be performed as surface application alone has been shown not to be as effective as a remedial treatment (Scheffrahn et al., 1998). The monoterpene, limonene (a natural product) will kill drywood termites on contact when injected into galleries or applied to uncoated wood surfaces (RH Scheffrahn, University of Florida, personal communication, 2004).

Fumigation ('tenting') is a highly technical procedure that involves surrounding the structure with a gas-tight tarpaulin, sealing the tarpaulin to the ground, releasing an insecticidal gas inside the enclosure, and aerating the fumigant after a set exposure time. The overriding advantage of structural fumigation to control C. brevis and other drywood termites is that fumigation insures the eradication of this pest throughout the entire structure including all hidden or inaccessible infestations. Sulfuryl fluoride is the primary fumigant for C. brevis control in the USA. Osbrink et al. (1987) reported on sulfuryl fluoride toxicity to drywood termites under laboratory conditions.

Drywood termites are hidden inside the wood they infest, therefore it may be difficult to immediately verify the success of a given treatment. However, new detection methods may improve control verification (Quarles, 2004). A dispersal flight within a few years of treatment suggests either that the treatment was unsuccessful, infested wood was brought into the structure, or a hidden, untreated, infestation was present and remains to be treated. Accumulation of pellets, especially in a cone-shaped pattern, is also a sign of active drywood termites. All pellets should be removed after a treatment to ensure that colony activity has ceased. A re-treatment is warranted if new pellets are observed. Pellets may continue to trickle from the wood after successful control if the wood member is periodically subjected to vibrations or jarring such as a door or doorframe.

Early Warning Systems

C. brevis alates are attracted to lights. Therefore a light trap or sticky trap near a light can be used to monitor for C. brevis dispersal flights.

IPM Programmes

Although no data exist on the effectiveness of non-chemical methods, several might be considered to reduce the colonization potential of C. brevis in structures. These methods include alate exclusion, alate avoidance, the use of non-wood materials, nuptial chamber site reduction, and wood article inspection. Alate exclusion consists of 'tight' building practices, such as the use of exterior caulking and use of small mesh <1 mm openings) attic and window screening, but complete blockage of alate entry points is difficult. The reduction or elimination of outside lighting around buildings during dispersal flight season may prevent attraction of alates from neighbouring infested structures. Nail holes, cracks and crevices, used by C. brevis as foci for nuptial chamber construction should be sealed. All wooden furnishings being brought into buildings should be inspected for C. brevis infestation.

Non-chemical treatments for C. brevis and other drywood termites have been marketed at various times in the USA (Lewis and Haverty, 1996). Microwave energy, applied to relatively small sections of infested wood, kills termites by heating them. The electrocution method uses a hand-held 'gun', which is passed slowly over the infested wood. The high voltage and low current energy emitted by the probe electrocutes termites in the immediate application area, but metal interferes with this treatment. Wood replacement allows for absolute removal of a drywood termite infestation if it is isolated to a wood member that can be detached relatively easily, as for example, a fascia board or a door.

Due to technical challenges, heat treatments are usually not applied to the entire building, but are limited to known areas of infestation, and along with excessive cold, are classified as compartmental treatments. In the USA, heat treatments have been used to eradicate drywood termites from a portion of a house such as an attic, porch, or bedroom, or from an individual apartment or condominium unit inside a multi-family dwelling. Hot air is delivered using high-output propane heaters. Scheffrahn et al. (1997b) reported that C. brevis was killed when exposed to 50°C for more than or exactly 4 minutes regardless of humidity or prior heat acclimation. Similar results were later obtained on C. brevis populations in Hawaii, USA (Woodrow and Grace, 1998). Excessive cold is primarily used for treating wall voids or similar small enclosures in a structure. Liquid nitrogen is delivered into these voids until the temperature falls to a level lethal to drywood termites (Rust et al., 1997). Small wooden articles can be treated by placing them in warm ovens or freezers. Items placed in freezers should be sealed in bags to avoid condensation upon removal.