Coptotermes gestroi
(Asian subterranean termite)

Coptotermes gestroi is a very damaging termite, native to Southeast Asia, which has been introduced to China, the Americas, Italy and some Pacific islands. It is a threat to wooden structures wherever it occurs, and will also eat cardboard, paper and fabric. It feeds voraciously on any material that contains cellulose and will drill holes in other material such as rubber, plastic and styrofoam to reach food. Living trees can be weakened by C. gestroi consuming the heartwood, to the point where they can be brought down in a storm. It can eat structural timbers from the inside out, leaving a thin film of blistered surface wood. It is the most common termite species in built up areas in Singapore and Malaysia, and is responsible for 80% to 90% of the damage caused to man-made structures.

Coptotermes gestroi is endemic to Southeast Asia, from Assam through Burma and Thailand to Malaysia and the Indonesian archipelago (Kirton and Brown, 2003). Over the past century, human activity has spread this termite far beyond its native range. It is now found in Marquesas Island, Mauritius, Micronesia, Barbados, Lesser Antilles, Greater Antilles, Reunion Island, Hawaii, Florida (USA), Mexico, Taiwan and Fiji (Evans et al., 2013).

In the Caribbean, C. gestroi has invaded some natural woodland habitats. Recent collections from Caribbean islands include Antigua, Barbuda, Barbados, Cuba, Grand Cayman, Grand Turk, Jamaica (Montego Bay and Port Antonio), Little Cayman, Montserrat, Nevis, Providenciales, Puerto Rico (San Juan), St. Kitts and on a boat from the US Virgin Islands. It has also been collected in southern Mexico.

Human transportation is the primary means of migration for termite pests and shipboard infestations are the most likely means of human dispersal of C. gestroi. All substantial objects containing cellulose and adequate moisture may maintain small colonies of C. gestroi during their journey to new areas. These may include large wooden articles used in shipping, such as crates, pallets or shipping containers, lumbers, railway sleepers, wooden posts and planting containers holding soil. Alates are often found swarming out of infested boats (Su and Scheffrahn, 1987).

Coptotermes gestroi is primarily found in humid areas of the subtropical and tropical regions. However, the increasing use of central heating in buildings may promote its establishment into even colder regions.

Coptotermes gestroi is primarily found in humid areas of the subtropical and tropical regions (of up to 26° N). C. gestroi needs moist wood/soil substrate for successful colonization and succumbs quickly to desiccation.

In its natural habitat C. gestroi feeds on dead trees and wooden debris on the soil surface. However, as an exotic pest it is primarily found in populated urban environments, where it feeds on man-made structures (Su et al., 2003). They live underground and enter buildings through cracks, expansion joints and utility conduits. They sometimes form foraging tubes along the surface of the ground and the outside surfaces of structures.

Like most termite species, C. gestroi is an opportunistic feeder, consuming any material that contains cellulose. A large number of living plants are known to be attacked by C. gestroi, but it usually does not kill the plants unless the root system is significantly damaged (Fage, 1987). Pines (Pinus) and Brazil nut (Bertholletia excelsa) are susceptible to C. gestroi attack, but cabbage angelin (Andira inermis), massaranduba (Manilkara bidentata) and pink ipê (Handroanthus impetiginosus) are more resistant.

Genetics

Analysis of population structure in C. gestroi by Yeap et al. (2011) found moderate genetic differentiation, positively correlated with geographic distance, indicating a limited amount of gene flow between populations. Isolation-by-distance and low levels of diversity were observed in introduced populations, suggesting limited dispersal in these populations, which are probably only connected by occasional transfer of infected material by humans.

Reproductive biology

After swarming and landing on the ground, the alates shed their wings and search for a mate. Once a mate is found, the male and female search for a crevice in damp ground or wood, hollow out a small chamber and crawl inside.

The pair, now known as a king and queen, mate and within a few days the queen starts laying eggs, approximately 15-30. Within 2 to 4 weeks, young termites hatch from the eggs and are fed by the king and queen. The first instar larvae may develop into either workers or nymphs after their second moult (Albino and Costa-Leonardo, 2011). Nymphs can develop into alates after going through six instars (Albino and Costa-Leonardo, 2011), or into brachypterous neotenies that do not disperse but reproduce within the same colony (Vargo and Husseneder, 2009). Workers may develop into apterous neotenies, remain as workers, or develop onto pre-soldiers that will ultimately form soldiers (Vargo and Husseneder, 2009). Neotenic reproductives are capable of replacing or supplementing primary reproduction (Myles, 1999). By providing an alternative to dispersal by alate flight, neotenics enable the social organization to be maintained following the death of the primary reproductive. They also regulate population size over time (Lenz et al., 1986; Myles, 1999).

One to 2 months later, the queen lays the second batch of eggs, which will be eventually nursed by termites from the first egg batch. It may take 3 to 5 years before a colony reaches numbers substantial enough to cause severe damage and produce alates.

Activity patterns

Coptotermes gestroi dispersal flights or ‘swarms’, in which large numbers of alates leave the colony, occur at dusk or at night.

Population size and density

Sornnuwat(1996) determined that the foraging population of an average colony in Thailand was 1.13 to 2.75 million individuals.

Nutrition

Coptotermes gestroi feeds on a wide range of cellulose-containing materials and will create holes in such materials as rubber, plastic and styrofoam in its search for food. It also attacks living trees by consuming the heartwood.

Environmental requirements

Temperature and humidity are the two main limiting factors for the establishment of C. gestroi. This species is primarily found in humid areas of the subtropical and tropical regions. However, the increasing use of central heating in buildings may allow it to survive in colder regions.

Many small animals, including ants, lizards, toads and birds are opportunistic predators of Coptotermes alates during swarming, but these predators have no impact on the large populations of subterranean colonies.

Coptotermes gestroi foraging tubes are frequently seen on wooden surfaces and tree trunks. During the swarming season (April to June), elongated mud tubes that serve as flight exit slits may be seen. C. gestroi damage tends to occur in places with high moisture levels, such as bathrooms, kitchen sinks and leaky roofs. An acoustic emission device (AED) may be used to locate sites with feeding activity, but most AEDs have a limited detection range (Scheffrahn et al., 1993).

Monitoring stations can be set up to allow for targeted control (Su and Scheffrahn, 1998).

The following is adapted from Scheffrahn and Su (2000):

The soldiers of C. gestroi are similar to those of C. formosanus. Both species have a large fontanelle (opening on the forehead) and when viewed from above, both also have a tear drop-shaped head. However, the lateral profile of the top of the head just behind the fontanelle shows a weak bulge in C. gestroi that is absent in C. formosanus. As with C. formosanus, C. gestroi soldiers, which constitute about 10 to 15% of foraging groups, aggressively bite when challenged and exude a white mucus-like secretion from the fontanelle.

Coptotermes formosanus usually invades temperate climates (to 35° N latitude in the USA), whereas C. gestroi is limited to more tropical localities (to 26° N).

Microscopic examination of the fine hairs on the head revealed diagnostic differences between the two species: while C. gestroi soldiers have one pair of hairs near the rim of the fontanelle, in C. formosanus two pairs originate around the fontanelle.

The alates (winged forms) of C. gestroi are slightly smaller than those of C. formosanus (total length with wings about 13-14 mm vs. 14-15 mm and maximum head width 1.4 mm vs. 1.5 mm, respectively). The head, pronotum and dorsal abdomen of C. gestroi alates are dark brown, whereas those of C. formosanus are entirely a lighter yellow-brown or orange-brown. The darker pigmentation of the C. gestroi head provides a contrasting background for two light patches on the face called antennal spots; in contrast, the antennal spots in C. formosanus are barely, if at all, visible. The length of wing hairs is somewhat shorter in C. gestroi than in C. formosanus.

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.

The following is adapted from Su and Scheffrahn (2000):

SPS measures

Some quarantine regulations exist that prohibit the transportation of materials infested with termites, but there is need for effective enforcement of these regulations. Given the destructive nature of C. gestroi and its propensity to infest cargo onboard ships and wooden components of sailing vessels, interdiction efforts should centre on ports.

Preventative Practice

Wood pressure-treated with preservatives (creosote, pentachlorophenol, or inorganic salts such as chromated copper arsenate or CCA) are required by building codes for use at the point of wood-soil interface, primarily to prevent fungi decay. C. gestroi does not damage pressure-treated wood, but is still capable of by-passing the treated wood to infest untreated wood in structures. The combination of water and wood or other cellulose materials provides attractive conditions for C. gestroi. Leaky plumbing, air conditioning condensate and any portion of the building that may collect excessive amounts of moisture should be corrected to maintain a drier environment that is less attractive to the termite.

Biological control

Biological control of termites using nematodes (Wilson-Rich et al., 2007), bacteria (Osbrink et al., 2001) and especially with entomopathogenic fungi (Culliney and Grace, 2000; Sun et al., 2003; Verma et al., 2009) has been investigated. The entomopathogenic nematode species Steinernema carpocapsae and Heterorhabditis indica (Mankowski et al., 2005) and entomopathogenic fungus Metarhizium anisopliae (Metchnikoff, 1879) were found to be effective biological control agents against C. gestroi (Maketon et al., 2007).

Chemical control

The conventional method for control of subterranean termites is to place a chemical barrier between termites and the structure that is to be protected. Currently available termiticides include permethrin, cypermethrin, bifenthrin, imidacloprid, chlorfenapyr, chlorantraniliprole and fipronil. Pyrethroids such as permethrin, cypermethrin and bifenthrin repel termites from treatment barriers, whereas other termiticides prevent termite invasion by lethal contact.

For preconstruction treatment (applied before a building is constructed), soil termiticides are applied onto sub-slab soil before the foundation is poured. Post-construction treatment can be done by drilling holes through slabs and injecting insecticides under the foundations, or by drenching trenches dug in soil alongside building foundations.

Because C. gestroi colonies are usually large, application of soil termiticides beneath a structure may not impact the overall population of several million termites that inhabit galleries extending up to 90 m. In recent years, baits have become available to control termite populations near a structure. One such approach is a monitoring-baiting program that incorporates a bait matrix containing noviflumuron or hexaflumuron, both chitin synthesis inhibitors (CSI). Noviflumuron or hexaflumuron have been proven to eliminate colonies in field trials (Grace et al., 1996; Su and Scheffrahn, 1998; Su et al., 2003). Stations containing a monitoring device are first installed in soil surrounding a home. When termites are found in the station, the monitoring device is replaced with a tube containing the hexaflumuron-laced bait. Termites feeding in the stations then carry baits to other members of a colony, leading to the demise of the entire colony population.

Monitoring and surveillance (incl. remote sensing)

Coptotermes gestroi monitoring stations are placed around a house periodically examined to determine the timing and location of the bait application. Electronic sensors are available for automated monitoring (Su, 2002). Baits are applied only when the termites are found and only at the stations where termite activity is intercepted. After eliminating C. gestroi populations near the house, the monitoring resumes and the bait is applied if new termite activity is detected. The monitoring and baiting procedure form the basis for an ongoing programme to protect structures from C. gestroi infestations (Su and Scheffrahn, 1998).

17/07/14 Original text by:

Winnifred Aool, Natural Agricultural Research Laboratories, Kampala, Uganda