English

Noun

termites

1. Plural of termite

Termites, sometimes incorrectly called "white ants", are a group of social insects usually classified at the taxonomic rank of order Isoptera (but see also taxonomy below). As truly social animals, they are termed eusocial along with the ants and some bees and wasps. Termites mostly feed on dead plant material, generally in the form of wood, leaf litter, soil, or animal dung, and about 10% of the estimated 4,000 species (about 2,600 taxonomically known) are economically significant as pests that can cause serious structural damage to buildings, crops or plantation forests. Termites are major detrivores, particularly in the subtropical and tropical regions, and their recycling of wood and other plant matter is of considerable ecological importance.

As eusocial insects, termites live in colonies that, at maturity, number from several hundred to several million individuals. They are a prime example of decentralised, self-organised systems using swarm intelligence and use this cooperation to exploit food sources and environments that could not be available to any single insect acting alone. A typical colony contains nymphs (semi-mature young), workers, soldiers, and reproductive individuals of both genders, sometimes containing several egg-laying queens.

Social organization

Reproductives

A female that has flown, mated, and is producing eggs, is called a "queen". Similarly, a male that has flown, mated, and remains in proximity to a queen, is termed a "King". These anthropocentric terms have caused great misunderstanding of colony dynamics. Research using genetic techniques to determine relatedness of colony members is showing that the idea that colonies are only ever headed by a monogamous royal pair is wrong. Multiple pairs of reproductives within a colony are not uncommon. In the families Rhinotermitidae and Termitidae, and possibly others, sperm competition does not seem to occur (male genitalia are very simple and the sperm are anucleate), suggesting that only one male (king) generally mates within the colony.

At maturity, a primary queen has a great capacity to lay eggs. In physogastric species, the queen adds an extra set of ovaries with each moult, resulting in a greatly distended abdomen and increased fecundity, often reported to reach a production of more than two-thousand eggs a day. The distended abdomen increases the queen's body length to several times more than before mating and reduces her ability to move freely, though attendant workers provide assistance. The queen is widely believed to be a primary source of pheromones useful in colony integration, and these are thought to be spread through shared feeding (trophallaxis).

The king grows only slightly larger after initial mating and continues to mate with the queen for life. This is very different from ant colonies, in which a queen mates once with the male(s) and stores the gametes for life, and the male ants die shortly after mating.

The winged (or 'alate') caste, also referred to as the reproductive caste, are generally the only termites with well-developed eyes (although workers of some harvesting species do have well-developed compound eyes, and, in other species, soldiers with eyes occasionally appear). Termites on the path to becoming alates (going through incomplete metamorphosis) form a sub-caste in certain species of termites, functioning as workers ('pseudergates') and also as potential supplementary reproductives. Supplementaries have the ability to replace a dead primary reproductive and, at least in some species, several are recruited once a primary queen is lost.

In areas with a distinct dry season, the alates leave the nest in large swarms after the first good soaking rain of the rainy season. In other regions, flights may occur throughout the year or more commonly in the spring and autumn. Termites are relatively poor fliers and are readily blown downwind in windspeeds of less than 2 kph, shedding their wings soon after landing at an acceptable site, where they mate and attempt to form a nest in damp timber or earth.

Workers

Worker termites undertake the labours of foraging, food storage, brood, nest maintenance, and some of the defence effort in certain species. Workers are the main caste in the colony for the digestion of cellulose in food and are the most likely to be found in infested wood. This is achieved in one of two ways. In all termite families except the Termitidae, there are flagellate protists in the gut that assist in cellulose digestion. However, in the Termitidae, which account for approximately 60% of all termite species, the flagellates have been lost and this digestive role is taken up, in part, by a consortium of prokaryotic organisms. This simple story, which has been in Entomology textbooks for decades, is complicated by the finding that all studied termites can produce their own cellulase enzymes, and therefore can digest wood in the absence of their symbiotic microbes. Our knowledge of the relationships between the microbial and termite parts of their digestion is still rudimentary. What is true in all termite species, however, is that the workers feed the other members of the colony with substances derived from the digestion of plant material, either from the mouth or anus. This process of feeding of one colony member by another is known as trophallaxis and is one of the keys to the success of the group. It frees the parents from feeding all but the first generation of offspring, allowing for the group to grow much larger and ensuring that the necessary gut symbionts are transferred from one generation to another.

Termite workers are generally blind due to undeveloped eyes. Despite this limitation, they are able to create elaborate nests and tunnel systems using a combination of soil, chewed wood/cellulose, saliva, and faeces. Some species have been known to create such durable walls that industrial machinery has been damaged in an attempt to break their tall mounds. Some African and Australian species have mounds more than 4 metres high. The nest is created and maintained by workers with many distinct features such as housing the brood, water collection through condensation, reproductive chambers, and tunnel networks that effectively provide air conditioning and control the CO2/O2 balance. A few species even practice agriculture, with elaborate fungal gardens which are fed on collected plant matter, providing a nutritious mycelium on which the colony then feeds (see "Diet", below).

Soldiers

The soldier caste has anatomical and behavioural specializations, providing strength and armour which are primarily useful against ant attack. The proportion of soldiers within a colony varies both within and among species. Many soldiers have jaws so enlarged that they cannot feed themselves, but instead, like juveniles, are fed by workers. The pan-tropical sub-family Nasutitermitinae (which should probably have the South American species separated) have soldiers with the ability to exude noxious liquids through either a horn-like nozzle (nasus) or simple hole in the head (fontanelle). Fontanelles which exude defensive secretions are also a feature of the family Rhinotermitidae. Many species are readily identified using the characteristics of the soldiers' heads, mandibles, or nasus. Among the drywood termites, a soldier's globular ("phragmotic") head can be used to block their narrow tunnels. Termite soldiers are usually blind, but in some families, soldiers developing from the reproductive line may have at least partly functional eyes. It's generally accepted that the specialization of the soldier caste is principally a defence against predation by ants. The wide range of jaw types and phragmotic heads provides methods which effectively block narrow termite tunnels against ant entry. A tunnel-blocking soldier can rebuff attacks from many ants. Usually more soldiers stand by behind the initial soldier so once the first one falls another soldier will take the place. In cases where the intrusion is coming from a breach that is larger than the soldier's head, defence requires special formations where soldiers form a phalanx-like formation around the breach and blindly bite at intruders or shoot toxic glue from the nasus. This formation involves self-sacrifice because once the workers have repaired the breach during fighting, no return is provided, thus causing the death of all the defenders.

Termites undergo incomplete metamorphosis, with their freshly hatched young taking the form of tiny termites that grow without significant morphological changes (other than wings and soldier specializations). Some species of termite have dimorphic soldiers (up to three times the size of smaller soldiers). Though their value is unknown, speculation is that they may function as an elite class that defends only the inner tunnels of the mound. Evidence for this is that, even when provoked, these large soldiers do not defend themselves but retreat deeper into the mound. On the other hand, dimorphic soldiers are common in some Australian species of Schedorhinotermes that neither build mounds nor appear to maintain complex nest structures. Some termite taxa are without soldiers; perhaps the best known of these are the Apicotermitinae.

Diet

Termites are generally grouped according to their feeding behaviour. Thus, the commonly used general groupings are subterranean, soil-feeding, drywood, dampwood, and grass-eating. Of these, subterraneans and drywoods are primarily responsible for damage to human-made structures.

All termites eat cellulose in its various forms as plant fibre. Cellulose is a rich energy source (as demonstrated by the amount of energy released when wood is burned), but remains difficult to digest. Termites rely primarily upon symbiotic protozoa (metamonads) such as Trichonympha, and other microbes in their gut to digest the cellulose for them and absorb the end products for their own use. Gut protozoa, such as Trichonympha, in turn rely on symbiotic bacteria embedded on their surfaces to produce some of the necessary digestive enzymes. This relationship is one of the finest examples of mutualism among animals. Most so called "higher termites", especially in the Family Termitidae, can produce their own cellulase enzymes. However, they still retain a rich gut fauna and primarily rely upon the bacteria. Due to closely related bacterial species, it is strongly presumed that the termites' gut flora are descended from the gut flora of the ancestral wood-eating cockroaches, like those of the genus Cryptocercus.

Some species of termite practice fungiculture. They maintain a 'garden' of specialized fungi of genus Termitomyces, which are nourished by the excrement of the insects. When the fungi are eaten, their spores pass undamaged through the intestines of the termites to complete the cycle by germinating in the fresh faecal pellets. They are also well known for eating smaller insects in a last resort environment.

Mounds

Human interaction

Because of their wood-eating habits, termites sometimes do great damage to buildings and other wooden structures. Their habit of remaining concealed often results in their presence being undetected until the timbers are severely damaged and exhibit surface changes. Once termites have entered a building, they do not limit themselves to wood; they also damage paper, cloth, carpets, and other cellulosic materials. Often, other soft materials are damaged and may be used for construction. Particles taken from soft plastics, plaster, rubber, and sealants such as silicon rubber and acrylics are often employed in construction.

Termites usually avoid exposure to unfavourable environmental conditions. They tend to remain hidden in tunnels in earth and wood. Where they need to cross an impervious or unfavourable substrate, they cover their tracks with tubing made of faeces, plant matter, and soil. Sometimes these shelter tubes will extend for many metres, such as up the outside of a tree reaching from the soil to dead branches. Termite barrier systems used for protecting buildings aim to prevent concealed termite access, thus forcing the termites out into the open where they must form clearly visible shelter tubes to gain entry.

Termites can be major agricultural pests, particularly in Africa and Asia, where crop losses can be severe. Counterbalancing this is the greatly improved water infiltration where termite tunnels in the soil allow rainwater to soak in deeply and help reduce runoff and consequent soil erosion.

In many cultures, termites are used for food (particularly the alates), and termite nests are used widely in construction (the dirt is often dust-free) and as a soil amendment.

Humans have moved many wood-eating species between continents, but have also caused drastic population decline in others through habitat loss and pesticide application.

Avoiding termite troubles

Precautions:

• Avoid contact of susceptible timber with ground by using termite-resistant concrete, steel, or masonry foundation with appropriate barriers. Even so, termites are able to bridge these with shelter tubes, and it has been known for termites to chew through piping made of soft plastics and even some metals, such as lead, to exploit moisture. In general, new buildings should be constructed with embedded physical termite barriers so that there are no easy means for termites to gain concealed entry. While barriers of poisoned soil, so called termite pre-treatment, have been in general use since the 1970s, it is preferable that these be used only for existing buildings without effective physical barriers.
• The intent of termite barriers (whether physical, poisoned soil, or some of the new poisoned plastics) is to prevent the termites from gaining unseen access to structures. In most instances, termites attempting to enter a barriered building will be forced into the less favourable approach of building shelter tubes up the outside walls, and thus, they can be clearly visible both to the building occupants and a range of predators. Regular inspection by a competent (trained and experienced) inspector is the best defence.
• Timber treatment.
• Use of timber that is naturally resistant to termites such as Canarium australianum (Turpentine Tree), Callitris glaucophylla (White Cypress), or one of the Sequoias. Note that there is no tree species whose every individual tree yields only timbers that are immune to termite damage, so that even with well known termite-resistant timber types, there will occasionally be pieces that are attacked.

When termites have already penetrated a building, the first action is usually to destroy the colony with insecticides before removing the termites' means of access and fixing the problems that encouraged them in the first place. Baits (feeder stations) with small quantities of disruptive insect hormones or other very slow acting toxins have become the preferred least-toxic management tool in most western countries. This has replaced the dusting of toxins direct into termite tunnels that had been widely done since the early 1930s (originating in Australia). The main dust toxicants have been the inorganic metallic poison arsenic trioxide, insect growth regulators (hormones) such as Triflumuron and, more recently, fipronil. Blowing dusts into termite workings is a highly skilled process. All these slow-acting poisons can be distributed by the workers for hours or weeks before any symptoms occur and are capable of destroying the entire colony. More modern variations include chlorfluazuron, Diflubenzuron, hexaflumuron, and Novaflumuron as bait toxicants and fipronil and imidacloprid as soil poisons. Soil poisons are the least-preferred method of control as this requires much larger doses of toxin and results in uncontrollable release to the environment.

Termites in the human diet

The alates are nutritious, having a good store of fat and protein, and are palatable in most species with a nutty flavour when cooked. They are easily gathered at the beginning of the rainy season in Central and Southern Africa when they swarm, as they are attracted to lights and can be gathered up when they land on nets put up around a lamp. The wings are shed and can be removed by a technique similar to winnowing. They are best gently roasted on a hot plate or lightly fried until slightly crisp; oil is not usually needed since their bodies are naturally high in oil. Traditionally they make a welcome treat at the beginning of the rainy season when livestock is lean, new crops have not yet produced food, and stored produce from the previous growing season is running low.

Ecology

Ecologically, termites are important in nutrient recycling, habitat creation, soil formation and quality and, particularly the winged reproductives, as food for countless predators. The role of termites in hollowing timbers and thus providing shelter and increased wood surface areas for other creatures is critical for the survival of a large number of timber-inhabiting species. Larger termite mounds play a role in providing a habitat for plants and animals, especially on plains in Africa that are seasonally inundated by a rainy season, providing a retreat above the water for smaller animals and birds, and a growing medium for woody shrubs with root systems that cannot withstand inundation for several weeks. In addition, scorpions, lizards, snakes, small mammals, and birds live in abandoned or weathered mounds, and aardvarks dig substantial caves and burrows in them, which then become homes for larger animals such as hyenas and mongooses.

As detrivores, termites clear away leaf and woody litter and so reduce the severity of the annual bush fires in African savannas, which are not as destructive as those in Australia and the USA.

Globally, termites are found roughly between 50 degrees North & South, with the greatest biomass in the tropics and the greatest diversity in tropical forests and Mediterranean shrublands. Termites are also considered to be a major source of atmospheric methane, one of the prime greenhouse gases. Termites have been common since at least the Cretaceous period. Termites also eat bone and other parts of carcasses, and their traces have been found on dinosaur bones from the middle Jurassic in China.

Plant defences against termites

Many plants have developed effective defences against termites, and in most ecosystems, there is an observable balance between the growth of plants and the feeding of termites. Defence is typically achieved by secreting anti-feedant chemicals (such as oils, resins, and lignins) into the woody cell walls. This reduces the ability of termites to efficiently digest the cellulose. Many of the strongly termite-resistant tree species have heartwood timber that is extremely dense (such as Eucalyptus camaldulensis) due to accretion of these resins. Over the years there has been considerable research into these natural defensive chemicals with scientists seeking to add them to timbers from susceptible trees. A commercial product, "Blockaid", has been developed in Australia and uses a range of plant extracts to create a paint-on nontoxic termite barrier for buildings. In 2005, a group of Australian scientists "discovered" (announced) a treatment based on an extract of a species of Eremophila that repels termites. Tests have shown that termites are strongly repelled by the toxic material to the extent that they will starve rather than cross treated samples. When kept in close proximity to the extract, they become disoriented and eventually die. Scientists hope to use this toxic compound commercially to prevent termite feeding.

Taxonomy, evolution and systematics

Recent DNA evidence has supported the nearly 120-year-old hypothesis, originally based on morphology, that termites are most closely related to the wood-eating cockroaches (genus Cryptocercus), to which the singular and very primitive Mastotermes darwiniensis shows some telltale similarities. Most recently, this has led some authors to propose that termites be reclassified as a single family, Termitidae, within the order Blattaria, which contains cockroaches . However, most researchers advocate the less drastic measure of retaining the termites as Isoptera but as a group subordinate to true roaches, preserving the internal classification of termites .

Evolutionary history

The oldest unambiguous termite fossils date to the early Cretaceous, although structures from the late Triassic have been interpreted as fossilized termite nests. Given the diversity of Cretaceous termites, it is likely that they had their origin at least sometime in the Jurassic.

It has long been accepted that termites are closely related to cockroaches and mantids, and they are classified in the same superorder (Dictyoptera), but new research has shed light on the details of termite evolution. There is now strong evidence suggesting that termites are really highly modified, social, wood-eating cockroaches. A study conducted by scientists has found that endosymbiotic bacteria from termites and a genus of cockroaches, Cryptocercus, share the strongest phylogenetical similarities out of all other cockroaches. Both termites and Cryptocercus also share similar morphological and social features -- most cockroaches do not show social characteristics, but Cryptocercus takes care of its young and exhibits other social behaviour. As mentioned above, the primitive Giant Northern Termite (Mastotermes darwiniensis) exhibits numerous cockroach-like characteristics that are not shared with other termites.

Systematics

As of 1996, about 2,800 termite species are recognized, classified in seven familieshttp://www.utoronto.ca/forest/termite/speclist.htm. These are arranged here in a phylogenetic sequence, from the most basal to the most advanced:

• Mastotermitidae (1 species, Mastotermes darwiniensis)

• Hodotermitidae (3 genera, 19 species)
  • Hodotermitinae

• Kalotermitidae (22 genera, 419 species)

• Termopsidae (5 genera, 20 species)
  • Termopsinae
  • Porotermitinae
  • Stolotermitinae

• Rhinotermitidae (14 genera, 343 species)
  • Coptotermitinae Holmgren
  • Heterotermitinae Froggatt
  • Prorhinoterminae Quennedey & Deligne, 1975
  • Psammotermitinae Holmgren
  • Rhinotermitinae Froggatt
  • Stylotermitinae Holmgren, K & N, 1917
  • Termitogetoninae Holmgren

• Serritermitidae (1 species, Serritermes serrifer)

• Termitidae (236 genera, 1958 species)
  • Macrotermitinae (14 genera, 349 species)
  • Nasutitermitinae (91 genera, 663 species)
  • Amitermitinae (17 genera, 295 species)
  • Apicotermitinae (43 genera, 202 species)
  • Cubitermitinae (28 genera, 161 species)
  • Termitinae (43 genera, 288 species)

The most current classification of termites is summarized by Engel & Krishna (2004).

Termites as a source of power

One of the US Department of Energy's most enduring goals is to replace fossil fuels with renewable sources of cleaner energy, such as hydrogen produced from plant biomass fermentation. Termites may help reach this goal through metagenomics.

Termites are capable of producing up to two litres of hydrogen from fermenting a single sheet of paper, making them one of the planet's most efficient bioreactors. Termites achieve this high degree of efficiency by exploiting the metabolic capabilities of about 200 different species of microbes that inhabit their hindguts.

Hydrogen is normally created by using electricity to remove hydrogen molecules from water or natural gas, but the electricity is most often generated using fossil fuels that emit carbon pollutants. The microbial community in the termite gut efficiently manufactures large quantities of clean hydrogen. By sequencing the termite's microbial community, it may be possible to get a better understanding of these biochemical pathways.

Termites eat wood but cannot extract energy from the complex lignocellulose polymers within it. These polymers are broken down into simple sugars by fermenting bacteria in the termite's gut and using enzymes that produce hydrogen as a byproduct. A second wave of bacteria uses the simple sugars and hydrogen to make the acetate the termite requires for energy. If it can be determined which enzymes are used to create hydrogen, and which genes produce them, this process could be scaled up with bioreactors to generate hydrogen from woody biomass, such as poplar, in commercial quantities.

Sceptics regard this as unlikely to be a carbon-neutral commercial process due to the energy inputs. For decades, researchers have sought to house termites on a commercial scale (like worm farms) to break down woody debris and paper but funding has been scarce and the problems of developing a continuous process that does not disrupt the termites' homeostasis have not been overcome.

• Original article
• JGI - Organization responsible for sequencing the termite.

See also

• Decompiculture
• Stigmergy

References

• Evolution of the Insects
• Earthlife
• Termite terms
• Cretaceous termites

Further reading

Termites: evolution, sociality, symbioses, ecology

External links

• University of Nebraska page on Termites
• A summary of termite control methods
• University of California advice on Drywood Termites
• Termite Pest Control Information - USA National Pesticide Information Center
• Catalogue of the termites of the World
• Pictures of termites
• Transitional Species in Insect Evolution
• Did the Termites Cause Laterites?
• Cretaceous Termites and Soil Phosphorus
• Beneficial Uses of Termites
• Texas A&M University Department of Entomology - Center for Urban & Structural Entomology
• Biomimicry used in Eastgate Building, Zimbabwe
• The Soul of the White Ant - Eugène N. Marais
• Urban Entomology Program University of Toronto
• Harvard University fact sheet on Eastern Subterranean Termites
• Isoptera: termites (CSIRO Australia Entomology).
• 'Termite guts can save the planet', says Nobel laureate
• USA Pest Management Association's fact sheet on termites
• Termite Control Information from a US chemical supply company
• The "Termite Institute" is a thinly disguised BASF corporation site promoting the biocide fipronil. Be careful.