|
|
|
|
Termite
|
| |
|
| |
The termites 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 which are all placed in the separate order Hymenoptera. 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.
Discussion
Ask a question about 'Termite' Start a new discussion about 'Termite' Answer questions from other users |
Encyclopedia
The termites 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 which are all placed in the separate order Hymenoptera. 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.
Termites are sometimes called "white ants", though they are unrelated to true ants.
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 molt, 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 km/h, 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. 3/8"-5/8", yellow/brownish with one wing. 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. Some termite species do not have a true worker caste, instead relying on nymphs that perform the same work without moulting into a separate caste.
Termite workers usually have undeveloped eyes and are blind. Despite this limitation, they are able to create elaborate nests and tunnel systems (see 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 (The South American species of which are under review and are likely to deserve a separate taxon) 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.
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 leading to the death of all defenders. Another form of self-sacrifice is performed by South-East Asian tar-baby termites (Globitermes sulphureus). The soldiers of this species commit suicide by autothysis - rupturing a large gland just beneath the surface of their cuticle. The thick yellow fluid in the gland becomes very sticky on contact with the air, entangling ants or other insects who are trying to invade the nest.
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.
Arthur French worked in Uganda (1955-1969) on the subject of fungi and termites. There was some scientific literature, in French, by Belgians, but it dealt inadequately with the relationship between mushrooms and termites, and the best edible varieties were “termite mushrooms”. He did some work on them, with the help of the elderly Baganda women who gathered them, and published the results. For a year or two he was a world expert on termite mushrooms.
Nests
Termite workers build and maintain nests to house their colony. These are elaborate structures made using a combination of soil, mud, chewed wood/cellulose, saliva, and faeces. A nest has many functions such as to provide a protected living space and to collect water through condensation. There are reproductive chambers and some species even maintain fungal gardens which are fed on collected plant matter, providing a nutritious mycelium on which the colony then feeds (see "Diet", above). Nests are punctuated by a maze of tunnel-like galleries that effectively provide air conditioning and control the CO2/O2 balance, as well as allow the termites to move through the nest.
Nests are commonly built underground, in large pieces of timber, inside fallen trees or atop living trees. Some species build nests above-ground, and they can develop into mounds.
Mounds
Mounds (also known as "termitaria") occur when an above-ground nest grows beyond its initially concealing surface. They are commonly called "anthills" in Africa and Australia, despite the technical incorrectness of that name.
In tropical savannas the mounds may be very large, with an extreme of 9 metres (30 ft) high in the case of large conical mounds constructed by some Macrotermes species in well-wooded areas in Africa,. Two to three metres, however, would be typical for the largest mounds in most savannas. The shape ranges from somewhat amorphous domes or cones usually covered in grass and/or woody shrubs, to sculptured hard earth mounds, or a mixture of the two. Despite the irregular mound shapes, the different species in an area can usually be identified by simply looking at the mounds.
The sculptured mounds sometimes have elaborate and distinctive forms, such as those of the compass termite (Amitermes meridionalis & A. laurensis) which build tall wedge-shaped mounds with the long axis oriented approximately north-south. This orientation has been experimentally shown to help in thermoregulation.
The column of hot air rising in the above ground mounds helps drive air circulation currents inside the subterranean network. The structure of these mounds can be quite complex. The temperature control is essential for those species that cultivate fungal gardens and even for those that don't, much effort and energy is spent maintaining the brood within a narrow temperature range, often only plus or minus one degree C over a day.
In some parts of the African savanna, a high density of above-ground mounds dominates the landscape. For instance, in some parts of the Busanga Plain area of Zambia, small mounds of about 1 m diameter with a density of about 100 per hectare can be seen on grassland between larger tree- and bush-covered mounds about 25 m in diameter with a density around 1 per hectare, and both show up well on high-resolution satellite images taken in the wet season..
Shelter tunnels
Termites are very weak and fragile insects. They can be easily overpowered by ants and other predators when exposed. To avoid these perils termites cover their tracks with tubing made of faeces, plant matter, and soil. Thus the termites can remain hidden and wall out unfavourable environmental conditions. Sometimes these shelter tubes will extend for many metres, such as up the outside of a tree reaching from the soil to dead branches.
To a subterranean termite any breach of their tunnels or nest is a cause for alarm. When the Formosan subterranean termite (Coptotermes formosanus) and the Eastern subterranean termite (Reticulitermes flavipes) detect a potential breach, the soldiers will usually bang their heads apparently to attract other soldiers for defense and recruit additional workers to repair any breach.
Human interaction
Timber damage
Due to their wood-eating habits, many termite species can do great damage to unprotected 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.
Humans have moved many wood-eating species between continents, but have also caused drastic population decline in others through habitat loss and pesticide application.
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 Syncarpia glomulifera (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, a phenyl-pyrazole. 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
In many cultures, termites are used for food (particularly the alates). 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 West, 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.
Agriculture
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.
Building materials
Termite nests are used widely in construction (the dirt is often dust-free) and as a soil amendment.
Termites as a source of power
The US Department of Energy is researching ways to replace fossil fuels with renewable sources of cleaner energy, and termites are considered a possible way to reach this goal through metagenomics.
Termites may produce up to two litres of hydrogen from digesting 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. The microbial community in the termite gut efficiently manufactures large quantities of hydrogen; the complex lignocellulose polymers within wood are broken down into simple sugars by fermenting bacteria in the termite's gut, 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. By sequencing the termite's microbial community, the DOE hopes to get a better understanding of these biochemical pathways. If it can be determined which enzymes are used to create hydrogen, and which genes produce them, this process could potentially be scaled up with bioreactors to generate hydrogen from woody biomass, such as poplar, in commercial quantities.
Sceptics regard this as unlikely to become a carbon-neutral commercial process due to the energy inputs required to maintain the system. 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.
Ground Water divining in Ancient India
Varaha Mihira (505 C.E- 587 C.E), the famous astronomer, mathematician and astrologer of Ancient India, in his treatise "Brihat Samhita" also spelt "Vrahat Sanhita" refers to Dakargala (Sanskrit word meaning 'Science of Underground Water exploration'), wherein the role of termite knolls, as an indicator of underground water has been elaborately explained.
In Verse.S.54.9 of the Samhita, it is stated that sweet ground water would be found near a termite mound located east of a Jambu tree (botanical names - Eugenia Jambus,Engenia Jambolana), at a specific distance and a specific depth of 15 ft to the south of the tree.
The above verse has been justified with an explanation:
Without exception the water requirements of the insects are generally very high, and they need to protect themselves against fatal desiccation by living and working within the climatically sealed environment of their nest or within earth covered galleries. According to present level of research, the atmosphere within the nest has to be maintained practically saturation moisture level ( 99-100 % humidity). It is a matter of common observation that whenever a termite nest or runway, is damaged, the insects immediately rush to the breach and repairs it with wet soil brought up from within the nest. From an over-all consideration of the evidence it seems to be safe to conclude that, while normally the insects use every readily available source of water close to the ground surface, under condition of severe climatic stress, they can and they probably do descend to the water table, no matter how deep it may be. Hence, a well-developed, active, permanent colony of mound-building termites can be taken as an indication of underground springs in proximity.
Two examples mentioned in the referred publication are, a) termiteries seen in the Katanga province (Congo Kinhasa) right up to the hill slopes where springs emerge, b) in the dry jungle uplands of coastal zone of Karanataka state (old Mysore state) and c) in the Deccan Plateau area.
It is also asserted in the verse Vr.S.54.85 that among a group of termite mounds, a water vein is sure to be found below the taller of the mounds. Verse 52 mentions that in a desert region, if a group of five termite mounds are found, and if the middle one is in white colour, then water will be found within a depth of Fifty five Purushas (in Sanskrit one Purusha is equivalent to 7.5 ft) or 412.5 ft.
As a common observation of a combination of different symptoms, termite mounds are said to be found close to trees, and ancient Hindus exploited this knowledge in the exploration of underground springs..
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 families. 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)
- 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)
- Apicotermitinae (42 genera, 208 species)
- Foraminitermitinae (2 genera, 9 species)
- Macrotermitinae (13 genera, 362 species)
- Nasutitermitinae (80 genera, 576 species)
- Sphaerotermitinae (1 genera, 1 species)
- Syntermitinae (13 genera, 99 species)
- Termitinae (90 genera, 760 species)
The most current classification of termites is summarized by Engel & Krishna (2004).
See also
Further reading
External links
On the UF / IFAS Featured Creatures Web site
|
| |
|
|
