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ANIMALS
This article is from:
http://en.wikipedia.org/wiki/Termite

All text is available under the terms of the GNU Free Documentation License: http://en.wikipedia.org/wiki/Wikipedia:Text_of_the_GNU_Free_Documentation_License 

Termite

From Wikipedia, the free encyclopedia

 

Termites, sometimes known as white ants, are a group of eusocial insects usually classified at the taxonomic rank of order, Isoptera. Termites feed on dead plant material, generally in the form of wood, leaf litter or soil, and about 10% of the 4,000 odd species (about 2,600 taxonomically known) are economically important as pests that can cause serious structural damage to buildings, crops or plantation forests. Termites are significant detrivores, particularly in the subtropical and tropical regions, and their recycling of wood and other plant matter is of considerable ecological importance.

Appearance and morphology

Termites only superficially resemble ants; their "white ant" name arises from their similar size and social habits. Compared with ants, they are softer, whiter, shorter-legged, fatter and generally much slower moving. Most importantly, they are not at all closely related to ants. Ants, along with bees and wasps, belong to the Order Hymenoptera whereas termites are much closer to cockroaches and mantids and all three are sometimes clumped into a super order called Dictyoptera.

Termites have biting mouthparts and their soft bodies are small, rarely over 1 cm in length. They typically inhabit dark nests and tunnels, only venturing out when the winged alates emerge to leave their parent colony, when constructing shelter or, in the case of grass- and leaf-litter-feeders, when harvesting their food. The bodies of flying individuals are darker, while termites which remain in the nest are generally whitish with only their heads being lightly pigmented. The deciduous wings of termites are long and slender, in two pairs that are similarly sized and shaped. The name of the termites' order is derived from their having equal wings, iso-=equal and pteron=wing. The wings are quickly shed after flight with a simple body flick when the swarming termites find a new nest site, pair up and dig in. The remnant of a wing is a distinct triangular scale.

Social structure and behaviour

As social 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 sexes, sometimes containing several egg-laying queens.

Reproductives

Termite alates in the spring.
Enlarge
Termite alates in the spring.

A female that has flown, mated and is producing eggs, is termed a "Queen". Similarly, a male that has flown, mated and remains in proximity to a queen, is termed a "King". These anthropomorphic 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 headed by a monogamous royal pair is at least sometimes incorrect. Multiple pairs of reproductives within a colony are not uncommon, but for the families Rhinotermitidae and Termitidae,at least, 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 can lay several thousand eggs a day. In physogastric species, the queen adds an extra set of ovaries with each moult, resulting in a greatly distended abdomen and increased fecundity. The distended abdomen increases her size in some species to as much as 10 centimetres, hundreds of times the original size, effectively immobilizing her. In times where these huge queens must be moved to a new chamber it requires a group effort to move her and hundreds of workers are required to push her. The queen is widely believed to be a primary source of pheromones useful in colony integration. As a reward for attending workers a juice is secreted from the queen's posterior for the workers to drink. The king remains only slightly bigger than an average termite and continues to mate with the queen for life. This is very different from ant societies, which have colonies with only a queen which mates once with the male(s) and stores his gametes for life. Males in ant colonies die immediately after mating, unlike termite male alates, which become kings and live with the queen. The 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). Immature alates still going through incomplete metamorphosis form a sub-caste in certain species of termites, functioning as functional workers ('pseudergates') and also as potential supplementary reproductives. Supplementaries have the ability to replace a dead primary reproductive and in at least some species several are recruited once a primary queen is lost.

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. This is achieved in one of two ways. In all termite families except the Termitidae, there are flagellates (Protista) 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 as it frees the parents from feeding the young, allowing for the group to grow much larger and ensuring that the 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. A few species even practice agriculture, collecting plant matter to feed fungal gardens, upon which the colony then feeds.

Soldiers

Termites with some nasutes
Enlarge
Termites with some nasutes

The soldier caste has anatomical and behavioural specializations, primarily against ant attack. Many 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 classified using the characteristics of the soldiers' heads, mandibles or nasus due to distinct differences with each species. Among the drywood termites, a soldier's enlarged (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 have at least partly functional eyes. It's generally accepted that the specialization of the soldier caste is principally a defense against predation by ants. The wide range of jaw types and phragmotic heads provides methods to 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, defense requires special formations where soldiers form a phalanx-like formation around the breach blindly biting at intruders or shooting toxic glue from the nasus. This formation involves self sacrifice because once the breach is repaired during fighting by the workers no return is provided 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. Some species of termite have been known to have small groups of extremely large soldiers (3*normal size). Though their purpose is unknown speculation indicates that they are an elite class that defends only the inner tunnels of the mound. This is the commonly accepted belief because their size would be of great use in the large interior tunnels. Even when provoked, these large soldier termites will not defend themselves but merely travel deeper into the mound.

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 structures.

All termites eat cellulose in its various forms as plant fiber. Cellulose is a rich energy source (think of 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, absorbing 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 with bacteria dominant. 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 cockroachs, like those of the genus Cryptocercus.

Some species of termite practise fungiculture - they maintain a 'garden' of specialized fungi of genus Termitomyces, which are nourished by the excrement of the insects. When the fungi in turn are eaten, their spores pass undamaged through the intestines of the termites, to complete the cycle by germinating in the fresh faecal pellets. [1][2]

Mounds

In some regions, notably arid tropical savannas, termites construct extremely large and elaborate mounds which house their colonies. These mounds can have very 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. Some mounds can reach heights of 6 metres, but most species build mounds of less than two metres' height. 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.

Human interaction

The result of an infestation is severe wood damage.
Enlarge
The result of an infestation is severe wood damage.

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 just to wood, also damaging 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 gallery constuction

Termites try to 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. Most termite barrier systems used for buildings aim to prevent concealed termite access, thus forcing them out into the open where they must form clearly visible shelter tubes to gain entry.

Avoiding termite troubles

Precautions:

  • Avoiding 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 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 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 be clearly visible both to the building occupants and a range of predators. Regular inspection by a competent person isthe best defence.
  • Timber treatment.
  • Use of timber that is naturally resistant to termites such as Canarium australianum known as the Turpentine Tree, Callitris glacophylla, the White Cypress or one of the Sequoias. Note that there is no tree where species every individual tree yields timber that is 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, removing their means of access and destroying the colony with insecticides are usually effective means of stopping further damage. Feeder stations (baits) 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 which had been widely done since the early 1930's (originating in Australia). The main dust toxicant have been the inorganic metallic poison arsenic trioxide and, more recently, the insect growth regulator, Triflumuron. These slow-acting poisons can be distributed by the workers for considerable periods (hours to weeks) before any symptoms occur and are capable of destroying the entire colony. More modern variations include chlorfluazuron and hexaflumuron as bait toxicants and fipronil and imidacloprid was soil poisons. Soil poisons are the least-preferred method of control.

Plant defences against termites

Many plants have developed effective defences against termites and in most ecosystems there is an obervable balance between the growth of plants and the feeding of termites. Typically defence is achieved by secreting into the woody cell walls, antifeedant chemicals (such as oils, resins and lignins) which reduce 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, "BlockaidTM", has been developed in Australia which uses a range of plant extracts to create a paint-on non-toxic 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 is repellent termites [3]. Tests have shown that termites are strongly repelled by the toxic material to the extent that they will starve rather than cross treated samples and when kept in close proximity to the extract become disoriented and eventually die. These scientists hope to use this toxic compound commercially to prevent termite feeding.

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. 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.

Relationships and 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 [4]. 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. [5] 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 behavior. Additionally, the primitive termite Mastotermes darwiniensis exhibits numerous cockroach-like characteristics that are not shared with other termites.

References

  • Earthlife
  • Termite terms
  • Cretaceous termites
  1. ^ The evolution of fungus-growing termites and their mutualistic fungal symbionts by Duur K. Aanen, Paul Eggleton, Corinne Rouland-Lefèvre, Tobias Guldberg-Frøslev, Søren Rosendahl & Jacobus J. Boomsma
  2. ^ Fungus-farming insects: Multiple origins and diverse evolutionary histories by Ulrich G. Mueller & Nicole Gerardo
  3. ^ Plant extract stops termites dead
  4. ^ Gay and Calaby 1970 Termites of the Australian region. in; Krishna K Weesner FM eds. Biology of Termites, Vol. II Academic Press NY p401
  5. ^ Evidence for Cocladogenesis Between Diverse Dictyopteran Lineages and Their Intracellular Endosymbionts

External links

  • University of Nebraska page on Termites
  • A summary of termite control methods
  • University of California advice on Drywood Termites
  • African Pygmies - Termites gathering
  • 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
  • Termite Control - Alternative Measures in USA. Warning: confuses toxic barriers with physical barriers.
  • Isoptera: termites (CSIRO Australia Entomology).
Retrieved from "http://en.wikipedia.org/wiki/Termite"
 


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