Cellulose was discovered in 1838 by the French chemist Anselme Payen, who isolated it from plant matter and determined its chemical formula. Cellulose was used to produce the first successful thermoplastic polymer, celluloid, by Hyatt Manufacturing Company in 1870. Production of rayon ("artificial silk") from cellulose began in the 1890s and cellophane was invented in 1912. Hermann Staudinger
determined the polymer structure of cellulose in 1920. The compound was
first chemically synthesized (without the use of any biologically
derived enzymes) in 1992, by Kobayashi and Shoda.
Cellulose has no taste, is odorless, is hydrophilic with the contact angle of 20–30 degrees, is insoluble in water and most organic solvents, is chiral and is biodegradable. It was shown to melt at 467 °C in pulse tests made by Dauenhauer et al. (2016). It can be broken down chemically into its glucose units by treating it with concentrated mineral acids at high temperature.
Cellulose is derived from D-glucose units, which condense through β(1→4)-glycosidic bonds. This linkage motif contrasts with that for α(1→4)-glycosidic bonds present in starch and glycogen.
Cellulose is a straight chain polymer. Unlike starch, no coiling or
branching occurs and the molecule adopts an extended and rather stiff
rod-like conformation, aided by the equatorial conformation of the
glucose residues. The multiple hydroxyl groups on the glucose from one chain form hydrogen bonds with oxygen atoms on the same or on a neighbor chain, holding the chains firmly together side-by-side and forming microfibrils with high tensile strength. This confers tensile strength in cell walls where cellulose microfibrils are meshed into a polysaccharide matrix.
The high tensile strength of plant stems and of the tree wood also
arises from the arrangement of cellulose fibers intimately distributed
into the lignin
matrix. The mechanical role of cellulose fibers in the wood matrix
responsible for its strong structural resistance, can somewhat be
compared to that of the reinforcement bars in concrete, lignin playing here the role of the hardened cement paste
acting as the "glue" in between the cellulose fibers. Mechanical
properties of cellulose in primary plant cell wall are correlated with
growth and expansion of plant cells. Live fluorescence microscopy techniques are promising in investigation of the role of cellulose in growing plant cells.
A triple strand of cellulose showing the hydrogen bonds (cyan lines) between glucose strands
Cotton fibres represent the purest natural form of cellulose, containing more than 90% of this polysaccharide.
Compared to starch, cellulose is also much more crystalline. Whereas starch undergoes a crystalline to amorphous transition when heated beyond 60–70 °C in water (as in cooking), cellulose requires a temperature of 320 °C and pressure of 25 MPa to become amorphous in water.
Several types of cellulose are known. These forms are
distinguished according to the location of hydrogen bonds between and
within strands. Natural cellulose is cellulose I, with structures Iα and Iβ. Cellulose produced by bacteria and algae is enriched in Iα while cellulose of higher plants consists mainly of Iβ. Cellulose in regenerated cellulose fibers is cellulose II. The conversion of cellulose I to cellulose II is irreversible, suggesting that cellulose I is metastable
and cellulose II is stable. With various chemical treatments it is
possible to produce the structures cellulose III and cellulose IV.
Many properties of cellulose depend on its chain length or degree of polymerization,
the number of glucose units that make up one polymer molecule.
Cellulose from wood pulp has typical chain lengths between 300 and 1700
units; cotton and other plant fibers as well as bacterial cellulose have
chain lengths ranging from 800 to 10,000 units. Molecules with very small chain length resulting from the breakdown of cellulose are known as cellodextrins; in contrast to long-chain cellulose, cellodextrins are typically soluble in water and organic solvents.
The chemical formula of cellulose is (C6H10O5)n where n is the degree of polymerization and represents the number of glucose groups.
Plant-derived cellulose is usually found in a mixture with hemicellulose, lignin, pectin and other substances, while bacterial cellulose is quite pure, has a much higher water content and higher tensile strength due to higher chain lengths.
Cellulose consists of fibrils with crystalline and amorphous regions. These cellulose fibrils may be individualized by mechanical treatment of cellulose pulp, often assisted by chemical oxidation or enzymatic treatment, yielding semi-flexible cellulose nanofibrils generally 200 nm to 1 μm in length depending on the treatment intensity. Cellulose pulp may also be treated with strong acid to hydrolyze the amorphous fibril regions, thereby producing short rigid cellulose nanocrystals a few 100 nm in length. These nanocelluloses are of high technological interest due to their self-assembly into cholesteric liquid crystals, production of hydrogels or aerogels, use in nanocomposites with superior thermal and mechanical properties, and use as Pickering stabilizers for emulsions.
Processing
Biosynthesis
In plants cellulose is synthesized at the plasma membrane by rosette terminal complexes (RTCs). The RTCs are hexameric protein structures, approximately 25 nm in diameter, that contain the cellulose synthase enzymes that synthesise the individual cellulose chains. Each RTC floats in the cell's plasma membrane and "spins" a microfibril into the cell wall.
RTCs contain at least three different cellulose synthases, encoded by CesA (Ces is short for "cellulose synthase") genes, in an unknown stoichiometry. Separate sets of CesA
genes are involved in primary and secondary cell wall biosynthesis.
There are known to be about seven subfamilies in the plant CesA superfamily, some of which include the more cryptic, tentatively-named Csl (cellulose synthase-like) enzymes. These cellulose syntheses use UDP-glucose to form the β(1→4)-linked cellulose.
Bacterial cellulose is produced using the same family of proteins, although the gene is called BcsA for "bacterial cellulose synthase" or CelA for "cellulose" in many instances. In fact, plants acquired CesA from the endosymbiosis event that produced the chloroplast. All cellulose synthases known belongs to glucosyltransferase family 2 (GT2).
Cellulose synthesis requires chain initiation and elongation, and the two processes are separate.
Cellulose synthase (CesA) initiates cellulose polymerization using a steroid primer, sitosterol-beta-glucoside, and UDP-glucose. It then utilizes UDP-D-glucose precursors to elongate the growing cellulose chain. A cellulase may function to cleave the primer from the mature chain.
Cellulose is also synthesised by tunicate animals, particularly in the tests of ascidians (where the cellulose was historically termed "tunicine" (tunicin)).
Breakdown (cellulolysis)
Cellulolysis is the process of breaking down cellulose into smaller polysaccharides called cellodextrins or completely into glucose units; this is a hydrolysis
reaction. Because cellulose molecules bind strongly to each other,
cellulolysis is relatively difficult compared to the breakdown of other polysaccharides. However, this process can be significantly intensified in a proper solvent, e.g. in an ionic liquid.
At temperatures above 350 °C, cellulose undergoes thermolysis (also called 'pyrolysis'), decomposing into solid char, vapors, aerosols, and gases such as carbon dioxide. Maximum yield of vapors which condense to a liquid called bio-oil is obtained at 500 °C.
Semi-crystalline cellulose polymers react at pyrolysis
temperatures (350–600 °C) in a few seconds; this transformation has been
shown to occur via a solid-to-liquid-to-vapor transition, with the
liquid (called intermediate liquid cellulose or molten cellulose) existing for only a fraction of a second. Glycosidic bond cleavage produces short cellulose chains of two-to-seven monomers comprising the melt. Vapor bubbling of intermediate liquid cellulose produces aerosols, which consist of short chain anhydro-oligomers derived from the melt.
Continuing decomposition of molten cellulose produces volatile compounds including levoglucosan, furans, pyrans, light oxygenates and gases via primary reactions. Within thick cellulose samples, volatile compounds such as levoglucosan undergo 'secondary reactions' to volatile products including pyrans and light oxygenates such as glycolaldehyde.
Hemicelluloses are polysaccharides related to cellulose that comprise about 20% of the biomass of land plants. In contrast to cellulose, hemicelluloses are derived from several sugars in addition to glucose, especially xylose but also including mannose, galactose, rhamnose, and arabinose. Hemicelluloses consist of shorter chains – between 500 and 3000 sugar units. Furthermore, hemicelluloses are branched, whereas cellulose is unbranched.
Regenerated cellulose
Cellulose
is soluble in several kinds of media, several of which are the basis of
commercial technologies. These dissolution process is reversible and
are used in the production of regenerated celluloses (such as viscose and cellophane) from dissolving pulp.
The most important solubilizing agent is carbon disulfide in the presence of alkali. Other agents include Schweizer's reagent, N-methylmorpholine N-oxide, and lithium chloride in dimethylacetamide.
In general these agents modify the cellulose, rendering it soluble.
The agents are then removed concomitant with the formation of fibers. Cellulose is also soluble in many kinds of ionic liquids.
The history of regenerated cellulose is often cited as beginning with George Audemars, who first manufactured regenerated nitrocellulose fibers in 1855. Although these fibers were soft and strong -resembling silk- they had the drawback of being highly flammable. Hilaire de Chardonnet perfected production of nitrocellulose fibers, but manufacturing of these fibers by his process was relatively uneconomical. In 1890, L.H. Despeissis invented the cuprammonium process – which uses a cuprammonium solution to solubilize cellulose – a method still used today for production of artificial silk.
In 1891, it was discovered that treatment of cellulose with alkali and
carbon disulfide generated a soluble cellulose derivative known as viscose.
This process, patented by the founders of the Viscose Development
Company, is the most widely used method for manufacturing regenerated
cellulose products. Courtaulds purchased the patents for this process in 1904, leading to significant growth of viscose fiber production.
By 1931, expiration of patents for the viscose process led to its
adoption worldwide. Global production of regenerated cellulose fiber
peaked in 1973 at 3,856,000 tons.
Regenerated cellulose can be used to manufacture a wide variety
of products. While the first application of regenerated cellulose was as
a clothing textile, this class of materials is also used in the production of disposable medical devices as well as fabrication of artificial membranes.
Cellulose esters and ethers
The hydroxyl groups (−OH) of cellulose can be partially or fully reacted with various reagents to afford derivatives with useful properties like mainly cellulose esters and cellulose ethers (−OR). In principle, although not always in current industrial practice, cellulosic polymers are renewable resources.
The cellulose acetate and cellulose triacetate are film- and
fiber-forming materials that find a variety of uses. The nitrocellulose
was initially used as an explosive and was an early film forming
material. With camphor, nitrocellulose gives celluloid.
Cellulose for industrial use is mainly obtained from wood pulp and from cotton.
Paper products: Cellulose is the major constituent of paper, paperboard, and card stock. Electrical insulation paper: Cellulose is used in diverse forms as insulation in transformers, cables, and other electrical equipment.
Fibers: Cellulose is the main ingredient of textiles. Cotton and synthetics (nylons) each have about 40% market by volume. Other plant fibers (jute, sisal, hemp) represent about 20% of the market. Rayon, cellophane and other "regenerated cellulose fibers" are a small portion (5%).
Consumables: Microcrystalline cellulose (E460i) and powdered cellulose (E460ii) are used as inactive fillers in drug tablets
and a wide range of soluble cellulose derivatives, E numbers E461 to
E469, are used as emulsifiers, thickeners and stabilizers in processed
foods. Cellulose powder is, for example, used in processed cheese to
prevent caking inside the package. Cellulose occurs naturally in some
foods and is an additive in manufactured foods, contributing an
indigestible component used for texture and bulk, potentially aiding in defecation.
Building material: Hydroxyl bonding of cellulose in water produces a
sprayable, moldable material as an alternative to the use of plastics
and resins. The recyclable material can be made water- and
fire-resistant. It provides sufficient strength for use as a building
material. Cellulose insulation made from recycled paper is becoming popular as an environmentally preferable material for building insulation. It can be treated with boric acid as a fire retardant.
The major combustible component of non-food energy crops is cellulose, with lignin second. Non-food energy crops produce more usable energy than edible energy crops (which have a large starch component), but still compete with food crops for agricultural land and water resources. Typical non-food energy crops include industrial hemp, switchgrass, Miscanthus, Salix (willow), and Populus (poplar) species. A strain of Clostridium bacteria found in zebra dung, can convert nearly any form of cellulose into butanol fuel.
Termites are eusocialinsects that are classified at the taxonomic rank of infraorderIsoptera, or alternatively as epifamily Termitoidae, within the order Blattodea (along with cockroaches). Termites were once classified in a separate order from cockroaches, but recent phylogenetic studies indicate that they evolved from cockroaches, as they are deeply nested within the group, and the sister group to wood eating cockroaches of the genus Cryptocercus. Previous estimates suggested the divergence took place during the Jurassic or Triassic. More recent estimates suggest they have an origin during the Late Jurassic, with the first fossil records in the Early Cretaceous. About 3,106 species are currently described, with a few hundred more left to be described. Although these insects are often called "white ants", they are not ants, and are not closely related to ants.
Like ants and some bees and wasps from the separate order Hymenoptera,
termites divide as "workers" and "soldiers" that are usually sterile.
All colonies have fertile males called "kings" and one or more fertile
females called "queens". Termites mostly feed on dead plant material and cellulose, generally in the form of wood, leaf litter, soil, or animal dung. Termites are major detritivores, particularly in the subtropical and tropical regions, and their recycling of wood and plant matter is of considerable ecological importance.
Termites are among the most successful groups of insects on Earth, colonising most landmasses except Antarctica.
Their colonies range in size from a few hundred individuals to enormous
societies with several million individuals. Termite queens have the
longest known lifespan of any insect, with some queens reportedly living
up to 30 to 50 years. Unlike ants, which undergo a complete
metamorphosis, each individual termite goes through an incomplete metamorphosis that proceeds through egg, nymph, and adult stages. Colonies are described as superorganisms because the termites form part of a self-regulating entity: the colony itself.
Termites are a delicacy in the diet of some human cultures and
are used in many traditional medicines. Several hundred species are
economically significant as pests that can cause serious damage to
buildings, crops, or plantation forests. Some species, such as the West Indian drywood termite (Cryptotermes brevis), are regarded as invasive species.
Etymology
The infraorder name Isoptera is derived from the Greek wordsiso (equal) and ptera (winged), which refers to the nearly equal size of the fore and hind wings. "Termite" derives from the Latin and Late Latin word termes ("woodworm, white ant"), altered by the influence of Latin terere ("to rub, wear, erode") from the earlier word tarmes. A termite nest is also known as a termitary or termitarium (plural termitaria or termitariums). In earlier English, termites were known as "wood ants" or "white ants". The modern term was first used in 1781.
Taxonomy and evolution
The external appearance of the giant northern termite Mastotermes darwiniensis is suggestive of the close relationship between termites and cockroaches.
Termites were formerly placed in the order Isoptera. As early as 1934
suggestions were made that they were closely related to wood-eating
cockroaches (genus Cryptocercus, the woodroach) based on the similarity of their symbiotic gut flagellates.
In the 1960s additional evidence supporting that hypothesis emerged
when F. A. McKittrick noted similar morphological characteristics
between some termites and Cryptocercusnymphs. In 2008 DNA analysis from 16S rRNA sequences supported the position of termites being nested within the evolutionary tree containing the order Blattodea, which included the cockroaches. The cockroach genus Cryptocercus shares the strongest phylogenetical similarity with termites and is considered to be a sister-group to termites. Termites and Cryptocercus share similar morphological and social features: for example, most cockroaches do not exhibit social characteristics, but Cryptocercus takes care of its young and exhibits other social behaviour such as trophallaxis and allogrooming. Termites are thought to be the descendants of the genus Cryptocercus. Some researchers have suggested a more conservative measure of retaining the termites as the Termitoidae, an epifamily within the cockroach order, which preserves the classification of termites at family level and below. Termites have long been accepted to be closely related to cockroaches and mantids, and they are classified in the same superorder (Dictyoptera).The oldest unambiguous termite fossils date to the early Cretaceous,
but given the diversity of Cretaceous termites and early fossil records
showing mutualism between microorganisms and these insects, they
possibly originated earlier in the Jurassic or Triassic.Possible evidence of a Jurassic origin is the assumption that the extinct Fruitafossor consumed termites, judging from its morphological similarity to modern termite-eating mammals. The oldest termite nest discovered is believed to be from the Upper Cretaceous in West Texas, where the oldest known faecal pellets were also discovered. Claims that termites emerged earlier have faced controversy. For example, F. M. Weesner indicated that the Mastotermitidae termites may go back to the Late Permian, 251 million years ago, and fossil wings that have a close resemblance to the wings of Mastotermes of the Mastotermitidae, the most primitive living termite, have been discovered in the Permian layers in Kansas. It is even possible that the first termites emerged during the Carboniferous. The folded wings of the fossil wood roach Pycnoblattina, arranged in a convex pattern between segments 1a and 2a, resemble those seen in Mastotermes, the only living insect with the same pattern. Krishna et al.,
though, consider that all of the Paleozoic and Triassic insects
tentatively classified as termites are in fact unrelated to termites and
should be excluded from the Isoptera. Other studies suggest that the origin of termites is more recent, having diverged from Cryptocercus sometime during the Early Cretaceous.
Macro image of a worker.
The primitive giant northern termite (Mastotermes darwiniensis)
exhibits numerous cockroach-like characteristics that are not shared
with other termites, such as laying its eggs in rafts and having anal
lobes on the wings. It has been proposed that the Isoptera and Cryptocercidae be grouped in the clade "Xylophagodea". Termites are sometimes called "white ants" but the only resemblance to the ants is due to their sociality which is due to convergent evolutionwith termites being the first social insects to evolve a caste system more than 100 million years ago.
Termite genomes are generally relatively large compared to those of
other insects; the first fully sequenced termite genome, of Zootermopsis nevadensis, which was published in the journal Nature Communications, consists of roughly 500Mb, while two subsequently published genomes, Macrotermes natalensis and Cryptotermes secundus, are considerably larger at around 1.3Gb.
As of 2013, about 3,106 living and fossil termite species
are recognised, classified in 12 families; reproductive and/or soldier
castes are usually required for identification. The infraorder Isoptera
is divided into the following clade and family groups, showing the
subfamilies in their respective classification:
The Neoisoptera, literally meaning "newer termites" (in an evolutionary sense), are a recently coined nanorder
that include families commonly referred-to as "higher termites",
although some authorities only apply this term to the largest family Termitidae.
The latter characteristically do not have Pseudergate nymphs (many
"lower termite" worker nymphs have the capacity to develop into
reproductive castes: see below). Cellulose digestion in "higher termites" has co-evolved with eukaryotic gut microbiota and many genera have symbiotic relationships with fungi such as Termitomyces; in contrast, "lower termites" typically have flagellates and prokaryotes in their hindguts. Five families are now included here:
Termites are found on all continents except Antarctica. The diversity of termite species is low in North America and Europe (10 species known in Europe and 50 in North America), but is high in South America, where over 400 species are known. Of the 3,000 termite species currently classified, 1,000 are found in Africa,
where mounds are extremely abundant in certain regions. Approximately
1.1 million active termite mounds can be found in the northern Kruger National Park alone. In Asia, there are 435 species of termites, which are mainly distributed in China. Within China, termite species are restricted to mild tropical and subtropical habitats south of the Yangtze River. In Australia, all ecological groups of termites (dampwood, drywood, subterranean) are endemic to the country, with over 360 classified species. Because termites are highly social and abundant, they represent a disproportionate amount of the world's insect biomass. Termites and ants comprise about 1% of insect species, but represent more than 50% of insect biomass.
Due to their soft cuticles, termites do not inhabit cool or cold habitats.
There are three ecological groups of termites: dampwood, drywood and
subterranean. Dampwood termites are found only in coniferous forests,
and drywood termites are found in hardwood forests; subterranean
termites live in widely diverse areas. One species in the drywood group is the West Indian drywood termite (Cryptotermes brevis), which is an invasive species in Australia.
Termites are usually small, measuring between 4 to 15 millimetres (0.16 to 0.59 in) in length. The largest of all extant termites are the queens of the species Macrotermes bellicosus, measuring up to over 10 centimetres (4 in) in length. Another giant termite, the extinct Gyatermes styriensis, flourished in Austria during the Miocene and had a wingspan of 76 millimetres (3.0 in) and a body length of 25 millimetres (0.98 in).
Most worker and soldier termites are completely blind as they do not have a pair of eyes. However, some species, such as Hodotermes mossambicus, have compound eyes which they use for orientation and to distinguish sunlight from moonlight. The alates (winged males and females) have eyes along with lateral ocelli. Lateral ocelli, however, are not found in all termites, absent in the families Hodotermitidae, Termopsidae, and Archotermopsidae. Like other insects, termites have a small tongue-shaped labrum and a clypeus;
the clypeus is divided into a postclypeus and anteclypeus. Termite
antennae have a number of functions such as the sensing of touch, taste,
odours (including pheromones), heat and vibration. The three basic
segments of a termite antenna include a scape, a pedicel (typically shorter than the scape), and the flagellum (all segments beyond the scape and pedicel). The mouth parts contain a maxillae, a labium, and a set of mandibles. The maxillae and labium have palps that help termites sense food and handling.
Consistent with all insects, the anatomy of the termite thorax consists of three segments: the prothorax, the mesothorax and the metathorax. Each segment contains a pair of legs.
On alates, the wings are located at the mesothorax and metathorax,
which is consistent with all four-winged insects. The mesothorax and
metathorax have well-developed exoskeletal plates; the prothorax has
smaller plates.
Diagram showing a wing, along with the clypeus and leg
Termites have a ten-segmented abdomen with two plates, the tergites and the sternites. The tenth abdominal segment has a pair of short cerci. There are ten tergites, of which nine are wide and one is elongated. The reproductive organs are similar to those in cockroaches but are more simplified. For example, the intromittent organ
is not present in male alates, and the sperm is either immotile or
aflagellate. However, Mastotermitidae termites have multiflagellate
sperm with limited motility. The genitals in females are also simplified. Unlike in other termites, Mastotermitidae females have an ovipositor, a feature strikingly similar to that in female cockroaches.
The non-reproductive castes of termites are wingless and rely
exclusively on their six legs for locomotion. The alates fly only for a
brief amount of time, so they also rely on their legs.
The appearance of the legs is similar in each caste, but the soldiers
have larger and heavier legs. The structure of the legs is consistent
with other insects: the parts of a leg include a coxa, trochanter, femur, tibia and the tarsus. The number of tibial spurs on an individual's leg varies. Some species of termite have an arolium, located between the claws, which is present in species that climb on smooth surfaces but is absent in most termites.
Unlike in ants, the hind-wings and fore-wings are of equal length. Most of the time, the alates are poor flyers; their technique is to launch themselves in the air and fly in a random direction.
Studies show that in comparison to larger termites, smaller termites
cannot fly long distances. When a termite is in flight, its wings remain
at a right angle, and when the termite is at rest, its wings remain
parallel to the body.
Caste system
Caste system of termites A – King B – Queen C – Secondary queen D – Tertiary queen E – Soldiers F – Worker
Worker termites undertake the most labour within the colony, being
responsible for foraging, food storage, and brood and nest maintenance. Workers are tasked with the digestion of cellulose
in food and are thus the most likely caste to be found in infested
wood. The process of worker termites feeding other nestmates is known as
trophallaxis. Trophallaxis is an effective nutritional tactic to convert and recycle nitrogenous components.
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 may rely on nymphs to perform work without
differentiating as a separate caste.
Workers may be male or female and are usually sterile, especially in
termites that have a nest site that is separate from their foraging
site. Sterile workers are sometimes termed as true workers while those
that are fertile, as in the wood-nesting Archotermopsidae, are termed as
false workers.
The soldier caste has anatomical and behavioural specialisations, and their sole purpose is to defend the colony.
Many soldiers have large heads with highly modified powerful jaws so
enlarged they cannot feed themselves. Instead, like juveniles, they are
fed by workers. Fontanelles, simple holes in the forehead that exude defensive secretions, are a feature of the family Rhinotermitidae. Many species are readily identified using the characteristics of the soldiers' larger and darker head and large mandibles. Among certain termites, soldiers may use their globular (phragmotic) heads to block their narrow tunnels. Different sorts of soldiers include minor and major soldiers, and nasutes, which have a horn-like nozzle frontal projection (a nasus). These unique soldiers are able to spray noxious, sticky secretions containing diterpenes at their enemies. Nitrogen fixation plays an important role in nasute nutrition.
Soldiers are usually sterile but some species of Archotermopsidae are
known to have neotenic forms with soldier-like heads while also having
sexual organs.
The reproductive caste of a mature colony includes a fertile female and male, known as the queen and king. The queen of the colony is responsible for egg production for the colony. Unlike in ants, the king mates with her for life. In some species, the abdomen of the queen swells up dramatically to increase fecundity, a characteristic known as physogastrism.
Depending on the species, the queen starts producing reproductive
winged alates at a certain time of the year, and huge swarms emerge from
the colony when nuptial flight begins. These swarms attract a wide variety of predators.
Life cycle
A young termite nymph. Nymphs first moult into workers, but others may further moult to become soldiers or alates.
Termite,
and shed wings from other termites, on an interior window sill.
Shedding of wings is associated with reproductive swarming.
Termites are often compared with the social
Hymenoptera (ants and various species of bees and wasps), but their
differing evolutionary origins result in major differences in life
cycle. In the eusocial Hymenoptera, the workers are exclusively female.
Males (drones) are haploid and develop from unfertilised eggs, while
females (both workers and the queen) are diploid and develop from
fertilised eggs. In contrast, worker termites, which constitute the
majority in a colony, are diploid
individuals of both sexes and develop from fertilised eggs. Depending
on species, male and female workers may have different roles in a
termite colony.
The life cycle of a termite begins with an egg, but is different from that of a bee or ant in that it goes through a developmental process called incomplete metamorphosis, with egg, nymph and adult stages. Nymphs resemble small adults, and go through a series of moults as they grow. In some species, eggs go through four moulting stages and nymphs go through three.
Nymphs first moult into workers, and then some workers go through
further moulting and become soldiers or alates; workers become alates
only by moulting into alate nymphs.
The development of nymphs into adults can take months; the time
period depends on food availability, temperature, and the general
population of the colony. Since nymphs are unable to feed themselves,
workers must feed them, but workers also take part in the social life of
the colony and have certain other tasks to accomplish such as foraging,
building or maintaining the nest or tending to the queen. Pheromones regulate the caste system in termite colonies, preventing
all but a very few of the termites from becoming fertile queens.
Queens of the eusocial termite Reticulitermes speratus are capable of a long lifespan without sacrificing fecundity. These long-lived queens have a significantly lower level of oxidative damage, including oxidative DNA damage, than workers, soldiers and nymphs. The lower levels of damage appear to be due to increased catalase, an enzyme that protects against oxidative stress.
Reproduction
Alates swarming during nuptial flight after rain
Termite alates only leave the colony when a nuptial flight takes place. Alate males and females pair up together and then land in search of a suitable place for a colony.
A termite king and queen do not mate until they find such a spot. When
they do, they excavate a chamber big enough for both, close up the
entrance and proceed to mate.
After mating, the pair never go outside and spend the rest of their
lives in the nest. Nuptial flight time varies in each species. For
example, alates in certain species emerge during the day in summer while
others emerge during the winter.
The nuptial flight may also begin at dusk, when the alates swarm around
areas with many lights. The time when nuptial flight begins depends on
the environmental conditions, the time of day, moisture, wind speed and
precipitation.
The number of termites in a colony also varies, with the larger species
typically having 100–1,000 individuals. However, some termite colonies,
including those with many individuals, can number in the millions.
The queen only lays 10–20 eggs in the very early stages of the
colony, but lays as many as 1,000 a day when the colony is several years
old.
At maturity, a primary queen has a great capacity to lay eggs. In some
species, the mature queen has a greatly distended abdomen and may
produce 40,000 eggs a day. The two mature ovaries may have some 2,000 ovarioles each.
The abdomen increases the queen's body length to several times more
than before mating and reduces her ability to move freely; attendant
workers provide assistance.
The
king grows only slightly larger after initial mating and continues to
mate with the queen for life (a termite queen can live between 30 to
50 years); this is very different from ant colonies, in which a queen
mates once with the males and stores the gametes for life, as the male
ants die shortly after mating. If a queen is absent, a termite king produces pheromones which encourage the development of replacement termite queens. As the queen and king are monogamous, sperm competition does not occur.
Termites going through incomplete metamorphosis on the path to
becoming alates form a subcaste in certain species of termite,
functioning as potential supplementary reproductives. These
supplementary reproductives only mature into primary reproductives upon
the death of a king or queen, or when the primary reproductives are
separated from the colony.
Supplementaries have the ability to replace a dead primary
reproductive, and there may also be more than a single supplementary
within a colony. Some queens have the ability to switch from sexual reproduction to asexual reproduction. Studies show that while termite queens mate with the king to produce colony workers, the queens reproduce their replacements (neotenic queens) parthenogenetically.
The neotropical termite Embiratermes neotenicus and several other related species produce colonies that contain a primary king accompanied by a primary queen or by up to 200 neotenic queens that had originated through thelytokous parthenogenesis of a founding primary queen. The form of parthenogenesis likely employed maintains heterozygosity in the passage of the genome from mother to daughter, thus avoiding inbreeding depression.
Behaviour and ecology
Diet
Termite faecal pellets
Termites are detritivores,
consuming dead plants at any level of decomposition. They also play a
vital role in the ecosystem by recycling waste material such as dead
wood, faeces and plants. Many species eat cellulose, having a specialised midgut that breaks down the fibre. Termites are considered to be a major source (11%) of atmospheric methane, one of the prime greenhouse gases, produced from the breakdown of cellulose. Termites rely primarily upon symbiotic protozoa (metamonads) and other microbes such as flagellateprotists in their guts to digest the cellulose for them, allowing them to absorb the end products for their own use.
The microbial ecosystem present in the termite gut contains many
species found nowhere else on Earth. Termites hatch without these
symbionts present in their guts, and develop them after fed a culture
from other termites. Gut protozoa, such as Trichonympha, in turn, rely on symbiotic bacteria embedded on their surfaces to produce some of the necessary digestive enzymes. Most higher termites, especially in the family Termitidae, can produce their own cellulase enzymes, but they rely primarily upon the bacteria. The flagellates have been lost in Termitidae. Researches have found species of spirochetes living in termite guts capable of fixing atmospheric nitrogen to a form usable by the insect.
Scientists' understanding of the relationship between the termite
digestive tract and the microbial endosymbionts 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. Judging from closely related bacterial species, it is strongly presumed that the termites' and cockroach's gut microbiota derives from their dictyopteran ancestors.
Certain species such as Gnathamitermes tubiformans have seasonal food habits. For example, they may preferentially consume Red three-awn (Aristida longiseta) during the summer, Buffalograss (Buchloe dactyloides) from May to August, and blue grama Bouteloua gracilis during spring, summer and autumn. Colonies of G. tubiformans consume less food in spring than they do during autumn when their feeding activity is high.
Various woods differ in their susceptibility to termite attack;
the differences are attributed to such factors as moisture content,
hardness, and resin and lignin content. In one study, the drywood
termite Cryptotermes brevis strongly preferred poplar and maple
woods to other woods that were generally rejected by the termite
colony. These preferences may in part have represented conditioned or
learned behaviour.
Some species of termite practice fungiculture. They maintain a "garden" of specialised 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. Molecular evidence suggests that the family Macrotermitinae
developed agriculture about 31 million years ago. It is assumed that
more than 90 percent of dry wood in the semiarid savannah ecosystems of
Africa and Asia are reprocessed by these termites. Originally living in
the rainforest, fungus farming allowed them to colonise the African
savannah and other new environments, eventually expanding into Asia.
Depending on their feeding habits, termites are placed into two
groups: the lower termites and higher termites. The lower termites
predominately feed on wood. As wood is difficult to digest, termites
prefer to consume fungus-infected wood because it is easier to digest
and the fungi are high in protein. Meanwhile, the higher termites
consume a wide variety of materials, including faeces, humus, grass, leaves and roots. The gut in the lower termites contains many species of bacteria along with protozoa, while the higher termites only have a few species of bacteria with no protozoa.
A Matabele ant (Megaponera analis) kills a Macrotermes bellicosus termite soldier during a raid.
Among all predators, ants are the greatest enemy to termites. Some ant genera are specialist predators of termites. For example, Megaponera is a strictly termite-eating (termitophagous) genus that perform raiding activities, some lasting several hours. Paltothyreus tarsatus is another termite-raiding species, with each individual stacking as many termites as possible in its mandibles before returning home, all the while recruiting additional nestmates to the raiding site through chemical trails. The Malaysian basicerotine ants Eurhopalothrix heliscata
uses a different strategy of termite hunting by pressing themselves
into tight spaces, as they hunt through rotting wood housing termite
colonies. Once inside, the ants seize their prey by using their short
but sharp mandibles. Tetramorium uelense
is a specialised predator species that feeds on small termites. A scout
recruits 10–30 workers to an area where termites are present, killing
them by immobilising them with their stinger. Centromyrmex and Iridomyrmex colonies sometimes nest in termite mounds,
and so the termites are preyed on by these ants. No evidence for any
kind of relationship (other than a predatory one) is known. Other ants, including Acanthostichus, Camponotus, Crematogaster, Cylindromyrmex, Leptogenys, Odontomachus, Ophthalmopone, Pachycondyla, Rhytidoponera, Solenopsis and Wasmannia, also prey on termites. In contrast to all these ant species, and despite their enormous diversity of prey, Dorylus ants rarely consume termites.
Ants are not the only invertebrates that perform raids. Many sphecoid wasps and several species including Polybia and Angiopolybia are known to raid termite mounds during the termites' nuptial flight.
Parasites, pathogens and viruses
Termites
are less likely to be attacked by parasites than bees, wasps and ants,
as they are usually well protected in their mounds. Nevertheless, termites are infected by a variety of parasites. Some of these include dipteran flies, Pyemotes mites, and a large number of nematode parasites. Most nematode parasites are in the order Rhabditida; others are in the genus Mermis, Diplogaster aerivora and Harteria gallinarum. Under imminent threat of an attack by parasites, a colony may migrate to a new location. Certain fungal pathogens such as Aspergillus nomius and Metarhizium anisopliae are, however, major threats to a termite colony as they are not host-specific and may infect large portions of the colony; transmission usually occurs via direct physical contact. M. anisopliae is known to weaken the termite immune system. Infection with A. nomius
only occurs when a colony is under great stress. Over 34 fungal species
are known to live as parasites on the exoskeleton of termites, with
many being host-specific and only causing indirect harm to their host.
Because
the worker and soldier castes lack wings and thus never fly, and the
reproductives use their wings for just a brief amount of time, termites
predominantly rely upon their legs to move about.
Foraging behaviour depends on the type of termite. For example,
certain species feed on the wood structures they inhabit, and others
harvest food that is near the nest.
Most workers are rarely found out in the open, and do not forage
unprotected; they rely on sheeting and runways to protect them from
predators.
Subterranean termites construct tunnels and galleries to look for food,
and workers who manage to find food sources recruit additional
nestmates by depositing a phagostimulant pheromone that attracts
workers. Foraging workers use semiochemicals to communicate with each other, and workers who begin to forage outside of their nest release trail pheromones from their sternal glands. In one species, Nasutitermes costalis,
there are three phases in a foraging expedition: first, soldiers scout
an area. When they find a food source, they communicate to other
soldiers and a small force of workers starts to emerge. In the second
phase, workers appear in large numbers at the site. The third phase is
marked by a decrease in the number of soldiers present and an increase
in the number of workers. Isolated termite workers may engage in Lévy flight behaviour as an optimised strategy for finding their nestmates or foraging for food.
Competition
Competition between two colonies always results in agonistic behaviour
towards each other, resulting in fights. These fights can cause
mortality on both sides and, in some cases, the gain or loss of
territory. "Cemetery pits" may be present, where the bodies of dead termites are buried.
Studies show that when termites encounter each other in foraging
areas, some of the termites deliberately block passages to prevent other
termites from entering.
Dead termites from other colonies found in exploratory tunnels leads to
the isolation of the area and thus the need to construct new tunnels.
Conflict between two competitors does not always occur. For example,
though they might block each other's passages, colonies of Macrotermes bellicosus and Macrotermes subhyalinus are not always aggressive towards each other. Suicide cramming is known in Coptotermes formosanus. Since C. formosanus
colonies may get into physical conflict, some termites squeeze tightly
into foraging tunnels and die, successfully blocking the tunnel and
ending all agonistic activities.
Among the reproductive caste, neotenic queens may compete with
each other to become the dominant queen when there are no primary
reproductives. This struggle among the queens leads to the elimination
of all but a single queen, which, with the king, takes over the colony.
Ants and termites may compete with each other for nesting space.
In particular, ants that prey on termites usually have a negative impact
on arboreal nesting species.
Communication
Hordes of Nasutitermes on a march for food, following and leaving trail pheromones
Most termites are blind, so communication primarily occurs through chemical, mechanical and pheromonal cues.
These methods of communication are used in a variety of activities,
including foraging, locating reproductives, construction of nests,
recognition of nestmates, nuptial flight, locating and fighting enemies,
and defending the nests. The most common way of communicating is through antennation.
A number of pheromones are known, including contact pheromones (which
are transmitted when workers are engaged in trophallaxis or grooming)
and alarm, trail and sex pheromones.
The alarm pheromone and other defensive chemicals are secreted from the
frontal gland. Trail pheromones are secreted from the sternal gland,
and sex pheromones derive from two glandular sources: the sternal and
tergal glands.
When termites go out to look for food, they forage in columns along the
ground through vegetation. A trail can be identified by the faecal
deposits or runways that are covered by objects. Workers leave
pheromones on these trails, which are detected by other nestmates
through olfactory receptors. Termites can also communicate through mechanical cues, vibrations, and physical contact. These signals are frequently used for alarm communication or for evaluating a food source.
When termites construct their nests, they use predominantly
indirect communication. No single termite would be in charge of any
particular construction project. Individual termites react rather than
think, but at a group level, they exhibit a sort of collective
cognition. Specific structures or other objects such as pellets of soil
or pillars cause termites to start building. The termite adds these
objects onto existing structures, and such behaviour encourages building
behaviour in other workers. The result is a self-organised process
whereby the information that directs termite activity results from
changes in the environment rather than from direct contact among
individuals.
Termites can distinguish nestmates and non-nestmates through
chemical communication and gut symbionts: chemicals consisting of
hydrocarbons released from the cuticle allow the recognition of alien
termite species.
Each colony has its own distinct odour. This odour is a result of
genetic and environmental factors such as the termites' diet and the
composition of the bacteria within the termites' intestines.
Termites rely on alarm communication to defend a colony.
Alarm pheromones can be released when the nest has been breached or is
being attacked by enemies or potential pathogens. Termites always avoid
nestmates infected with Metarhizium anisopliae spores, through vibrational signals released by infected nestmates.
Other methods of defence include intense jerking and secretion of
fluids from the frontal gland and defecating faeces containing alarm
pheromones.
In some species, some soldiers block tunnels to prevent their
enemies from entering the nest, and they may deliberately rupture
themselves as an act of defence. In cases where the intrusion is coming from a breach that is larger than the soldier's head, soldiers form a phalanx-like formation around the breach and bite at intruders. If an invasion carried out by Megaponera analis is successful, an entire colony may be destroyed, although this scenario is rare.
To termites, any breach of their tunnels or nests is a cause for
alarm. When termites detect a potential breach, the soldiers usually
bang their heads, apparently to attract other soldiers for defence and
to recruit additional workers to repair any breach.
Additionally, an alarmed termite bumps into other termites which causes
them to be alarmed and to leave pheromone trails to the disturbed area,
which is also a way to recruit extra workers.
Nasute termite soldiers on rotten wood
The pantropical subfamily Nasutitermitinae has a specialised caste of soldiers, known as nasutes, that have the ability to exude noxious liquids through a horn-like frontal projection that they use for defence. Nasutes have lost their mandibles through the course of evolution and must be fed by workers. A wide variety of monoterpene hydrocarbon solvents have been identified in the liquids that nasutes secrete. Similarly, Formosan subterranean termites have been known to secrete naphthalene to protect their nests.
Soldiers of the species Globitermes sulphureus commit suicide by autothysis –
rupturing a large gland just beneath the surface of their cuticles. The
thick, yellow fluid in the gland becomes very sticky on contact with
the air, entangling ants or other insects that are trying to invade the
nest. Another termite, Neocapriterme taracua,
also engages in suicidal defence. Workers physically unable to use
their mandibles while in a fight form a pouch full of chemicals, then
deliberately rupture themselves, releasing toxic chemicals that paralyse
and kill their enemies. The soldiers of the neotropical termite family Serritermitidae
have a defence strategy which involves front gland autothysis, with the
body rupturing between the head and abdomen. When soldiers guarding
nest entrances are attacked by intruders, they engage in autothysis,
creating a block that denies entry to any attacker.
Workers use several different strategies to deal with their dead,
including burying, cannibalism, and avoiding a corpse altogether. To avoid pathogens, termites occasionally engage in necrophoresis, in which a nestmate carries away a corpse from the colony to dispose of it elsewhere. Which strategy is used depends on the nature of the corpse a worker is dealing with (i.e. the age of the carcass).
A species of fungus
is known to mimic termite eggs, successfully avoiding its natural
predators. These small brown balls, known as "termite balls", rarely
kill the eggs, and in some cases the workers tend to them. This fungus mimics these eggs by producing a cellulose-digesting enzyme known as glucosidases. A unique mimicking behaviour exists between various species of Trichopsenius beetles and certain termite species within Reticulitermes. The beetles share the same cuticlehydrocarbons
as the termites and even biosynthesize them. This chemical mimicry
allows the beetles to integrate themselves within the termite colonies. The developed appendages on the physogastric abdomen of Austrospirachtha mimetes allows the beetle to mimic a termite worker.
Some species of ant are known to capture termites to use as a
fresh food source later on, rather than killing them. For example, Formica nigra captures termites, and those who try to escape are immediately seized and driven underground. Certain species of ants in the subfamily Ponerinae conduct these raids although other ant species go in alone to steal the eggs or nymphs. Ants such as Megaponera analis attack the outside of mounds and Dorylinae ants attack underground. Despite this, some termites and ants can coexist peacefully. Some species of termite, including Nasutitermes corniger, form associations with certain ant species to keep away predatory ant species. The earliest known association between Azteca ants and Nasutitermes termites date back to the Oligocene to Miocene period.
An ant raiding party collecting Pseudocanthotermes militaris termites after a successful raid
54 species of ants are known to inhabit Nasutitermes mounds, both occupied and abandoned ones. One reason many ants live in Nasutitermes mounds is due to the termites' frequent occurrence in their geographical range; another is to protect themselves from floods. Iridomyrmex also inhabits termite mounds although no evidence for any kind of relationship (other than a predatory one) is known. In rare cases, certain species of termites live inside active ant colonies.
Some invertebrate organisms such as beetles, caterpillars, flies and
millipedes are termitophiles and dwell inside termite colonies (they are
unable to survive independently).
As a result, certain beetles and flies have evolved with their hosts.
They have developed a gland that secrete a substance that attracts the
workers by licking them. Mounds may also provide shelter and warmth to
birds, lizards, snakes and scorpions.
Termites are known to carry pollen and regularly visit flowers, so are regarded as potential pollinators for a number of flowering plants. One flower in particular, Rhizanthella gardneri, is regularly pollinated by foraging workers, and it is perhaps the only Orchidaceae flower in the world to be pollinated by termites.
Many plants have developed effective defences against termites.
However, seedlings are vulnerable to termite attacks and need additional
protection, as their defence mechanisms only develop when they have
passed the seedling stage. Defence is typically achieved by secreting antifeedant chemicals into the woody cell walls. This reduces the ability of termites to efficiently digest the cellulose.
A commercial product, "Blockaid", has been developed in Australia that
uses a range of plant extracts to create a paint-on nontoxic termite barrier for buildings. An extract of a species of Australian figwort, Eremophila, has been shown to repel termites;
tests have shown that termites are strongly repelled by the toxic
material to the extent that they will starve rather than consume the
food. When kept close to the extract, they become disoriented and
eventually die.
Relationship with the environment
Termite
populations can be substantially impacted by environmental changes
including those caused by human intervention. A Brazilian study
investigated the termite assemblages of three sites of Caatinga under different levels of anthropogenic disturbance in the semi-arid region of northeastern Brazil were sampled using 65 x 2 m transects.
A total of 26 species of termites were present in the three sites, and
196 encounters were recorded in the transects. The termite assemblages
were considerably different among sites, with a conspicuous reduction in
both diversity and abundance with increased disturbance, related to the
reduction of tree density and soil cover, and with the intensity of
trampling by cattle and goats. The wood-feeders were the most severely
affected feeding group.
A termite nest can be considered as being composed of two parts, the
inanimate and the animate. The animate is all of the termites living
inside the colony, and the inanimate part is the structure itself, which
is constructed by the termites.
Nests can be broadly separated into three main categories: subterranean
(completely below ground), epigeal (protruding above the soil surface),
and arboreal (built above ground, but always connected to the ground
via shelter tubes). Epigeal nests (mounds) protrude from the earth with ground contact and are made out of earth and mud.
A nest has many functions such as providing a protected living space
and providing shelter against predators. Most termites construct
underground colonies rather than multifunctional nests and mounds.
Primitive termites of today nest in wooden structures such as logs,
stumps and the dead parts of trees, as did termites millions of years
ago.
To build their nests, termites primarily use faeces, which have many desirable properties as a construction material.
Other building materials include partly digested plant material, used
in carton nests (arboreal nests built from faecal elements and wood),
and soil, used in subterranean nest and mound construction. Not all
nests are visible, as many nests in tropical forests are located
underground. Species in the subfamily Apicotermitinae are good examples of subterranean nest builders, as they only dwell inside tunnels.
Other termites live in wood, and tunnels are constructed as they feed
on the wood. Nests and mounds protect the termites' soft bodies against
desiccation, light, pathogens and parasites, as well as providing a
fortification against predators.
Nests made out of carton are particularly weak, and so the inhabitants
use counter-attack strategies against invading predators.
Arboreal carton nests of mangrove swamp-dwelling Nasutitermes are enriched in lignin
and depleted in cellulose and xylans. This change is caused by
bacterial decay in the gut of the termites: they use their faeces as a
carton building material. Arboreal termites nests can account for as
much as 2% of above ground carbon storage in Puerto Rican mangrove swamps. These Nasutitermes nests are mainly composed of partially biodegraded wood material from the stems and branches of mangrove trees, namely, Rhizophora mangle (red mangrove), Avicennia germinans (black mangrove) and Laguncularia racemose (white mangrove).
Some species build complex nests called polycalic nests; this
habitat is called polycalism. Polycalic species of termites form
multiple nests, or calies, connected by subterranean chambers. The termite genera Apicotermes and Trinervitermes are known to have polycalic species.
Polycalic nests appear to be less frequent in mound-building species
although polycalic arboreal nests have been observed in a few species of
Nasutitermes.
Nests are considered mounds if they protrude from the earth's surface. A mound provides termites the same protection as a nest but is stronger.
Mounds located in areas with torrential and continuous rainfall are at
risk of mound erosion due to their clay-rich construction. Those made
from carton can provide protection from the rain, and in fact can
withstand high precipitation. Certain areas in mounds are used as strong points in case of a breach. For example, Cubitermes colonies build narrow tunnels used as strong points, as the diameter of the tunnels is small enough for soldiers to block. A highly protected chamber, known as the "queens cell", houses the queen and king and is used as a last line of defence.
Species in the genus Macrotermes arguably build the most complex structures in the insect world, constructing enormous mounds.
These mounds are among the largest in the world, reaching a height of 8
to 9 metres (26 to 29 feet), and consist of chimneys, pinnacles and
ridges. Another termite species, Amitermes meridionalis,
can build nests 3 to 4 metres (9 to 13 feet) high and 2.5 metres
(8 feet) wide. The tallest mound ever recorded was 12.8 metres (42 ft)
long found in the Democratic Republic of the Congo.
The sculptured mounds sometimes have elaborate and distinctive forms, such as those of the compass termite (Amitermes meridionalis and A. laurensis),
which builds tall, wedge-shaped mounds with the long axis oriented
approximately north–south, which gives them their common name. This orientation has been experimentally shown to assist thermoregulation.
The north–south orientation causes the internal temperature of a mound
to increase rapidly during the morning while avoiding overheating from
the midday sun. The temperature then remains at a plateau for the rest
of the day until the evening.
Nasutiterminae shelter tubes on a tree trunk provide cover for the trail from nest to forest floor.
Termites construct shelter tubes, also known as earthen tubes or mud
tubes, that start from the ground. These shelter tubes can be found on
walls and other structures.
Constructed by termites during the night, a time of higher humidity,
these tubes provide protection to termites from potential predators,
especially ants.
Shelter tubes also provide high humidity and darkness and allow workers
to collect food sources that cannot be accessed in any other way.
These passageways are made from soil and faeces and are normally brown
in colour. The size of these shelter tubes depends on the number of food
sources that are available. They range from less than 1 cm to several
cm in width, but may be dozens of metres in length.
Relationship with humans
As pests
Termite mound as an obstacle on a runway at Khorixas (Namibia)
Termite damage on external structure
Owing to their wood-eating habits, many termite species can do
significant damage to unprotected buildings and other wooden structures.
Termites play an important role as decomposers of wood and vegetative
material, and the conflict with humans occurs where structures and
landscapes containing structural wood components, cellulose derived
structural materials and ornamental vegetation provide termites with a
reliable source of food and moisture.
Their habit of remaining concealed often results in their presence
being undetected until the timbers are severely damaged, with only a
thin exterior layer of wood remaining, which protects them from the
environment. Of the 3,106 species known, only 183 species cause damage; 83 species cause significant damage to wooden structures. In North America, 18 subterranean species are pests;
in Australia, 16 species have an economic impact; in the Indian
subcontinent 26 species are considered pests, and in tropical Africa,
24. In Central America and the West Indies, there are 17 pest species. Among the termite genera, Coptotermes has the highest number of pest species of any genus, with 28 species known to cause damage.
Less than 10% of drywood termites are pests, but they infect wooden
structures and furniture in tropical, subtropical and other regions.
Dampwood termites only attack lumber material exposed to rainfall or
soil.
Drywood termites thrive in warm climates, and human activities
can enable them to invade homes since they can be transported through
contaminated goods, containers and ships. Colonies of termites have been seen thriving in warm buildings located in cold regions. Some termites are considered invasive species. Cryptotermes brevis,
the most widely introduced invasive termite species in the world, has
been introduced to all the islands in the West Indies and to Australia.
Termite damage in wooden house stumps
In addition to causing damage to buildings, termites can also damage food crops.
Termites may attack trees whose resistance to damage is low but
generally ignore fast-growing plants. Most attacks occur at harvest
time; crops and trees are attacked during the dry season.
The damage caused by termites costs the southwestern United
States approximately $1.5 billion each year in wood structure damage,
but the true cost of damage worldwide cannot be determined. Drywood termites are responsible for a large proportion of the damage caused by termites. The goal of termite control is to keep structures and susceptible ornamental plants free from termites.;
Structures may be homes or business, or elements such as wooden fence
posts and telephone poles. Regular and thorough inspections by a
trained professional may be necessary to detect termite activity in the
absence of more obvious signs like termite swarmers or alates inside or
adjacent to a structure. Termite monitors made of wood or cellulose
adjacent to a structure may also provide indication of termite foraging
activity where it will be in conflict with humans. Termites can be
controlled by application of Bordeaux mixture or other substances that contain copper such as chromated copper arsenate. In the United states, application of a soil termiticide with the active ingredient Fipronil, such as Termidor SC or Taurus SC, by a licensed professional, is a common remedy approved by the Environmental Protection Agency for economically significant subterranean termites.
A growing demand for alternative, green, and "more natural"
extermination methods has increased demand for mechanical and biological
control methods such as Orange Oil.
To better control the population of termites, various methods have been developed to track termite movements. One early method involved distributing termite bait laced with immunoglobulin G
(IgG) marker proteins from rabbits or chickens. Termites collected from
the field could be tested for the rabbit-IgG markers using a
rabbit-IgG-specific assay.
More recently developed, less expensive alternatives include tracking
the termites using egg white, cow milk, or soy milk proteins, which can
be sprayed on termites in the field. Termites bearing these proteins can
be traced using a protein-specific ELISA test.
Mozambican boys from the Yawo tribe collecting flying termites
These flying alates were collected as they came out of their nests in the ground during the early days of the rainy season.
43 termite species are used as food by humans or are fed to livestock. These insects are particularly important in impoverished countries where malnutrition is common, as the protein
from termites can help improve the human diet. Termites are consumed in
many regions globally, but this practice has only become popular in
developed nations in recent years.
Termites are consumed by people in many different cultures around the world. In many parts of Africa, the alates are an important factor in the diets of native populations.
Groups have different ways of collecting or cultivating insects;
sometimes collecting soldiers from several species. Though harder to
acquire, queens are regarded as a delicacy. Termite alates are high in nutrition with adequate levels of fat and protein. They are regarded as pleasant in taste, having a nut-like flavour after they are cooked.
Alates are collected when the rainy season begins. During a
nuptial flight, they are typically seen around lights to which they are
attracted, and so nets are set up on lamps and captured alates are later
collected. The wings are removed through a technique that is similar to
winnowing. The best result comes when they are lightly roasted on a hot plate or fried until crisp. Oil
is not required as their bodies usually contain sufficient amounts of
oil. Termites are typically eaten when livestock is lean and tribal
crops have not yet developed or produced any food, or if food stocks
from a previous growing season are limited.
In addition to Africa, termites are consumed in local or tribal areas in Asia and North and South America. In Australia, Indigenous Australians are aware that termites are edible but do not consume them even in times of scarcity; there are few explanations as to why. Termite mounds are the main sources of soil consumption (geophagy) in many countries including Kenya, Tanzania, Zambia, Zimbabwe and South Africa. Researchers have suggested that termites are suitable candidates for human consumption and space agriculture, as they are high in protein and can be used to convert inedible waste to consumable products for humans.
In agriculture
Scientists have developed a more affordable method of tracing the movement of termites using traceable proteins.
Termites can be major agricultural pests, particularly in East Africa
and North Asia, where crop losses can be severe (3–100% in crop loss in
Africa).
Counterbalancing this is the greatly improved water infiltration where
termite tunnels in the soil allow rainwater to soak in deeply, which
helps reduce runoff and consequent soil erosion through bioturbation. In South America, cultivated plants such as eucalyptus, upland rice and sugarcane
can be severely damaged by termite infestations, with attacks on
leaves, roots and woody tissue. Termites can also attack other plants,
including cassava, coffee, cotton, fruit trees, maize, peanuts, soybeans and vegetables.
Mounds can disrupt farming activities, making it difficult for farmers
to operate farming machinery; however, despite farmers' dislike of the
mounds, it is often the case that no net loss of production occurs. Termites can be beneficial to agriculture, such as by boosting crop yields
and enriching the soil. Termites and ants can re-colonise untilled land
that contains crop stubble, which colonies use for nourishment when
they establish their nests. The presence of nests in fields enables
larger amounts of rainwater to soak into the ground and increases the
amount of nitrogen in the soil, both essential for the growth of crops.
The termite gut has inspired various research efforts aimed at replacing fossil fuels with cleaner, renewable energy sources. Termites are efficient bioreactors, capable of producing two litres of hydrogen from a single sheet of paper.
Approximately 200 species of microbes live inside the termite hindgut,
releasing the hydrogen that was trapped inside wood and plants that they
digest. Through the action of unidentified enzymes in the termite gut, lignocellulosepolymers are broken down into sugars and are transformed into hydrogen. The bacteria within the gut turns the sugar and hydrogen into cellulose acetate, an acetateester of cellulose on which termites rely for energy. Community DNA sequencing of the microbes in the termite hindgut has been employed to provide a better understanding of the metabolic pathway. Genetic engineering may enable hydrogen to be generated in bioreactors from woody biomass.
The development of autonomous robots
capable of constructing intricate structures without human assistance
has been inspired by the complex mounds that termites build.
These robots work independently and can move by themselves on a tracked
grid, capable of climbing and lifting up bricks. Such robots may be
useful for future projects on Mars, or for building levees to prevent flooding.
Termites use sophisticated means to control the temperatures of their mounds. As discussed above,
the shape and orientation of the mounds of the Australian compass
termite stabilises their internal temperatures during the day. As the
towers heat up, the solar chimney effect (stack effect) creates an updraft of air within the mound.
Wind blowing across the tops of the towers enhances the circulation of
air through the mounds, which also include side vents in their
construction. The solar chimney effect has been in use for centuries in
the Middle East and Near East for passive cooling, as well as in Europe by the Romans.
It is only relatively recently, however, that climate responsive
construction techniques have become incorporated into modern
architecture. Especially in Africa, the stack effect has become a
popular means to achieve natural ventilation and passive cooling in
modern buildings.
In culture
The pink-hued Eastgate Centre
The Eastgate Centre is a shopping centre and office block in central Harare, Zimbabwe, whose architect, Mick Pearce, used passive cooling inspired by that used by the local termites.
It was the first major building exploiting termite-inspired cooling
techniques to attract international attention. Other such buildings
include the Learning Resource Center at the Catholic University of Eastern Africa and the Council House 2 building in Melbourne, Australia.
Few zoos hold termites, due to the difficulty in keeping them
captive and to the reluctance of authorities to permit potential pests.
One of the few that do, the Zoo Basel in Switzerland, has two thriving Macrotermes bellicosus
populations – resulting in an event very rare in captivity: the mass
migrations of young flying termites. This happened in September 2008,
when thousands of male termites left their mound each night, died, and
covered the floors and water pits of the house holding their exhibit.
African tribes in several countries have termites as totems, and for this reason tribe members are forbidden to eat the reproductive alates.
Termites are widely used in traditional popular medicine; they are used
as treatments for diseases and other conditions such as asthma, bronchitis, hoarseness, influenza, sinusitis, tonsillitis and whooping cough. In Nigeria, Macrotermes nigeriensis
is used for spiritual protection and to treat wounds and sick pregnant
women. In Southeast Asia, termites are used in ritual practices. In
Malaysia, Singapore and Thailand, termite mounds are commonly worshiped
among the populace.
Abandoned mounds are viewed as structures created by spirits, believing
a local guardian dwells within the mound; this is known as Keramat
and Datok Kong. In urban areas, local residents construct red-painted
shrines over mounds that have been abandoned, where they pray for good
health, protection and luck.
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