THE TERMITE | Description, Types, Infestations, & Facts

Macrotermes bellicosus is one of nearly 2,000 species of termites and the genus Macrotermes is widely distríbuted through Africa and South-East Asia. The species M. bellicosus is one of the largest termites, with a complex, highly evolved colonial organization. All termites live in colonies, those of M. bellicosus reaching a size of hundreds of thousands over many years.

Although termites are sometimes called "white ants", they are not ants, nor are they closely related to them.

The nest. Some termites build nests in wood, some in trees and posts, and some below the ground but M. bellicosus, though it begins its nest below ground, forms large mounds or towers of soil. The nest is constructed of sand and clay. The workers burrow into the subsoil bringing back a sand grain and a "mouthful" of clay which becomes moistened with saliva. The sand particle is stuck in position in the nest and cemented with the mortar of clay and saliva. Building activities are most intense at the beginning of the wet season.

If clay is abundant in the subsoil and rainfall is low, the nest is a tapering column up to 9 metres high, but if clay is in short supply and the rainfall is high, the building material cannot withstand the eroding action of rain so well and a dome-shaped nest, about 2 metres high, results. The mound does not appear until the colony is several years old but thereafter it growsrapidly, reaching perhaps one-third of its final height in the first year.

The main part of the colony, the "hive", is in the mound just above ground level and inside the mound is a maze of passages, some of which lead away under the soil to reach supplies of wood and vegetation up to 100 metres away. One or more vertical shafts run to the summit of the nest Inside the nest, the temperature is fairly constant at about 30 C and often lower than outside, and the humidity also remains steady at about 90 per cent. This high humidity keeps the nest material permanently plastic and the internal architec- ture of the nest is constantly being altered. The interior of the nest provides an almost unvarying environment, making the termites independent of changes in climate outside. Even if termites have to pass over the ground in search of food, they construct covered runways which protect them from drying out and from certain predators.

Food. On the whole, termites live on the cellulose of woody vegetation, many species burrowing into dead wood of trees and in buildings. There is no cellulose-digesting enzy termite's body, and so indirect methods of digestion are important. Some species have single-celled organisms (protozoa) in their intestines and it is these protozoa which digest the cellulose, while the protozoa themselves are a source olroou intestinal for the termite. Macrotermes bellicosus has no intestinal protozoa but constructs fungus combs in the nest.

The fungus combs consist of spongy masses of wood-pulp derived from the faeces, covered with a mycelium of fungal nyphae and sporangia. It seems very likely that the fungus digests the wood to a stage that can be utilized by the termites.

Life cycle. At certain times of the year termites Swarm. In M. bellicosus this takes place at the beginning of the rainy season and at night. Workers make passages to the outside of the nest and hundreds of winged, reproductive forms take off and fly, some eventually being dispersed hundreds of yards over the surrounding countryside depending on air movements. When the female alights she raises her abdomen, and may give ofl a scent which attracts the male. When he arrives, both insects shed their wings by a special contraction of the thorax which breaks them off along a line of weakness near the base. The pair now "parades, running over the ground with the female leading at first, until she enters a crevice in the ground where a cavity can be hollowed out to start the nest.

Mating takes place and about one week after reaching the nest site, the female lays eggs, though only a few at first. These hatch into nymphs which are probably fed by internal secretions from the parents since the fungus comb is not yet prepared. After about two moults, the nymphs become workers and take over the task of nest construction, food collection and care of the young, leaving the original female, the. queen, to lay eggs sometimes at the rate of one every two seconds. Such a highly specialized reproductive machine does the queen become that her abdomen, with its reproductive organs and eggs, enlarges out of all proportion to her head and thorax, the soft membrane between the segments growing to give an abdomen of perhaps 10 cm long, with the original brown cuticle left as widely separated plates. The workers enclose the queen in a thick, clay cell at about ground level and she is cleaned and fed by them, probably from regurgitated, partially digested woodpulp. The workers take away the eggs as she lays them.

The queen may live for a great many years and the original male or "king stays with her in the cell, fertilizing the eggs. If the queen dies or ceases to lay eggs the colony may fail, but in many species, possibly including M. bellicosus, secondary repro- ductives arise.

The "castes". The nymphs are wingless and undergo an incomplete metamorphosis through perhaps ten instars, in the last two of which wing buds and full-sized wings appear.

The workers, however, are male or female nymphs which have moulted three times or more and in which the development of reproductive organs is suppressed. Their cuticles remain soft and pale, but after the second instar their mandibles harden and can be used to chew wood and construct tunnels. The workers form the bulk of the colony and they collect food, attend to the fungus comb, enlarge and repair the nest, make tunnels through the soil, look after the eggs, and feed the young nymphs, soldiers, king and queen with regurgitated food.

The soldiers are developed after the third instar They have enormous, well cuticularized heads which accom- modate the powerful muscles needed for working their long jaws. The soldiers form about 5 per cent of the colony and defend it against the intrusions of ants, either by snapping with their jaws or by blocking the passage-ways with their heads.

They are fed by the workers in much the same way as thee nymphs.

The reproductives are those nymphs which complete their metamorphosis, developing wings and com- pound eyes. They normally arise during the dry season and are ready to swarm when the rains begin. If swarming is prevented by climatic conditions, e.g. no rain, the workers bite off the wings of the reproductives who revert to the status of workers as their reproductive organs degenerate.

Secondary reproductives. If the queen dies, her place may be taken by either winged reproductives waiting to swarm but kept back by the workers who bite off their wings, or by third instar nymphs whose reproductive capabilities are in some way accelerated without any further moulting. In either case, several secondary reproductives will be needed to replace the egg laying capacity of the original queen

Caste determination. It seems that after the third instar, the eventual fate of the nymph is settled, i.e. whether it will become a worker, soldier or reproductive. It is most likely that this is determined by conditions within the colony, for the egg and first two nymphal instars retain the potential to become any one of the three forms. If soldiers are experimentally removed from termite colonies which have been raised in the laboratory, more soldiers are produced from third instar nymphs to restore the balance. Similarly, if soldiers are added, some are killed by workers.

Only from laboratory colonies is it possible to determine the life-span of individual termites and the duration of the intermediate stages, but in one species studied in this way, the eggs hatch after about three weeks and from one to four weeks elapse between each instar, the period increasing with later instars. This species thus requires about six to seven months to produce reproductive forms and the individuals have a life- span of two years. Similar figures are not available for M. bellicosus since laboratory colonies have not been successfully established.

Economic importance. Although termites normally eat dead vegetation, their tunnels may weaken plant stems, causing them to collapse ar giving access to fungus and other diseases. Where bark is gnawed from trees, the phloem may be interrupted, causing the death of the tree. The mud runways with which some species cover the plants to reach dead wood may cause the plant, e.g. tea, to wither and collapse. Cocoa trees, sugar cane, young coconut trees, cotton and wheat plants are amongst crops that may be affected by termites. Macrotermes is not of very great importance in this respect but its nest-mounds get in the way of agricultural machinery and have to be blown up with explosives or levelled with bulldozers, thus increasing the cost of mechanized farming, road construction and building-site clearance.

Perhaps the most familiar termite damage is to the wooden fabric of buildings and furniture. Various, earth-dwelling species, though not M. bellicosus, tunnel underground from their nests and enter the building through its foundations or any wooden part in contact with the ground. To obtain the wood for their food they make extensive tunnels through the structures, weakening them and eventually causing their collapse. Since the insects make no openings to the outside, or do so only at an advanced stage of the invasion, the owner is frequently unaware of their presence until it is too late 

Prevention of termite damage. Buildings should be constructed on solid concrete or be raised on masonry piers. In either case, termites may still gain access by building their Covered runways over the masonry to reach the wood.

projecting ledge round the concrete base or pier will prevent even this method of access. Great care must be taken to see that ho unprotected wooden part of the building is in contact with the ground (e.g. steps). The earth round the building can be impregnated with insecticides such as BHC which may prevent the termites tunnelling through to the structures for several years.

None of these precautions is proof against the species of termites which fly to buildings and establish nests in the wood- work. The only measure against this type of invasion is to use wood which is naturally resistant to termite attack or that has been soaked in chemicals which repel the insects.

Predators. Vast numbers of winged termites are eaten at the time of swarming. In the air they are snapped up by birds such as hawks and swallows, and on the ground by lizards, toads and spiders. In the nest, the termites are subject to attacks by "ant eating mammals such as the ant-bear or aardvark which burrows into the mound and licks out the termites with a long thin tongue. The covered, over-ground runways are broken open to reach the termites within by birds of various kinds

Man and ants are also the enemies of termites. Ants carry off the workers that are working outside the nest and may invade and destroy a colony; man captures and eats the swarming reproductives or digs out the queen as a special delicacy

THE TERMITE | Description, Types, Infestations, & Facts THE TERMITE | Description, Types, Infestations, & Facts Reviewed by Admin on October 18, 2022 Rating: 5

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