In this article we will discuss about Termites:- 1. Introduction to Termites 2. Habit and Habitat of Termites 3. Morphology 4. Life history 5. Economic Importance 6. Control
1. Introduction to Termites:
Termites commonly called white ants are soft-bodied, social and polymorphic insects having two pairs of similar deciduous wings and live together forming large communities. The termites, however, are among the most destructive insects so far as man is concerned but in nature they help in decomposing the dead vegetation and enriching the soil.
Though the termites are called white ants but they are neither completely white in colour nor ants; one can easily differentiate these from ants by the absence of a constriction or peduncle between the thorax and the abdomen, in addition to some other morphological and behavioural characteristics.
However, more than 1700 species of termites are known today. Some common genera are Macrotermes, Mastotermes, Odontotermes, Kalotermes, Nasutitermes, Leucotermes, Coptotermes, Achotermopsis, Zootermopsis, etc.
2. Habit and Habitat of Termites:
The termites are nocturnal and they prefer to live in eternal darkness. They cannot withstand the exposure of dry air and, therefore, they construct tunnels in the earth and wood. The termites are best known nest building insects.
Since, they bore through wood causing much damage, they can digest wood with the help of symbiotic flagellates, such as Trichonympha campanula living in their intestine and passed on from generation to generation. These are social insects forming large communities and well marked polymorphic individuals.
Primitive termites live in galleries bored in wood, dead trees, structural timbers and wooden buildings. Some termites make tunnels in the ground, they destroy roots of grasses, vegetation and crops. More advanced termites make huge maunds called termitaria which are up to 6 metres high, they are made of excavated mud, wood and excreta mixed with saliva, their walls become hard as rocks.
Wood-eating termites (Termopsis) have no workers, they form galleries in decaying logs. Calotermes, Neotermes and Mastotermes bore into dry wood, such as posts, furniture and wooden buildings.
Calotermes bores into stems of tea plants in Sri Lanka. Leucotermes and Captotermes live in the ground, and through the soil they enter the woodwork of buildings making passages of mud for concealment. Indian termite Odontotermes includes both underground dwellers and maund builders. Termitaria are made mostly in Africa, Sri Lanka and Australia.
In maunds and termitaria is a maze of passages, chambers, royal chamber and special cells for storing food or cultivating fungus gardens. Nocturnal foraging parties of workers go out to collect vegetable food which is stored in special cells. Workers go above to collect seeds, grass and vegetation, these are cut up and stored in special cells, or granaries.
3. Morphology of Termites:
(i) Shape, Size and Colour of Termites:
The body size is variable; from small to moderate-size. They are yellow, brown, black or pale coloured insects having weak sclerotized bodies.
(ii) Structure of Termites:
The body has distinct three regions, the head, thorax and abdomen. The integument or skin covering the body is soft, delicate, thin and highly sensitive. The head bears a pair of compound eyes which are often functionless, a pair of antennae and the mouth parts are biting and chewing type with well developed mandibles. The neck has prominent lateral sclerites. Pro-notum is prominent.
There are two pairs of long, narrow similar wings, each with a basal suture from where the wing can be cast off. There are three pairs of walking legs; tarsi are 4-jointed with a pair of claws. Abdomen has 10 segments ending in a pair of short 2 to 6 jointed cerci, in male the ninth segment has a pair of anal stylets.
(iii) Termite Community:
Termites differ from other social insects in having a large number of castes.
Basically, a termite community includes two forms:
1. Reproductive Forms or Castes:
There are three types of reproductive castes which are fertile males and females.
These are as follows:
A. Macropterous forms or winged forms:
Macropterous forms or winged forms or first reproductive caste are sexually perfect males and females, they are the ancestors of community from which other forms have been derived, they have two pairs of large, equal-sized wings which project beyond the abdomen at rest. Body is chitinised and dark brown.
Compound eyes are well developed and there is a pair of ocelli. Brain and sex organs are larger than in others. Males and females leave the nest, lead a brief aerial life, shed their wings at the basal sutures, then they come together in pairs and mate, after which they find a place for a new nest.
Each pair is a dealated king and queen or primary royal pair, they have stumps of shed wings, king and queen are permanently associated, they are monogamous. The queen becomes large by growth of its abdomen. Now, they are the originators of a new colony.
B. Brachypterous Forms or Short Winged Forms:
Brachypterous forms or short winged forms or second reproductive caste are sexually mature males and females but they are nymphal in appearance, they have short wing buds only, body is less chitinised and pale-coloured. Compound eyes are not dark, brain and sex organs are smaller.
They are subterranean and do not leave the nest. If the primary king or queen dies, its place is taken by brachypterous individuals forming substitute or complemental king or queen, such queens produce fewer eggs, there may be several substitute kings and queens in one nest and they are polygamous.
C. Apterous (wingless) Forms:
Apterous (wingless) forms or third reproductive caste look like nymphal workers, they have no wings, cuticle is colourless, compound eyes are vestigial and ocelli are absent, they have both males and females. Apterous forms are rare and found only in lower termites, e.g., Leucotermes, they are known as ergatoid kings and queens, they may be several.
In all three reproductive castes there is remarkable post-embryonic growth, especially in the female.
The fertilised female develops into a queen which is 5 to 7.5 cm long, the increase in size is due to enlargement of the abdomen only, the head and thorax remain normal, the terga and sterna of abdomen do not grow, but the pleural membranes expand tremendously, this is due to an increase in the size of ovaries and fat body, so that the queen becomes a large, inert, egg-laying individual.
The queen formed from the macropterous female is the largest. The queen lives for 6 to 15 years and lays a million eggs in its life. It was once believed that the destruction of the queen Would ultimately kill out the community but this is not so because brachypterous or apterous queens will form and continue the community.
2. Sterile Forms or Castes:
There are two types of wingless (apterous) sterile castes. These are males and females in which sex organs are rudimentary and non-functional.
These are of two types:
A. Sterile Workers:
Sterile workers are apterous, sterile males and females in which sex organs have atrophied and are non-functional.
A worker has its integument very little chitinised and body is pale-coloured, it looks like a nymph, head is wide pointing downwards, compound eyes are absent, and in some species ocelli are also absent. Workers may be dimorphic, in one the head and mandibles are larger than in the other form, e.g., in Odontotermes.
In some workers are trimorphic with small intermediate and larger sizes, e.g., Termes. The number of workers in a community is very large, and with the exception of reproduction and defence, they perform all duties, looking after eggs and the young, finding food, planting and cultivating fungi, making nests, and feeding the queen and soldiers.
They also lick and groom each other. Because of their gnawing habit the workers destroy crops, wood and human belongings and cause tremendous loss to man.
B. Sterile Soldiers:
Sterile soldiers are apterous males and females with no sex organs. A soldier has a large chitinous head, big mandibles and colour is pale.
Soldiers are of two types:
(a) Mandibulate soldiers have large powerful mandibles but no frontal rostum,
(b) Nasute soldiers have small mandibles and a median frontal rostrum on the head. Soldiers defend the community, mandibulate soldiers with their mandibles and nasute soldiers by exuding a viscid repellent fluid through the frontal rostrum. At times soldiers plug the burrows with their heads.
Food of termites consists of wood, vegetation, faecal matter of termites, cast off skins and the dead of the colony. Some termites cultivate fungus gardens, they are made of a reddish brown, spongy comb produced by workers form vegetable matter and excreta, on the comb fungal hyphae grow producing white patches.
Fungus gardens are grown in chambers located near the centre of the nest, they communicate with a royal chamber in which the king and queen live. The queen is fed by workers only on saliva and fungal hyphae.
The eggs and nymphs develop in fungal chambers or nurseries, workers tend and feed the nymphs on fungus and vegetable matter which are partly predigested by workers, thus, symbiotic flagellates are transferred to nymphs. The nymphs develop either into fertile males and females which can leave the nest and new colonies, or into sterile workers or soldiers.
4. Life History of Termites:
The life history and the origin of caste system in termites is extremely complicated.
The life history of termite can be explained as under:
(i) Swarming and Mating:
Usually equal number of males and females of macropterous and brachypterous forms leave their nest in huge numbers or great swarms at definite times of the year, generally after the first showers of rain on the onset of rainy season. This is called swarming. Swarming may occur either at night or even during the day; it depends upon the species of termite.
The termites are not true fliers and, hence, after a short flight they come down to the ground, their wings are shed off and they become dealated. One male and one female pair, referred to as royal couple, they search for a sheltered place either in wood or on the ground.
After getting a suitable place, they excavate a nuptial chamber, where copulation takes place. The flight of termites is not a true nuptial flight because copulation does not take place in air unless they come to the ground. In the paired dealated individuals, male becomes the king which cohabits the female, the queen for the whole life. These individuals now become the originators of a new colony.
(ii) New Colony:
As referred to, that the royal pair copulate in the nuptial chamber. After copulation, the queen lays cluster of eggs, from these eggs nymphs are hatched out. These nymphs develop into workers. When workers are formed in large numbers, they take up different duties like feeding and attending the royal pair and enlarging the nest.
Then the nymphs hatching out from the eggs develop into the soldiers. Thus, in the early months and years of the formation of a new colony workers and soldiers are only formed and then macropterous or brachypterous forms are produced.
The queen undergoes drastic modifications attaining a size nearly 20 to 30 thousand times larger than the worker, the head and thorax reduced to a large extent. The entire body appears to be made of abdomen only. It becomes an egg laying individual and on an average it lays nearly 4000 eggs in a day and millions of eggs in its life time.
When the power of fecundity (egg-laying) ceases, it dies and devoured by the other members of the colony. The king, however, undergoes less remarkable change, its body gets inflated due to well-fed condition but inert life.
The eggs are oval, elongated, smooth and pale coloured. Development is gradual and metamorphosis is not complete. The nymphs which hatch out from the eggs are like the adults except that they are smaller in size, have no traces of wings and sexually immature. The nymphs undergo several moultings to attain adulthood.
(v) Differentiation of Castes and Determination of Sex:
The formation of different castes in a community from similar eggs has been explained by various theories. However, these theories are based on complex interaction of hormones, pheromones, availability of food supply and social behaviour, etc.
So far sex determination is concerned, it is noticed that male gametes possess one sex-chromosome less than those of the female gametes. Thus, the genetic constitution of male may be represented as AAX and that of the female as AAXX (where, A symbolizes autosomes and X sex chromosomes).
Therefore, male gametes may possess either AX or A and female gametes possess AX only (all ova are alike genetically). When ovum (AX) is fertilised with male gamete having A X, a zygote with AAXX is produced which develops into a female and when an ovum (A X) is fertilised with male gamete having A, a zygote with AA X is produced which develops into a male.
5. Economic Importance of Termites:
Termites are the cause of huge damage to man. Since, their main food is cellulose, hence, they injure and destroy the wood work of houses, timbers, furniture’s, railway sleepers, wooden bridges, boats, telegraph poles, books, large orchard trees like mango, apple, coconut, citrus, guava, chiku and many field crops like sugarcane, groundnut, tea, coffee, cotton, potato plants, etc., are badly damaged by them.
Though termites cause a great deal of damage, they are also useful, they render service to mankind by consuming dead wood and vegetable products, they aid in agriculture by enriching the soil with their faecal matter, and by making the soil permeable to air and moisture exactly in the same way as earthworms.
In addition, they are also useful as they constitute food to several animals like birds, reptiles, rodents, etc. Natives of South East Africa consume queens of termites as a delicious dish.
Besides termites other insects also live in termite habitations, they are called termitophilous fauna and consist mostly of beetles. Some are treated as true guests by termites, some are indifferently tolerated guests, while others are scavengers and predators. In some cases more than one species of termites may live in the same habitation.
6. Control of Termites:
The control measures of termites can be adopted as per their abode.
However, following steps can be taken to control their menace:
1. In fields termitaria should be destroyed by pouring kerosene oil, carbon bi-sulphate, etc.
2. Nests can also be fumigated by sulphur, arsenic and kerosene oil.
3. Timbers when infected are treated by drilling holes at intervals and filling and sealing them with insecticides like sodium fluoride, calcium arsenate, etc.
4. The queen should be searched out from established colonies and killed.
5. The plantation pits should be treated by 0.2% dieldrin.
6. The orchard trees can be protected by termites by spraying 1 per cent dieldrin.
7. Crop fields should be dusted by 10 per cent BHC at the rate of 20 to 25 kg per hectare before sowing.
8. Wooden foundation, if any should not touch the soil and, hence, should be cemented at the ground level and should be painted by some insecticides.
9. In recent days anti-termite treatment is advised to undertake at the foundation level of the buildings.
10. The affected parts of trees can be sprayed with paris green; trunk of trees should be banded by coal-tar or DDT from the ground level.