The termites, commonly called white-ants, are among the common insect pests belonging to the order Isoptera. They are found abundantly and widely in tropical and sub-tropical regions of the world. They live in large communities, mostly in underground nests and are familiar because of their depredations. They make small earthen mounds or earthen passages that are visible above the ground.
On opening a portion of an earthen passage, greyish white, wingless insects are seen moving towards or away from the centre of their nest, where the queen of the colony resides. They belong to many families and their nesting behaviour is characteristic of every group. All of them have one thing in common that they are social creatures.
The termites are social insects and their colony organization is based on a caste-system. In a colony, there are numerous workers, lots of soldiers, one queen, a king and a good number of complementary or the colonizing forms of true but immature males and females.
Castes of Termites:
The various castes and their duties are described below:
A. Productive Castes:
1. Colonizing Individuals:
These are winged individuals of both sexes and are produced in large numbers during the rainy season. When the temperature and moisture conditions are optimum, they emerge from the parent colony and hover over street lamps early in the evening, usually after a shower of rain. The wings are meant for the nuptial flight only and when they have mated, the wings usually drop off.
Most of the winged insects are eaten up by frogs, lizards and snakes. A pair that happens to escape may start a new colony in a crevice in the soil as the queen and the king of a colony. To start with, they themselves attend to the foraging and other duties which, later on, are performed by the workers.
2. Queen:
This is the only perfectly developed female in the colony. She develops either from colonizing individuals described above or from the wingless forms (complementals) present in an established colony. She attains a much larger size when developed from the former caste.
The queen of Microtermes obesi Holmgren measures 5.0-7.5 cm in length. She has a creamy-white abdomen marked with transverse dark brown stripes. Her reproductive system occupies almost the entire abdomen. She is a phenomenal “egg-laying machine”, laying one egg per second or 70,000-80,000 eggs in 24 hours.
There is only one queen in a colony and normally she lives from 5 to 10 years, but there are cases on record in which the queen lived for 20 years. The queen is fed by the workers on the choicest food, and is housed in a special area referred to as the ‘royal chamber’ which is situated in the centre of the nest, at depth of about 0.5 metre below the ground surface.
3. King:
A king develops from an unfertilized egg and becomes fully developed by consuming a superior diet. He is the father of the colony and is a constant companion of the queen, living with her in the ‘royal chamber’. He is much smaller than the queen and is slightly bigger than the colonizing individuals. He mates with the queen from time to time and, thus, aids her in laying fertilized eggs from which the colonizing forms and workers develop. The king’s life is much shorter than that of the queen and, when he dies, he is replaced by a new one.
4. Complementary Castes:
They are short-winged or wingless creatures of both sexes and lead a subterranean life. In the event of the untimely death of the king or queen in a colony, the complementary castes replace them. They are induced by the workers to undergo sexual development.
B. Sterile Castes:
1. Workers:
The workers develop from the fertilized eggs but remain stunted as they are reared on ordinary food. Numerically, they are the most abundant in a colony but are smaller than the soldiers. Their mandibles are well developed and are adapted to the gnawing of wood.
The workers shun light and need high humidity for their survival. These conditions are maintained inside the tunnels in which they move about in search of food. Often these earthen galleries are above ground and run for long distances. The food of the termites consists of timber, wood, and dry stems of plants, sugarcane setts sown in the field, paper, books or any other article that contains cellulose.
Except for the reproduction and defence of the community, practically all other duties are performed by the workers. They take care of the eggs and the young ones and remove them to safe places at the time of danger. They also tend and feed the queen, collect food and cultivate a fungus food (ambrosia) in underground gardens.
When a new colony is established, the earlier broods of workers construct a hemispherical chamber for the queen and it is connected with innumerable galleries. In certain species, the workers also construct a high mound above the ground which is known as the termitarium. Since the workers have to collect all provisions for the colony, they are notoriously destructive.
2. Soldiers:
The soldiers develop from unfertilized eggs and remain comparatively underdeveloped. They are the most specialized members of the community and can be readily recognized by the large head and strongly chitinized sickle-shaped mandibles. In a colony, two well- defined types of soldiers can be distinguished.
(a) The mandibulate type with large and powerful jaws, but with no frontal rostrum.
(b) The nasute type in which there is a median frontal rostrum, but the jaws are small or vestigial.
The former type of soldiers defends the colony by fighting the intruders and the latter type repels them by spraying an abnoxious smelling fluid through the rostrum.
Life-Cycle of Termites:
In the rainy season when atmospheric conditions are favourable, the colonizing forms leave their parent colony. As they are weak fliers, they do not travel a long distance unless aided by wind. As a rule, a particular species swarms at about the same time of season. The members of the swarm comprise individuals of both sexes.
They are attracted to light where they mix with individuals of the neighbouring swarms. A great majority of them fall prey to many types of predators and only a few individuals survive in the end. Sooner or later the survivors fall down and cast their wings and mate before or after shedding them. Both the male and female participate in the early operations of forming a nest by excavating small burrows or galleries or the nuptial chambers.
In the beginning only a few eggs are laid and are looked after by them and the newly hatched nymphs are fed by the parents themselves. They develop into workers and then take over all the brooding. During the first season, the reproductive castes are usually not produced. Gradually, the queen grows in size and the number of eggs laid increases.
The eggs hatch after one week during the summer and within 6 weeks the larvae develop to form soldiers or workers, as the case may be. The reproductive castes, when produced, mature in 1-2 years. The queen is capable of laying many millions of eggs during her life, which is very difficult to estimate, but probably 6-9 years is the approximate span.
The nests of many termites grow fungus gardens in the centre, near about the ‘royal chamber’. The fungus grows into a comb-like structure and is fed to the royal pair and the larvae.
In addition to the various castes in a termite nest, there live such insects as beetles, flies, thrips, some species of Collembola, Acarina, Diplopoda and Chilopoda. A termite mound may also afford shelter to lizards, snakes, scorpions and certain birds. All these creatures live either as symbionts for mutual benefits or as guests.
The family Termitidae contains over one-half the known species of termites and is economically very important.
A level account of the important species is given below:
(i) Globitermes sulphureus (Haviland) occurs from Myanmar to Malaysia and Vietnam. It attacks dead wood. The nest is largely underground, with a small dome-shaped part (cemented earth) projecting out; this visible ‘mound’ is 80 cm high and 60 cm in diameter at the base. Swarming occurs from January to May.
(ii) Eremotermes spp. are small, dull white, delicate looking termites which live underground and usually attack roots. E. dehraduni Roonwal & Sen-Sarma attacks the “Camphor”- yielding bush, Ocimum kilimandscharicum, in nurseries in North India. E. paradoxalis Holmgren is a pest of sugarcane in India.
(iii) Microcerotermes spp. are small, slender termites which live underground and often build globular carton nests which are either fully or partially buried in the ground. M. minor Holmgren is a pest of eucalyptus saplings in nurseries in India.
(iv) Macrotermes gilvus (Hagen) is a large, mound-building species, which occurs throughout South-east Asia. Its large, dome shaped earthen mound has a broad base and it goes up to about 3.5 m in height above the ground. The termite attacks wood-work in buildings in Malaysia and Indonesia and is also a sporadic pest of sugarcane there.
(v) Odontotermes spp. include several small to medium-sized species. They build large earthen mounds which sometimes rise to 2 or 3 metres in height above the ground.
Some of the important species are mentioned here:
(a) O. assanuthi Holmgren is widespread in India and is a mound-builder in the South. It is an important pest of sugarcane. Swarming in this species occurs in June and July.
(b) O. ceylonicus (Wasmann) infests buildings in Sri Lanka and it does considerable damage to wood-work. It nests in the ground.
(c) O. feae (Wasmann) occurs in India, Sri Lanka and South-east Asia. It is a serious pest of wood-work in buildings in India and Myanmar and also attacks eucalyptus seedlings in India. Swarming occurs from June to September.
(d) O. formosanus (Shiraki) occurs from eastern India to Vietnam and Taiwan. It attacks living plants and is a serious pest of sugarcane and young camphor trees in Taiwan.
(e) O. microdentatus Roonwal & Sen-Sarma, occurs in Uttar Pradesh, Madhya Pradesh and Bihar. It builds large, domeshaped mounds and is a pest of eucalyptus seedlings.
(f) O. obesus (Rambur) is one of the most common termites in Pakistan, India, Bangladesh and Myanmar. It is an important pest of several economic crops like sugarcane, wheat, barley, cotton, groundnut, tea, coconut palm, sunn-hemp, vegetables including chillies and several fruit trees including mango, citrus, seedlings of eucalyptus and many grasses. It builds tall, sub-cylindrical, earthen mounds which rise above the ground up to about 2.4 m which often possess a number of flat, vertical butteresses all around. Swarming occurs at the beginning of the monsoons.
(g) O. parvidens Holmgren & Holmgren extends from Pakistan via India to Myanmar. It attacks the bark of several trees and may also kill standing plantations of teak, by girdling the trunk. It is also a pest of tea in north-eastern India. The nest lies underground and the species swarms from February to April.
(h) O. redemanni (Wasmann) occurs in Bengal, South India and Sri Lanka. It attacks woodwork in buildings and coconut palm. It builds tall, subconical earthen mounds which go up to about 2 metres in height. Swarming occurs during the monsoon in eastern India and in November and December in Sri Lanka.
(i) O. wallonensis (Wasmann) is widespread in India, especially in deciduous forests. It builds large, irregularly-shaped earthen mounds with a number of rounded, open mouthed chimneys jutting out from the mound surface. It attacks wood-work in buildings and is also a pest of sugarcane as well as Casuarina and shisham (Dalbergia sissoo) trees.
(vi) Hypotermes obsuriceps (Wasmann) is found in eastern India, Sri Lanka and Vietnam. It builds large, broad-based, sub-conical earthen mounds in Sri Lanka, and it attacks timber in houses and also the living coconut palm. In Vietnam it is a pest of living palms and rubber trees.
(vii) Microtermes obesi Holmgren is widespread in South Asia. It is a serious pest of wheat, barley, oats, millets (bajra), maize, sugarcane, groundnut, tea, jute, mulberry, several vegetables and garden plants. Swarming occurs mostly in July and August.
(viii) M. mycophagus (Desneux) is an arid zone species and occurs from Pakistan to western India. Swarming occurs from late June to early September.
(ix) M. pakistanicus Ahmad is found from India to Malaya. It is a serious pest of tea and other plants in Malaysia. It nests underground.
(x) M insperatus Kemmer is a serious pest of wood- work in houses and also attacks dead portions of living trees in Java.
(xi) Nasutitermes spp. are small to medium-sized termites. Soldiers generally have a rounded, nasutiform head which projects forward into an elongated, pointed rostrum. Nests are generally rounded and ball-like which are made of wood-carton and are lodged in branches of trees. A member of the genus Nasutitermes attacks wheat in India. In Borneo and Vietnam, N. matangensis matangensoides (Holmgren) is highly destructive to timber in houses, while N. panayensis (Oshima) occupies a similar position in the Philippines.
(xii) Trinervitermes biformis (Wasmann) is found in India and Sri Lanka. It is serious pest of several plants, e.g. wheat, sugarcane, cotton, groundnut, and several fruit trees, vegetables and grasses. The nest is generally subterranean, but in South India a small mound is built.
Damage Caused by Termites:
The termites live on cellulose which they obtain from dead and living vegetable matter. To obtain their food, they destroy wood-work, household articles, fences and wooden poles that come into contact with the soil. They also damage fruit and shade-trees, such crops are wheat, maize, sorghum, sugarcane, chillies and peas. They also make complimentary colonies in houses near the roof and damage the books and other material stored in cup-boards.
Control of Termites:
1. When a colony is established, it is not so easy to eradicate the pest. The only sure method is to reach the centre of the nest and kill the queen and the complementary forms. Since the termite tunnels run for hundreds of metres, it is often difficult to locate the royal chamber. However, in the mound-forming species of termites, it is much easier to locate the centre which lies in the mound or just below it.
2. To avoid the attack of white-ants in cultivated fields, care should be taken not to use green manure or raw farmyard manure.
3. Insecticidal control.
(a) Fruit Trees:
(i) In new plantations, the pits should be treated with 0.2 per cent lindane emulsion or crude-oil emulsion before planting the trees. This is done by thoroughly mixing 0.25 kg of crude-oil emulsion and a little arsenic in about 4 baskets of subsoil taken from the pit. The treated soil is returned to the pit.
(ii) To protect the tree trunks, spraying them with 1 per cent lindane is effective.
(iii) To protect the roots, 0.5 per cent chlorpyriphos or lindane or 3 per cent sanitary fluid in the irrigation basin should be applied.
(b) Field Crops:
(i) For protecting chillies in small plots, 3 per cent sanitary fluid should be applied to the soil. When large areas are to be treated, the sanitary fluid is put in a canvas bag at the rate of 25-35 litres per hectare. The bag is suspended in the irrigation channel.
(ii) Soaking the sugarcane setts in 0.5 per cent chlorpyriphos suspension or 0.25 per chlorpyiphos emulsion in furrows at the time of planting, saves them from termite attack. Alternatively, apply 25 kg of fipronil 0.3G mixed in 50 kg of sand per ha in the furrows and cover the sugarcane setts by planking.
(iii) Wheat seed treatment before sowing, with 400 ml emulsion of chlorpyriphos 20EC or 600 ml of fipronil 5SC in 2.5 litres of water per 100 kg seed remains effective for the crop season. Soil application of chlorpyriphos 4G @ 20 kg per ha or fipronil 0.3G @ 12.5 kg per ha at the time of field preparation is quite effective.
(c) Buildings:
A galvanised sheet of iron with its outer edge turned downwards when placed just above the damp-proof layer makes the house white-ant-proof. Wooden structures such as door frames should not directly touch the ground and should be raised on a cement layer.
An insecticidal barrier between the ground and wood-work in building should be made by treating the soil beneath the building and around foundations with 0.5 per cent chlorpyriphos. The solution should be applied at the rate of 5 litres per m2.
4. To protect wood-work, paint it with solignum. The cupboards, almirahs, shelves, etc. should be sprayed with chlorpyriphos frequently. The place from where the galleries originate in the house should be either sprinkled over or injected with 0.5 per cent lindane or chlorpyriphos suspension in water.
If wooden structures have already been attacked the injection of 0.5 per cent chlorpyriphos emulsions with a hypodermic needle into the wood and in the crevices is the only remedy. For a lasting relief the nests should be located in the vicinity and destroyed by flooding them with the insecticide emulsions.
5. Mounds of termite, if any, in the area should be treated with 0.5 per cent chlorpyriphos after breaking open the earthen structure and making holes with an iron bar. The insecticidal emulsion should be used at the rate of 4 litres per m3 of the mound.