(Insecta: Isoptera)
Termites are small to medium sized, soft bodied insects that very in colour from pale-white to dark brown. They are commonly known as white ants, which are considered to be the most destructive insects to our crops, forests, orchards, timber and houses, a title received by them due to their wood-feeding habit.
They are one of those few animal species that survive exclusively on cellulose and carry cellulose-digesting flagellates inside their intestines to help them in this difficult task. Being shy and photophobous, they make underground nests called termatoria, in which they maintain constant temperature and humidity, even when outside ground temperature rises to above 60 degrees, by constructing intricate over ground natural air conditioners called termite-hills.
There are six recognised families of termites in the world, viz. Hodotermitidae, Rhinotermitidae, Termitidae, Kalotermitidae, Indotermitidae and Mastotermitidae, the last one is endemic to Australia. Termitidae is the largest family and highly evolved. They are soil inhabiting and build nests both underground and huge termite mounds over ground. Species of Odontotermes build conspicuous mounds above ground, population in each one of which may range from 4500-90,000 individuals. Microtermes are small and many of them serious pests of crops. The family Kalotermitidae are wood-inhabiting termites that do not form a well-organised nest, which is without a queen cell as they can multiply through substitute reproductive castes.
Damage: Termites cause serious damage to wood used in buildings etc. About a dozen species are injurious to crops. The list of crops damaged is large because they would eat up anything containing cellulose. Young plants die quickly because the roots or shoots are cut. Termites loosen the soil around roots due to which trees and plants become prone to lodging in rain and storm. Loose soil also leads to loss of irrigation water and soil erosion. Losses due to termites have been estimated to be from 5-35%.
Biology: Termites were the first animals which started living in colonies and developed a well organised social system about 300 million years ago. Although termites do not exceed 3-4 mm in size, their queen is a 4 inch long giant that lies in the royal chamber motionless. Hence workers have to take care of all its daily chores. Termite queen is an egg-laying machine that lays up to 60,000 eggs per day.
Generally all termites can lay at the rate of 6000-7000 egg per day. If a queen is lost by accident or death, nymphs in various stages of development are quickly matured to neotenic female forms which can lay eggs, possibly parthenogenetically. The other castes, workers and soldiers are highly devoted to the colony, working incessantly and tirelessly, demanding nothing in return from the society. Soldiers have long dagger-like mandibles with which they defend their nest and workers chew the wood to feed to the queen and larvae and grow fungus gardens for lean periods. Nasutes are specialized soldiers which specialize in chemical warfare.
In breeding season which usually coincides with the rains, newly produced males and females in large numbers grow wings, have nuptial flight, disperse to long distances, make pairs and find a new place to start a colony. The phenomenon is known as swarming. After nuptial flight, the males and females pair off, shed their wings and move away. They both then dig a pit and first batch of 100 to 300 eggs 3-10 days after swarming. The eggs have an incubation period of 20-40 days and the hatched nymphs all develop into workers which make new galleries and enlarge the nest. Queen settles down and undergoes physogastry, a phenomenon in which abdomen of the queen enlarges enormously by the expansion of the intersegmental membranes, the sclerites appearing only as brown spots.
Ecology: Termites maintain high humidity, about 85-90%, in their nests and grow fungus gardens which also retain humidity. With the fall in moisture contents in the upper layer of soil, termites migrate to the deeper layers. They live in galleries made by feeding on dry and moist wood. Spare space in galleries is blocked out by brown faecal matter cemented together.
Cellulose in any form is the food of termites. Some ingest large quantities of soil along with debris and decomposed wood. Workers collect and grind the food and feed it to other castes mixed with saliva. Digestion of cellulose in primitive termites is by a flagellate protozoan, Trichonympha, which abound in the rectal pouch of termites. Young termites have to get it in their intestine by feeding on the faecal matter of the adults.
TERMITE CONTROL
Different control techniques have to be applied in different situations in order to control termites. They fall in the following categories.
Use of resistant material: Resistant timber against Hodotermes indicolla has been achieved by the Forest Research Institute. However, much success has not been achieved against more serious species. Conifer trees are resistant because they contain resin.
Treatment of material with chemicals: Many chemicals such as creosote, Ascu, copper or zinc resinates, aldrin, dieldrin, DDT and BHC showed promise in protecting timber. This is done by surface treatment of timber, mudwall poisoning or by soil poisoning. Two percent solution of aldrin 40 EC and dieldrin 18 EC gave protection for 4 years.
Creosote pressure impregnation is currently the standard recommendation for almost permanent termite proofing of timber. A mixture of dieldrin and copper nephthelate has also been recommended for long term timber preservation.
Use of barriers in buildings: Zinc chroride or copper sulphate 20% was tried for treating soil which formed barriers. Good cementation and termite shields of copper plates are dependable barriers. Parathion in very light dilution was found to be more effective sol poison than DDT, BHC or chlordane.
Destruction of termite nests: Destruction of termite mounds gave only temporary relief because accessary reproductives could be quickly formed after queen’s death. Chemical treatment of nests was found more effective. Application of 3% sodium or potassium cyanide or arsenic dust, creosote + kerosene at 1: 3, carbon disulphide and dichlorobenzene were very effective in wiping out termite nests. Aldrin and dieldrin have been found to give more lasting control even in low concentrations.
Protection of crops and trees: Destruction of nests is only a minor aspect of termite control. Before adopting chemical control, the relationship between the crop cycle and the seasonal behaviour of termites, effects of such treatments on soil and crops and on human being should be kept in mind. Generally application a few inches below soil and preceding the planting gives best results.
Control on trees: Treatment of soils with naphthalene, paris green, white arsenic, calcium cyanide or dichlorobenzene is useful. For protecting living trees, spraying the bark with the same chemicals or with lime or by applying a band of GAMBIR (gum of Terra japonica) or KATTHA (extract of Acacia catechu) mixed with lime gives protection. Coal tar bands can also be applied on tree trunks. FRI’s recommendation is to use 5% dust of aldrin 30EC or dieldrin 20EC @ 30-35 kg per acre. Other treatments include fuel oil, phenol, castor oil or coal tar spray or banding on the trees.
Control on field crops: There is hardly any crop that is not liable to termite damage. The following crops are particularly susceptible to termite attack.
Jute. Jute is attacked by Microtermes obesi, which can be controlled by soil application with aldrin 5% dust or heptachlor dust 5% @ 15 kg per acre. On the standing crop parathion 0.01% gives good control on the stems.
Wheat. Soil treatment before sowing should be done either by green manuring with neem or Calotropis leaves or by white arsenic or paris green or by BHC or heptachlor 5% dust. Seed treatment is done by soaking wheat seeds in 0.25% mercuric chloride or 0.55% copper sulphate for 12 hours.
Cotton. Soil treatment can be done as mentioned above and sevin and heptachlor give good protection to cotton plants.
Sugarcane. Aldrin or dieldrin even at low doses give prolonged protection if applied in soil before sowing. Sett treatment with 0.25% mercuric chloride or with coal tar is recommended. Soil application of aldrin or dieldrin gives protection even to the standing crop.