Eusociality in termites

Termites are diploid eusocial insects belonging to the order ‘Isoptera’. They thus satisfy the three conditions of eusociality.

1. There is cooperation in looking after the young.
2. Reproductive castes cared for by non-reproductive.
3. There is an overlap of at least two-generations contributing to colony labour.

On the basis of reproduction, termites have two castes

1. Reproductive caste
2. Non-reproductive or sterile caste

1. Reproductive caste:- Reproductive or fertile castes are of three types.
   Macropterus:- They are primary forms which developed into king and queen. They have well developed wings, eyes, brain and sex organ. These forms mate, loose their wings and start the colony.
   Brachypterous:- They have vestigial wings. If the macropterus king or queen dies, it’s place is taken up by the brachypterous forms forming substitute king and queen.
   Apterous:- They are worker like substitute king and queen and called ergatoid kings and queens, they are rare and found only in primitive termites.
2. Non-reproductive caste:-
   They are mainly 2 types:-
   1. Workers
   2. Soldiers

   1. Workers:- Both male and female workers are small sized, wingless, sterile forms, most numerous in colony. Taking care of the eggs, collect food, feed and tend the queen. Cuitive fungus garden in the colony.

   2. Soldiers:- Wingless larger in size than worker and sterile. Possess well developed mouth parts.
      They are two types;-
      (i) Mandibulate
      (ii) Nasute

Formation of new colony:- Reproductive casts disperse from a colony during the rainy season. This is called swarming. After a brief fight called nuptial fight. The male and female fall in the ground and shed their wings and then they mate and form a small burrow in the ground, called nuptial chamber. The female starts laying eggs. The male helped her for laying eggs and make the colony. The egg laying queen gradually increases in size by her become large abdomen, in this stage it is called Physogastric female (Queen). When the egg laying capacity of the female is decrease, it is not fed by the workers and it dies of starvation. The production of various sterile castes from similar diploid eggs depends on variation in feeding and pheromonal control. Pheromones produced by queen and king at critical level suppress the ovarian development of newly reared workers.

Feeding:- Termites largely feed on wood(cellulose). In many species of termites, their hind guts contain huge number of symbiotic bacteria and flagellate protozoa. These microorganisms enable the termites to utilise the normally indigestible substances. These microorganisms are lost when cuticular lining of the hind gut is shed at ecdysis. However a newly moulted individual will be feed by special anal secretions rich in these microorganisms. They are fed by anal secretion of group members, sometimes by oral secretion of workers. Thus trophallaxis i.e. exchange of oral liquid and anal secretions is very important to enable the termites to digest their food.

Evolution of eusociality:- Termites are diploid animals they are all developed from similar eggs. The coefficient of genetic relatedness among siblings in a termite colony. Termites are dependent on symbiotic protozoans to digest cellulose in their gut and they get these through contact with group members. This fact however does not necessitate the evolution of sterile casts, eusociality are given by the following factors.

1. Family associations in food rich habitats.
2. Slow development.
3. Opportunities for nest inheritance.
4. High risk dispersal.
5. Advantages of group living.