Few animals belonging to the order Isoptera and Hymenoptera of class Insecta, exhibit social behaviour. These animals live in complex societies and are referred to as eusocial. Eusociality is an extreme form of social behavior found in just a few types of animals and is characterized by:
- Occurrence of polymorphic forms each assigned with a different function
- The presence of several generations in a single hive/nest at the same time
- Worker members of the colony which provide food and care for the reproductives and the early developmental stages of the colony.
- Division of labor with queens that reproduce a lot
General characteristics of social insects
The following are the characters commonly possessed by all the social insects:
- Parental care: Parental care is an instinct behavior whereby the young ones are provided with food, shelter and defense by the parents as a part of the family relationship. The social life in insects is linked with parental care. Parental care paves way for stronger association between the parents and the young ones. Parental care includes activities like providing the young ones with food, cleaning the nests, feeding the young and queen, removal of debris and bodies, arranging eggs in proper chambers, protecting the queen from all adversities, cooling the nest in summer season.
- Rich nests: The nests of all social insects are rich in structure which helps in protection, storage of food and maintenance of broods. The following table summarizes the nest richness of various social insects:
|Position of nest
|Material of nest
||Leaves, wood, soil
|Shape of nest
||Chambers & galleries
||Chambers & galleries
|Nest built by
||Females & workers
||Females/males & workers
||Female/male & workers
|Population of nest
||Pollen & Nectar
||Vegetables, wood, insects
||Wood & insects
||In some species
- Polymorphism: Polymorphism is the occurrence of several forms within the same species. It refers to specialization of individuals within a species. In the animals exhibiting polymorphism, individuals at the center of the colony develop gonads and reproduce sexually. Individuals at the periphery expose themselves to danger of combat, and do not reproduce sexually. This is also an example of altruistic behavior. The polymorphic individuals are sometimes called super-organisms, as in polymorphic individuals the unit for natural selection is not a single individual but the whole colony. The social insects are the most prominent examples of super-organisms. They are found in two orders of class Insecta namely Isoptera and Hymenoptera.
- Termites included in the order Isoptera have typical sexual reproduction, and ants, bees and wasps included in order Hymenoptera have haplo-diploid sex determination. The general structure of these super-organisms is that there are only one or very few reproductive females, small numbers of reproductive males, and large numbers of non-reproductives that provide food and care for the reproductives and the early developmental stages of the colony. In termites, non-reproductives include are both male and female where as in Hymenoptera the non-reproductives include only females. In most of these super-organisms, reproductives and non-reproductives are genetically identical, and environmental factors control the development, by suppressing the developmental capabilities of reproductives.
- Large population: Al the individuals of the social insects species live in an integrated manner and hence the term colony is commonly used to describe their complex society. These colonies are matriarch or in other words, all the members of the colony are the offspring of a single female and so all of them have similar genotype. Also these colonies do not accept the members form other colonies of same species.
- Extra populations: Some aphids, beetles, mites etc. are attracted into the nests of ants and termites by the high temperature and surplus food. These extra populations are protected and fed by the ants and termites. In return the ant and termite populations feed on a fluid secreted by them. Sometimes intruders and thieves rob the social insects of their food. Some beetles live in the nest of the ant and feed on the ant larvae. All these form the extra populations of the social insects.
- Cohesiveness of the colony: Cohesiveness is a measure of the attraction of the group to its members and the resistance to leave it. The sense of team spirit and the willingness of its members to coordinate their efforts are very important for the group to perform best as a biological unit. All the members of the insect society live in a coordinated manner. As a result of this various castes which differ in structure and function are formed. And these castes cannot live independently. All the members of the colony work in cooperation and they reap mutual benefit of the work done. The success of these insects is measured in terms of the colony and not individually. The members of the castes are bound by chemical and physiological mechanisms.
- Liberal food facility: After laying the eggs, stingless bees and some other insects provide sufficient mass of food for development of the larvae which hatch out of the eggs. This phenomenon is known as mass provisioning of the food. At the same time, other social insects daily feed their young ones continuously and extensively. The young ones are fed until they metamorphose into adults. For example, in the ant colony army ants hunt insects or flesh; pastoral ants feed on the honey dew produced by aphids. Also the pastoral ants carry the aphids into the overwintering locations to protect them from predators. Harvesting ants gather and store seeds in summer to tide them throughout the winter.
- Finally the leaf cutter ants or fungus growing ants grow their own crop of fungi. These ants cut and carry the leaves underground to serve as a substrate for growing fungi. These ants feed on the fungi. Protection of the colony and self: Protection of the individual self is done with the help of protective devices like stings and jaws. Stings are present in most of the bees and also in few ant species. Also well-developed jaws are present in stingless bees, soldier ants and termites. Sometimes for the protection of the colony or nest, few guards are posted at certain locations. These guards protect the nest and attack the intruders. Finally the nests are made in such protective locations which have the possibility of rapid exit during danger. Insects also take care that their nests have numerous side exits.
- Trophallaxis: Exchange or sharing of food between the insects of different species is called as trophallaxis. For example, termites and ants feed each other from mouth to mouth. Similarly young ones exchange food with the adults. Also beetles, aphids and coccids are fed by ants and then in return ants drink a fluid secreted by them. This is a form of mutual feeding. Trophallaxis is an important phenomenon in determination and regulation of castes in termite colony. During trophallaxis, ectohormones with certain inhibitory substances are passed on to the young nymphs and this prevents them from developing into individuals of same sex or caste. Consequently the number of individuals in a particular caste is maintained.
- Communication: Communication is an interesting feature found both in social and nonsocial insects. Insects use chemical, visual, tactile and auditory signals as a means of communication with each other. Chemical communication occurs with the help of body secretions called pheromones. Pheromones pass out of the body and help in regulating and coordinating the colony activities. For example, ants deposit substances on their way which act as trail markers and help them return to their homes after foraging trip. Similarly visual, tactile, and auditory signals help in various activities of the colony.
- Swarming: The behaviour of the insects to come out of the nest in large numbers to relieve the overcrowding is called as swarming. It takes place during spring or early summer seasons. Swarming occurs for feeding and migration. It is also a means of the colony reproduction or in other words founding of new colonies. The queen and the males mate during swarming flight and this is also known as nuptial or marriage flight.
SOCIAL ORGANIZATION OF TERMITES
The termite life cycle has the three castes, the reproductives, the soldiers and the workers. Due to the fact that termites are hemimetabolous insects, even the nymphs take part in the social life and have their specific tasks to accomplish. In case of termites, once the caste of an individual is determined, development into other castes is still possible. Soldiers also called as inter-castes, may turn into workers or even into reproductives, if there is a shortage of individuals of other castes. This process of development in to other castes is controlled by pheromones. In the case of the queen, there is a specific ‘queen’ pheromone, preventing other individuals from turning into queens. Only if the queen is removed or dies, does the lack of the specific pheromone promote the development of a new queen.
Reproductives- Reproductives have compound eyes and are more or less brown due to their sclerotized cuticle. Developing reproductives have wing buds, wings or wing stumps. Reproductives can be further divided into:
Alates: They are young winged reproductives of both sexes. From time to time about 100 to 1000 alates leave the colony for a mating and colonizing flight. After mating a pair settles down at a suitable site like a rotting scar on a tree to establish a new colony.
De-alates: These are the alates that cast their wings after the colonizing flight and successively turn into queens and kings. Initially only a few eggs are laid and brought up by a female de-alate. As the number of individuals in the colony grows, more workers are available to help the young queen to care for the brood. After three to five years the number of individuals is already so large, that the colony of this pest species can turn into the damaging stage.
Queen and king: They are the main reproductive individuals in a colony. Once there are many workers to help the queen, her only job is to produce tremendous number of offsprings. A large queen may lay more than 1000 eggs per day. The life span of a queen can be as much as 50 years.
Neotenics: They assist the queen in laying eggs, once her productivity decreases. When the queen has died or deteriorated, one of the neotenics takes her place and so they are also known as Secondary queens. Hence, the removal of a queen from her colony does not necessarily mean the end of the colony
Workers: They are sterile, wingless and blind males and females. Their cuticle is unpigmented and not hardened; therefore the animals are confined to a dark and moist environment. Workers build the nest and galleries, they fetch food, care for the brood and feed reproductives and soldiers. The life span of a worker is about one to two years.
Soldiers: Just like workers, they are also sterile, wingless and blind males and females with an unpigmented, unsclerotized cuticle. Soldiers defend their colony from intruders by the use of powerful jaws or by ejecting a white sticky repellent from an opening on their head. Soldiers can’t feed themselves; they have to be fed by workers. Usually the number of soldiers is much smaller than the number of workers. Soldiers can be mandibulate or nasute depending on the species. Therefore soldiers can be used for the identification of termite species. The life span of the soldiers is about one to two years.
SOCIAL ORGANIZATION OF APIS
Honey bee is a social insect. The nest of the honey bee is known as the bee-hive. The population of an average sized colony consists of 30 to 50 thousand individuals.
A colony is termed ‘weak’ or ‘strong’ according to the number of worker bees it possesses. There are three types of individuals in a colony, namely the Queen, worker and drone. Due to the existence of several morphological forms, bees are said to be a polymorphic species. All these three castes depend on each other for their existence. Drones and queen are concerned only with reproductive function and so the workers have to perform all the other duties of the colony.
The following is the description of each type of member of the bee colony,
Queen: It is a diploid, fertile female. The presence of queen in a colony is a must. The size of the body of queen is much larger than other castes of bees of the colony. Her legs are strong as she always has to walk about on the comb. The queen has a sting curved like a scimitar at the tip of the abdomen, which is a modification of the egg-laying organ known as ovipositor. The sting serves as an organ of defense. She never uses it against anybody except her own caste. The queen is responsible for laying eggs for a colony. She lays about 1000 to 1500 eggs every day and lives for about two to three years. She lays both fertilized eggs (from which females develop) and unfertilized eggs (from which males develop).
Worker: It is a diploid, sterile female. The size of a worker is the smallest among all the other castes but they constitute majority population of the bees in a colony. The following are the functions of worker bees,
- Collection of honey,
- Producing royal jelly for feeding the community,
- Raising larvae and young ones,
- Cleaning the comb,
- Making wax,
- Constructing the beehive,
- Defending and protecting the hive,
- Clearing the debris and dead bees,
- Maintaining the temperature of the hive
Numerous adaptations have occurred in the worker bees for performing various functions. The body is covered with branched hairs so that when a bee visits a flower, pollen grains adhere to the hairs and other parts of the body. The worker cleans off pollen grains with special structures, the antenna cleaners on each foreleg, pollen brushes on all legs and pollen combs on hind legs. All pollen is stored in the pollen basket present on the outer surface of tibiae on hind legs.
Water and nectar are gathered by means of sucking mouthparts which are modifications of the maxillae and labium. Workers are provided by a sting at the tip of the abdomen which is a modified ovipositor. The sting is used to protect the colony from the enemies. A large poison storage sac is connected with the base of the sting. Two acidic and one alkaline gland mix their secretion to form poison which is injected by the operation of muscles to other animals. During the withdrawal from the prey’s body, the stings along with other poison apparatus are torn off, resulting in the death of that particular bee. Workers are female but are incapable of producing eggs. The life span of a worker bee is about 4 to 5 months.
Types of worker bees
Worker bees are again of different types depending on the type of work they do,
Laying worker: These worker bees lay unfertilized eggs in the absence of the queen bee. Drones develop from these unfertilized eggs.
Nurse workers: These worker bees are 1-10 days old. They serve the queen with troyal jelly which contains more mandibular secretion. These nurse workers also serve the larvae and drones with honey and beebread which is the combination of pollen and honey. Nurse workers also help in cleaning the beehive.
House workers: These workers are 10-20 days old. These workers perform house cleaning, comb building, accepting nectar and pollen for foragers and finally guard the hive. The special wax glands are present on the abdominal segments of these worker bees. The wax glands secrete bee wax. Bee wax is used in making walls and caps of the comb. These workers also transfer the eggs with larva to make new queen.
Field workers: These workers are 20 days plus older. These workers travel to distant places to collect the nectar, pollen grains and resin from the flowers. They convert the nectar into honey with the help of the enzymes present in their crop. The honey and pollen grains are deposed by these workers into the storage chambers. The field workers also make propolis from the resin collected from the flowers and tree saps. Propolis which is special bee glue is used to seal the cracks in the comb.
The field workers perform two types of dances namely round dance and waggle dance. Through these dances, bees communicate about the source of food and the distance & direction of food source from the hive.
Drone: It is haploid, fertile male. The drones are born out of unfertilized eggs in the brood chamber. The males are larger than workers and are quite noisy. They have large wings, robust body and reduced mouthparts. They are unable to gather food, but they voraciously eat the food fed to them by the worker bees. They are stingless and their sole function is to fertilize the queen during the nuptial flight after which they are starved to death. They are designated only for mating. The number of drones in a colony varies from 200-300. The drone develops parthenogenetically from unfertilized eggs. Drones live only for a short period of time.
- Discuss the general characteristics of social insects.
- Write few points about each member of a bee colony.
- Write about social organization of Honeybees.
- Write the functions of each member of a termite colony?
- Describe social organization of termites.
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