The social organization of the honey-bees is established by the living of all individuals within the colony and they show the mutual cooperation among the members of the colony, and exhibit the overlapping generations.
At least there is a division of labour among the different types of honey-bees in the colony or hive. The different forms or types of insects having a particular function live in the colony, called the castes.
Caste System:
Thousands of bees (50,000 to 1,00,000 or more) which live in a hive are of three different forms:
(1) Workers (infertile females),
(2) Drones (males) and
(3) Queens (fertile females) (Fig. 18.74A).
The phenomenon of existence of several morphological forms with separate functions in a species is known as polymorphism. So honey-bees are well known as social and polymorphic insects.
The true social organization (eusociality) of honey-bees is well understood in the study of Apis mellifera. They live in colonies in hives and each bee-colony includes several thousands of bees which consist of one queen, several hundred drones and tens of thousands of worker bees (50,000-80,000 or more).
Both queen and workers are female and diploid. Drones are males and haploid. A strong or healthy colony is called when the maximum number of workers is found in the colony.
Queen bee:
Generally a single matured queen is present in each hive. The size of the queen is nearly 2.5 times longer than that of a worker bee. If is characterized by the long tapering abdomen, well-proportioned body, short and golden coloured wings and colour of the legs. They are 2.8 times heavier than the worker bees.
The queen possesses a curved sting at the tip of the abdomen which is known as ovipositor. The function of the queen is reproduction and lays about 1000- 2000 eggs every day depending upon seasonal variation and seasonal factors. The eggs may be either fertilized or unfertilized.
Depending on the type of food supplied to the newly developed larvae by the nursing workers the eggs may develop either queen or workers. The drones or males are produced by the laying of unfertilized eggs (i.e. parthenogenetically). The queen deposits each egg in a cell prepared by the worker bees (Fig. 18.80).
After three days the eggs hatch into small larvae. The larva which is fed with a special food called ‘royal jelly’ develops into queen. The royal jelly is a high proteinous substance produced by the hypopharyngeal glands of the workers.
The larva which is selected to become queen is taken before the third day of development in a special chamber, called queen’s chamber. The queen lives five to eight years on average and her fertility decreases with the increase of age. The sting of the queen serves an ovipositor for lying of eggs and is also used for defence. The sting is used only when she meets another rival queen.
The queen secretes a kind of chemical substance with hormonal properties from the mandibular glands, called pheromone or queen substance which inhibits the growth of ovaries of workers and control the activities of all bees within the hive. She can attract the workers towards the queen and stimulates the workers to build wax cells for worker bees and drones but prevents in the building of queen cells.
The Dutch naturalist Swammerdam (1673) remarked that queen is the mother of the entire colony and has no food collecting organs. Johann Dzierzan, a German scientist reported in 1980 that the queen bee is the centre of the bee family and the mother of all the young bees.
When the queen becomes matured she leaves the hive with some drones and takes several nuptial flights and mates with a drone. After copulation the drone dies soon after and the queen stores enough sperm in the spermatheca to last her lifetime. The queen after copulation returns in her old hive and is looked after by nurse workers, known as her retinue.
With the increase of the age the egg laying capacity of the queen loses, the workers choose a three day old egg. This egg after hatching into larva is fed with royal jelly and it develops a new queen in about 16 days. At that time the old queen leaves the hive along with some workers to establish a new colony.
Drones:
The drones are the male members of the bee colony and are haploid each genetically. The drones take 24 days to develop from the egg to adult. They have no food (pollen and nectar) collecting organs. So the drones are totally dependent on worker bees for food. They feed on the honey during spring and summer months provided by worker bees and are driven out in autumn from the hive.
Function:
The main function is to fertilize the queens. They also help to maintain the warmth of the hive which is necessary for the hatching of the eggs.
Workers:
The size of worker bee is small but they constitute the majority in a hive. They are produced by the fertilized eggs laid by the queen. It takes 20 days from egg to adult and life span is about 6 weeks.
Function:
All the time in their lives is spent for the maintenance of the hives and caring for their members. Workers are involved in hive construction, clean the cells of the hives collect the nectar, pollen and water and store within the cell properly. Water is required for the preparation of royal jelly from pollen for food and for dissolving crystalline honey.
They repair the cracks in the walls of the comb and polish the walls with propolis. The workers also maintain the optimum temperature within the hive by fanning during summer, and in severe winter when the temperature falls sharply they gather outside the hive and reduce the temperature loss of the surface of the hive.
It is assumed that workers always remain busy in their duties but A. I. Root, an American scientist often pass remark during his lectures that the workers slept in night heavily than during the day. If any intruder bee happens to fly into the hive, the workers not only kill the intruder but push the body out from the hive as a sign of warning to others.
Swarming and Formation of New Colony:
During the early summer swarming happens to avoid the overcrowding in the old hive. The old queen, several thousand workers and hundreds of drones come out from the old hive and fly together in search of a suitable place for the formation of new colonies, In the new hives, the different castes live together, in which division of labour is well pronounced.
Nuptial Flight and Copulation:
About a week after emergence from her chamber, the new queen flies in air with many drones. The copulation takes place in the air with a drone and the queen receives the spermatophores from the drone. After copulation, the genital parts of the drone are forced out and the drone dies immediately.
It was believed that the queen copulates only once in her life but recent observations have shown that they can mate more than twice in her life time. The flight of one queen with several drones in air for copulation is called nuptial flight.
The honey bee family is an excellent example of social life. The different castes depend on each other for survival as well as co-operating with the developing broods in the hive.
Hive or Comb:
The worker bees construct hive with the help of wax secreted from the wax-secreting glands of the abdomen. They repair the cracks of the walls of hive with propolis (resinous substance collected by bees from different parts of plants for use as glue) and balm collected from the plants and is used in the construction of comb.
The propolis is used as a glue to bind broken parts, and balm is taken for polishing inner walls. Each bee hive contains thousands of hexagonal cells arranged in two vertical rows.
These cells are of 5 types:
1. Queen cells:
These are a very few in number in a hive. They are larger than the other cells and vase-shaped, and are situated at the margin of the comb. These cells are used for queen rearing.
2. Drone cells:
There are about 200 drone cells in each hive and are smaller than the queen cells. The drones are reared in these cells.
3. Worker cells:
Majority number of cells is worker cells and each cell is about 5 mm across. The workers are reared in these cells.
4. Brood cells:
The larvae of the honey bee are reared in these cells.
5. Storage cells:
These cells are meant for the storage of honey and pollen.
Role of Hormone for Social Organization:
The mandibular glands of queens are situated in the head and open at the base of mandible. The queen secretes a kind of chemical substance that inhibits the development of ovaries of worker bees.
A British researcher, C. G. Butler found that the nature of the inhibiting substance was oxy-deconoic acid, a substance with hormonal properties that controls the activities of all bees in the hive. The queen bee secretes a pheromone by mandibular gland and attracts drones.
Language of Honey Bee:
Bees are known to have some method of communication amongst themselves.
Karl Von Frisch, a vienna born scientist and great experimenter on the behaviour of honey bees, discovered the communication mechanism and decoded the ‘language of bees’ in 1946. He was a Noble Prize winner in 1973. As soon as one bee finds a source of nectar, it immediately conveys the source and direction of the source to other bees of the same community.
They perform certain rythmic movements and emit odours that are easily received by other bees. When the source is nearer to hive (within 100 metres), reporter bee or forager or worker bee performs a round dance (Fig. 18.75A), turning in a circle, once to left then to right and repeating the same movement for 1½ minutes in one place.
Round dance informs the distance of source of food which is less than 100 metres but cannot give the indication of direction.
If the source is further away, the reporter bee performs a tail wagging dance (Fig. 18.75B). It runs towards the direction straight ahead for a short distance, wagging the abdomen, makes a 360° turn towards left, runs ahead once again and turns right. This is repeated for several times.
These dances are closely watched by other bees in the hive and then immediately they come out in search of the source. The wagging dance informs their sisters of the hive both direction and distance of the source of food (nectar or pollen) discovered by the worker bees and is considered as language of bee. The direction of straight run indicates the direction of source of food and tempo of the dance also indicates distance.
Odours play a vital role in their communication. Sudden death of queen bee is relayed to 60,000 or more bees of the hive in less than an hour. Healthy queen secretes an aromatic substance called ‘queen substance’ which is licked off by her nurse bees.
When the queen dies the secretion stops and the absence of the queen substance is immediately relayed to all the members of the colony. The message being conveyed to all members of the colony; they at once set about the vital task of rearing a new queen.