Chapter 3 Anatomy of the honeybee
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The honeybee has been described as the most useful of all insects known to man, because it provides man, as well as other forms of life, with basic services vital to their survival. This the insect has been able to do because nature has endowed it with the special organs which enable it to live a peculiar way of life. To understand the creature, a closer study must be made of its anatomical structure which enables it, and it alone, to perform such functions as gathering and ripening nectar, collecting pollen and propolis, producing wax, etc., and incidentally fertilizing flowering plants.
Like all insects, the honeybee has three main parts: head, thorax and abdomen.
1. THE HEAD
Triangular in shape, the head has five eyes, a pair of antennae, and mouth parts consisting, among other organs, of two mandibles, the proboscis, etc.
a) The eyes: The seeing apparatus of the bee consists of a pair of compound eyes and three small simple eyes, called the ocelli. The compound eyes are composed of several thousands of simple light-sensitive cells, called ommatidia, which enable the bee to distinguish light and colour and to detect directional information from the sun's ultraviolet rays. The eyes of the drone are larger by far than those of the worker or the queen bee, occupying a large proportion of the total volume of the head. They assist him to locate the queen as he pursues her during the mating flight.
b) The antennae are a pair of sensitive receptors whose base is situated in the small socket-like membraneous areas of the head wall. They move freely in every direction. The antennae's functions are to feel or touch and to smell, and thus to guide the bee outside and inside the hive, to differentiate floral and pheromone odours, and to locate hive intruders.
c) The mandibles are a pair of jaws suspended from the head and parts of the bee's mouth. The insect uses them to chew wood when redesigning the hive entrance, to chew pollen and to work wax for comb-building. They also permit any activity requiring a pair of grasping instruments.
d) The proboscis: Unlike the proboscis of all other sucking insects, that of the honeybee is not a permanent functional organ; it is improvised temporarily by assembling parts of the maxillae and the labium to produce a unique tube for drawing up liquids such as sweet juices, nectar, water and honey. The insect releases it when needed for use, then withdraws and folds it back beneath the head when it is not needed.
2. THE THORAX
The armour-plated mid-section of an insect, the thorax, supports two pairs of wings and three pairs of legs, and carries the locomotor, or "engine", and the muscles that control the movement of the head, the abdomen and the wings.
a) The legs: Each pair of legs differs in size and shape from the other two pairs and is Jointed into six segments, with a pair of claws at the tip which help the insect to cling to surfaces. The leg can be flexed at any of the six joints. Its primary function is to help the bee to walk and run, but various parts also serve special purposes other than locomotion. For example, the brushes on the inner surface of the fifth segment, (the tarsus) of the two front legs are used for sweeping pollen and other particles from the head, eyes and mouth parts. The same tarsi of the mid-legs serve as brushes for cleaning the thorax, while the spines found at the end of the fourth sections (tibiae) are used for removing the pellets of pollen and for cleaning the wings. Two important parts to note on the legs are the antenna cleaners on the front legs and the pollen baskets on the hind legs.
i) The antenna cleaner, located on the inner margin of the tibia of the forelegs, consists of a deeply-cut semi-circular notch, equipped with a comb-like row of small spines. All three castes - drone, queen, worker -- have this cleaning apparatus.
ii) Pollen baskets: The tibiae of the hind legs of the worker bee carry a special apparatus, called the corbiculae, or pollen baskets, which enables her to carry pollen into the hive. These pollen baskets, concave in shape, are surrounded with several long hairs which bind the contents into an almost solid mass, allowing the worker to carry the load safely home.
b) The wings of the honeybee, like those of most insects, are thin, flat and two-layered. The front pair is much longer than the rear. The worker's wings are used both for flight and for ventilating the hive, while the drone and the queen use theirs for flight only.
3. THE ABDOMEN
Like the thorax, the abdomen is armour-plated. It contains such vital parts as the heart, the honey sac, the stomach, the intestines, the reproductive organ, and the sting. As seen from the outside, only six segments can be observed, but the adult honeybee has nine, while the larva has ten.
4. INTERNAL ORGANS
The interest of the beekeeper is usually focused on those parts of the bee which make it capable of producing honey and wax and performing other duties necessary for its survival. Among these are the hypopharyngeal gland, the wax gland, the scent or pheromone glands, the queen's pheromone glands, and the sting with the passion gland.
a) The hypopharyngeal gland is located in the head of the worker bee, in front of the brain. It starts to mature three days after the bee's emergence, and develops only when the insect secretes royal jelly to feed the young larvae and the queen.
b) The wax gland, located in the lower part of the young worker's abdomen, releases wax between a series of four overlapping plates, called sterna, below the abdomen. The worker begins to secrete wax 12 days after emerging; six days later, the gland degenerates and the worker stops comb-building.
c) Scent glands: The worker bee produces three main scents. The gland beneath the sting produces a special pheromone consisting mainly of isopental acetate, which it sprays around the spot of the sting. The odour stimulates other workers to pursue and sting the victim. A second alarm pheromone, released by glands at the base of the mandibles, has the same function. A third gland, located near the rear of the abdomen, produces a pheromone which, when released by scout bees, attracts swarms of other bees to move toward them.
d) Queen's pheromone glands: In the queen bee's mandibles are located special glands which produce and release pheromones called the queen substances, which enable her to identify members of the colony, to inhibit ovary development in worker bees, to prevent the workers from building queen cells, to help a swarm or colony to move as a cohesive unit, and to attract drones during mating flights. The absence of the queen substance (e.g. when the queen dies) produces opposite responses, i.e. worker bees begin to develop ovaries and to build queen cells, and a swarm searching for accommodation will not cluster but will divide into smaller groups that cannot support the normal life of a bee colony.
e) The sting of the worker bee is designed to perforate the skin of her enemies and to pump poison into the wound. It has about ten barbs, so that when it is thrust into flesh, the bee cannot pull it back again. It breaks off with the poison sac always attached to it, enabling more poison to penetrate for as long as it remains in the flesh. The bee's sting is lodged in a special sheath and is released only when the need arises. The sting of the queen bee is longer than that of the worker. It is used only to fight and kill rival queens in the hive. The drone has no sting and is totally defenceless.
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