Chapter 2 Honeybee biology

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A. Colony members
B. Development of the honeybee
C. Colony growth cycle; swarming
D. Colony defence
E. Foraging
F. Temperature regulation
G. Communication and recruitment to crops

 

A thorough understanding of basic honeybee biology is one of the most important requisites for success in beekeeping. Notwithstanding the fact that they have been kept by man for thousands of years, A. cerana and A. mellifera still retain all their natural biological characteristics. As compared with the other farm animals, they have not been truly domesticated, in that their life history, social organization, behaviour, physio-ecological characteristics and genetic composition have not been significantly altered by man. The honeybees of today are very much like their predecessors of millions of years ago. They live in a tightly-knit social organization in which each individual member of each caste and sex plays a specific role in the survival of the colony and thus improves the chances of continuity of the species. An individual honeybee cannot long survive when it is separated from its colony.

Anthropomorphically, honeybees may appear to possess social intelligence and a reasoning mind, and such misconceptions often lead to colony mismanagement. The fascinating social behaviour of honeybees is uniquely the result of millions of years of evolution through natural selection. It is not an exhibition of a high level of cleverness. Bees behave, or react to environmental stimuli, in a fairly predictable manner. Most of what they do and how they do it is in essence genetically programmed, and only through proper techniques of manipulation can beekeepers put the colonies to work.

 

A. Colony members

Every honeybee colony is a family, consisting of a single fertile female, the queen, which is the mother of the colony; a large number (ranging from several thousand to tens of thousands) of infertile females, the workers; and, at certain times of the year, several hundred male drones. Taken together, these three categories are referred to as castes.

(1) The Queen

Being the sole member of the female reproductive caste, the queen is indispensable for the survival of the colony. A mated queen serves the colony in two essential functions: laying fertilized and unfertilized eggs, and secreting substances known as pheromones, required for the stability of the colony's social order.

Within a few days of having mated in mid-air with about ten drones, the queen begins to lay eggs, and continues to do so until she is physiologically exhausted. The larvae of female bees (queens and workers) will hatch from the fertilized eggs, while the unfertilized eggs yield drone larvae. Factors determining whether fertilized or unfertilized eggs are to be laid include the size of the cells in the comb and the mechanism underlying the functioning of the queen's reproductive organs. During the mating process, the queen stores sperm from the drones in a storage organ, the spermatheca, within her abdomen. By controlling the opening and closing of the spermatheca, the queen can allow sperm cells to fertilize her eggs or prevent them from doing so. The fertilized eggs are deposited in small worker cells, while the unfertilized eggs are laid in the larger drone cells: the queen can determine cell size and cleanliness by passing her head into the cell and using her front legs to measure its internal width.

Healthy, sufficiently mated A. mellifera queens can lay as many as 1500 to 2000 eggs a day, provided that the colony is strong, that the queen is sufficiently fed and that there is sufficient empty comb space to accommodate the eggs. The workers partially control the queen's egg-laying by regulating the amount of food fed to the queen and by their preparation of empty cells; they also cannibalize the eggs when a food shortage occurs.

Worker bees recognize their queen not by her physical structure but by her scent, given off by the pheromones she secretes. These pheromones, which consist of about 30 organic compounds, have both direct and indirect effects on the colony's social behaviour. During the nuptial flight, they serve as sex attractants, drawing the drones to the queen. Inside the hive, they assist in stabilizing the colony: the workers are aware of the queen's whereabouts by the presence or absence of pheromones. In A. mellifera colonies, some workers act as "messengers" in distributing the pheromones they obtain from direct contact with the queen to other workers within the hive. Under certain circumstances, the presence within the hive of pheromones will inhibit the untimely construction of queen cells: they also inhibit the development of the workers' ovaries, and during swarming they exercise a direct influence on swarm stabilization.

Pheromone communications within the colony constitute one of the most important components of the social life of all honeybee species. Since older queens secrete less pheromones as well as laying less well - than queens in their prime age, and although a queen can live for several years before being superseded by a younger one, professional beekeepers often requeen their colonies every one or two years, in order always to have queens at their maximum biological efficiency.

(2) The Drones

The drones are the male members of the honeybee society reared by the colony shortly before the swarming season begins. As already stated, several hundred drones may be reared by the colony, emerging from unfertilized eggs the queen lays in larger brood cells. In queenless colonies, workers whose ovaries have developed as a result of the lack of inhibiting action by the queen's pheromones can also lay eggs which, being unfertilized because the worker is unmated, also yield drones.

Drones possess no food-gathering apparatus: their sole biological function is to mate with queens. During the mating season, they are well fed by the workers before taking flight. A drone may make from 4 to 6 flights a day, but a smaller number is not uncommon. Drones from neighbouring colonies all fly to a place known as the "drone congregation area", where mating takes place. To ensure successful mating, several thousands of drones must be in the area, although the queen will mate with only about ten. The drone dies shortly after copulation.

When the mating season is nearing its end, the colony reduces its drone-rearing, and when the season is over, the rearing of drones ceases completely. The drones remaining in the hive gradually die of old age, negligence by the worker bees or starvation, or they may simply be expelled from the hive.

(3) The Workers

The workers are an infertile caste of female bees, developed from fertilized eggs. They are suited by their physiological and anatomical features to perform virtually all kinds of chores except reproduction, to increase the chances of the colony's survival. Factors determining the type of task to be executed by a worker include its physiological and anatomical state of readiness, and environmental stimuli, as well as the requirements of the colony to have a particular job done at a particular time.

Soon after emerging from its cell, a young worker receives food, in the form of either nectar or honey, from mature workers, and also helps herself to honey and pollen she finds in the colony's storage cells. In the first few days after she emerges, she is too weak to do anything except inspect and clean empty cells in preparation for food storage by the colony or egg-laying by the queen. During this period she consumes relatively large amounts of honey and pollen, and this directly affects the development of her hypopharyngeal and wax glands.

The secretion from this "nurse bee"'s hypopharyngeal glands, rich in fat and protein, is fed to the larvae, those of all ages in queen cells receiving large quantities; for this reason it is referred to as "royal jelly". Larvae in worker and drone cells receive this special diet only during the first days after hatching; during their later larval life they are fed on a mixture of honey and pollen.

At about the same time as the hypopharyngeal glands of the nurse bee develop, or shortly afterward, four pairs of wax glands, located below her abdominal segments also develop, under the stimulation of consumption of large amounts of honey. From these glands she secretes flakes of whitish wax, which are manipulated by worker bees, using their mandibles, in the process of comb construction and repair and in capping cells.

Under normal conditions, a worker bee is physiologically exhausted from the tasks of secreting royal jelly and wax when she reaches the age of about 14 to 18 days. A few days after this period are spent packing pollen in storage cells, the mouth-to-mouth retrieval of nectar from returning foragers, and occasionally guarding the hive entrance. When she is about three weeks old she ceases to be a "house bee" and becomes a "field bee". At this stage her flight muscles are sufficiently developed, and after orientation flights which enable her to locate the hive in relation to surrounding landmarks, she collects nectar, pollen, water and propolis and carries them back to the hive until she dies.

As already stated, physiological readiness is not the only factor exerting a direct influence on a worker to perform any specific task: environmental stimuli, the condition of the hive, and the colony's immediate requirements are among other factors regulating the type of work to be carried out and the number of bees to be involved in each task. When a colony is running out of space to accommodate brood and food stores, for example, or when combs have been damaged or destroyed, many workers will undertake the task of comb construction and repair; older workers who have already passed beyond the wax-secretion stage can, by consuming large quantities of honey or sugar syrup, reactivate their wax glands and participate in the construction work. Again, when a colony requires a relatively large population of nurse bees to tend the growing number of brood, the duration of royal jelly secretion by the existing nurse bees can be prolonged, provided that the colony has an ample supply of honey and pollen for them to consume. On the other hand, during a heavy honeyflow season younger workers can easily be recruited for foraging as field bees to increase the colony's food-gathering capacity.

 

B. Development of the honeybee

The first stage in the development of a worker bee occurs when the queen deposits a single fertilized egg at the bottom of a worker cell. After three days, the egg hatches to become a tiny first-instar larva, lying at the bottom of the cell and fed regularly by nurse bees. After successive stages of growth and moults, the larva completely covers the floor of the cell, and it then changes position, stretching out along the depth of the cell. When the larva is fully grown and no longer needs to be fed, house bees cap its cell with a thin layer of wax; unlike the flat cap of a honey-storage cell, the cap of a brood cell shows a slight protuberance.

At this stage the larva, henceforth called "sealed brood", spins a cocoon around itself and begins to pupate, i.e. to shed its last larval integument and differentiate into a pupa. The pupa has all the adult bee's distinct body parts, but they all adhere tightly to the bee's body, and some appendages are not yet fully expanded. Before emerging, the pupa grows gradually darker in colour. Finally, transformed into an adult, it slowly chews its way out of the cell. The complete metamorphosis from newly-laid egg to emerging adult worker requires a total of 21 days: three as an egg, six as a larva, and 12 as a pupa.

For a drone, life begins when the queen deposits an unfertilized egg in a larger drone-brood cell at the bottom of the comb. Like the eggs of worker brood, drone-brood eggs require three days to hatch, and as for worker larvae, nurse bees feed drone larvae, which uncurl along the depth of the cell when their bodies fill the cell floors. When the larvae are fully grown, the nurse bees cease feeding them, their cells are capped, they spin their cocoons, and pupation takes place. It requires 24 days - three days longer than for worker bees - for a drone to develop, from newly-laid egg to emerging adult. Emerging drones are fed on honey and royal jelly until they are about a week old. Their flight activity begins when they are from 6 to 8 days old, but they are sexually mature only when aged from 12 to 14 days.

A honeybee colony will rear a new queen or queens under two circumstances: in the colony reproduction process known as swarming or in an attempt to replace an old queen with a younger one (supersedure) or to create a new queen in an emergency, when the old one is accidentally lost.

Whereas worker and drone brood are, as will be recalled, reared in hexagonal cells, queen development takes place in cells shaped somewhat like a groundnut. Queen cells are of three types: swarm cells, supersedure cells and emergency cells. Swarm queen cells are built along the lower edge of the comb, often in large numbers: as many as 20 cells of various ages may be seen in a colony. Supersedure queen cells, fewer in number, are generally about the same age and built perpendicular to the comb surface; they are usually formed from old, darker wax than swarm queen cells which, built at times of high food availability, usually consist of whiter, newly-secreted wax. The distinctive feature of emergency queen cells is that they are expanded from ordinary worker cells already containing young larvae, and appear to protrude directly from worker-brood cells on the surface of the comb.

The development period of a queen is significantly more rapid than those of workers and drones: 16 days from egg to adult. The queen larva is well provided by nurse bees with royal jelly for her entire stage of development: it is deposited very frequently in the cell, and the queen larva simply lies on a bed of its food; the remains of uneaten royal jelly is often seen in the cell after the young queen emerges. Although larvae destined to become queens and workers are genetically similar in that both are hatched from fertilized eggs, qualitative and quantitative differences in the diet they receive, particularly in the early stages of their larval lives, determine major differences in their anatomical and physiological development.

 

C. Colony growth cycle; swarming

If a honeybee colony is relatively safe from damage or destruction by its natural enemies, if it has an ample supply of forage, and if the queen and the workers have been performing their duties in an optimum manner, it will eventually outgrow its hive space. When this occurs, the colony is ready to reproduce itself by swarming.

In temperate regions, natural food is available to honeybee colonies only in spring and summer, when warm ambient temperatures permit flights and active foraging. The colony is most busily engaged in brood-rearing during this period, until hive overcrowding and congestion signal the colony to swarm. During the cold autumn and winter months, however, colonies raise only a small amount of brood, depending for their survival on their stored food.

Such a clearly-defined annual cycle does not exist to the same extent in tropical regions, where colonies of indigenous Apis cerana and introduced temperate races of A. mellifera rear brood whenever their food supply is plentiful. Overcrowding of the hive can thus occur at almost any time, and swarming under tropical conditions occurs not annually, but when the seasonal availability of forage permits. Thus, under normal conditions a temperate-zone colony of A. mellifera casts out a single swarm yearly, while tropical races of A. cerana may cast out several successive swarms, each of such secondary and tertiary swarms being accompanied by an unmated queen.

In preparation for swarming, a colony builds new queen cells and rears young queens. At the same time the old queen receives less food and loses weight, acquiring the capacity to fly. Before the new queens emerge, from 30% to 70% of the colony's worker population fill their stomachs with honey as a food reserve and leave the parent hive in search of a new home site.

Upon leaving the hive, usually accompanied by the old queen, the swarm settles near the parent hive until scout bees have located a new site. If the queen is lost at this stage, the swarm will return to the parent hive, since it cannot function without a queen.

 

D. Colony defence

Colony defence is a duty of the workers. Bees over two weeks old are frequently involved in guarding the hive, most of them having been relieved from their tasks of brood-rearing and comb construction and repair. Their hypopharyngeal glands no longer function at full efficiency, but their poison glands are in the prime stage of development.

Guard bees recognize members of their own colony by a hive odour specific to each colony. Having the same odour, returning foragers have no difficulty in passing through the hive entrance, but most foreign intruders, including worker bees from other colonies with a different odour, are repelled by the defending guards.

The stings of workers of all species of Apis are anatomically similar, being composed of three shafts and barbed at the tip. When a worker bee stings her enemy, the sting, along with its poison sac and part of the gut adjoining the base of the bee's last abdominal segment, is torn from her body and remains in the enemy's flesh when she pulls away. If the sting is left untouched, the muscles controlling the pumping movement of the poison sac continue to function, injecting the bee's venom into the enemy's body. Her last abdominal segment torn away, the worker soon dies, however, from the loss of blood and body fluid through the open wound.

At the same time as she stings her enemy, the worker releases an alarm pheromone from glands near the base of the sting, to alert other workers and indicate the whereabouts of the enemy. The alarm pheromone, which smells to man like synthetic banana oil, is isopentyl acetate. Easily diffused through the air, it brings a rapid response from the workers in the hive.

 

E. Foraging

Under normal conditions, worker bees begin to forage when they are about 2 to 3 weeks old. Foraging is the last chore in the life of a worker. Once she has begun foraging, she continues in this activity for the rest of her life. Foragers are sometimes called "field bees".

Part of the colony's stored honey is invested in foraging activity: before taking off on a flight a field bee consumes a certain amount of honey to ensure that she will have a sufficient energy supply for her round-trip journey. To obtain a full load of nectar and/or pollen in a single trip, she may have to visit several hundred flowers. The amount of energy she expends, related to the amount of food she collects, is determined largely by such factors as the species of forage, floral density per unit area, the distance from the hive, and weather conditions. Despite opinions to the contrary, flight productivity does not necessarily depend on the capability of the worker bee or of her race.

In the collection of nectar and pollen there is no specialization or division of labour among foragers. There are, however, both qualitative and quantitative differences among flowering plant species as regards nectar and pollen production: not all plant species possess nectaries (glands secreting nectar), and for a forager to collect nectar, the nectaries must be attainable by the bee's proboscis or tongue. Nectaries may be located on many parts of the blossom: base of the stamen and stigma, petals and sepals. Moreover, some plant species have extrafloral nectaries that may be visited by bees.

A forager may appear to prefer the nectar of one flower species over another. This is because it is to her advantage to visit flowers producing greater quantities of nectar with a higher sugar concentration. Further, the sugar concentration in the nectar of a given plant species may vary from one place to another, or from one time of day to another, or even from one plant to another in the same species. If high-quality nectar is available, a forager of Apis mellifera can carry as much as 70 to 80 mg of nectar per load.

Workers of all honeybee species carry nectar internally, part of their alimentary canal being modified to form a "honey sac" or "honey stomach" to accommodate their nectar load. On returning to the hive, the forager regurgitates the nectar to one or more house bees, by which it will be converted into honey. They add to the nectar the enzyme invertase, through whose action the sucrose sugar in the nectar is split into fructose and glucose, the sugars predominant in honey. Using their proboscises, the house bees expose the nectar as a thin film, thus increasing its surface area and ensuring the more rapid evaporation of the water it contains.

The entire body of a worker bee, particularly her thorax, is densely covered with fine, branched hairs, on which pollen grains are caught when the bee works on a flower. She sometimes uses her mandibles to chew off the anthers, or deliberately rolls over the anthers to acquire the pollen. The tibiae of the bee's hind legs are equipped with rows of short setae, which she uses to scrape the pollen from her body and to form it into pellets, sometimes regurgitating a slight quantity of nectar to provide moisture and adhesiveness for this purpose.

The pellets, attached to "pollen baskets" on the bee's rear tibiae, are carried back to the hive, where the load is deposited by itself in a pollen-storage cell. Whereas cells containing ripe honey are capped, pollen-storage cells are not: the bees tightly pack pollen to about two thirds of the capacity of the cell and coat the top surface of the pollen in each cell with honey, This protects the pollen against spoiling.

In addition to collecting nectar and pollen as the colony's food, field bees collect plant gum (propolis) and also water. Propolis, which is exuded by certain plants, often to protect wounds on their surface, is rich in tannin and displays antibiotic activity. It is an adhesive material, which the bees use in comb construction, to coat the interior of the hive, and to seal cracks. In collecting propolis, a field bee uses her mandibles to bite the substance from the plant surface and carries it back on her rear legs to the hive, where the house bees, in their turn, use their mandibles to remove it from the forager.

The honeybee colony needs water for two purposes only: to cool the hive and to dilute the honey fed to the larvae. Like nectar, water is collected by the field bee through her proboscis and is carried back to the hive in her honey stomach, being regurgitated to the house bees on arrival. During the heat of the day, some foragers may switch from nectar to water collection, or they may prefer to collect nectars with a low sugar concentration, whose water concentration is correspondingly higher.

 

F. Temperature regulation

Honeybees, like all other insects, are unable to control their body temperature internally according to changes in the ambient temperature; for this reason they are referred to as "cold-blooded animals". However, although the individual bee cannot control its body temperature, a populous honeybee colony can regulate the interior temperature of the hive, particularly within the area surrounding the developing brood. In normal colonies, the brood-nest temperature is maintained at a remarkably constant 32-36 C.

By fanning their wings, evaporating the water film at the proboscises of the workers, and dispersing drops of water in empty cells, a honeybee colony can reduce its temperature markedly. When water is available, a colony of Apis mellifera can withstand an external heat of 70 C.

When the external temperature is low, on the contrary, the bees reduce heat losses by clustering together, and the lower the temperature, the more compact the cluster. In addition, in order to generate more body heat, the worker bees will consume more food, especially honey: more heat is released as a result of the increased rate of food metabolism.

The survival ability of honeybee colonies during severe winter months depends on whether the colony has enough workers, adequately provisioned with food. Insulating the hive wall and decreasing the volume of the hive can also improve the effectiveness of the colony's thermal regulation. In the temperate regions,, colonies of A. mellifera survive by forming clusters around the brood nest, the bees at the surface of the cluster and those within it changing their respective positions at intervals. In this manner, A. mellifera colonies can survive temperatures as low as -40 C.

The regulation of brood-nest temperature is not confined to the European races of A. mellifera which further do not lose this behaviour characteristic on being transferred to tropical regions. Tropical honeybee species and races can also regulate their brood-nest temperature to a certain extent, but they are able to survive only mildly cold temperatures, generally not below 0 C.

 

G. Communication and recruitment to crops

Communication among its members is one of the most important biological attributes of the honeybee colony. All species employ two principal modes of social communication: pheromones and dance "language".

Pheromone communication among the members of a colony plays an essential role in regulating its social life. Apart from the queen pheromones and the alarm pheromone mentioned above, scent-gland pheromones, known as Nasomov pheromones, are used by workers of A. mellifera to mark the site of a food that has little or no scent, in order to assist other foragers in locating the site. The same pheromones are also used extensively by workers in indicating the hive location, and during the process of swarming.

In addition to chemical communication through pheromones, workers of all honeybee species are able to attract their nest-mates to a crop by dancing, scouts announcing the discovery of a new home site or, more often, food source in this manner. The distance from the hive and the direction of the food source are conveyed through a dance "language", which has two important basic forms: the round dance and the tail-wagging dance. The round dance indicates that food is near the hive, and therefore does not give a direction, but the tail-wagging dance gives more details. The distance is indicated by the speed with which the dancer completes her dance cycle, while the direction is shown by the angle of deflection from the vertical made by the bee's abdomen while in movement, which is equal to the angle formed by the lines between the food source, the hive entrance and the sun. If the line of movement is upward, it signifies that the foragers should fly toward the sun, and vice versa. Further, if the dance indicates the presence of nectar, the scout will pause and give a small quantity of the nectar to her fellow-workers, while if the source consists of pollen, she will allow the others to inspect or perceive the odour of the pollen. Finally, the intensity of the dance indicates the richness of the food source: a vigorous dance, indicating a rich source, will attract numerous recruits, while a slower dance, indicating a poorer source, will on the contrary attract fewer recruits.


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