The bee is one of the insects most familiar to us. Phrases like "as busy as a bee" and "as angry as a bee" are regularly heard. The image of a bee industriously buzzing over a flower is a stereotypical picture of summer. Most of us are probably less familiar with the fact that bees perform vital functions in nature generally and, specifically, in food production, both for humans and animals. Bees are also a form of life where the female is dominant.
There are about 3,000 species of bees. They survive almost completely on pollen (powder consisting of the male sex cells produced by the flowers of seed-bearing plants) as a source of protein, fat, minerals and vitamins, and nectar as an energy source. Bees are dependent on flowers and many plants have become dependent on bees for pollination (a process whereby the pollen fertilises female plant sex cells to form the seed).
The best known bee is the honeybee (apis mellifera), which has a completely social lifestyle. The honeybee community consists of thousands of bees divided into three castes - the queen (sexually productive female), the drone (male) and the worker (sterile female). Bees can only live in the bee colony (hive). Each caste has a different function.
The queen is the only sexually productive female and is mother of all the others. She has a prodigious capacity for laying eggs; at peak she can lay over 1,500 eggs per day (equivalent to the weight of her own body). The queen is fed exclusively on the highly-nutritious royal jelly secreted by the worker bees.
The queen is much larger than drones or workers. Her jaws have sharp teeth, whereas drones and workers have toothless jaws. The queen has a smooth sting organ which she can use repeatedly, with no danger to herself. Worker bees have a barbed sting that becomes embedded in the flesh of the victim. In trying to withdraw the sting, the worker tears away part of her abdomen and dies.
The worker bees always greatly outnumber the drones. They cannot mate or reproduce but they secrete wax, build the honeycomb, gather pollen, nectar and water, convert the nectar into honey, feed the larvae (immature free-living forms), and clean and defend the hive. The workers also maintain the temperature of the nest at 93F, the optimum for hatching eggs and rearing the young. Worker bees generally live for six to eight weeks.
The male drone is stingless and defenceless. His one function is to mate with new queens. After mating, which always takes place in the open air on the wing, the drone dies immediately. As autumn approaches, the drones are driven from the hive by the workers and left to perish. It ain't much fun being a male honeybee.
The highly-social behaviour of honeybees is orchestrated by scent, sound and dance signals. The queen emits a chemical scent (pheromone), which inhibits the workers from developing sexually and laying eggs. Low concentrations of pheromone cause the workers to rear a new queen.
When a worker locates a worthwhile new source of food, she returns to the hive and performs a symbolic dance to indicate the direction, distance and quality of the find to the others. Direction is communicated by a waggle run where the bee walks forward on the upright honeycombs at the same angle from the vertical (up towards the sun, down away from sun) as the angle that the food is in relation to the line connecting the hive to the horizontal direction of the sun.
Distance is communicated by the number of waggle runs per unit time, and the quality of the food by the vigour of the shaking during the waggle run.
In the highly social bees, the honeybee and the stingless (trigona) species, the queen lives for several years and the colonies are perennial rather than annual. Up to 150,000 individuals may inhabit these colonies. About a week after emerging, the honeybee queen makes a nuptial flight, during which she mates with several drones. She stores the sperm in a sac, called the spermatheca, in a sufficient quantity to fertilise all the eggs she will lay over her life of up to five years.
The queen can control the production of male or female offspring. To produce male offspring (drones), she lays unfertilised eggs. A fertilised egg will develop into a female, either a worker or a queen. The workers have the power to produce new queens from any of the female eggs. For the first two days, all larvae are fed the very nutritious royal jelly. After this, larvae destined to become workers or drones are switched to a diet of honey and pollen, whereas those destined to become queens continue to be fed only on royal jelly.
Colonies of honeybees reproduce themselves by swarming. In this process, a queen leaves the hive accompanied by about half of the worker bees. A suitable new nest site is identified and a new hive is established. Another queen, with the remainder of the workers, continues the life of the old colony.
Although most is known about the social bees, the majority of the world's bee species are solitary. In the solitary species, a female builds a nest cell, stocks the cell with a mixture of pollen and nectar, lays an egg on the food and seals the nest cell, allowing the larva to develop and emerge up to a year later. Examples of solitary bees are mason bees, leaf-cutter bees, alkali bees and carpenter bees.
Some bees have a primitive social organisation. The best-known example is the bumblebee. Here, a female that has mated the previous autumn (the queen) emerges in spring from an underground hibernacula, where she over-wintered, and starts up her own colony.
At the start the queen does all the work - foraging, nest-building and egg-laying. After she has produced sterile female workers, they take over most of the work and the queen is restricted mostly to egg-laying. In late summer, the queen produces large numbers of sexuals - males (drones) and new queens. The colony now can contain up to several hundred individuals. The workers, drones and old queen die off in autumn and the new queens disperse and hibernate.
Bees, in particular the honeybee, are the most economically valuable of all insects. It might be thought that this is because of the production of honey and beeswax. But the bee's greatest usefulness is the pollination of crops. By going from flower to flower, bees carry out cross-pollination. The pollen is carried on the legs of worker bees. This is of great importance for the pollination of crops and natural flora.
In North America, it is estimated that humans are dependent on bee pollination for up to one third of their food. Bumblebees alone are worth billions of dollars for clover pollination. Bees pollinate over 2,500 species of crop plants and ensure seed crops of innumerable native plants that maintain ground cover, feed birds and animals, and prevent soil erosion.
Social bees build up large stores of pollen and honey and contain large numbers of larvae. The nests are tempting targets for many animals and for humans. Bees have evolved a defence mechanism, the sting. In the domestic honeybee, selective breeding has eliminated those bees most inclined to sting.
In Asia and Africa, bees have evolved highly-organised and effective defences. The African strain of honeybee (apis mellifera scutellata) was accidentally released in Brazil in 1957. It hybridised with the local honeybee and the new aggressive strain of so-called "killer bees" has colonised most of South America and is advancing northwards at about 80km per year. I will describe this phenomenon in next week's article.
William Reville is a senior lecturer in biochemistry at UCC.