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Temporal range: Oligocene–Recent
|European honey bee carrying nectar back to the hive, with pollen attached|
Honey bees (or honeybees) are a subset of bees in the genus Apis, primarily distinguished by the production and storage of honey and the construction of perennial, colonial nests out of wax. Honey bees are the only extant members of the tribe Apini, all in the genus Apis. Currently, there are only seven recognised species of honey bee with a total of 44 subspecies, though historically, anywhere from six to eleven species have been recognised. Honey bees represent only a small fraction of the approximately 20,000 known species of bees. Some other types of related bees produce and store honey, but only members of the genus Apis are true honey bees.
Origin, systematics and distribution
Honey bees appear to have their centre of origin in South and South East Asia (including the Philippines), as all but one (i.e. Apis mellifera), of the extant species are native to that region. Notably, living representatives of the earliest lineages to diverge ( Apis florea and Apis andreniformis) have their centre of origin there.
The first Apis bees appear in the fossil record at the Eocene–Oligocene (23–56 Mya) boundary, in European deposits. The origin of these prehistoric honey bees does not necessarily indicate that Europe is where the genus originated, only that it occurred there at that time. There are few known fossil deposits in South Asia, the suspected region of honey bee origin, and fewer still have been thoroughly studied.
No Apis species existed in the New World during human times before the introduction of Apis melifera by Europeans. There is only one fossil species documented from the New World, Apis nearctica, known from a single 14-million-year old specimen from Nevada.
The close relatives of modern honey bees—e.g. bumblebees and stingless bees—are also social to some degree, and social behaviour seems a plesiomorphic trait that predates the origin of the genus. Among the extant members of Apis, the more basal species make single, exposed combs, while the more recently evolved species nest in cavities and have multiple combs, which has greatly facilitated their domestication.
Most species have historically been cultured or at least exploited for honey and beeswax by humans indigenous to their native ranges. Only two of these species have been truly domesticated, one ( Apis mellifera) at least since the time of the building of the Egyptian pyramids, and only that species has been moved extensively beyond its native range.
Today's honey bees constitute three clades.
The chromosome counts of female bees for the three clades are Micrapis 2N=16, Megapis 2N=16, Apis 2N=32. Drones of all species have 1N chromosome counts. The genome of Apis has been mapped.
Drones (males) are produced from unfertilized eggs and therefore represent only the DNA of the queen that laid the eggs, i.e. have only a mother. Workers and queens (both female) result from fertilized eggs and therefore have both a mother and a father. A modified form of parthenogenesis controls sex differentiation. The sex allele is polymorphic and so long as two different variants are present, a female bee results. If both sex alleles are identical, diploid drones are produced. Honeybees detect and destroy diploid drones after the eggs hatch.
Queens typically mate with multiple drones on more than one mating flight. Once mated, they lay eggs and fertilize them as needed from sperm stored in the spermatheca. Since the number of sex alleles is limited—about 18 are known in Apis—there is a high probability that a queen will mate with one or more drones having sex alleles identical with one of the sex alleles in the queen. It is therefore typical for a queen to produce a percentage of diploid drone eggs.
Apis florea and Apis andreniformis are small honey bees of southern and southeastern Asia. They make very small, exposed nests in trees and shrubs. Their stings are often incapable of penetrating human skin, so the hive and swarms can be handled with minimal protection. They occur largely sympatrically though they are very distinct evolutionarily and are probably the result of allopatric speciation, their distribution later converging. Given that A. florea is more widely distributed and A. andreniformis is considerably more aggressive, honey is—if at all—usually harvested from the former only. They are the most ancient extant lineage of honey bees, maybe diverging in the Bartonian (some 40 million years ago or slightly later) from the other lineages, but among themselves do not seem to have diverged a long time before the Neogene.
There is one recognised species in subgenus Megapis. It usually builds single or a few exposed combs on high tree limbs, on cliffs, and sometimes on buildings. They can be very fierce. Periodically robbed of their honey by human "honey hunters", colonies are easily capable of stinging a human being to death when provoked.
- Apis dorsata, the giant honey bee, is native and widespread across most of South and Southeast Asia.
- Apis dorsata binghami, the Indonesian honey bee, is classified as the Indonesian subspecies of the giant honey bee or a distinct species; in the latter case, A. d. breviligula and/or other lineages would probably also have to be considered species.
- Apis dorsata laboriosa, the Himalayan honey bee, was initially described as a distinct species. Later, it was included in A. dorsata as a subspecies based on the biological species concept, though authors applying a genetic species concept have suggested it should be considered a species. Essentially restricted to the Himalayas, it differs little from the giant honey bee in appearance, but has extensive behavioural adaptations that enable it to nest in the open at high altitudes despite low ambient temperatures. It is the largest living honey bee.
- Eastern species
These are three or four species. The reddish Koschevnikov's bee ( Apis koschevnikovi) from Borneo is well distinct; it probably derives from the first colonization of the island by cave-nesting honey bees. Apis cerana, the Eastern honey bee proper, is the traditional honey bee of southern and eastern Asia, kept in hives in a similar fashion to Apis mellifera, though on a much smaller and regionalised scale. It has not been possible yet to resolve its relationship to the Bornean Apis cerana nuluensis and Apis nigrocincta from the Philippines to satisfaction; the most recent hypothesis is that these are indeed distinct species but that A. cerana is still paraphyletic, consisting of several good species.
- European/Western/Common honey bee
Apis mellifera, the most commonly domesticated species, was the third insect to have its genome mapped. It seems to have originated in eastern tropical Africa and spread from there to Northern Europe and eastwards into Asia to the Tien Shan range. It is variously called the European, Western or Common honey bee in different parts of the world. There are many subspecies that have adapted to the local geographic and climatic environments, and in addition, hybrid strains such as the Buckfast bee have been bred. Behavior, colour and anatomy can be quite different from one subspecies or even strain to another.
Regarding phylogeny, this is the most enigmatic honey bee species. It seems to have diverged from its Eastern relatives only during the Late Miocene. This would fit the hypothesis that the ancestral stock of cave-nesting honey bees was separated into the Western group of E Africa and the Eastern group of tropical Asia by desertification in the Middle East and adjacent regions, which caused declines of foodplants and trees that provided nest sites, eventually causing gene flow to cease. The diversity of subspecies is probably the product of a largely Early Pleistocene radiation aided by climate and habitat changes during the last ice age. That the Western honey bee has been intensively managed by humans for many millennia – including hybridization and introductions – has apparently increased the speed of its evolution and confounded the DNA sequence data to a point where little of substance can be said about the exact relationships of many A. mellifera subspecies.
Apis mellifera are not native to the Americas and therefore were not present upon the arrival of the European explorers and colonists. There were, however, other native bee species kept and traded by indigenous peoples. In 1622, European colonists brought the dark bee ( A. m. mellifera) to the Americas, followed later by Italian bees (A. m. ligustica) and others. Many of the crops that depend on honey bees for pollination have also been imported since colonial times. Escaped swarms (known as "wild" bees, but actually feral) spread rapidly as far as the Great Plains, usually preceding the colonists. Honey bees did not naturally cross the Rocky Mountains; they were transported by the Mormon pioneers to Utah in the late 1840s, and by ship to California in the early 1850s.
Africanized bees (known colloquially as "killer bees") are hybrids between European stock and one of the African subspecies A. m. scutellata; they are often more aggressive than and do not create as much of a surplus as European bees, but are more resistant to disease and are better foragers. Originating by accident in Brazil, they have spread to North America and constitute a pest in some regions. However, these strains do not overwinter well, and so are not often found in the colder, more northern parts of North America. On the other hand, the original breeding experiment for which the African bees were brought to Brazil in the first place has continued (though not as intended). Novel hybrid strains of domestic and re-domesticated Africanized bees combine high resilience to tropical conditions and good yields. They are popular among beekeepers in Brazil.
Two species of honey bee, A. mellifera and A. cerana indica, are often maintained, fed, and transported by beekeepers. Modern hives also enable beekeepers to transport bees, moving from field to field as the crop needs pollinating and allowing the beekeeper to charge for the pollination services they provide, revising the historical role of the self-employed beekeeper, and favoring large-scale commercial operations.
Colony collapse disorder (CCD)
Beekeepers in Western countries have been reporting slow declines of stocks for many years, apparently due to impaired protein production, changes in agricultural practice, or unpredictable weather. In early 2007, abnormally high die-offs (30–70% of hives) of European honey bee colonies occurred in North America; such a decline seems unprecedented in recent history. This has been dubbed "Colony collapse disorder" (CCD); it is unclear whether this is simply an accelerated phase of the general decline due to stochastically more adverse conditions in 2006, or a novel phenomenon. Research has so far failed to determine what causes it, but the weight of evidence is tentatively leaning towards CCD being a syndrome rather than a disease as it seems to be caused by a combination of various contributing factors rather than a single pathogen or poison.
As in a few other types of eusocial bees, a colony generally contains one queen bee, a fertile female; seasonally up to a few thousand drone bees or fertile males; and a large seasonally variable population of sterile female worker bees. Details vary among the different species of honey bees, but common features include:
1. Eggs are laid singly in a cell in a wax honeycomb, produced and shaped by the worker bees. Using her spermatheca, the queen actually can choose to fertilize the egg she is laying, usually depending on what cell she is laying in. Drones develop from unfertilised eggs and are haploid, while females (queens and worker bees) develop from fertilised eggs and are diploid. Larvae are initially fed with royal jelly produced by worker bees, later switching to honey and pollen. The exception is a larva fed solely on royal jelly, which will develop into a queen bee. The larva undergoes several moltings before spinning a cocoon within the cell, and pupating.
2. Young worker bees clean the hive and feed the larvae. When their royal jelly producing glands begin to atrophy, they begin building comb cells. They progress to other within-colony tasks as they become older, such as receiving nectar and pollen from foragers, and guarding the hive. Later still, a worker takes her first orientation flights and finally leaves the hive and typically spends the remainder of her life as a forager.
3. Worker bees cooperate to find food and use a pattern of "dancing" (known as the bee dance or waggle dance) to communicate information regarding resources with each other; this dance varies from species to species, but all living species of Apis exhibit some form of the behaviour. If the resources are very close to the hive, they may also exhibit a less specific dance commonly known as the "Round Dance".
4. Honey bees also perform tremble dances, which recruit receiver bees to collect nectar from returning foragers.
5. Virgin queens go on mating flights away from their home colony, and mate with multiple drones before returning. The drones die in the act of mating.
6. Colonies are established not by solitary queens, as in most bees, but by groups known as " swarms", which consist of a mated queen and a large contingent of worker bees. This group moves en masse to a nest site that has been scouted by worker bees beforehand. Once they arrive, they immediately construct a new wax comb and begin to raise new worker brood. This type of nest founding is not seen in any other living bee genus, though there are several groups of Vespid wasps that also found new nests via swarming (sometimes including multiple queens). Also, stingless bees will start new nests with large numbers of worker bees, but the nest is constructed before a queen is escorted to the site, and this worker force is not a true "swarm".
In cold climates honey bees stop flying when the temperature drops below about 10 °C (50 °F) and crowd into the central area of the hive to form a "winter cluster". The worker bees huddle around the queen bee at the center of the cluster, shivering in order to keep the centre between 27 °C (81 °F) at the start of winter (during the broodless period) and 34 °C (93 °F) once the queen resumes laying. The worker bees rotate through the cluster from the outside to the inside so that no bee gets too cold. The outside edges of the cluster stay at about 8–9 °C (46–48 °F). The colder the weather is outside, the more compact the cluster becomes. During winter, they consume their stored honey to produce body heat. The amount of honey consumed during the winter is a function of winter length and severity but ranges in temperate climates from 15 to 50 kg (30 to 100 pounds).
Species of Apis are generalist floral visitors, and will pollinate a large variety of plants, but by no means all plants. Of all the honey bee species, only Apis mellifera has been used extensively for commercial pollination of crops and other plants. The value of these pollination services is commonly measured in the billions of dollars.
Honey is the complex substance made when the nectar and sweet deposits from plants and trees are gathered, modified and stored in the honeycomb by honey bees as a food source for the colony. All living species of Apis have had their honey gathered by indigenous peoples for consumption, though for commercial purposes only Apis mellifera and Apis cerana have been exploited to any degree. Honey is sometimes also gathered by humans from the nests of various stingless bees. In 1911 a bee culturists estimated that a quart of honey represented bees flying over an estimated 48,000 miles to gather the pollen needed for the nectar to produce the honey.
Worker bees of a certain age will secrete beeswax from a series of glands on their abdomens. They use the wax to form the walls and caps of the comb. As with honey, beeswax is gathered for various purposes.
Bees collect pollen in the pollen basket and carry it back to the hive. In the hive, pollen is used as a protein source necessary during brood-rearing. In certain environments, excess pollen can be collected from the hives of A. mellifera and A. cerana. It is often eaten as a health supplement.
Propolis or bee glue is created from resins, balsams and tree saps. Those species of honey bees that nest in tree cavities use propolis to seal cracks in the hive. Dwarf honey bees use propolis to defend against ants by coating the branch from which their nest is suspended to create a sticky moat. Propolis is consumed by humans as a health supplement in various ways and also used in some cosmetics.
Sexes and castes
There are two sexes of honey bee: females (workers and queens); and males (or drones). A caste is a different form, morphologically or reproductively, within the same sex of a species. In sum, there are three types of honey bees: drones, workers and queens; two sexes: male and female; and two female castes: queens and workers.
Males or drones are typically haploid, having only one set of chromosomes. They are produced by the queen if she chooses not to fertilize an egg; or by a non-fertilized laying worker. Diploid drones may be produced if an egg is fertilized but is homozygous for the sex-determination allele. Drones take 24 days to develop and may be produced anywhere from summer through autumn. Drones have large eyes used to locate queens during mating flights. Drones do not have a sting.
Workers are female and have two sets of chromosomes. They are produced from an egg that the queen has selectively fertilized from stored sperm. Workers typically develop in 21 days. A typical colony may contain as many as 60,000 worker bees. Workers exhibit a wider range of behaviors than either queens or drones. Their duties change upon the age of the bee in the following order (beginning with cleaning out their own cell after eating through their capped brood cell): feed brood; receive nectar; clean hive; guard duty; and foraging. Some workers engage in other specialized behaviors, such as "undertaking" (removing corpses of their nestmates from inside the hive).
Workers have morphological specializations: including the corbiculum or pollen basket, abdominal glands that produce beeswax, brood-feeding glands, and barbs on the sting. Under certain conditions (for example, if the colony becomes queenless), a worker may develop ovaries.
Queen honey bees, like workers, are female. They are created at the decision of the worker bees by feeding a larva only royal jelly throughout its development, rather than switching from royal jelly to pollen once the larva grows past a certain size. Queens are produced in oversized cells and develop in only 16 days. Queens have a different morphology and behavior from worker bees. In addition to the greater size of the queen, she has a functional set of ovaries, and a spermatheca, which stores and maintains sperm after she has mated. The sting of queens is not barbed like a worker's sting, and queens lack the glands that produce beeswax. Once mated, queens may lay up to 2,000 eggs per day. Queens produce a variety of pheromones that regulate behaviour of workers, and helps swarms track the queen's location during the migratory phase.
All honey bees live in colonies where the workers will sting intruders as a form of defense, and alarmed bees will release a pheromone that stimulates the attack response in other bees. The different species of honey bees are distinguished from all other bee species (and virtually all other Hymenoptera) by the possession of small barbs on the sting, but these barbs are found only in the worker bees. The sting and associated venom sac of honey bees are also modified so as to pull free of the body once lodged ( autotomy), and the sting apparatus has its own musculature and ganglion, which allow it to keep delivering venom once detached. The worker dies after the sting is torn from its body. Despite common belief, it is the only species of bee to die after stinging.
It is presumed that this complex apparatus, including the barbs on the sting, evolved specifically in response to predation by vertebrates, as the barbs do not usually function (and the sting apparatus does not detach) unless the sting is embedded in fleshy tissue. While the sting can also penetrate the flexible exoskeletal joints in appendages of other insects (and is used in fights between queens), in the case of Apis cerana defense against other insects such as predatory wasps is usually performed by surrounding the intruder with a mass of defending worker bees, who vibrate their muscles so vigorously that it raises the temperature of the intruder to a lethal level. It was previously thought that the heat alone was responsible for killing intruding wasps, but recent experiments have demonstrated that it is the increased temperature in combination with increased carbon dioxide levels within the ball that produces the lethal effect. This phenomenon is also used to kill a queen perceived as intruding or defective, an action known to beekeepers as balling the queen, named for the ball of bees formed.
In the case of those honey bee species with open combs (e.g., A. dorsata), would-be predators are given a warning signal that takes the form of a " Mexican wave" that spreads as a ripple across a layer of bees densely packed on the surface of the comb when a threat is perceived, and consists of bees momentarily arching their bodies and flicking their wings.
Honey bees are known to communicate through many different chemicals and odours, as is common in insects, but also using specific behaviours that convey information about the quality and type of resources in the environment, and where these resources are located. The details of the signalling being used vary from species to species; for example, the two smallest species, Apis andreniformis and Apis florea, dance on the upper surface of the comb, which is horizontal (not vertical, as in other species), and worker bees orient the dance in the actual compass direction of the resource to which they are recruiting.
Both the Atharva Veda and the ancient Greeks associated lips anointed with honey with the gift of eloquence and even of prescience. The priestess at Delphi was the "Delphic Bee". The Quran has a chapter titled The Bee.
A community of honey bees has often been employed throughout history by political theorists as a model of human society:
"This image occurs in Aristotle and Plato; in Virgil and Seneca; in Erasmus and Shakespeare; in Marx and Tolstoy."
Honey bees, signifying immortality and resurrection, were royal emblems of the Merovingians, revived by Napoleon. The bee is the heraldic emblem too of the Barberini.