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Revision as of 21:57, 23 October 2006
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| Bees | |
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| Osmia ribifloris | |
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| (unranked): | Anthophila ( = Apiformes)
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Andrenidae | |
Bees (a monophyletic lineage within the superfamily Apoidea, presently classified by the unranked taxon name Anthophila) are flying insects, closely related to wasps and ants. There are approximately 20,000 species of bees, and they may be found on every continent except Antarctica. Bees are adapted for feeding on nectar and pollen, the former primarily as an energy source, and the latter primarily for protein and other nutrients. Most pollen is used as food for larvae.
Bees have a long proboscis that enables them to obtain the nectar from flowers. Bees have antennae almost universally made up of thirteen segments in males and twelve in females. They all have two pairs of wings, the back pair being the smaller of the two; in a very few species, one sex or caste has relatively short wings that make it difficult or impossible to fly.
Many species of bees are poorly known. The smallest bee is a dwarf bee (Trigona minima) and it is about 2.1 mm (5/64") long. The largest bee in the world is Megachile pluto, which can be as large as 39 mm (1.5"). The most common type of bee in North America is the Halictidae, or sweat bee, though this may come as a surprise to natives, as they are so small and often mistaken for wasps.
Pollination
Bees play an important role in pollinating flowering plants, and are the major type of pollinators in ecosystems that contain flowering plants. Bees may focus on gathering nectar or on gathering pollen, depending on their greater need at the time. Bees gathering nectar may accomplish pollination, but bees that are deliberately gathering pollen are more efficient pollinators. It is estimated that one third of the human food supply depends on insect pollination, most of this accomplished by bees.
Most bees are fuzzy and carry an electrostatic charge, thus aiding in the adherence of pollen. Female bees periodically stop foraging and groom themselves to pack the pollen into the scopa, which is on the legs in most bees, and on the ventral abdomen on others, and modified into specialized pollen baskets on the legs of honeybees and their relatives. Many bees are opportunistic foragers, and will gather pollen from a variety of plants, but many others are oligolectic, gathering pollen from only one or a few types of plant. A small number of plants produce nutritious floral oils, rather than pollen, which are gathered and used by oligolectic bees. One small subgroup of stingless bees (called "vulture bees") is specialized to feed on carrion, and these are the only bees that do not use plant products as food. Pollen and nectar are usually combined together to form a "provision mass", which is often soupy, but can be firm, and formed into various shapes (typically spheroid), and stored in a small chamber (a "cell"), with the egg deposited on the mass. The cell is typically sealed after the egg is laid, and the adult and larva never interact directly (a system called "mass provisioning").
Bees are extremely important as pollinators in agriculture, with contract pollination having overtaken the role of honey production for beekeepers in many countries. Monoculture and pollinator decline have increasingly caused honeybee keepers to become migratory so that bees can be concentrated in areas of pollination need at the appropriate season. Many other species of bees are increasingly cultured and used to meet agricultural pollination need. Bees also play a major, though not always understood, role in providing food for birds and wildlife. Many of these bees survive in refuge in wild areas away from agricultural spraying, only to be poisoned in massive spray programs for mosquitoes, gypsy moths, or other pest insects.
Visiting flowers is a dangerous occupation, with very high mortality rates. Many assassin bugs and crab spiders hide in flowers to capture unwary bees. Others are lost to birds in flight. Insecticides used on blooming plants can kill large numbers of bees, both by direct poisoning and by contaminating their food supply. A honeybee queen may lay 2000 eggs per day during spring buildup, but she also must lay 1000 to 1500 eggs per day during the foraging season, simply to replace daily casualties.
The population value of bees depends partly on the individual efficiency of the bees, but also on the population. Thus, while bumblebees have been found to be about ten times more efficient pollinators on cucurbits, the total efficiency of a colony of honeybees is much greater, due to greater numbers. Likewise, during early spring orchard blossoms, bumblebee populations are limited to only a few queens, thus they are not significant pollinators of early fruit.
Bee evolution
Bees, like ants, are essentially a highly specialized form of wasp. While the first definite fossil bees date from only forty million years ago, there is genetic and partial fossil evidence that they evolved alongside flowers, at least 140 million years ago[1]. The ancestors of bees were wasps in the family Crabronidae, and therefore predatory on other insects, and the switch from insect prey to pollen may have resulted from the use of prey insects that were themselves flower visitors, and partially covered in pollen when they were fed to the wasp larvae. This same evolutionary scenario has also occurred within the vespoid wasps, where the group known as "pollen wasps" also evolved from predatory ancestors.
The earliest animal-pollinated flowers were pollinated by insects such as beetles, so the syndrome of insect pollination was well-established before bees first appeared; the novelty is that bees are specialized as pollination agents, with behavioral and physical modifications that specifically enhance pollination, so are much more efficient at the task than beetles, flies, butterflies, pollen wasps, or any other pollinating insects. The appearance of such floral specialists is believed to have driven the adaptive radiation of both the angiosperms, and, in turn, the bees themselves.
Eusocial and semisocial bees
Bees may be solitary, or may live in various sorts of communities. The most advanced of these are eusocial colonies, found among the honeybees, bumblebees, and stingless bees. Sociality is believed to have evolved separately many times within the bees.
In some species, groups of cohabiting females may be sisters, and if there is a division of labor within the group, then they are considered semisocial.
If, in addition to a division of labor, the group consists of a mother and her daughters, then the group is called eusocial. The mother is considered the "queen" and the daughters are "workers". These castes may be purely behavioral alternatives, in which case the system is considered "primitively eusocial" (similar to many paper wasps), and if the castes are morphologically discrete, then the system is "highly eusocial".
There are many more species of primitively eusocial bees than highly eusocial bees, but they have been rarely studied, and the biology of most such species is almost completely unknown. The vast majority of such species are in the family Halictidae, or "sweat bees". Colonies are typically small, with a dozen or fewer workers, and the only physical difference between queens and workers is average size, if they differ at all. Most species have a single-season colony cycle, even in the tropics, and only mated females (future queens, or "gynes") hibernate (called diapause). A few species have long active seasons, and attain colony sizes in the hundreds. The orchid bees include a number of primitively eusocial species, as well, with similar biology. Certain species of allodapine bees (relatives of carpenter bees) also have primitively eusocial colonies, with unusual levels of interaction between the adult bees and the developing brood; this is called "progressive provisioning", when a larva's food is supplied gradually as it develops, and this system is also seen in honeybees and some bumblebees.
Highly eusocial bees live in colonies, each of which has a single queen, together with workers and, at certain stages in the colony cycle, drones. When humans provide a home for a colony, the structure is called a hive. A honeybee hive can typically contain up to about 40,000 individual bees at their annual peak, which occurs in the spring, but usually have fewer.
Bumblebees
Bumblebees (Bombus terrestris, B. pratorum, et al.) are eusocial in a manner quite similar to the eusocial Vespidae such as hornets, as the queen initiates a nest on her own (unlike queens of honeybees and stingless bees, which start nests via swarms, in the company of a substantial worker force). Bumblebee colonies typically have from 50 to 200 individual bees at peak population, which occurs in mid to late summer. Nest architecture is simple, limited by the size of the nest cavity (pre-existing), and colonies are rarely perennial. Interestingly, bumblebee queens sometimes seek winter safety in honeybee hives, where they are sometimes found dead in the spring by beekeepers, presumably stung to death by the honeybees. It is not known whether any succeed in winter survival in such an environment.
Stingless bees
Stingless bees are very diverse in behavior, but all are highly eusocial. They practice mass provisioning, complex nest architecture, and perennial colonies.
Honey bees
The true honey bees have arguably the most complex social behavior among the bees. The European honey bee, Apis mellifera is the best-known bee species, and one of the best-known of all insects.
Africanized honey bee
Africanized bees, also called the killer bee, are a lineage derived from experiments to cross European and African honey bees by Warwick E. Kerr. An estimated 26 queen bees escaped his lab in South America, and have since spread throughout the Americas. Africanized honey bees are more defensive than European honey bees.
Solitary and communal bees
Most other bees, including familiar species of bee such as the Eastern carpenter bee (Xylocopa virginica), alfalfa leafcutter bee (Megachile rotundata), orchard mason bee (Osmia lignaria) and the hornfaced bee (Osmia cornifrons) are solitary in the sense that every female is fertile. There are no worker bees for these species. Solitary bees typically produce neither honey nor beeswax. They are immune from acarine and Varroa mites, but have their own unique parasites, pests and diseases. (See diseases of the honeybee.)
Solitary bees are important pollinators, as pollen is gathered for provisioning the nests with food for their brood. Often it is mixed with nectar to form a paste-like consistency. Many solitary bees have very advanced types of pollen carry structures on their bodies. Most solitary bees are wild, with a few species being increasingly cultured for pollination.
Solitary bees are often oligoleges, in that they only visit one or more species of plant (unlike honeybees and bumblebees which are generalists). In a few cases only one species of bee can pollinate a plant species, and some plants are endangered because their pollinator is dying off.
Solitary bees create nests in hollow reeds, holes in wood, or, most commonly, in tunnels in the ground. The female typically creates a compartment (a "cell") with an egg and some provisions for the resulting larva, then seals it off. A nest may consist of numerous cells. When the nest is in wood, usually the last (those closer to the entrance) contain eggs that will become males. The adult does not care for the brood, and usually dies after making one or more nests. The males typically emerge first and are ready for mating when the females emerge. Providing nest boxes for solitary bees is increasingly popular for gardeners. Solitary bees are either stingless or very unlikely to sting (only in self defense).
While solitary females each make individual nests, some species are gregarious, preferring to make nests near others of the same species, giving the appearance to the casual observer that they are social.
In some species, however, multiple females share a common nest, but each makes and provisions her own cells independently; this type of group is called "communal", and is not uncommon. The primary advantage appears to be that a nest entrance is easier to defend when there are multiple females using that same entrance on a regular basis.
Cleptoparasitic bees
Cleptoparasitic bees, commonly referred to as "cuckoo bees" because their behavior is similar to that of cuckoo birds, occur in several bee families, though the name is technically best applied to the apid subfamily Nomadinae. Females of these bees lack pollen-collecting structures (the scopa) and do not construct their own nests. Rather, they typically enter the nests of pollen-collecting species, and lay their eggs in cells provisioned by the host bee. When the cuckoo bee larva hatches, it consumes the host larva's pollen ball, and (if the female cleptoparasite has not already done so) kills and eats the host larva itself. In a few cases where the hosts are social species, the cleptoparasite remains in the host nest and lays many eggs, sometimes even killing the host queen and replacing her.
Many cleptoparasitic bees are closely related to, and resemble, their hosts (i.e., the subgenus Psithyrus, which are parasitic bumble bees that infiltrate nests of species in the subgenus Bombus); this common pattern gave rise to the ecological principle known as "Emery's Rule". Others parasitize bees in different families, like Townsendiella, a nomadine apid, one species of which is a cleptoparasite of the melittid genus Hesperapis, while the other species attack halictid bees.
Miscellaneous
Bees figure prominently in mythology. See Bee (mythology).
Bees are the favorite meal of Merops apiaster, a bird. Other common predators are kingbirds, mockingbirds, and dragonflies.
Yellowjackets and hornets, especially when encountered as flying pests, are often mischaracterized as "bees".
Despite the bee's painful sting and the typical attitude towards insects as annoying or disgusting pests, people generally hold bees in high regard. This is most likely due to their usefulness (as pollinators and especially as producers of honey), their social nature, as well as their diligence. Although a bee sting can be deadly to some, bees are generally regarded as non-aggressive insects if left alone. Bees are used to advertise many products, particularly honey and foods made with honey, thus being one of the few insects used on advertisements.
The phrase "busy as a bee" reflects their gentle, hard-working nature.
Gallery
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Honeybee on a Sphaeralcea flower. Mesa, Az -
Honeybee in a Sphaeralcea flower. Mesa, Az -
Sweat bee, Agapostemon virescens (female) on a Coreopsis flower. Madison, Wi -
Bumblebee, Bombus sp. startles Agapostemon virescens. Madison, Wi -
See also
- Bee anatomy (mouth)
- Characteristics of common wasps and bees
- Honeybee
- Honeybee life cycle
- Western honeybee
- Bee-eater, predator
- Schmidt Sting Pain Index
References
- Grimaldi, D. and Engel, M.S. (2005). Evolution of the Insects. Cambridge University Press. ISBN 0-521-82149-5.
{{cite book}}: Check date values in:|year=(help)CS1 maint: multiple names: authors list (link) CS1 maint: year (link) - The Bees of the World, C. D. Michener (2000)