Bee
2007 Schools Wikipedia Selection. Related subjects: Insects, Reptiles and Fish
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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 25,000 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 flight difficult or impossible.
Many species of bees are poorly known. The smallest bee is the 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 are the many species of Halictidae, or sweat bees, though this may come as a surprise to natives, as they are so small and often mistaken for wasps or flies.
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 honey bees 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. It is 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, especially the domesticated Western honey bee, with contract pollination having overtaken the role of honey production for beekeepers in many countries. Monoculture and pollinator decline have increasingly caused honey bee 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 the 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 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 contamination of their food supply. A honey bee 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 honey bees 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. The ancestors of bees were wasps in the family Crabronidae, and therefore predators of other insects. The switch from insect prey to pollen may have resulted from the consumption of prey insects that were flower visitors and were partially covered with 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 oldest bee fossil, of the genus Melittosphex, is 100 million years old and supports the theory that bees evolved from wasps . Other partial fossil evidence show that they evolved alongside flowers, at least 140 million years ago .
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 behavioural and physical modifications that specifically enhance pollination, and are much more efficient at the task than beetles, flies, butterflies, pollen wasps, or any other pollinating insect. The appearance of such floral specialists is believed to have driven the adaptive radiation of the angiosperms, and, in turn, the bees themselves.
Eusocial and semisocial bees
Bees may be solitary or may live in various types 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 behavioural 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. The biology of most such species is almost completely unknown. The vast majority are in the family Halictidae, or "sweat bees". Colonies are typically small, with a dozen or fewer workers, on average. 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 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 "progressive provisioning"; a larva's food is supplied gradually as it develops. This system is also seen in honey bees and some bumblebees.
Highly eusocial bees live in colonies. Each colony 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 honey bee hive can contain up to 40,000 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. 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 large worker force). Bumblebee colonies typically have from 50 to 200 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. 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 unknown whether any survive winter in such an environment.
Stingless bees
Stingless bees are very diverse in behaviour, but all are highly eusocial. They practice mass provisioning, complex nest architecture, and perennial colonies.
Honey bees
The true honey bees (genus Apis) have arguably the most complex social behaviour 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 killer bees, are a hybrid strain of Apis mellifera derived from experiments to cross European and African honey bees by Warwick E. Kerr. Several queen bees escaped his laboratory in South America and have 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, and typically inhabits a nest she constructs herself. 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 nest 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 carrying 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 provide 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, 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 called "cuckoo bees" because their behaviour is similar to 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. 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. 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 in the same genus attack halictid bees.
Gallery
 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 |
 Bumblebee, Bombus sp. on a Coreopsis flower. Madison, Wi |