Thursday, 8 August 2013

Bee

Bees are flying insects closely related to wasps and ants, and are known for their role inpollination and for producing honey and beeswax. Bees are a monophyletic lineage within the superfamily Apoidea, presently classified by the unranked taxon name Anthophila. There are nearly 20,000 known species of bees in seven to nine recognized families,[1] though many are undescribed and the actual number is probably higher. They are found on every continent except Antarctica, in every habitat on the planet that contains insect-pollinatedflowering plants.
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 (a complex “tongue”) that enables them to obtain the nectar from flowers. They have antennae almost universally made up of 13 segments in males and 12 in females, as is typical for the superfamily. Bees all have two pairs of wings, the hind 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, but none are wingless.
The smallest bee is Trigona minima, a stingless bee whose workers are about 2.1 mm (5/64″) long. The largest bee in the world is Megachile pluto, a leafcutter bee whose females can attain a length of 39 mm (1.5″). Members of the family Halictidae, or sweat bees, are the most common type of bee in the Northern Hemisphere, though they are small and often mistaken for wasps or flies.
The best-known bee species is the European honey bee, which, as its name suggests, produces honey, as do a few other types of bee. Human management of this species is known as beekeeping or apiculture.
Bees are the favorite meal of Merops apiaster, the bee-eater bird. Other common predators are kingbirdsmockingbirdsbeewolves, and dragonflies.

Contents

Pollination

Bees play an important role in pollinating flowering plants, and are the major type ofpollinator in ecosystems that contain flowering plants. Bees either focus on gathering nectar or on gathering pollen depending on demand, especially in social species. 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 which is accomplished by bees, especially the domesticatedEuropean honey bee[citation needed]Contract pollination has overtaken the role of honey production for beekeepers in many countries. Monoculture and the massive decline of many bee species (both wild and domesticated) have increasingly caused honey bee keepers to become migratory so that bees can be concentrated in seasonally varying high-demand areas of pollination.
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Honey bees (Apis mellifera) in cactus flower, immersed in Pollen
Most bees are fuzzy and carry an electrostatic charge, which aids in the adherence of pollen. Female bees periodically stop foraging and groom themselves to pack the pollen into thescopa, 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, while 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“).
In New Zealand scientists discovered that three genera of native bees have evolved to open flower buds of the native mistletoe Peraxilla tetrapetala. The buds cannot open themselves but are visited by birds such as the tui and bellbird which twist the top of the ripe bud. That action releases a mechanism which causes the petals to suddenly spring open, giving access to the nectar and pollen. However, when observing the native bees in the Canterburyprovince in the South Island, the scientists were astonished to see the bees biting the top off the buds, then pushing with their legs, occasionally popping open the buds to allow the bees to harvest the nectar and pollen, and therefore aid in the pollination of the mistletoe which is in decline in New Zealand. Nowhere else in the world have bees demonstrated ability to open explosive bird-adapted flowers.[2]
Visiting flowers can be a dangerous occupation. Many assassin bugs and crab spiders hide in flowers to capture unwary bees. Other bees are lost to birds in flight. Insecticides used on blooming plants kill many 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, mostly to replace daily casualties, most of which are workers dying of old age. Among solitary and primitively social bees, however, lifetime reproduction is among the lowest of all insects, as it is common for females of such species to produce fewer than 25 offspring.
The population value of bees depends partly on the individual efficiency of the bees, but also on the population itself. 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, and thus are not significant pollinators of early fruit.

Pollinator decline

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Morphology of a female honey bee
See also : Pollinator decline
From 1972 to 2006, there was a dramatic reduction in the number of feral honey bees in the US, which are now almost absent.[3] At the same time there was a significant though somewhat gradual decline in the number of colonies maintained by beekeepers. This decline includes the cumulative losses from all factors, such as urbanization, pesticide use, trachealand Varroa mites, and commercial beekeepers‘ retiring and going out of business. However, in late 2006 and early 2007 the rate of attrition reached new proportions, and the termcolony collapse disorder was coined to describe the sudden disappearances.[4] After several years of research and concern, a team of scientists headed by Jerry Bromenshenk published a paper in October 2010 saying that a new DNA-based virus, invertebrate iridescent virus or IIV6, and the fungus Nosema ceranae were found in every killed colony the group studied. In their study they found that neither agent alone seemed deadly, but a combination of the virus and Nosema ceraneae was always 100% fatal. Bromenshenk said it is not yet clear whether one condition weakens the bees enough to be finished off by the second, or whether they somehow compound the other’s destructive power. “They’re co-factors, that’s all we can say at the moment. They’re both present in all these collapsed colonies.”[5][6][7]Investigations into the phenomenon had occurred amidst great concern over the nature and extent of the losses.[8] In 2009 some reports from the US suggested that 1/3 of the honey bee colonies did not survive the winter,[9] though normal winter losses are known to be around 25%.[10]At the end of May 2012, the Swiss government reported that about half of the bee population had not survived the winter. The main cause of the decline was thought to be the parasite varroa.[11]
Apart from colony collapse disorder, many of the losses outside the US have also been attributed to other causes. Pesticides used to treat seeds, such as Clothianidin andImidacloprid, have been considered prime suspects.[12][13] Other species of bees such asmason bees are increasingly cultured and used to meet the agricultural pollination need.[14]
Native pollinators include bumblebees and solitary bees, which often survive in refuges in wild areas away from agricultural spraying, but may still be poisoned in massive spray programs for mosquitoesgypsy moths, or other insect pests. Although pesticide use remains a concern, the major problem for wild pollinator populations is the loss of the flower-rich habitat on which they depend for food.[citation needed] Throughout the northern hemisphere, the last 70 or so years have seen an intensification of agricultural systems, which has decreased the abundance and diversity of wild flowers.[15]
Legislation such as the UK’s Bees Act 1980 is designed to stop the decline of bees.[16]

Evolution

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A bee in the snow (Ukraine)
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Bees defend against wasp attacks
Bees, like ants, are a 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 which were flower visitors and were partially covered with pollen when they were fed to the wasp larvae. This sameevolutionary scenario has also occurred within the vespoid wasps, where the group known as “pollen wasps” also evolved from predatory ancestors. Up until recently, the oldest non-compression bee fossil had been Cretotrigona prisca in New Jersey amber and of Cretaceous age, a meliponine. A recently reported bee fossil, of the genus Melittosphex, is considered “an extinct lineage of pollen-collecting Apoidea sister to the modern bees”, and dates from the early Cretaceous (~100 mya).[17] Derived features of its morphology (“apomorphies”) place it clearly within the bees, but it retains two unmodified ancestral traits (“plesiomorphies”) of the legs (two mid-tibial spurs, and a slender hind basitarsus), indicative of its transitional status.
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, and are generally more efficient at the task than any other pollinating insect such as beetles, fliesbutterflies and pollen wasps. The appearance of such floral specialists is believed to have driven the adaptive radiation of the angiosperms, and, in turn, the bees themselves.
Among living bee groups, the “short-tongued” bee family Colletidae has traditionally been considered the most “primitive”, and sister taxon to the remainder of the bees. In the 21st century, however, some researchers have claimed that the Dasypodaidae is the basal group, the short, wasp-like mouthparts of colletids being the result of convergent evolution, rather than indicative of a plesiomorphic condition.[1] This subject is still under debate, and the phylogenetic relationships among bee families are poorly understood.

Eusocial and semisocial bees

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honey bee swarm
Bees may be solitary or may live in various types of communities. The most advanced of these are eusocial colonies[18] found among the honey bees, bumblebees, and stingless bees. Sociality, of several different types, 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 calle READ MORE

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