Nectar is a sugar-rich liquid produced by plants. It is produced in glands called nectaries, either within the flowers in which it attracts pollinating animals, or by extrafloral nectaries which provide a nutrient source to animal mutualists, which in turn provide anti-herbivore protection. Common nectar-consuming pollinators include bees, butterflies and moths, hummingbirds and bats.
Nectar is an ecologically important item, the sugar source for honey. It is also useful in agriculture and horticulture because the adult stages of some predatory insects feed on nectar such as almost all solitary wasps. In turn, these wasps then hunt agricultural pest insects as food for their young. For example, thread-waisted wasps (genus Ammophila) are known for hunting caterpillars that are destructive to crops.][
Nectar secretion increases as the flower is visited by pollinators. After pollination, the nectar is frequently reabsorbed into the plant.
Nectar is derived from Latin nectar, the favored drink of the gods, which in turn is the Latinized version of Greek νέκταρ, néktar, presumed to be a compound of the PIE roots *nek-, "death", and -*tar, "overcoming", i.e. has a similar etymology to ambrosia. The earliest recorded use of its current meaning, "sweet liquid in flowers," was in AD 1609.
Floral nectaries are generally located at the base of the perianth, so that pollinators are made to brush the flower's reproductive structures, the anthers and pistil, while accessing the nectar.
Extrafloral nectaries (also known as extranuptial nectaries) are nectar-secreting plant glands that develop outside of flowers and are not involved in pollination. They are highly diverse in form, location, size, and mechanism. They have been described in virtually all above-ground plant parts—including leaves (in which case they are known as foliar nectaries), petioles, stipules, cotyledons, fruits, and stems, among others. They range from single-celled trichomes to complex cup-like structures that may or may not be vascularized.
In contrast to floral nectaries, nectar produced outside the flower generally have a defensive function. The nectar attract predatory insects who will eat both the nectar and any plant-eating insects around, thus functioning as 'bodyguards'. Foraging predatory insects show a preference for plants with extrafloral nectaries, particularly some species of ants and wasps which have been observed to directly defend the plants. Among passion flowers, for example, extrafloral nectaries prevent herbivores by attracting ants and deterring two species of butterflies from laying eggs. In many carnivorous plants, extrafloral nectaries are also used to attract insect prey.
Extrafloral nectaries were originally believed to simply be excretory in nature (hydathodes). Their defensive functions were first recognized by the Italian botanist Federico Delpino in his important monograph Funzione mirmecofila nel regno vegetale (1886). Delpino's study was inspired by a disagreement between him and Charles Darwin with whom he corresponded with regularly. Darwin believed that extrafloral nectaries were simply hydathodes, while Delpino believed they had a defensive function, especially among myrmecophilic plants.
Extrafloral nectaries have been reported in over 3941 species of vascular plants belonging to 745 genera and 108 families. 99.7% of which belong to flowering plants (angiosperms), comprising 1.0 to 1.8% of all known species. They are most common among eudicots, occurring in 3642 species (of 654 genera and 89 families), particularly among rosids which comprise more than half of the known occurrences. The families showing the most number of recorded occurrences of extrafloral nectaries are Fabaceae, with 1069 species; Passifloraceae, with 438 species; and Malvaceae, with 301 species. The genera with the most number of recorded occurrences of extrafloral nectaries are Passiflora (322 species, Passifloraceae), Inga (294 species, Fabaceae), and Acacia (204 species, Fabaceae). Other genera with extrafloral nectaries include Salix (Salicaceae), Prunus (Rosaceae) and Gossypium (Malvaceae).
Foliar nectaries have also been observed in 39 species of ferns belonging to 7 genera and 4 families of Cyatheales and Polypodiales. They are absent, however, in bryophytes, gymnosperms, early angiosperms, magnoliids, and members of Apiales among the eudicots. Phylogenetic studies and the wide distribution of extrafloral nectaries among vascular plants point to multiple independent evolutionary origins of extrafloral nectaries in at least 457 independent lineages.
Although its main ingredient is natural sugar (i.e., sucrose (table sugar), glucose, and fructose), nectar is a brew of many chemicals. For example, the Nicotiana attenuata, a tobacco plant native to the US state of Utah, uses several volatile aromas to attract pollinating birds and moths. The strongest such aroma is benzyl acetone, but the plant also adds bitter nicotine, which is less aromatic and therefore may not be detected by the bird until after taking a drink. Researchers speculate the purpose of this addition is to drive the bird away after only a sip, motivating it to visit other plants to fill its hunger, and therefore maximizing the pollination efficiency gained by the plant for a minimum nectar output. Neurotoxins such as aesculin are present in some nectars such as that of the California Buckeye. All twenty of the normal amino acids found in protein have been identified in various nectars, with alanine, arginine, serine, proline, glycine, isoleucine, threonine, and valine being the most prevalent.
is a fine to coarse powder containing the microgametophytes of seed plants, which produce the male gametes (sperm cells). Pollen grains have a hard coat that protects the sperm cells during the process of their movement from the stamens to the pistil of flowering plants or from the male cone to the female cone of coniferous plants. When pollen lands on a compatible pistil or female cone (i.e., when pollination has occurred), it germinates and produces a pollen tube that transfers the sperm to the ovule (or female gametophyte). Individual pollen grains are small enough to require magnification to see detail. The study of pollen is called palynology and is highly useful in paleoecology, paleontology, archeology, and forensics.
Pollen itself is not the male gamete. Each pollen grain contains vegetative
(only a single cell in most flowering plants but several in other seed plants) and a generative
containing two nuclei: a tube nucleus (that produces the pollen tube) and a generative nucleus (that divides to form the two sperm cells). The group of cells is surrounded by a cellulose-rich cell wall called the intine, and a resistant outer wall composed largely of sporopollenin called the exine.
Pollen is produced in the 'microsporangium' (contained in the anther of an angiosperm flower, male cone of a coniferous plant, or male cone of other seed plants). Pollen grains come in a wide variety of shapes (most often spherical), sizes, and surface markings characteristic of the species (see electron micrograph, right). Pollen grains of pines, firs, and spruces are winged. The smallest pollen grain, that of the forget-me-not (Myosotis
spp.), is around 6 µm (0.006 mm) in diameter. Wind-borne pollen grains can be as large as about 90–100 µm.
In angiosperms, during flower development the anther is composed of a mass of cells that appear undifferentiated, except for a partially differentiated dermis. As the flower develops, four groups of sporogenous cells form within the anther. The fertile sporogenous cells are surrounded by layers of sterile cells that grow into the wall of the pollen sac. Some of the cells grow into nutritive cells that supply nutrition for the microspores that form by meiotic division from the sporogenous cells. In a process called microsporogenesis
, four haploid microspores are produced from each diploid sporogenous cell (microsporocyte), after meiotic division. After the formation of the four microspores, which are contained by callose walls, the development of the pollen grain walls begins. The callose wall is broken down by an enzyme called callase and the freed pollen grains grow in size and develop their characteristic shape and form a resistant outer wall called the exine and an inner wall called the intine. The exine is what is preserved in the fossil record.
The pollen wall protects the sperm while the pollen grain is moving from the anther to the stigma; it protects the vital genetic material from drying out and solar radiation. The pollen grain surface is covered with waxes and proteins, which are held in place by structures called sculpture elements on the surface of the grain. The outer pollen wall, which prevents the pollen grain from shrinking and crushing the genetic material during desiccation, is composed of two layers. These two layers are the tectum and the foot layer, which is just above the intine. The tectum and foot layer are separated by a region called the columella, which is composed of strengthening rods. The outer wall is constructed with a resistant biopolymer called sporopollenin. The pollen tube passes through the wall by way of structures called apertures.
Pollen apertures are various modifications of the wall of the pollen grain that may involve thinning, ridges and pores. They serve as an exit for the pollen contents and allow shrinking and swelling of the grain caused by changes in moisture content. The elongated apertures/ furrows in the pollen grain are called colpi (singular: colpus), which along with pores, are a major criterion for the identification of classes of pollen.
The orientation of furrows (relative to the original tetrad of microspores) classify the pollen as colpate
. Eudicots have three colpi (tricolpate
) or pollen shapes that are evolutionarily derived from tricolpate pollen. Other groups having one sulcus (monosulcate
Except in the case of some submerged aquatic plants, the mature pollen-grain has a double wall, a thin delicate wall of unaltered cellulose (the endospore or intine
) and a tough outer cuticularized exospore or exine
. The exine often bears spines or warts, or is variously sculptured, and the character of the markings is often of value for identifying genus, species, or even cultivar or individual. In some flowering plants, germination of the pollen grain often begins before it leaves the microsporangium, with the generative cell forming the two sperm cells.
The transfer of pollen grains to the female reproductive structure (pistil
in angiosperms) is called pollination
. This transfer can be mediated by the wind, in which case the plant is described as anemophilous
(literally wind-loving). Anemophilous plants typically produce great quantities of very lightweight pollen grains, sometimes with air-sacs. Non-flowering seed plants (e.g. pine trees) are characteristically anemophilous. Anemophilous flowering plants generally have inconspicuous flowers. Entomophilous
(literally insect-loving) plants produce pollen that is relatively heavy, sticky and protein-rich, for dispersal by insect pollinators attracted to their flowers. Many insects and some mites are specialized to feed on pollen, and are called palynivores.
In non-flowering seed plants, pollen germinates in the pollen chamber, located beneath and inside the micropyle. A pollen tube is produced, which grows into the nucellus to provide nutrients for the developing sperm cells. Sperm cells of Pinophyta and Gnetophyta are without flagella, and are carried by the pollen tube, while those of Cycadophyta and Ginkgophyta have many flagella.
When placed on the stigma of a flowering plant, under favorable circumstances, a pollen grain puts forth a pollen tube, which grows down the tissue of the style to the ovary, and makes its way along the placenta, guided by projections or hairs, to the micropyle of an ovule. The nucleus of the tube cell has meanwhile passed into the tube, as does also the generative nucleus, which divides (if it hasn't already) to form two sperm cells. The sperm cells are carried to their destination in the tip of the pollen-tube.
A Russian theoretical biologist has suggested that the quantity of pollen reaching a pistillate flower can transmit ecological information and also regulate evolutionary plasticity in cross-pollinating plants. Plentiful pollen indicates optimum environmental conditions (for example a plant that is situated at the center of its natural range, in ideal growing conditions, with a large number of male plants nearby, and favorable weather conditions), whereas a small amount of pollen indicates extreme conditions (at the borders of its range, with a deficiency of male plants, and adverse weather conditions). Geodakian believes that the quantity of pollen reaching a pistillate flower defines the sex ratio, dispersion and sexual dimorphism of a plant population. High pollen quantity leads to a reduction of these characteristics and stabilization of a population. Small quantity leads to their increase and destabilization of a population.
Dependence of the secondary sex ratio on the amount of fertilizing pollen was confirmed on four dioecious plant species from three families — Rumex acetosa
(Polygonaceae), Melandrium album
(Cariophyllaceae), Cannabis sativa
and Humulus japonicus
(Cannabinaceae). (see summary of all these data in review article).
Dependence of offspring phenotype variety on amount of pollen was observed by Ter-Avanesyan in 1949. All three studied species of plants (cotton plant, black-eyed pea, and wheat) showed dependence in the direction forecast by the theory — fertilization with a small amount of pollen resulted in an increase in the diversity of the offspring. Ter-Avanesian writes that as a result of a limited pollination, "instead of homogenous sorts we get populations".
Pollen's sporopollenin outer sheath affords it some resistance to the rigours of the fossilisation process that destroy weaker objects; it is also produced in huge quantities. As such, there is an extensive fossil record of pollen grains, often disassociated from their parent plant. The discipline of palynology is devoted to the study of pollen, which can be used both for biostratigraphy and to gain information about the abundance and variety of plants alive — which can itself yield important information about paleoclimates. Pollen is first found in the fossil record in the late Devonian period]
[ and increases in abundance until the present day.
Nasal allergy to pollen is called pollinosis, and allergy specifically to grass pollen is called hay fever. Generally pollens that cause allergies are those of anemophilous plants (pollen is dispersed by air currents.) Such plants produce large quantities of lightweight pollen (because wind dispersal is random and the likelihood of one pollen grain landing on another flower is small), which can be carried for great distances and are easily inhaled, bringing it into contact with the sensitive nasal passages.
In the US, people often mistakenly blame the conspicuous goldenrod flower for allergies. Since this plant is entomophilous (its pollen is dispersed by animals), its heavy, sticky pollen does not become independently airborne. Most late summer and fall pollen allergies are probably caused by ragweed, a widespread anemophilous plant.
Arizona was once regarded as a haven for people with pollen allergies, although several ragweed species grow in the desert. However, as suburbs grew and people began establishing irrigated lawns and gardens, more irritating species of ragweed gained a foothold and Arizona lost its claim of freedom from hay fever.
Anemophilous spring blooming plants such as oak, birch, hickory, pecan, and early summer grasses may also induce pollen allergies. Most cultivated plants with showy flowers are entomophilous and do not cause pollen allergies.
The percentage of people in the United States affected by hay fever varies between 10% and 20%, and such allergy has proven to be the most frequent allergic response in the nation. There are certain evidential suggestions pointing out hay fever and similar allergies to be of hereditary origin. Individuals who suffer from eczema or are asthmatic tend to be more susceptible to developing long-term hay fever.
The most efficient way to handle a pollen allergy is by preventing contact with the material. Individuals carrying the ailment may at first believe that they have a simple summer cold, but hay fever becomes more evident when the apparent cold does not disappear. The confirmation of hay fever can be obtained after examination by a general physician.
Antihistamines are effective at treating mild cases of hay fever, this type of non-prescribed drugs includes loratadine, cetirizine and chlorphenamine. They do not prevent the discharge of histamine, but it has been proven that they do prevent a part of the chain reaction activated by this biogenic amine, which considerably lowers hay fever symptoms. A side effect of antihistamines is somnolence, and it is therefore recommended not to take these drugs while driving an automobile or during the consumption of alcoholic beverages. However, the side effects of these medications can vary from person to person.
Decongestants can be administered in different ways such as tablets and nasal sprays. Decongestants such as pseudoephedrine, xylometazoline and drixoral can be acquired as over-the-counter medications. Since oral decongestant drugs raise blood pressure levels, individuals with hypertension are advised to avoid them. The oral decongestant type can aggravate the symptoms of an enlarged prostate, making the process of urinating more complicated.
Most major classes of predatory and parasitic arthropods contain species that eat pollen, despite the common perception that bees are the primary pollen-consuming arthropod group. Many other Hymenoptera other than bees consume pollen as adults, though only a small number feed on pollen as larvae (including some ant larvae). Spiders are normally considered carnivores but pollen is an important source of food for several species, particularly for spiderlings, which catch pollen on their webs. It is not clear how spiderlings manage to eat pollen however, since their mouths are not large enough to consume pollen grains.]
[ Some predatory mites also feed on pollen, with some species being able to subsist solely on pollen, such as Euseius tularensis
, which feeds on the pollen of dozens of plant species. Members of some beetle families such as Mordellidae and Melyridae feed almost exclusively on pollen as adults, while various lineages within larger families such as Curculionidae, Chrysomelidae, Cerambycidae, and Scarabaeidae are pollen specialists even though most members of their families are not (e.g., only 36 of 40000 species of ground beetles, which are typically predatory, have been shown to eat pollen—but this is thought to be a severe underestimate as the feeding habits are only known for 1000 species). Similarly, Ladybird beetles mainly eat insects, but many species also eat pollen, as either part or all of their diet. Hemiptera are mostly herbivores or omnivores but pollen feeding is known (and has only been well studied in the Anthocoridae). Many adult flies, especially Syrphidae, feed on pollen, and three UK syrphid species feed strictly on pollen (syrphids, like all flies, cannot eat pollen directly due to the structure of their mouthparts, but can consume pollen contents that are dissolved in a fluid). Some species of fungus, including Fomes fomentarius
, are able to break down grains of pollen as a secondary nutrition source that is particularly high in nitrogen.
Although bats, butterflies and hummingbirds are not pollen eaters per se
, their consumption of nectar in flowers is an important aspect of the pollination process.
A variety of producers have started selling bee pollen for human consumption, often marketed as a food (rather than a dietary supplement). The largest constituent is carbohydrates, with protein content ranging from 7 to 35 percent depending on the plant species collected by bees.
Honey produced by bees from natural sources contains pollen derived p-coumaric acid, an antioxidant. .
The U.S. Food and Drug Administration (FDA) has not found any harmful effects of pollen consumption, except from the usual allergies. However, FDA does not allow pollen marketers in the United States to make health claims about their produce, as no scientific basis for these has ever been proven. Furthermore, there are possible dangers not only from allergic reactions but also from contaminants such as pesticides and from fungi and bacteria growth related to poor storage procedures. A manufacturers's claim that pollen collecting helps the bee colonies is also controversial.
In forensic biology, pollen can tell a lot about where a person or object has been, because regions of the world, or even more particular locations such a certain set of bushes, will have a distinctive collection of pollen species. Pollen evidence can also reveal the season in which a particular object picked up the pollen. Pollen has been used to trace activity at mass graves in Bosnia, catch a burglar who brushed against a Hypericum
bush during a crime, and has even been proposed as an additive for bullets to enable tracking them.
This article incorporates text from a publication now in the public domain:
Bees are flying insects closely related to wasps and ants, and are known for their role in pollination 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, 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-pollinated flowering 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 kingbirds, mockingbirds, beewolves, and dragonflies.
Bees play an important role in pollinating flowering plants, and are the major type of pollinator 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 domesticated European honey bee.][ 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.
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 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, 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 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 Canterbury province 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.
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.
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. 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, tracheal and 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 term colony collapse disorder was coined to describe the sudden disappearances. 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." Investigations into the phenomenon had occurred amidst great concern over the nature and extent of the losses. In 2009 some reports from the US suggested that 1/3 of the honey bee colonies did not survive the winter, though normal winter losses are known to be around 25%. 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.
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 and Imidacloprid, have been considered prime suspects. Other species of bees such as mason bees are increasingly cultured and used to meet the agricultural pollination need.
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 mosquitoes, gypsy 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.][ 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.
Legislation such as the UK's Bees Act 1980 is designed to stop the decline of bees. In April 2013 the European Union announced plans to restrict the use of certain pesticides to stop bee populations from declining further.
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 same evolutionary 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). 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, flies, butterflies 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. This subject is still under debate, and the phylogenetic relationships among bee families are poorly understood.
Bees may be solitary or may live in various types of communities. The most advanced of these are eusocial colonies 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 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 rarely been 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, many workers and, at certain stages in the colony cycle, drones. When humans provide the nest, it is called a hive. Honey bee hives can contain up to 40,000 bees at their annual peak, which occurs in the spring, but usually have fewer.
Bumblebees (Bombus terrestris, Bombus 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 honey bees 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 honey bee hives, where they are sometimes found dead in the spring by beekeepers, presumably stung to death by the honey bees. It is unknown whether any survive winter in such an environment.
Bumblebees are one of the more important wild pollinators, but have declined significantly in recent decades. In the UK, 2 species have become nationally extinct during the last 75 years while others have been placed on the UK Biodiversity Action Plan as priority species in recognition of the need for conservation action. In 2006 a new charity, the Bumblebee Conservation Trust, was established to coordinate efforts to conserve remaining populations through conservation and education. In 2011, the International Union for the Conservation of Nature set up the Bumblebee Specialist Group to review the threat status of all bumblebee species world-wide using the IUCN Red List criteria.
Stingless bees are very diverse in behavior, but all are highly eusocial. They practise mass provisioning, complex nest architecture, and perennial colonies.
The true honey bees (genus Apis) have arguably the most complex social behavior among the bees. The European (or Western) honey bee, Apis mellifera, is the best known bee species and one of the best known of all insects.
Africanized bees, also called killer bees, are a hybrid strain of Apis mellifera derived from experiments by Warwick Estevam Kerr to cross European and African honey bees. Several queen bees escaped from his laboratory in South America and have spread throughout the Americas. Africanized honey bees are more defensive than European honey 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 also diseases of the honey bee).
Solitary bees are important pollinators, and pollen is gathered for provisioning the nest with food for their brood. Often it is mixed with nectar to form a paste-like consistency. Some solitary bees have very advanced types of pollen-carrying structures on their bodies. A very few species of solitary bees are being increasingly cultured for commercial pollination. Most of these species belong to a distinct set of genera, namely: carpenter bees, sweat bees, mason bees, polyester bees, squash bees, dwarf carpenter bees, leafcutter bees, alkali bees, digger bees.
Solitary bees are often oligoleges, in that they only gather pollen from one or a few species/genera of plants (unlike honey bees and bumblebees which are generalists). No known bees are nectar specialists; many oligolectic bees will visit multiple plants for nectar, but there are no bees which visit only one plant for nectar while also gathering pollen from many different sources. Specialist pollinators also include bee species which gather floral oils instead of pollen, and male orchid bees, which gather aromatic compounds from orchids (one of the only cases where male bees are effective pollinators). In a very few cases only one species of bee can effectively pollinate a plant species, and some plants are endangered at least in part because their pollinator is dying off. There is, however, a pronounced tendency for oligolectic bees to be associated with common, widespread plants which are visited by multiple pollinators (e.g., there are some 40 oligoleges associated with creosote bush in the US desert southwest, and a similar pattern is seen in sunflowers, asters, mesquite, etc.)
Solitary bees create nests in hollow reeds or twigs, 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 once the egg is laid, 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, if ever).
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. Large groups of solitary bee nests are called aggregations, to distinguish them from colonies.
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 from predators and parasites when there are multiple females using that same entrance on a regular basis.
Cleptoparasitic bees, commonly called "cuckoo bees" because their behavior 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 in looks and size, (i.e., the Bombus subgenus Psithyrus, which are parasitic bumblebees that infiltrate nests of species in other subgenera of 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 dasypodaid genus Hesperapis, while the other species in the same genus attack halictid bees.
Four bee families (Andrenidae, Colletidae, Halictidae, and Apidae) contain some species that are crepuscular (these may be either the vespertine or matinal type). These bees have greatly enlarged ocelli, which are extremely sensitive to light and dark, though incapable of forming images. Many are pollinators of flowers that themselves are crepuscular, such as evening primroses, and some live in desert habitats where daytime temperatures are extremely high.
In M. Magnan 1934 French book Le vol des insectes, he wrote that he and a M. Saint-Lague had applied the equations of air resistance to bumblebees and found that their flight could not be explained by fixed-wing calculations, but that "One shouldn't be surprised that the results of the calculations don't square with reality". This has led to a common misconception that bees "violate aerodynamic theory", but in fact it merely confirms that bees do not engage in fixed-wing flight, and that their flight is explained by other mechanics, such as those used by helicopters.
In 1996 Charlie Ellington at Cambridge University showed that vortices created by many insects’ wings and non-linear effects were a vital source of lift; vortices and non-linear phenomena are notoriously difficult areas of hydrodynamics, which has made for slow progress in theoretical understanding of insect flight.
In 2005, Michael Dickinson and his Caltech colleagues studied honey bee flight with the assistance of high-speed cinematography and a giant robotic mock-up of a bee wing. Their analysis revealed that sufficient lift was generated by "the unconventional combination of short, choppy wing strokes, a rapid rotation of the wing as it flops over and reverses direction, and a very fast wing-beat frequency". Wing-beat frequency normally increases as size decreases, but as the bee's wing beat covers such a small arc, it flaps approximately 230 times per second, faster than a fruitfly (200 times per second) which is 80 times smaller.
Bees figure prominently in mythology and folklore and have been used by political theorists as a model for human society. Journalist Bee Wilson states that the image of a community of honey bees "occurs from ancient to modern times, in Aristotle and Plato; in Virgil and Seneca; in Erasmus and Shakespeare; Tolstoy, as well as by social theorists Bernard Mandeville and Karl Marx." They are found in heraldry where they can signify industriousness as in the Manchester bee in the crest of Manchester City Council.
Despite the honey bee's painful sting and the stereotype of insects as pests, bees are generally held in high regard. This is most likely due to their usefulness as pollinators and as producers of honey, their social nature, and their reputation for diligence. Bees are one of the few insects frequently used in advertisements in a positive manner, typically for products containing honey (such as Honey Nut Cheerios).
In ancient Egypt, the bee was seen to symbolize the lands of Lower Egypt, with the Pharaoh being referred to as "He of Sedge and Bee" (the sedge representing Upper Egypt).
In North America, yellowjackets and hornets, especially when encountered as flying pests, are often misidentified as bees, despite numerous differences between them.
Although a bee sting can be deadly to those with allergies, virtually all bee species are non-aggressive if undisturbed and many cannot sting at all. Humans are often a greater danger to bees, as bees can be affected or even harmed by encounters with toxic chemicals in the environment (see also bees and toxic chemicals).
In Indonesia bee larvae are eaten as a companion to rice, after being mixed with shredded coconut "meat", wrapped in banana leaves, and steamed.
Honey bees were found in Washington that were acting strangely, almost as if they were drunk. Tests were conducted on collected specimens, and it was found that they had been infected by the parasitic fly Apocephalus borealis (also known as the zombie fly). Bees infected by Apocephalus borealis have been dubbed as "zombie bees," or "zombees." The infection has spread to Oregon, California, and South Dakota. Tests are being conducted on bees in several other states to determine if the bees there are infected. Bees infected with the Apocephalus borealis fly cannot spread the infection to humans.
Source: ZomBee Watch
A honey bee, at Sandwip Island, Bangladesh