The immediate ancestors of bees werestinging wasps in the familyAmmoplanidae, which werepredators of other insects.[5] 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 may have occurred within thevespoid wasps, where thepollen wasps evolved from predatory ancestors.[6]
Based onphylogenetic analysis, bees are thought to have originated during theEarly Cretaceous (about 124 million years ago) on the supercontinent ofWest Gondwana, just prior to its breakup intoSouth America andAfrica. The supercontinent is thought to have been a largelyxeric environment at this time; modern bee diversity hotspots are also in xeric and seasonal temperate environments, suggesting strongniche conservatism among bees ever since their origins.[7]
Genomic analysis indicates that despite only appearing much later in the fossil record, all modern bee families had already diverged from one another by the end of the Cretaceous. TheMelittidae,Apidae, andMegachilidae had already evolved on the supercontinent prior to its fragmentation. Further divergences were facilitated by West Gondwana's breakup around 100 million years ago, leading to a deep Africa-South America split within both the Apidae and Megachilidae, the isolation of the Melittidae in Africa, and the origins of theColletidae,Andrenidae andHalictidae in South America. The rapid radiation of the South American bee families is thought to have followed the concurrent radiation offlowering plants within the same region. Later in the Cretaceous (80 million years ago), colletid bees colonizedAustralia fromSouth America (with an offshoot lineage evolving into theStenotritidae), and by the end of the Cretaceous, South American bees had also colonized North America.[7] The North American fossil taxonCretotrigona belongs to a group that is no longer found in North America, suggesting that many bee lineages went extinct during theCretaceous–Paleogene extinction event (the "K-Pg extinction").[7]
Following the K-Pg extinction, surviving bee lineages continued to spread into the Northern Hemisphere, colonizingEurope from Africa by thePaleocene, and then spreading east toAsia. This was facilitated by the warming climate around the same time, allowing bees to move to higher latitudes following the spread of tropical and subtropical habitats. By theEocene (~45 mya) there was already considerable diversity among eusocial bee lineages.[8][a] A second extinction event among bees is thought to have occurred due to rapid climatic cooling around theEocene-Oligocene boundary, leading to the extinction of some bee lineages such as the tribeMelikertini. During thePaleogene andNeogene periods, bee lineages expanded worldwide. This came about as continental drift and changing climates created new barriers and habitats, isolating populations and driving the evolution of many new tribes.[7]
TheAllodapini (within the Apidae) appeared around 53 Mya.[13]The Colletidae appear as fossils only from the lateOligocene (~25 Mya) to earlyMiocene.[14]The Melittidae are known fromPalaeomacropis eocenicus in theEarly Eocene.[15]The Megachilidae are known from trace fossils (characteristic leaf cuttings) from theMiddle Eocene.[16]The Andrenidae are known from the Eocene-Oligocene boundary, around 34 Mya, of the Florissant shale.[17]The Halictidae first appear in the Early Eocene[18] with species[19][20] found in amber. The Stenotritidae are known from fossil brood cells ofPleistocene age.[21]
The earliest animal-pollinated flowers were shallow, cup-shaped bloomspollinated by insects such asbeetles, so thesyndrome of insect pollination was well established before bees evolved. Bees represent a further step in this process, being specialized for pollination through behavioral and physical traits that specifically enhance the task and make them the most efficient pollinating insects. In a process ofcoevolution, flowers developed floral rewards[22] such asnectar and longer tubes, and bees developed longer tongues to extract the nectar.[23] Bees also developed structures known asscopal hairs andpollen baskets to collect and carry pollen. The location and type differ among and between groups of bees. Most species have scopal hairs on their hind legs or on the underside of their abdomens. Some species in the family Apidae havepollen baskets on their hind legs, while very few lack these and instead collect pollen in their crops.[2] The appearance of these structures drove theadaptive radiation of theangiosperms, and, in turn, bees themselves.[9] Bees and certain mites have indeed coevolved, with some bee species evolving specialized structures calledacarinaria that serve as lodgings for mites, demonstrating a mutualistic relationship. Mites residing in these acarinaria can benefit their bee hosts by eating fungi that attack pollen and brood, leading to reduced fungal contamination and improved bee survivorship.[24][25]
Phylogeny
External
Molecular phylogeny was used by Debevicet al, 2012, to demonstrate that the bees (Anthophila) arose from deep within theCrabronidaesensu lato, which was thus renderedparaphyletic. In their study, the placement of the monogenericHeterogynaidae was uncertain. The small familyMellinidae was not included in this analysis.[26]
Further studies by Sannet al., 2018, elevated the subfamilies (plus one tribe and one subtribe) ofCrabronidaesensu lato to family status. They also recovered the placement ofHeterogyna withinNyssonini and sunkHeterogynaidae. The newly erected family,Ammoplanidae, formerly a subtribe ofPemphredoninae, was recovered as the most sister family to bees.[27]
This cladogram of the bee families is based on Hedtke et al., 2013, which places the former families Dasypodaidae and Meganomiidae as subfamilies inside the Melittidae.[28] English names, where available, are given in parentheses.
Bees differ from closely related groups such as wasps by having branched or plume-likesetae (hairs), combs on the forelimbs for cleaning their antennae, small anatomical differences in limb structure, and the venation of the hind wings. In females, the seventh dorsal abdominal plate is also divided into two half-plates.[29]
A pair of largecompound eyes which cover much of the surface of the head. Between and above these are three small simple eyes (ocelli) which provide information on light intensity.[30]
Theantennae usually have 13 segments in males and 12 in females, and aregeniculate, having an elbow joint part way along. They house large numbers of sense organs that can detect touch (mechanoreceptors), smell and taste; and small, hairlike mechanoreceptors that can detect air movement so as to "hear" sounds.[30]
Themouthparts are adapted for both chewing and sucking by having both a pair ofmandibles and a longproboscis for sucking up nectar.[30]
The thorax has three segments, each with a pair of robust legs, and a pair of membranous wings on the hind two segments. The front legs ofcorbiculate bees bear combs for cleaning the antennae. In many species the hind legs bear pollen baskets, flattened sections with incurving hairs to secure the collected pollen. The wings are synchronized in flight, and the somewhat smaller hind wings connect to the forewings by a row of hooks along their margin which connect to a groove in the forewing.
The abdomen has nine segments, the hindermost three being modified into the sting.[30]
Many bees are brightly colored, displaying contrasting bands of yellow, orange, or red against black. These colors function asaposematic signals, warning potential predators that the insect may sting or otherwise defend itself,[31] although similar warning patterns are also seen in many harmless insects that mimic bees or wasps, a form of Batesian mimicry.[32]
The largest species of bee is thought to be Wallace's giant beeMegachile pluto, whose females can attain a length of 39 millimeters (1.54 in).[33] The smallest species may be dwarf stingless bees in the tribeMeliponini whose workers are less than 2 millimeters (0.08 in) in length.[34]
Willing to die for their sisters: worker honey bees killed defending their hive againstyellowjackets, along with a dead yellowjacket. Suchaltruistic behaviour may be favoured by thehaplodiploidsex determination system of bees.
According toinclusive fitness theory, an organism can increase its evolutionary success not only by increasing its own offspring, but also by helping close relatives reproduce. In genetic terms, cooperation is favored when the cost to the helper is less than the product of relatedness and benefit. This condition is more easily met inhaplodiploid species such as bees, where the genetic relationships create strong incentives for cooperative behavior.[35][36][37][38]
Haplodiploidy alone does not explain the evolution of eusociality. Some eusocial species such astermites are not haplodiploid. Conversely, many haplodiploid species, including most bees, are not eusocial, and even among eusocial bees, queens often mate with several males, producing half sisters that share only about a quarter of their genes.[39] However, since single mating appears to be the ancestral condition in all eusocial lineages studied so far, haplodiploidy may still have played an important role in the early evolution of eusocial behaviour in bees.[37]
Bees may be solitary or may live in various types of community.Eusociality appears to have arisen independently at least three times in halictid bees.[40] The most advanced of these formeusocial colonies; these are characterized by cooperative brood care and adivision of labour into reproductive and non-reproductive adults, with overlapping generations.[41] This division of labour creates specialized groups within eusocial societies, calledcastes. In some species, groups of cohabiting females are sisters. If these sisters share a division of labour, the group is described assemisocial. When the group instead includes a mother (the queen) and her daughters (the workers), it is considered eusocial. If the castes differ only in behavior and size, as in many paper wasps, the system is primitively eusocial. When the castes show clear morphological differences, the system is described as highly eusocial.[23]
True honey bees (genusApis, with eight species) are highly eusocial, and are among the best known insects. Their colonies are established byswarms, consisting of a queen and several thousand workers. There are 29 subspecies of one of these species,Apis mellifera, native to Europe, the Middle East, and Africa.Africanized bees are a hybrid strain ofA. mellifera that escaped from experiments involving crossing European and African subspecies; they are extremely defensive.[42]
Many bumblebees are eusocial, similar to the eusocialVespidae such ashornets in that the queen initiates a nest on her own rather than by swarming. 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 pre-existing nest cavity, and colonies rarely last more than a year.[44] In 2011, theInternational Union for Conservation of Nature set up the Bumblebee Specialist Group to review the threat status of all bumblebee species worldwide using theIUCN Red List criteria.[45]
There are many more species of primitively eusocial than highly eusocial bees, but they have been studied less often. Most are in the familyHalictidae, or "sweat bees". Colonies are typically small, with a dozen or fewer workers, on average. Queens and workers differ only in size, if at all. Most species have a single season colony cycle, even in the tropics, and only mated females hibernate. A few species have long active seasons and attain colony sizes in the hundreds, such asHalictus hesperus.[46] Some species are eusocial in parts of their range and solitary in others,[47] or have a mix of eusocial and solitary nests in the same population.[48] Theorchid bees (Apidae) include some primitively eusocial species with similar biology. Someallodapine bees (Apidae) form primitively eusocial colonies, withprogressive provisioning: a larva's food is supplied gradually as it develops, as is the case in honey bees and some bumblebees.[49]
Solitary and communal bees
Most other bees, including familiar insects such ascarpenter bees,leafcutter bees andmason bees are solitary in the sense that every female is fertile, and typically inhabits a nest she constructs herself. There is no division of labor, so these nests lack queens andworker bees. Solitary bees typically produce neither honey norbeeswax. Bees collect pollen to feed their young, and have the necessary adaptations to do this. However, certain wasp species such aspollen wasps have similar behaviours, and a few species of beescavenge from carcasses to feed their offspring.[29] Solitary bees are important pollinators; they gather pollen to provision their nests with food for their brood. Often it is mixed with nectar to form a paste-like consistency. Some solitary bees have advanced types of pollen-carrying structures on their bodies. Very few species of solitary bee are being cultured for commercial pollination. Most of these species belong to a distinct set ofgenera which are commonly known by their nesting behavior or preferences, namely the carpenter bees,sweat bees, mason bees,plasterer bees,squash bees,dwarf carpenter bees, leafcutter bees,alkali bees anddigger bees.[50]
Most solitary bees arefossorial, digging nests in the ground in a variety of soil textures and conditions, while others create nests in hollowreeds or twigs, or holes inwood. 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. Solitary bees are very unlikely to sting (only in self-defense, if ever), and some (esp. in the familyAndrenidae) are stingless.[51][52]
While solitary, females each make individual nests.[53] Some species, such as the European mason beeHoplitis anthocopoides,[54] and theDawson's Burrowing bee,Amegilla dawsoni,[55] are gregarious, preferring to make nests near others of the same species, and giving the appearance of being social. Large groups of solitary bee nests are calledaggregations, to distinguish them fromcolonies. 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 multiple females use that same entrance regularly.[54]
The life cycle of both solitary and social bees involves the laying of an egg, the development through several moults of a leglesslarva, apupa in which the insect undergoescomplete metamorphosis, and the emergence of a winged adult. Most solitary bees and bumble bees in temperate climatesoverwinter as adults or pupae and emerge in spring when increasing numbers of flowering plants come into bloom. The males usually emerge first and search for females with which to mate. Like the other members of Hymenoptera, bees arehaplodiploid; the sex of a bee is determined by whether or not the egg is fertilized. After mating, a female stores the sperm, and determines which sex is required at the time each individual egg is laid, fertilized eggs producing female offspring and unfertilized eggs, males. Tropical bees may have several generations in a year and no restingdiapause stage.[56][57][58][59]
The egg is generally oblong, slightly curved and tapering at one end. Solitary bees, lay each egg in a separate cell with a supply of mixed pollen and nectar next to it. This may be rolled into a pellet or placed in a pile and is known as mass provisioning. Social bee species provision progressively, that is, they feed the larva regularly while it grows. The nest varies from a hole in the ground or in wood, in solitary bees, to a substantial structure with wax combs in bumblebees and honey bees.[60]
In most species, bee larvae are whitish grubs, roughly oval and bluntly-pointed at both ends. They have 15 segments andspiracles in each segment for breathing. They have no legs but move within the cell, helped by tubercles on their sides. They have short horns on the head, jaws for chewing food and an appendage on either side of the mouth tipped with a bristle. There is a gland under the mouth that secretes a viscous liquid which solidifies into thesilk they use to produce a cocoon. The cocoon is semi-transparent and the pupa can be seen through it. Over the course of a few days, the larva undergoes metamorphosis into a winged adult. When ready to emerge, the adult splits its skin dorsally and climbs out of theexuviae and breaks out of the cell.[60]
In the 1930s, calculations based on theaerodynamics of fixed wings appeared to show that insect flight was impossible, with results taken from equations meant for aircraft to wings that beat rapidly through short arcs. The author of the study remarked that "one should not be surprised that the results of the calculations do not square with reality," but this comment was later taken out of context and gave rise to the myth that "the bumblebee should not be able to fly."[61][62]
In fact, those early models were never suited to describe how insects fly. Studies later showed that bees and many other insects producelift through swirlingvortices that form along the leading edge of the wing.[63][64] High-speed imaging and robotic wing experiments confirmed that lift in bees results from rapid wing reversals and high wing-beat frequency, which together sustain the airflow needed to stay in the air.[65][66]
TheethologistKarl von Frisch showed that honey bees communicate by thewaggle dance, a pattern of movement that informs other workers about the direction and distance to food. He showed that honey bees use the sun as their main compass but can still locate its position on cloudy days by reading the polarization pattern of skylight.[67] They usespatial memory with a "rich, map-like organization".[68]
Digestion
The gut of bees is relatively simple, but multiple metabolic strategies exist in the gutmicrobiota.[69] Pollinating bees consume nectar and pollen, which require different digestion strategies by somewhat specialized bacteria. While nectar is a liquid of mostlymonosaccharide sugars and so easily absorbed, pollen contains complexpolysaccharides: branchingpectin andhemicellulose.[70] Approximately five groups of bacteria are involved in digestion. Three groups specialize in simple sugars (Snodgrassella and two groups ofLactobacillus), and two other groups in complex sugars (Gilliamella andBifidobacterium). Digestion of pectin and hemicellulose is dominated by bacterialcladesGilliamella andBifidobacterium respectively. Bacteria that cannot digest polysaccharides obtain enzymes from their neighbors, and bacteria that lack certain amino acids do the same, creating multipleecological niches.[71]
Although most bee species eatnectar andpollen, some do not. Thevulture bees in the genusTrigona, consume carrion and the immature stages of wasps, turning meat into a honey-like substance.[72] Bees drinkguttation drops from leaves for energy and nutrients.[73]
Ecology
Floral relationships
Most bees aregeneralists, collecting pollen from a range of flowering plants. Some arespecialists, gathering pollen only from one or a few species or genera of closely related plants.[74] Some genera in Melittidae and Apidae are highly specialized for collecting plant oils as well as or instead of nectar; they mix the oils with pollen to feed their larvae.[75] Male orchid bees in some species gather aromatic compounds fromorchids, which is one of the few cases where male bees are effective pollinators. All bees are able to detect desirable flowers by recognizing ultraviolet patterning on flowers, and by floral odors.[76] Bumblebees can in addition detect flowers' electromagnetic fields.[77] Once landed, a bee uses nectar quality[76] and pollen taste to determine whether to continue visiting similar flowers.[78]
In rare cases, aplant species may only be effectively pollinated by a single bee species; some plants areendangered in part because their pollinator is threatened. Such specialist bees are however strongly associated with common, widespread plants visited by multiple pollinator species. For example, in the arid southwestern United States, the creosote bush (Larrea tridentata) supports more than forty bee species that specialize in collecting its pollen.[79]
Many bees areaposematically colored, typically orange and black, warning of their ability to defend themselves with a powerful sting. As such they are models forBatesian mimicry by non-stinging insects such asbee-flies,robber flies andhoverflies,[80] all of which gain a measure of protection by superficially looking and behaving like bees.[80]
Bees are themselvesMüllerian mimics of other aposematic insects with the same color scheme, includingwasps,lycid and other beetles, and many butterflies and moths (Lepidoptera) which are themselves distasteful, often through acquiring bitter and poisonous chemicals from their plant food. All the Müllerian mimics, including bees, benefit from the reduced risk of predation that results from their easily recognized warning coloration.[81]
Bees are mimicked by plants such as thebee orchid which imitates both the appearance and the scent of a female bee; male bees attempt to mate (pseudocopulation) with the furry lip of the flower, thus pollinating it.[82]
Brood parasites occur in several bee families including theapid subfamilyNomadinae.[83] Females of these species lack pollen collecting structures (thescopa) 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 often the host egg also.[84] In particular, the Arctic species of Bumblebee,Bombus hyperboreus, is an aggressive brood parasite that invades and enslaves colonies of other bumblebees within the same subgenus,Alpinobombus.[85] Unlike most socially parasitic bumblebees, which have lost the ability to collect pollen,B. hyperboreus retains functional pollen baskets and has been observed gathering pollen and nectar in the field.[86] This retention of foraging ability may be an adaptation to the severe Arctic climate, in which the short breeding season and limited availability of host colonies favor flexibility and a degree of metabolic self-reliance.[87]
In Southern Africa, hives of African honeybees (A. mellifera scutellata) are being destroyed by parasitic workers of the Cape honeybee,A. m. capensis. These laydiploid eggs ("thelytoky"), escaping normalworker policing, leading to the colony's destruction; the parasites can then move to other hives.[88]
Thecuckoo bees in theBombus subgenusPsithyrus are closely related to, and resemble, their hosts in looks and size. This common pattern gave rise to the ecological principle "Emery's rule". Others parasitize bees in different families, likeTownsendiella, anomadineapid, two species of which are cleptoparasites of thedasypodaid genusHesperapis,[89] while the other species in the same genus attackshalictid bees.[90]
Nocturnal bees
Four bee families (Andrenidae,Colletidae,Halictidae, andApidae) contain some species that arecrepuscular. Most are tropical or subtropical, but some live in arid regions at higher latitudes. These bees have greatly enlargedocelli, which are extremely sensitive to light and dark, though incapable of forming images. Some have refracting superposition compound eyes: these combine the output of many elements of their compound eyes to provide enough light for each retinal photoreceptor. Their ability to fly by night enables them to avoid many predators, and to exploit flowers that produce nectar only or also at night.[91]
Vertebrate predators of bees includebee-eaters,shrikes andflycatchers, which make short sallies to catch insects in flight.[92] Swifts and swallows[92] fly almost continually, catching insects as they go. Thehoney buzzard attacks bees' nests and eats the larvae.[93] Thegreater honeyguide interacts with humans by guiding them to the nests of wild bees. The humans break open the nests and take the honey and the bird feeds on the larvae and the wax.[94] Among mammals, predators such as thebadger dig up bumblebee nests and eat both the larvae and any stored food.[95]
Somemites of the genusTarsonemus are associated with bees. They live in bee nests and ride on adult bees for dispersal. They are presumed to feed on fungi, nest materials or pollen. However, the impact they have on bees remains uncertain.[99]
The bee-eater,Merops apiaster, specializes in feeding on bees; here a male catches a nuptial gift for his mate.
Bees are exposed to a wide range of chemical stressors, both natural and synthetic, though their relative impacts differ sharply. Comparative toxicological studies indicate that synthetic insecticides, such asneonicotinoids, are 1,000 to 10,000 times more acutely toxic to honeybees than commonly encountered naturalalkaloids such asnicotine andcaffeine, which are among the most thoroughly studied plant secondarymetabolites.[100]
Insecticides remain the most damaging chemical stressor for bees.Neonicotinoids such asImidacloprid,Clothianidin, andThiamethoxam interfere with navigation, thermoregulation, and immune responses even at sub-lethal concentrations.[101] Long-term exposure reduces colony growth, foraging success, and queen survival in both laboratory and field conditions.[102][103] Following EFSA's 2018 risk assessment, outdoor agricultural uses of these active ingredients were banned throughout the European Union.[104][105][106] Other synthetic insecticides, including organophosphates and pyrethroids, as well as some fungicide mixtures, act synergistically with parasites and pathogens such asVarroa destructor, a parasitic mite of honeybees, andNosema ceranae, compounding the physiological stress on colonies.[107][108]Industrial emissions and road traffic release traces ofheavy metals such ascadmium,lead, and zinc, which can accumulate in hive products and bee tissues.[109] These metals induce oxidative stress, developmental abnormalities and altered foraging behaviour.[110] These substances are much less acutely toxic than insecticides, however their persistence and the fact that they are found everywhere results in chronic exposure that weakens immunity and increases disease susceptibility.[111][112]
A minority of flowering plants produce secondary metabolites that can become toxic to pollinators when concentrated. Alkaloids, saponins and glycosides in species such asAesculus californica (California buckeye) andRhododendron spp. (grayanotoxins) can deter feeding or cause mortality.[113] However, because their occurrence is sporadic and seasonal, natural floral toxins rarely affect colonies at a population level.
Chemical stressors affecting pollinators are best characterized by their acute and sublethal toxicity as well as ecological impact. In this way, synthetic insecticides consistently present the greatest risk across meta-analyses, followed by fungicides and certain industrial pollutants.[114] Natural floral toxins (plant secondary metabolites) are typically sublethal. As well, they rarely drive population declines and are minor in impact compared to anthropogenic chemicals.[115]
Overall, synthetic agrochemicals (particularly insecticides and some fungicides) and industrial pollutants remain the dominant chemical drivers of pollinator decline,[116]whereas the majority of natural floral toxins have sublethal impacts that do not generally contribute to major population-level effects.[117][118]
Gold plaques embossed with winged bee goddesses.Camiros,Rhodes. 7th century BC.
Homer'sHymn to Hermes describes three bee-maidens with the power ofdivination and thus speaking truth, and identifies the food of the gods as honey. Sources associated the bee maidens withApollo and, until the 1980s, scholars followed Gottfried Hermann (1806) in incorrectly identifying the bee-maidens with theThriae.[119] Honey, according to a Greek myth, was discovered by a nymph calledMelissa ("Bee"); and honey was offered to the Greek gods fromMycenean times. Bees were also associated with theDelphic oracle and the prophetess was sometimes called a bee.[120]
Humans have kept honey bee colonies, commonly inhives, for millennia.[128] Depictions of humans collecting honey from wild bees date to 15,000 years ago; efforts to domesticate them are shown in Egyptian art around 4,500 years ago.[129] Simple hives and smoke were used.[130][131]
Among Classical Era authors, beekeeping with the use of smoke is described in Aristotle'sHistory of Animals Book 9.[128] The account mentions that bees die after stinging; that workers remove corpses from the hive, and guard it; castes including workers and non-workingdrones, but "kings" rather than queens; predators including toads and bee-eaters; and thewaggle dance, with the "irresistible suggestion" ofάροσειονται ("aroseiontai", it waggles) andπαρακολουθούσιν ("parakolouthousin", they watch).[132][b] Beekeeping is described in detail byVirgil in hisGeorgics; it is mentioned in hisAeneid, and inPliny'sNatural History.[132]
From the 18th century, European understanding of the colonies and biology of bees allowed the construction of the moveable comb hive so that honey could be harvested without destroying the colony.[133][134]
Bees play an important role inpollinatingflowering plants, and are the major type ofpollinator in manyecosystems that contain flowering plants. It is estimated that one third of the human food supply depends onpollination by insects, birds and bats, most of which is accomplished by bees, whether wild or domesticated.[135][136]
Since the 1970s, there has been a general decline in the species richness of wild bees and other pollinators, probably attributable to stress from increased parasites and disease, the use of pesticides, and a decrease in the number of wild flowers. Climate change probably exacerbates the problem.[137] This is a major cause of concern, as it can cause biodiversity loss and ecosystem degradation as well as increase climate change.[138]
Contract pollination has overtaken the role of honey production forbeekeepers in many countries. After the introduction ofVarroa mites,feral honey bees declined dramatically in the US, though their numbers have since recovered.[139][140] The number of colonies kept by beekeepers declined slightly, throughurbanization, systematic pesticide use,tracheal andVarroa mites, and the closure of beekeeping businesses. In 2006 and 2007 the rate of attrition increased, and was described ascolony collapse disorder.[141] In 2010 invertebrate iridescent virus and the fungusNosema ceranae were shown to be in every killed colony, and deadly in combination.[142][143][144][145] Winter losses increased to about 1/3.[146][147]Varroa mites were thought to be responsible for about half the losses.[148]
Apart from colony collapse disorder, losses outside the US have been attributed to causes including pesticide seed dressings, usingneonicotinoids such asclothianidin,imidacloprid andthiamethoxam.[149][150] From 2013 theEuropean Union restricted some pesticides to stop bee populations from declining further.[151] In 2014 theIntergovernmental Panel on Climate Change report warned that bees faced increased risk of extinction because ofglobal warming.[152] In 2018 the European Union decided to ban field use of all three major neonicotinoids; they remain permitted in veterinary, greenhouse, and vehicle transport usage.[153]
Farmers have focused on alternative solutions to mitigate these problems. By raising native plants, they provide food for native bee pollinators likeLasioglossum vierecki[154] andL. leucozonium,[155] leading to less reliance on honey bee populations.
Honey is a natural product produced by bees and stored for their own use, but its sweetness has always appealed to humans. Before domestication of bees was even attempted, humans were raiding their nests for their honey. Smoke was often used to subdue the bees and such activities are depicted inrock paintings in Spain dated to 15,000 BC.[124] Honey bees are used commercially to producehoney.[156]
As food
Bees are considerededible insects. In countries where peopleeat insects, thebee brood (larvae, pupae and surrounding cells[157]) of bees (primarily stingless species) may be eaten. In theIndonesian dishbotok tawon from Central and EastJava, bee larvae are eaten as a companion torice, after being mixed with shreddedcoconut, wrapped inbanana leaves, and steamed.[158][159]
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