Bee
Bees are winged insects that form a monophyletic clade Anthophila within the superfamily Apoidea of the order Hymenoptera, with over 20,000 known species in seven recognized families. Some species – including honey bees, bumblebees, and stingless bees – are social insects living in highly hierarchical colonies, while over 90% of bee species – including mason bees, carpenter bees, leafcutter bees, and sweat bees – are solitary. Members of the most well-known bee genus, Apis, are known to construct hexagonally celled waxy nests called hives.
Unlike the closely related wasps and ants, who are carnivorous/omnivorous, bees are herbivores that specifically feed on nectar and pollen, the former primarily as a carbohydrate source for metabolic energy, and the latter primarily for protein and other nutrients for their larvae. They are found on every continent except Antarctica, and in every habitat on the planet that contains insect-pollinated flowering plants. The most common bees in the Northern Hemisphere are the Halictidae, or sweat bees, but they are small and often mistaken for wasps or flies. Bees range in size from tiny stingless bee species, whose workers are less than long, to the leafcutter bee Megachile pluto, the largest species of bee, whose females can attain a length of. Vertebrate predators of bees include primates and birds such as bee-eaters; insect predators include beewolves and dragonflies.
Bees are best known for their ecological roles as pollinators and, in the case of the best-known species, the western honey bee, for producing honey, a regurgitated and dehydrated viscous mixture of partially digested monosaccharides kept as food storage of the bee colony. Pollination management via bees is important both ecologically and agriculturally, and the decline in wild bee populations has increased the demand and value of domesticated pollination by commercially managed hives of honey bees. Human beekeeping or apiculture has been practiced as a discipline of animal husbandry for millennia, since at least the times of Ancient Egypt and Ancient Greece. Bees have appeared in mythology and folklore, through all phases of art and literature from ancient times to the present day, although primarily focused in the Northern Hemisphere where beekeeping is far more common. In Mesoamerica, the Maya have practiced large-scale intensive meliponiculture since pre-Columbian times.
Evolution
The immediate ancestors of bees were stinging wasps in the family Ammoplanidae, which were 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 may have occurred within the vespoid wasps, where the pollen wasps evolved from predatory ancestors.Based on phylogenetic analysis, bees are thought to have originated during the Early Cretaceous on the supercontinent of West Gondwana, just prior to its breakup into South America and Africa. The supercontinent is thought to have been a largely xeric environment at this time; modern bee diversity hotspots are also in xeric and seasonal temperate environments, suggesting strong niche conservatism among bees ever since their origins.
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. The Melittidae, Apidae, and Megachilidae 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 the Colletidae, Andrenidae and Halictidae in South America. The rapid radiation of the South American bee families is thought to have followed the concurrent radiation of flowering plants within the same region. Later in the Cretaceous, colletid bees colonized Australia from South America, and by the end of the Cretaceous, South American bees had also colonized North America. The North American fossil taxon Cretotrigona belongs to a group that is no longer found in North America, suggesting that many bee lineages went extinct during the Cretaceous–Paleogene extinction event.
Following the K-Pg extinction, surviving bee lineages continued to spread into the Northern Hemisphere, colonizing Europe from Africa by the Paleocene, and then spreading east to Asia. 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 the Eocene there was already considerable diversity among eusocial bee lineages. A second extinction event among bees is thought to have occurred due to rapid climatic cooling around the Eocene-Oligocene boundary, leading to the extinction of some bee lineages such as the tribe Melikertini. During the Paleogene and Neogene 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.
Fossils
The oldest non-compression bee fossil is Cretotrigona prisca, a corbiculate bee of Late Cretaceous age found in New Jersey amber. A fossil from the early Cretaceous, Melittosphex burmensis, was initially considered "an extinct lineage of pollen-collecting Apoidea sister to the modern bees", but subsequent research has rejected the claim that Melittosphex is a bee, or even a member of the superfamily Apoidea to which bees belong, instead treating the lineage as incertae sedis within the Aculeata.The Allodapini appeared around 53 Mya.
The Colletidae appear as fossils only from the late Oligocene to early Miocene.
The Melittidae are known from Palaeomacropis eocenicus in the Early Eocene.
The Megachilidae are known from trace fossils from the Middle Eocene.
The Andrenidae are known from the Eocene-Oligocene boundary, around 34 Mya, of the Florissant shale.
The Halictidae first appear in the Early Eocene with species found in amber. The Stenotritidae are known from fossil brood cells of Pleistocene age.
Coevolution
The earliest animal-pollinated flowers were shallow, cup-shaped blooms pollinated by insects such as beetles, so the syndrome 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 of coevolution, flowers developed floral rewards such as nectar and longer tubes, and bees developed longer tongues to extract the nectar. Bees also developed structures known as scopal hairs and pollen 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 have pollen baskets on their hind legs, while very few lack these and instead collect pollen in their crops. The appearance of these structures drove the adaptive radiation of the angiosperms, and, in turn, bees themselves. Bees and certain mites have indeed coevolved, with some bee species evolving specialized structures called acarinaria 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.Phylogeny
External
Molecular phylogeny was used by Debevic et al, 2012, to demonstrate that the bees arose from deep within the Crabronidae sensu lato, which was thus rendered paraphyletic. In their study, the placement of the monogeneric Heterogynaidae was uncertain. The small family Mellinidae was not included in this analysis.Further studies by Sann et al., 2018, elevated the subfamilies of Crabronidae sensu lato to family status. They also recovered the placement of Heterogyna within Nyssonini and sunk Heterogynaidae. The newly erected family, Ammoplanidae, formerly a subtribe of Pemphredoninae, was recovered as the most sister family to bees.
Internal
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. English names, where available, are given in parentheses.Characteristics
Bees differ from closely related groups such as wasps by having branched or plume-like setae, 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.Bees have the following characteristics:
- A pair of large compound eyes which cover much of the surface of the head. Between and above these are three small simple eyes which provide information on light intensity.
- The antennae usually have 13 segments in males and 12 in females, and are geniculate, having an elbow joint part way along. They house large numbers of sense organs that can detect touch, smell and taste; and small, hairlike mechanoreceptors that can detect air movement so as to "hear" sounds.
- The mouthparts are adapted for both chewing and sucking by having both a pair of mandibles and a long proboscis for sucking up nectar.
- 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 of corbiculate 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.
- Many bees are brightly colored, displaying contrasting bands of yellow, orange, or red against black. These colors function as aposematic signals, warning potential predators that the insect may sting or otherwise defend itself, although similar warning patterns are also seen in many harmless insects that mimic bees or wasps, a form of Batesian mimicry.