The Bombyliidae (bee flies) are one of the largest families of Diptera, with over 5,000 valid species described worldwide. Their high diversity may be due to the parasitoid habit of the majority of their larvae (Du Merle, 1975; Price, 1980; Yeates and Greathead 1996). Adults feed on nectar and pollen, and no doubt feature prominently in angiosperm pollination syndromes (Armstrong, 1979; Grimaldi, 1988; Heard et al., 1990), although few species have been studied in detail. Bee flies occur on all continents except Antarctica, however their highest diversities occur in semi-arid and arid environments (Hull, 1973).
The family includes a wide variety of morphological forms, such as the enormous Palirika marginicollis (Gray), with irridescent green-blue body scales recalling those found on the wings of a Morpho butterfly, and striking black and hyaline wings spanning 45 mm; and the tiny, delicate, humpbacked yellow and black species of Glabellula Bezzi with hyaline wings and a body length about 1 mm.
This structural diversity is reflected in the higher classification of the family, with a total of 31 subfamilies proposed to date. Up until recently the subfamilies of Bombyliidae were based on classifications formulated early this century, and those divisions did not accurately reflect the cladistic relationships within the family. The subfamilies were divided further into tribes by Hull (1973).
Numerical cladistic analyses of particular subgroups of Bombyliidae have appeared only in the last few years (Evenhuis, 1990, 1993; Yeates, 1988, 1989, 1990, 1991a, b; 1994, Yeates and Lambkin 1998, Lambkin et al. 2003). The family was catalogued by Evenhuis and Greathead (1999).
Yeates (1992) affirmed Theodore's (1983) suggestion that Prorates Melander showed affinities with the window flies, and moved the entire Proratinae except Apystomyia Melander, to the Scenopinidae, forming the two most plesiomorphic subfamilies, the Caenotinae and Proratinae. Yeates (1994) placed Apystomyia in the Hilarimorphidae, as the sister family to the Bombyliidae. With the Proratinae removed, the Bombyliidae are a much more homogenous group, however their monophyly remains weakly supported at present.
Bee flies are large, fat, and hairy, often with a long, rigid proboscis. They are excellent mimics of bees, and may have black and yellow stripes along the abdomen. The adults are avid seekers of nectar from various flowers, although a few species feed on pollen. They are important pollinators, and can reach the nectaries of many wildflowers that are inaccessible to other flies. Their larvae are brood parasites on various species of bees and wasps.
Almost all known larval Bombyliidae are parasitic, and undergo hypermetamorphosis whilst developing through the larval instars (Yeates and Greathead, 1997). This feature was considered synapomorphic for the family by Woodley (1989). Other asiloid fly larvae are free-living predators which do not undergo hypermetamorphosis, however the larval habits of the Hilarimorphidae are unknown. The larvae of at least some members of the bombyliid subfamilies Mythicomyiinae (Andersson, 1974) and Heterotropinae (Yeates and Irwin, 1992) are free-living and do not undergo hypermetamorphosis. These occurrences appear as apomorphic reversals on the cladogram, rather than plesiomorphies.
All Bombyliidae have lost wing vein M3 (Hennig, 1973; Mühlenberg, 1971). This apomorphy is not particularly compelling because it also occurs independently within other asiloid families such as the Scenopinidae, Mydidae, and Hilarimorphidae.
The occipital chambers are sclerotised pockets on the inner wall of the head capsule adjacent to the occipital foramen (Zaytsev, 1986, 1992). They appear in the most plesiomorphic bombyliid subfamilies, however they are lost in the more advanced subfamilies.
Occipital apodemes are internal sclerotised ridges which run dorsoventrally on either side of the occipital chambers. They are only found in the Bombyliidae, but are apomorphically lost in numerous instances, especially within clade 9.
The highly derived sperm pump of the female spermatheca found in the Bombyliidae also appears to be apomorphic for the family, although superficially similar pumps appear in some Asilidae according to Theodor (1976). The ultrastructure of the various components of the pump in Bombyliidae has been studied by Mühlenberg (1970).
Evolution and Systematics
Discussion of Phylogenetic Relationships
The phylogenetic research of Yeates (1994) resulted in a reclassification of the family which recognised a total of 15 subfamilies in a sequenced classification (Nelson, 1974) shown in the tree above. This classification recognises each successive branch from the backbone of the cladogram in Yeates (1994) as a subfamily.
In attempting to make as little change as possible to the existing classification whilst reflecting the cladistic results obtained, Yeates (1994) recognised only one new taxon at subfamily level, the Lordotinae. Some traditional subfamilies such as the Usiinae and Phthiriinae, and Toxophorinae, Systropodinae and Geroninae, form monophyletic branches from the main stem of the cladogram and were united into single subfamilies. The Cythereinae was found to be broadly polyphyletic and some of its components were distributed to other subfamilies. The majority of traditional subfamilies, such as the Mythicomyiinae, Oligodraninae, Oniromyiinae, Anthracinae and Tomomyzinae were monophyletic, forming single branches from the main stem of the cladogram and were retained unchanged.
Molecular Biology and Genetics
Statistics of barcoding coverage
Specimen Records: 1493
Specimens with Sequences: 1196
Specimens with Barcodes: 1160
Species With Barcodes: 91
Public Records: 105
Public Species: 8
Public BINs: 18
The Bombyliidae are a large family of flies comprising hundreds of genera, but the lifecycles of most species are known poorly, or not at all. They range in size from very small (2 mm in length) to very large for flies (wingspan of some 40 mm). When at rest, many species hold their wings at a characteristic "swept back" angle. Adults generally feed on nectar and pollen, some being important pollinators, often with spectacularly long probosces adapted to plants such as Lapeirousia species with very long, narrow floral tubes. In parts of East Anglia, locals refer to them as beewhals, thanks to their tusk-like appendages. Many Bombyliidae superficially resemble bees and accordingly the prevalent common name for a member of the family is bee fly. Possibly the resemblance is aposematic, affording the adults some protection from predators.
The larval stages are predators or parasitoids of the eggs and larvae of other insects. The adult females usually deposit eggs in the vicinity of possible hosts, quite often in the burrows of beetles or wasps/solitary bees. Although insect parasitoids usually are fairly host-specific, often highly host-specific, some Bombyliidae are opportunistic and will attack a variety of hosts.
While the Bombyliidae include a large number of species in great variety, most species do not often appear in abundance, and for its size this is one of the most poorly known families of insects. At least 4,500 species are described, and certainly thousands yet remain to be described.
Although the morphology of beeflies varies in detail, adults of most bee flies are characterized by some morphological details that make recognition easy. The dimensions of the body vary, depending on the species, from 1.0 mm to 2.5 cm. The form is often compact and the integument is covered with dense and abundant hair. The livery is usually inconspicuous and colours such as brown, blackish- grey, and light colors like white or yellow predominate. Many species are mimics of Hymenoptera Apoidea.
The head is round, with a convex face, often holoptic in males. The antennae are of the type aristate composed of three to six segments, with the third segment larger than the others; the stylus is absent (antenna of three segments) or is composed of one to three flagellomeres (antenna of four to six segments). The mouthparts are modified for sucking and adapted for feeding on flowers. The length varies considerably: for example, the Anthracinae have short mouthparts, with the labium terminating in a large fleshy labellum, in Bombyliinae; in Phthiriinae, the tube is considerably longer, and in Bombyliinae more than four times the length of the head.
The legs are long and thin and the front legs are sometimes smaller and more slender than the middle and rear legs. Typically, they are provided with bristles at the apex of the tibiae, without empodia and, sometimes, also without pulvilli . The wings are transparent, often hyaline or evenly colored or with bands. The alula are well developed and in the rest position the wings are kept open and horizontal in a V shape revealing the sides of the abdomen.
The abdomen is generally short and wide, subglobose-shaped, cylindrical, or conical, composed of six to eight apparent uriti apparent. The remaining urites are part of the structure of the external genitalia. The abdomen of the females often ends with spinous processes, used in ovideposition. In Anthracinae and Bombyliinae, a diverticulum is present in the eighth urite, in which the eggs are mixed with sand before being deposited.
The wing venation, although variable within the family, has some common characteristics that can be summarized basically in the particular morphology of the branches of the radial sector and the reduction of the forking of the media. The costa is spread over the entire margin and the subcosta is long, often ending on the distal half of the costal margin.The radius is almost always divided into four branches, with fusion of the branches R 2 and R 3, and is characterized by the sinuosity of the end portions of the branches of the radial sector. The venation presents a marked simplification compared to other Asiloidea and, in general, to other lower Brachycera. M 1 is always present and converges on the margin or, sometimes, of R 5. M 2 is present and reaches the margin, or is absent. M 3 is always absent and merged with M 4. The discal cell is usually present. The branch M 3 +4 is separated from the discal cell at the distal posterior vertex, so the mid-cubital connects directly to the posterior margin of the discal cell.The cubital and anal veins are complete and end separately on the margin or converge joining for a short distance Consequently the cell cup may be open or closed.
The larvae of most bee flies are of two types. Those of the first type are elongated and cylindrical in shape and have a metapneustic or amphipneustic tracheal system, provided with a pair of abdominal spiracles and, possibly, a thoracic pair. Those of the second type are stubby and eucephalic and have one pair of spiracles positioned in the abdomen.
Adults favour sunny conditions and dry, often sandy or rocky areas. They have powerful wings and are found typically in flight over flowers or resting on the bare ground exposed to the sun (watch video) They significantly contribute to cross pollination of plants, becoming the main pollinators of some plant species of desert environments. Unlike the majority of glyciphagous dipterans, the bee flies feed on pollen (from which they meet their protein requirements). A similar trophic behavior occurs among the hoverflies, another important family of Diptera pollinators. They are often recognizable by their stocky shapes, by their hovering behavior, and for the particular length of their mouthparts as they lean forward into flowers. Unlike hoverflies, which settle on the flower as do bees and other pollinating insects, the bee flies behave like Sphingidae and generally feed hovering in the air and using their front legs to stabilize their position.
Despite the high number of species of this family, the biology of juveniles of most species is poorly understood. The postembryonic development is of the type hypermetamorphic, with parasitoid or hyperparasitoid larvae. Exceptions are the larvae of Heterotropinae, whose biology is similar to that of other Asiloidea, with predatory larvae that do not undergo hypermetamorphosis. Hosts of bee flies belong to different orders of insects, but mostly are among the holometabolous orders. Among these are Hymenoptera, in particular the superfamilies of Vespoidea and Apoidea, beetles, other flies, and moths. Larvae of some species including Villa sp. feed on ova of Orthoptera. Bombylius major larvae are parasitic on solitary bees including Andrena. Anthrax anale is a parasite of tiger beetle larvae, and A. trifasciata is a parasite of the wall bee. Several African species of Villa and Thyridanthrax are parasitic pupae of tsetse flies. Villa morio is parasitic on the beneficial ichneumonid species Banchus femoralis. The larvae of Dipalta are parasitic on antlions.
The behavior of known forms is similar to that of the larvae of Nemestrinoidea: the first instar larva of is a planidium while the other stages have a parasitic habitus. The eggs are laid usually in a future host or at the nest where the host develops. The planidium enters the nest and undergoes changes before starting to feed.
The family is worldwide (Palearctic ecozone, Nearctic ecozone, Afrotropic ecozone, Neotropic ecozone, Australasian ecozone, Oceania ecozone, Indomalaya ecozone), but has the greatest biodiversity in tropical and subtropical arid climates. In Europe, 335 species are distributed among 53 genera.
The systematics of bee flies are the most uncertain of any family of lower Brachycera. Willi Hennig(1973) placed the bee flies in the superfamily of Nemestrinoidea, on the basis of analogies in the behaviour of the larvae, positioning the superfamily in Tabanomorpha inside the infraorder Homoeodactyla Boris Borisovitsch Rohdendorf (1974) dealt with the family in a separate superfamily (Bombyliidea), linking it to the superfamily of Asilidea. Currently the close correlation either positions the bee-flies within the superfamily Asiloidea sensu Rohdendorf (Asilidea)or they are included with the families separated by Rohdendorf in the superfamily of Asiloidea. Currently, the close correlation either positions the bee-flies within the superfamily Asiloidea sensu Rohdendorf (Asilidea) or they are included with the families separated by Rohdendorf in the superfamily of Asiloidea.
Clade showing relationship of Asiloidea
The internal systematic of bee-flies is uncertain. In the past, 31 subfamilies were well defined, but the family is thought to be polyphyletic (sensu lato). In the 1980s and '90s, the family has undergone several revisions: Webb (1981) finally moved the genus Hilarimorpha into their own family (Hilarimorphidae). Zaitzev (1991) moved the genus Mythicomyia and several other minor genera in the family Mythicomyiidae, Yeates (1992, 1994) shifted the entire subfamily of Proratinae, with the exception of Apystomyia, into the family of Scenopinidae and subsequently the genus Apystomyia into the family Hilarimorphidae. Nagatomi & Liu (1994) moved Apystomyia into a family of their own (Apystomyiidae. After these revisions, the bee flies sensu stricto have a greater morphological homogeneity, but the monophyly of the family still remains dubious and, consequently, the internal classification.
Overall, the family includes about 4700 described species, distributed among 230 genera. The internal arrangement varies according to the source, according to the different frameworks the authors attribute to tribes and subfamilies. To divide the family, often this scheme is used:
Bombyliid fly on Bidens laevis
|Wikispecies has information related to: Bombyliidae|
- Alan Weaving; Mike Picker; Griffiths, Charles Llewellyn (2003). Field Guide to Insects of South Africa. New Holland Publishers, Ltd. ISBN 1-86872-713-0.
- Hull, Frank Montgomery, Bee flies of the world: the genera of the family Bombyliidae Washington, Smithsonian Institution Press 1973 ISBN 0-87474-131-9. Downloadable from: http://www.archive.org/details/beefliesofworl2861973hull
- Willi Hennig, 1973. Diptera (Zweiflüger). In J.G. Helmcke, D. Starck, H. Vermuth Hanbuch der Zoologie, Eine Naturgeschichte der Stämme des Tierreiches. IV. Band: Arthropoda - 2- Hälfte: Insecta. 2. Teil: Spezielles. Berlin, De Gruyter, 1973. pp. 1-337. ISBN 311004689X.
- Boris B. Rohdendorf, Brian Hocking, Harold Oldroyd, George E. Ball. The Historical Development of Diptera. University of Alberta, 1974: 75-77. ISBN 088864003X.
- Webb D.W., 1981 Hilarimorphidae. in: McAlpine J.F. (Ed.), Manual of Nearctic Diptera. Agriculture Canada, Ottawa, pp. 603-605.
- Zaitzev, V.F. , 1991 On the phylogeny and systematics of the dipteran superfamily Bombylioidea (Diptera). Entomol. Obozr. 70  : 716–36.
- Yeates, D.M., 1992 Towards a monophyletic Bombyliidae (Diptera): the removal of the Proratinae (Diptera: Scenopinidae). American Museum Novitates 3051: 1-30.
- Yeates & Lambkin, The Tree of Life, op. cit..
- Bowden, J.,1980 Family Bombyliidae. pp. 381–430. In R.W. Crosskey (ed.), Catalogue of the Diptera of the Afrotropical Region, 1437 pp., London: British Museum (Natural History)
- Engel, E.O., 1932-1937. Bombyliidae. In: Die Fliegen der paläarktischen Region 4(3) ( Erwin Lindner, ed.): 1-619, pl. 1-15. E. Schweizerbart, Stuttgart.). Old and outdated, not easy to get and expensive but some of the only keys to taxa in the Palaearctic Region.
- Greathead & Evenhuis (Greathead, D.J., & N.L. Evenhuis, 1997. Family Bombyliidae. In: Contributions to a manual of Palaearctic Diptera Volume 2 (L. Papp & B. Darvas, eds.): 487-512. Science Herald, Budapest.) provide a key to the Palaearctic genera and (may) give references to available generic revisions.
- Evenhuis, N.L. 1991. Catalog of genus-group names of bee flies (Diptera: Bombyliidae) Bishop Museum Bulletin of Entomology 5: 1–105.
- Evenhuis, N.L. & Greathead, D.J. 1999. World catalog of bee flies (Diptera: Bombyliidae). Backhuys Publishers, Leiden, 756 pp. online
- Hull, F.M. 1973. Bee flies of the world. The genera of the family Bombyliidae.Washington (Smithsonian Institution Press) 687 pp. Keys subfamilies, genera (many generic placements superseded by Evenhuis & Greathead, 1999).
- Yeates, David K. 1994. The cladistics and classification of the Bombyliidae (Diptera: Asiloidea). Bulletin of the American Museum of Natural History ; no. 219, 191 pp.
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