Therevidae are a family of Diptera Asiloidea commonly known as stiletto flies. The family contains about 1,600 described species worldwide, most diverse in arid and semi-arid regions with sandy soils. The larvae are predators of insect larvae in soil.
Adults are small or medium-sized with a body length of 2.4 to 18 mm.. The abdomen is long and slender and the integument is hairy. The cuticle can have colors ranging from black to yellow, but often the background colour is masked by the tomentum.
The head is large, generally holoptic in males, dichoptic in females and has three ocelli . The antennae are relatively short, with the scape and pedicel pubescent; the scape has an elongated shape, the pedicel is very short and the first flagellomere is elongated conical, the apex bearing a compound stylus with 1-3 segments. The mouthparts type is sucking-the labium ending in two fleshy labella.
The thorax is broad and moderately convex, with long bristles (macrotrichae). The legs are long and slender, with femora and tibiae bearing bristles; the tibiae are without apical spurs and the tarsi are provided with empodia or without the median pretarsal. The wings are well developed, hyaline or opaque, often with pigmentation of the veins located at the termination of the transverse and longitudinal veins.
The abdomen is elongated, consisting of eight apparent uriti. It is tapered posteriorly and convex or flattened dorsally. The abdominal end of females is generally provided with spinous processes.
The wing venation is relatively complex but without a particular conformation to distinguish Therevidae from other families of Asiloidei. The radius is divided into four branches, with R 2 +3 undivided. The branch R 4 is long and winding and reaches the costal margin, the branch R 5 terminates on the posterior border, so the second submarginal cell is open at the apex of the wing. The media is divided into four branches, all independent but with M 3 and M 4 convergent. The transverse medial vein closes the discal cell. This has an elongated shape and terminates at the apex with three angles from which the first three branches of media spring. The fourth branch, M 4 (or CuA 1 according to a different interpretation), originate from the apex of the posterior basal discal cell. The cubit and anal converge on a short common branch before reaching the apex.
The larva is apodous and eucepalic, cylindrical, very long and thin and with tapered ends. The integument is smooth, white or rosé. The head capsule is well developed but narrower than the other regions.
Knowledge of the biology of Therevidae is limited and fragmented. The life-cycle is usually carried out in a single generation per year, although some European Therevidae hav a cycle of two or more years. The overwintering stage is represented by the mature larva. The postembryonic development in known forms, five instars and pupation takes place in the spring.
The larvae, like those of other Asiloidea have an entomophagous diet and they live as predators. They are generally found on dry sandy soils and dry litter. Larvae also be located in other substrates such as decomposing organic matter and under the bark of trees. Among the prey are included the larvae and pupae of Diptera , Coleoptera and Lepidoptera. The observation of the behaviour of known forms highlights voracious feeding and agile movements. When exposed to light, the larvae of Therevidae,dig back into the substrate with rapid movements.
Adults are feed mainly on nectar , honeydew and pollen , but it seems that they occasionally feed on liquid secretions of animal or vegetable origin. They are found in various environments and can be found in streams, meadows, open woodlands, or, like many other asiloids, in dry and sandy places or onbeaches. At rest they choose various substrates according to the species: some species rest on the ground, others on rocks, vegetation, intertidal debris, etc.. They are generally diurnal and move in short, quick flights. Despite the semi-arid habitats adults of Therevidae are particularly attracted to the water You can therefore find,them especially in arid areas, near pools of water or any other similar source.
Systematics and phylogeny
Because the family Therevidae is essentially little known and characterized by morphological and ethological similarities with other Brachycera , the history of the taxonomy of Therevidae is accompanied by multiple revisions. In the past many therevids were classified in other families, as well as other Brachycera being classified within the Therevidae. Since the 1970s much reclassification has taken place, led in particular by Lyneborg and Irwin. Revision of the higher taxa, based on the phylogenetic relationships between the different groups of Asiloidei given a better understanding of the ranks of families and subfamilies.
The family of Therevidae, sensu lato, was identified with a polyphyletic clade that only after the removal of some subfamilies and the resulting movement in other more or less phylogenetically close families of Asiloidei , became more consistent with the phylogenetic relationships. It now refers to a monophyletic clade that the Anglo-Saxon dipterologists call the Therevoid clade (clade of "Terevoidi"). This group does not have an identity at the level of higher taxon to the rank of family, but stands as a grouping of families within the superfamily of Asiloidea .
Clade showing relationship of Asiloidea
At present there are over 1, 600 known species. The after taxonomic revisions by Lyneborg (1976) and Winterston et al. (2001) the family is divided into four subfamilies, among which the most representative in size and diffusion, is that of Therevinae:
- Agapophytinae : 12 genera.
- Phycinae : 13 genera.
- Therevinae : 84 genera.
- Xestomyzinae : 12 genera.
To the 121 living genera are added extinct genera, dating back to the Cenozoic, Dasystethos , Glaesorthactia , Kroeberiella and Palaeopherocera In doubt is Helicorhaphe  .
Habitat and distribution
The ' habitat of Therevidae is more varied than that of other Asiloidea but as in Asiloidea preferred ecosystems better suit the larvae, so these insects are more common in thickets of xerophilous plants (garrigue and maquis, in deserts and on sandy beaches.
The family of Therevidae is represented in all zoogeographical regions of the Earth. Therevinae are present in all continents, with a lower frequency in the eastern region . The Phycinae have spread to the Afrotropical and the Holarctic. The Xestomyzinae are mainly Afrotropical. The Agapophytinae are endemic to the Australasia ecozone.
In Europe only the subfamilies are represented:- Phycinae , with two genera, and Therevinae , with 15 genera. A total of 98 species are reported, two thirds of which belong to the genus Thereva.
Cole, F.R., 1923. A revision of the North American two-winged flies of the family Therevidae. Proceedings of the U.S. National Museum, 62(4), 1-140.
Cole, F.R., 1960 Stiletto-flies of the genus Furcifera Kröber (Diptera: Therevidae). Annals of the Entomological Society of America, 53, 160-169.
Gaimari, S.D., & M.E. Irwin , 2000. Phylogeny, classification, and biogeography of the cycloteline Therevinae (Insecta: Diptera: Therevidae). Zoological Journal of the Linnean Society, 129, 129-240.
Irwin, M.E., & L. Lyneborg, 1981. The genera of Nearctic Therevidae. Illinois Natural History Bulletin, (1980) 32, 193-277.
Irwin, M.E., & D.W. Webb, 1992. Brasilian Therevidae (Diptera): a checklist and descriptions (sic) of species. Acta Amazonica, (1991) 21, 85-121.
Kröber, O. , 1911. Die Thereviden Süd- und Mittelamerikas. Annales Musei Nationalis Hungarici, 9, 475-529. Keys genera, species.
Kröber, O. , 1912. Die Thereviden der indo-australischen Region. Keys genera, species.
Kröber, O. , 1913. Therevidae.Genera.Ins. Keys (then) world genera. Keys genera, species.
Kröber, O. , 1914. Beiträge zur Kenntnis der Thereviden und Omphraliden. Jahrbuch der Hamburgischen Wissenschaftlichen Anstalten, (1913) 31, 29-74.
Kröber, O. , 1924_1925. Therevidae. Fiegen palaerakt. Reg. 4 (26):1-60
Kröber, O. , 1928. Neue und wenig bekannte Dipteren aus den Familien Omphralidae, Conopidae, und Therevidae. Konowia Zeitschrift für Systematische Insektenkunde, 7, 113-134.
Kröber, O. , 1931. The Therevidae (Diptera) of South Africa. Ann. Transv. Mus.. 14:103-134. (see also Lyneborg).
Lyneborg, L. 1972. A revision of the Xestomyza-group of Therevidae. (Diptera). Annals of the Natal Museum 21: 297–376. Keys African genera, species.
Lyneborg, L. 1976. A revision of the Therevine stiletto-flies (Diptera: Therevidae) of the Ethiopian Region. Bull. British Mus. (Nat. Hist.). Entomology 33 (3): 191-346. Keys subfamilies and genera of Thervinae.
Malloch, J. R. 1932. Rhagionidae, Therevidae. British Museum (Natural History). Dept. of Entomology [eds] Diptera of Patagonia and South Chile, based mainly on material in the British Museum (Natural History). Part V. Fascicle 3. - Rhagionidae (Leptidae), Therevidae, Scenopenidae, Mydaidae, Asilidae, Lonchopteridae. pp. 199–293. Keys genera, species.
Mann, JS.1928-1933 Revisional notes on Australian Therevidae. Part 1. Australian Zoologist, 5, 151–. 194 (1928); Part 2 6:17-49 (1929); Part 3 7:325-344. (1933).
Mating (species from Queensland, Australia)
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