4 species occur in South Africa: Triplasius bivittatus Loew, T. lateralis (Fabricius), T. namaquensis (Hesse), T. tinctus (Walker).
Diagnosis Genus Triplaius:
Crossvein r-m as long or longer than m-m; venation in radial sector unstable, often with appendices and sometimes with interradial vein complete (3 submarginal cells); vestiture shaggy but with long hair at sides of abdomen only, bristles fine not numerous, hair brown to blackish with contrasting short white scale-like hairs forming notopleural stripes on the thorax and spots or bands on the abdomen.
(1) Triplasius namaquensis (Hesse, 1938)
Species description by Hesse:
https://www.biodiversitylibrary.org/page/40845178#page/62/mode/1up
Wings (text-fig. 5) with appendices or stumps in marginal and submarginal cells, which are often irregular, sometimes joined on to margin of wing and thus producing a reticulate appearance, with the anterior darker part less marked off from the posterior part, which itself is also mottled to a certain extent; pubescence with the paler elements on frons, on sides of face, on pleurae, and on sides of venter distinctly paler and even more straw-coloured whitish, with the transverse band of whitish scaling on abdomen above more diffuse and the scaling towards apical part of abdomen above more greyish, the white band on each side of thorax distinctly broader and with a broad central band of greyish white scaling on disc of thorax and also on frons.
Illustration in Hesse 1928:
Hesse, A.J. 1938. A revision of the Bombyliidae (Diptera) of southern Africa. [Part I]. Annals of the South African Museum 34
https://www.biodiversitylibrary.org/page/40845178#page/131/mode/1up
(2) Triplasius lateralis (Fabricius, 1805)
Species description by Hesse:
https://www.biodiversitylibrary.org/page/40845178#page/62/mode/1up
Wings with only 2 submarginal cells, with 4 dark spots in the more hyaline posterior part: one at base of second submarginal cell, one at apex of first posterior cell, one on cross vein between discoidal and second posterior cells,and a smaller or minute one onvein at base of third posterior cell, and also with 2 larger spots on apical cross veins of basal cells; pubescence with the paler elements on sides of face, pleurae, and on sides of venter more rufous, purplish, or mauvish reddish.
Description by Loew:
https://www.biodiversitylibrary.org/item/35325#page/200/mode/1up
Illustration by Wiedemann:
Fig. 5: https://www.biodiversitylibrary.org/item/50649#page/665/mode/1up
(3) Triplasius bivittatus (Loew, 1855)
Description by Hesse:
https://www.biodiversitylibrary.org/page/40845178#page/62/mode/1up
Wings with 2 or usually 3 submarginal cells, usually without rounded spots, but with infuscations along basal parts of veins and cross veins of second and third submarginal cells, along basal veins of second and third posterior cells, often broken up into spots and often with a more distinct spot near apex of vein between anal and axillary cells; pubescence with the paler elements on sides of face, on pleurae and sides of venter usually paler or more straw-coloured in certain lights.
Description by Loew:
https://www.biodiversitylibrary.org/item/35325#page/199/mode/1up
Illustration of wing in Hull 1973:
Hull, F.M. 1973. Bee flies of the world. The genera of the family Bombyliidae.Washington (Smithsonian Institution Press)
https://www.biodiversitylibrary.org/item/102774#page/500/mode/1up
(4) Triplasius tinctus (Walker, 1849)
This species is only described by Walker, apparently not known in the other publications.
Description in:
Walker, F. 1849. List of the specimens of dipterous insects in the collection of the British Museum. Part II. British Museum (Natural History), London.
https://www.biodiversitylibrary.org/item/119308#page/57/mode/1up
Head black, and clothed with long black hairs above and in front, and with short red hairs about the base of the feelers, hoary and clothed with white hairs behind and beneath; hypostoma tawny : eyes red, with a bronze tinge: mouth black, a little shorter than the chest: feelers black, as long as the head; first joint thickly beset with hairs ; second joint short; third joint slightly tapering from the base to the tip, longer than the first and the second; fourth joint very small:
chest rich brown, clothed with short reddish brown hairs, and having a stripe of white hairs on each side; scutcheon adorned with red hairs: breast and under-side of abdomen hoary, and clothed with white hairs, the former having a tuft of red hairs on each side by the base of the wing:
abdomen black, clothed with tawny hairs and with black bristles, which are most frequent towards the tip:
legs ferruginous, clothed with white hairs and black bristles, the latter chiefly on the shanks; feet pubescent, piceous towards the tips:
wings slightly gray, blackish brown at the base and along the fore borders; the dark colour occupies less than half the surface, its border is not clearly defined, and it blends imperceptibly with the gray; wing-ribs and veins piceous, the latter black towards the tips; poisers tawny.
