Vockeroth (1969) suggested the name vitiensis would be available as a subspecific name for those populations of grandicornis with more abundant wing microtrichia if such a name were required.
Synonyms:
Syrphus melanurus Bigot, 1884: 97.
Syrphus pusilla Macquart, 1847: 77.
Syrphus australiensis Goot, 1964: 220.
Syrphus obesus Hutton, 1901: 41.
Syrphus huttoni Goot, 1964: 220.
Syrphus grandicornis Macquart, 1842: 96.
Syrphus vitiensis Bezzi, 1928: 71.
Metasyrphus fasciatus Shiraki, 1963: 186.
Syrphus sydneyensis Macquart, 1846: 263.
Ischiodon scutellaris Bryan, 1934: 412.
From Vockeroth (1969).
Small, rather robust species with yellow-margined mesonotum, broad yellow fasciae or paired maculae on abdomen, and very large male genitalia.
Head: Eye bare. Face yellow, not at all pollinose. Pedicel very short, transverse apically on inner surface; basoflagellomere large, 1.6 times as long as broad, bluntly rounded apically. Arista slightly shorter than basoflagellomere.
Thorax: Scutum shining black with broad well-defined pale yellow lateral margin which may be considerably narrowed posteriorly. Scutellum pale yellow, most of disc usually slightly brownish. Pleura mostly shining black, dorsal posterior part of anepisternum pale yellow, densely white pollinose, the white pollen extending ventrad across anepisternum onto katepisternum where it forms a large semicircular macula. Anterodorsal corner of katepisternum with a tuft of pile. Dorsal and ventral katepisternal pile patches broadly separated posteriorly; below anterior end of dorsal patch is a group of slightly shorter and sparser hairs which are inclined slightly dorsad instead of slightly ventrad as are those in the dorsal patch. Metasternum bare. Wing with R4+5 ending well before wing apex, its apical section curved slightly forward but less than in lschiodon. Microtrichia greatly reduced, absent or nearly so from basal half of wing, more abundant on apical half but membrane with at least very narrow bare areas along all longitudinal veins extending almost or quite to their apices. Legs and tarsal claws simple.
Abdomen oval, flattened, with strong margin from before middle of tergum 2 to end of tergum 5. Terga 2 to 4 each with a pair of large yellow maculae, those on 3 and 4 broadly reaching the base of the tergum and often narrowly or broadly joined. Sterna yellow, often with dark central maculae or subapical fascia. Female with tergum 8 very much narrower than 7, weakly sclerotized, and usually retracted or nearly so under tergum 7.
Male genitalia: Sternite 8 (the last dorsal pregenital sclerite) in profile projecting scarcely if at all beyond tergite 9. Tergite 9 in profile sub quadrangular, broader posteriorly. Surstyli, sternite 9, superior lobes, base of aedeagus, and sublateral aedeagal processes slightly asymmetrical; apex of aedeagus strongly asymmetrical. Surstylus directed caudad, elongate, very narrow basally, slightly twisted, and irregularly broadened to uneven subtruncate apex; surstylar apodeme very short, broad, lying ventromediad of base of surstylus, covered laterally by strong minutely tuberculate membrane. Sternite 9 articulated at posteroventral angle of tergite 9, projecting caudad almost to level of apex of surstylus, posteroventrally with very broad deep anteriorly expanded emargination, and with strongly sclerotized anterior margin. Superior lobe strongly compressed, bare, subtriangular in profile, with slightly produced and subacute posteroventral angle, the two superior lobes moderately convergent dorsally. Aedeagus rather heavily sclerotized, not divided into separate basal and distal portions. Base of aedeagus broadly subtriangular both in ventral view and in profile; laterally on each side with a long slender sub cylindrical process which is slightly enlarged towards apex and ends in a broader, ventrally directed, flat flange; ventromedially slightly rugose, produced into a sub cylindrical distal portion which curves slightly dorsad, becomes rapidly wider at 1/3 its length, and ends in a swollen, extremely complex, highly asymmetrical structure with rather strongly sclerotized inner rods, hooks, and plates and with membranous apical sheaths.
Variation. The specimens of Simosyrphus examined by Vockeroth (1969) all seem to belong to one species, grandicornis (Macq.), but they show considerable variation in the abundance of wing microtrichia. Specimens from various parts of Australia have the microtrichia on the apical half of the wing rather sparse, with extensive bare areas along the veins. Those from New Caledonia are slightly variable but usually have the microtrichia a little more dense. In specimens from the Loyalty Islands, New Hebrides, Fiji, and Samoa the microtrichia are almost always quite dense and closely spaced, with only extremely narrow bare areas along the main longitudinal veins extending not quite to their apices. Specimens from Hawaii have sparse and scattered microtrichia, suggesting an Australian origin for the Hawaiian population. Vockeroth (1969) could detect no constant differences between the male terminalia of specimens from Australia and from Fiji, although the exact shape and degree of asymmetry of the surstyli show very slight individual variation.
Simosyrphus grandicornis (Macquart, 1842).
Macquart, P.J.M. (1842) Dipteres exotiques nouveaux ou peu connus. Tome deuxieme.--2e partie. Mémoires de la Société Royale des Sciences, de l'Agriculture, et des Arts à Liège 1841(1): 65-200, 22 pls.
The genera Simosyrphus and Ischiodon have probably caused more confusion than any other group in Syrphinae (Vockeroth 1969). They have been synonymized with one another, and placed in the these two genera or in Xathogramma, Sphaerophoria, or elsewhere. As Vockeroth (1969) wrote, the two speceis of Ischiodon and S. grandicornis have a similar habitus and colour pattern, a similar head shape and colour, a reduced second antennal segment, a large basoflagellomere and a short arista, a strongly margined abdomen, large male genitalia, a wing with very reduced microtrichia and with R4+5 upcurved apically and ending appreciably before the wing apex, and peculiar and distinctive katepisternal hairing. However, the species of Ischiodon, aegyptius (Wied.) and scutellaris (Fab.), although showing many differences in the genitalia, have sternite 9 articulated with tergite 9 in a normal manner, sternite 9 with a broad elaborate process arising in the anterior emargination, and the aedeagus (although highly modified) clearly divisible into basal and distal portions. S. grandicornis is abundantly different in all these features. The two species of Ischiodon also have a well-developed and exposed tergite 8 in the female, a ventral process on the metatrochanter in the male, a rather slender abdomen with arcuate yellow fasciae and, in the male, a strongly protruding sternite 8, an elongate subacute basoflagellomere, and a yellow macula on dorsal part of katepisternum. Simosyrphus differs in all these characters.
Both genera have been always related, as mentioned by Vockeroth (1969). Rotheray and Gilbert (1999) reported Ischiodon as sister group of the genus Scaeva in their analysis based on larval characters. In 2006, Laska et al. (2006) combined Ischiodon as junior synonym of Simosyrphus based on larval and molecular evidences. Later, Mengual et al. (2008) reported the genus Ischiodon (as Simosyrphus) as sister group of Scaeva. Mengual (in litt.) using molecular characters recovered the non-monophyly of the group Ischiodon + Simosyrphus, resolving Pseudodoros (Pseudodoros) as sister group of Ischiodon. Thus, we here accept them as two different genera.
unless otherwise stated