Omegasyrphus Giglio-Tos

Reemer, Menno & Stahls, Gunilla, 2013, Generic revision and species classification of the Microdontinae (Diptera, Syrphidae), ZooKeys 288, pp. 1-213 : 51

Omegasyrphus Giglio-Tos stat. n. Figs 254-256

Omegasyrphus Giglio-Tos, 1891: 4. Type species: Microdon coarctatus Loew, 1864: 74, by subsequent designation of Giglio-Tos (1892: 3).

Description.

Body length: 7-9 mm. Small, dark flies with relatively short antennae and characteristically shaped abdomen. Head slightly wider than thorax. Face convex; about as wide as or narrower than an eye. Lateral oral margins hardly produced. Vertex flat or slightly produced, densely pilose. Occiput ventrally narrow, dorsally widened. Eye bare. Eye margins in male slightly converging at level of frons, with mutual distance 2.5-3 times width of antennal fossa. Antennal fossa about as wide as high. Antenna shorter than distance between antennal fossa and anterior oral margin; basoflagellomere as long as or longer than scape, oval; bare. Postpronotum pilose. Scutellum semicircular; with calcars. Anepisternum sulcate; entirely pilose. Anepimeron entirely pilose. Katepimeron moderately convex; with wrinkled texture; bare. Wing: vein R4+5 with posterior appendix; vein M1 perpendicular to vein R4+5; postero-apical corner of cell r4+5 rectangular to weakly rounded, with small appendix; crossvein r-m located between basal 1/6 to 1/5 of cell dm. Abdomen 2.5-3 times as long as wide; with characteristic shape: widest point about halfway tergite 2, which has strongly arcuate lateral margins and pair of depressed areas dorsally; tergites 3-4 narrower and almost parallel-sided. Tergites 3 and 4 fused. Sternite 1 pilose. Male genitalia: phallus furcate near apex, with dorsal process long and whip-like, ventral process very short; epandrium with ventrolateral ridge.

Diagnosis.

Vein R4+5 with posterior appendix. Antenna shorter than distance between antennal fossa and anterior oral margin. Tergite 2 with strongly arcuate lateral margins, tergites 3-4 narrower and almost parallel-sided. Sternite 2 and 3 separated by membrane that is much less wide than sternite 2.

Discussion.

This group was treated as a subgenus of Microdon by Thompson (1981b). Based on the phylogenetic evidence of Reemer and Ståhls (in press) this ranking cannot be maintained. Instead, Omegasyrphus is treated as a distinct genus. Thompson (1981b), who gives a key to the North American species, points out that species level taxonomy is necessary for this genus. This is still true.

Diversity and distribution.

Described species: 5. North and Central America, from South Dakota in the U.S.A. southward to Guatemala. The south border of this range is marked by Microdon brunnipennis Hull, 1944, which was described as a variety of Microdon baliopterus Loew, 1872 by Hull (1944b). The assignment of this taxon to Omegasyrphus is based only on this description, as the type has not been examined.