Microdon (Omegasyrphus) biluminiferus Hull
Microdon (Omegasyrphus) biluminiferus Hull, 1944.
Hull, F. M. (1944) Studies of flower flies (Syrphidae) in the Vienna Museum (Natural History). Journal of the Washington Academy of Sciences 34, 398-404.
Microdon (Omegasyrphus) biluminiferus Hull, 1944.
Hull, F. M. (1944) Studies of flower flies (Syrphidae) in the Vienna Museum (Natural History). Journal of the Washington Academy of Sciences 34, 398-404.
Omegasyrphus was established for some small Microdon species with a distinctive abdominal shape: 2nd segment is widened, flattened, flared, with its lateral margin subcircular, thickened and rounded; and the rest of abdomen (3rd–5th segments) narrowed and cylindrical (Hull 1949: 309).
Omegasyrphus species have first two abdominal segments with three distinct depressions, two lateral ones and an anterior medial one; abdomen more or less parallel-sided; scutellum with apical calcar; vein R4+5 with an appendix extending posteriorly into cell R4+5; vein M1 rounded, not angulate, without a appendix; face convex, without mystax; metatibia without long pile along dorsal edge, forming a distinct brush.
Adapted from original description (Hull 1944).
MALE.
Characterized by the slender form and the large hyaline maculae at the base of the brownish abdomen. Related to such species as baliopterus Loew.
Head: short, much wider than the thorax. The ocelli are raised into a very conspicuous, round, subglobose, vertical dome, in front of which is a marked crease. The front, beginning at this crease, is rather short and barely longer than the pedicel. The antennae are thus set high upon the head; they are elongate. The pedicel is barely longer than wide, the basoflagellomere nearly five times as long as the pedicel and the scape about as long as basoflagellomere, or barely longer. The basoflagellomere is subtruncate and flattened at tip, widened in the middle, with a lateral crease and with a deeply thickened arista, which is only two-thirds the length of the segment. First two segments dark brown, basoflagellomere lighter. The vertex and the front and upper part of the face are very dark shining brown, the lower part of the face and gena light shining brown. There is a thick band of silvery-yellow pile on the lower sides of the face which is continued narrowly up the sides of the face, not quite to the level of the antennae. There is a bare shield-shaped spot above the antennae. The eyes are bare.
Thorax: very dark brown and covered with an appressed, setaceous-black pile; and on the suture there is a fascia of flattened, pale, brassy pile and similar flattened pile in the posterior part of the midline, which is directed posteriorly and meets a broad, semicircular area of similar pile lying just in front of the scutellum and which is directed forward so as to intermesh with this. The scutellum is light brown, shining, roughly triangular on its posterior margin and terminates in two tiny, very close-set points. Postpronotum pilose. The pleura have a row of pale, sericeous, stiffened hairs. The metanotum is conspicuous and large. The halteres are orange, the calypter pale brown. Legs: light orange-brown, becoming almost golden yellow on the tibiae and tarsi. The metafemora are a little thickened, especially on the scar a third of the way from their bases. The thickening gradually extends throughout the remainder of each femur. There are no ventral spines. The last half of each of the metatibiae is rather thick, ending simply, with an oblique scar in the middle. Wings: considerably longer than the abdomen, very pale brown and thickly pilose. The spurious vein is chitinized, the posterior veins are brown; the anterior veins yellow, the stigmal cell pale yellow, the costal cell and the small area past it also yellow.
Abdomen: rather elongate, a little wider than the thorax; nearly four times as long as wide. The sides of the last two segments are nearly parallel but practically cylindrical; they are barely wider at the base of the third segment. The second segment is only a trifle wider in the middle than the third segment but is much flattened, especially over an area corresponding to the maculae, which are actually concave. The lateral, rope-like margin on the second segment is thick and prominent. The first segment is rather short, with a deep crease between it and the second segment. The second segment is neither cylindrical nor flat; it is rather inflated and marked on each side with a large, posteriorly pointed, anteriorly broad, quite hyaline macula, which is continuous on the sides with the translucent yellow margins and which is divided in the middle by a roughly triangular, black spot; its base lies on the posterior margin of the segment, its peak is narrowly continuous with the first segment. The remainder of the abdomen is very dark brown and densely appressed-setate with crevices for the setae; on the posterior margin of the third segment, not reaching the sides, there is a fascia of flat, golden, posteriolaterally directed pile, which is widely separated in the middle. A similar fascia on the fourth segment is equally separated, beginning about the middle of the segment, and obliquely directed away toward the posterior corners, after first being directed toward the midline. The hypopygium is perfectly rounded.
Male: Length 12 mm excluding of antennae; wings 10.2 mm. Antennae 2.5 mm (Hull 1944).
Species known from Brazil.