Microcercis Beschovski

Foster, George A., 2024, Revision of Nearctic Microcercis Beschovski (Diptera: Chloropidae), with Synonymy of Incertella Sabrosky, Zootaxa 5481 (4), pp. 401-439 : 405

Genus Microcercis Beschovski urn:lsid:zoobank.org:act:8691A5E8-49FF-4B0C-987E-74467C7968AA

Microcercis Beschovski, 1978: 28 [as subgenus of Oscinella ]. Type species: Oscinella trigonella Duda, 1933 . Type locality: Hungary (deposited in Hungarian Natural History Museum).

Incertella Sabrosky, 1980: 420 . Type species: Oscinella incerta Becker, 1912 . NEW SYNONYM

Incertella : Beschovski, 1981: 59–61 [ Microcercis trigonella moved to Incertella as subgenus; incorrect name priority].

Generic Diagnosis.— Head. Ocellar triangle nearly as wide as the vertex, half, or less the length of the frons, entirely tomentose or partially to entirely polished; frons yellow in species with fully tomentose ocellar triangle, black in species with polished triangle, frons with row of four or five fine orbital setae and many scattered short frontal setulae centrally, a row of fine setae on margin of ocellar triangle (fig. 5); postpedicel often angulate anterodorsally; facial carina triangulate between antennal bases (fig. 2), narrowing ventrally, reaching half height of face; face matte, with multiple minute papillae (fig. 3); eye with short, dense ommatrichia (fig. 4). Thorax. Scutum evenly, densely tomentose or polished, with setae in irregular to regular rows; scutellum tomentose, pleuron black, gray or yellow, with variable patterns of tomentum and color; one or two pairs laterally directed scapular setae between postpronotal lobes present (in M. bispina and M. dorsata only) or absent (fig. 7); one anterior and one or two posterior notopleural setae, dorsal posterior setula, if present, usually weak; one appressed dorsally directed ventral proepisternal seta (fig. 8); mid femoral organ about 20μm long, consisting of one or two tightly spaced rows of short warts, variable in number, each with a short, thick, sometimes flattened seta (as in figs. 9–11); first tarsomere of the hind leg with two to four ventral setae at base that are longer than the other ventral setae. Abdomen. Cerci small, most often triangular, quadrate, or nearly absent, widely separated; surstylus short, variously shaped but most often parallel sided with angulate or spatulate tip; hypandrium closed; female terminalia simple.

Discussion.—The tomentum of Nearctic Microcercis species has been variously characterized over the years, usually as heavily pollinose, as under a light microscope it can appear to consist of a dense mat of compact wool-like material. SEM micrographs (fig. 1) show that it consists of dense tomentum that occurs on smooth integument with no punctures or depressions at the base. The tomentum is consistent in length and diameter wherever it occurs on the body and is the same between all species. The tomentum is reclinate and generally measures about 12 μm. Cumming and Wood (2017) differentiate pruinosity as being “dust-like” and tomentum as being “pubescent”. While some chloropid genera clearly show a “dust-like” surface of the integument, the Microcercis species treated herein have a distinct pubescence while others, such as the type species M. trigonella have a polished triangle and scutum.

SEM micrographs of the frons of Microcercis (figs. 2, 5) reveal a similar lamellate pattern to that shown by SEM micrographs by Riccardi (2020) for Chaethippus Duda, 1930 , a Neotropical genus. However, the setulae on the dorsal edges of the lamellae in Chaethippus occur on spine-like extensions which she notes are unique to Chaethippus . Further analysis of this character in other Chloropidae might reveal whether or not this character is of generic importance.

Males of many species of Oscinellinae have one or two short rows, or a cluster, of setae on the anterodorsal surface of the mid femora (figs. 9–11). Ismay (1975) provided an analysis of the morphology and possible biological functions of the mid femoral organ (“femoral combs”) of British species of Oscinellinae . The illustrations, like those of Andersson (1977), Nartshuk and Andersson (2013) and Riccardi (2020) show the setae to be minute, short, straight spicules, often mounted on short, thick warts. SEM images of the femoral organ of the Nearctic Microcercis species show that the setae positioned on top of the short, thick warts can be much thicker, rounded and sometimes flatter than previous illustrations indicate. There may be one or two rows, or a cluster of these structures depending on the species. Occasionally, lateral to the thick setae, there are a few that are tear-drop shaped.

Species of Microcercis have a conspicuous subscutellum (fig. 6). A survey of other genera of the subfamily Oscinellinae shows that this feature is common in the subfamily. There seems to be no mention of this feature in available manuals of the world-wide chloropid fauna.

I have found little or no intraspecies variation in the pattern of tomentum on the lateral surfaces of the thorax, and it is generally a more reliable taxonomic character than color. Body and leg color can vary from very lightly colored to much darker forms within some species.

Among Nearctic Microcercis species the male genitalia show significant similarities in having short, triangular or quadrate, sometimes difficult to discern, widely separated cerci and short surstyli that vary from simple, spatulate structures to having tooth-like medial extensions or a pointed distal tip.