Colobostema Enderlein, 1926

Jean-Paul Haenni, 2013, A revision of the West Palaearctic species of Colobostema Enderlein, 1926 (Diptera, Scatopsidae). Part I. European subregion, Mitteilungen Der Schweizerischen Entomologischen Gesellschaft 86, pp. 199-242 : 201-205

Genus Colobostema Enderlein, 1926

Enderlein 1926: Zooi. Anz. 68: 140; Cook 1956: Ann. ent. Soc, Am. 49: 325-332; Cook 1971: Aust. J. ZooL, Suppl. Ser. 8: 9-29; Cook 1974: J. nat. Hist. 8: 62-64; Amorim 1982: Sist. filogén. Scatopsidae: 83-84 et cd.', Freeman 1985: Hdbk Ident. Br. Ins. 9(7): 38; Haenni 1993: Ent. Scand. 23: 405-414; Krivosheina 2001: Int. J. Dipteral. Res. 12(2): 73-77; Huerta 2013: Zootaxa 3619(2): 183-194.

Type species. Colobostema oldenbergi Enderlein, 1926 , by original designation (= Scatopse tristis Zetterstedt, 1850 )

Description. Comparatively medium to large sized scatopsids (1.5-2.5 mm), usually velvety black, dull, except on lower parts of pleurae, shining; presence of more or less extended pale (whitish to bright orange yellow) parts on tibiae and tarsi, hind comers of thorax posterior to wing bases and, in females only in European species, basal segments of antennal flagellum. Pilosity well developed, more or less adpressed, except on head and dorsum, where it is more erect; microtrichosity generally distributed on body and legs giving a dull appearance; microtrichosity absent from katepisternum, most of meron (except broad dorsal margin and narrow posterior margin), mediotergite, posterior half of outer surface of fore and mid coxae, inner surface of mid and hind trochanters, inner half of hind coxa; consequently all these parts are shining black. Due to the dense microtrichosity, parts of the body, especially tibiae and tarsi, can appear whitish grey, more or less pollinose according to the direction of light. On the other hand old specimens in collections are very often faded and appear generally entirely brown, more or less blackish. Wings more or less infuscated, greyish to brownish, covered with dense microtrichosity. Halters with knob dark, grey or brown, and lighter, fulvous stem.

Head rounded, as wide as high, not laterally compressed, eyes densely micropilose, dichoptic in both sexes or hardly touching in one point above the antennae in some males; 3 well developed ocelli; antennae as long as thorax, about twice as long as head height, scape shorter than high, pedicel more or less cup-shaped, longer than wide, flagellum 8-segmented, widening toward apex, easy to count, last segment about twice as long as penultimate; flagellomere setation irregularly distributed; in females of some species, basal flagellomeres 1-4 more or less yellowish; face wide, pilose; labellae small, stipes fused proximally, palpi 1-segmented, short, with a subapical sensorial pit on inner face.

Thorax stouter than in most other scatopsid genera, not laterally compressed, scutum approximately as wide as long, rather quadrate in shape; supraalar setae developed, but not arranged in a regular row; shorter setae scattered over scutum and scutellum; following groups of setae present on pleural sclerites: anepistemal, upper epistemal, subalar, subspiracular; spiracular sclerite broad, longer than high, more or less triangular in shape, setose, with large, submedian spiracular opening; postnotal phragma well developed.

Wings densely covered with microtrichia, macrotrichia present only on sclerotized anterior veins; posterior veins brownish, darker than membrane; M, and M9 vanishing shortly before reaching wing margin, M, with a marked bend at basal third to fourth, often bearing a short spurious vein directed toward R4+5, more or less apparent according to the angle of view; CuA9 with a smooth double curve. Halters elongate, with knob longer than stem, bearing a few setae on stem.

Legs simple, of the usual type in Scatopsidae , densely pilose; posterior legs much longer than anterior and median pairs; anterior coxa elongated, all femora and tibiae simple, tarsi simple, length of tarsomeres decreasing from tarsomeres 1 to 4, 5th longer than 4th; claws simple, empodium well developed.

Abdomen with 7 pregenital segments; stemite l sclerotized; tergite 2 with a paired lunula-shaped zone with modified microtrichia along the anterior margin; segment 7 (pregenital) diversely modified in males of different species, always with a nearly complete, heavily sclerotized narrow basal ring; sternite 7 widened, laterally encompassing tergite 7; tergite 7 with posterior margin either produced or with a medial incision, frequently with an inner posterior fold, asymmetric in some species; spiracles of segment 7 on sides of stemite.

Genitalia: not rotated in male, sclerites fused in some degree to form a genital capsule; epandrium bilobed apically, lobes generally acute in West Palaearctic species, variously modified, tending to asymmetry; parameres well developed, heavily sclerotized; gonocoxites large, well developed; aedeagus with tip diversely modified; spermatic pump lying free in the abdomen. In female tergite 7 simple to more or less deeply notched medially on posterior margin; sternite 8 bearing a pair of valvifers, in some species a pair of basal submedian sclerotized plates; cercus large; spermatheca rounded, simple.

Diagnosis. The species belonging to the genus Colobostema are rather stout bodied, velvety black scatopsids with long antennae, broad quadrate thorax and variable yellowish or whitish annulation on legs and sometimes on antennae. This peculiar habitus among scatopsids makes this genus quite easily recognizable, even with bare eyes, which is quite unusual for this family. Rounded head with dichoptic eyes in both sexes (or hardly holoptic in some males) together with notum broad. quadrate, practically as wide as long, not compressed laterally, allow easy recognition of Colobostema from other genera of Scatopsini except Holoplagia , Colobostema differs from the latter by the absence of a complete cross-vein connecting M j and R4+5 (with at most a weakly developed, anteriorly directed short spurious vein arising from bend of M, towards R4+5). Other characteristic features are antennae very apparent, large, as long as thorax or even longer and about twice as long as head height, flagellomeres usually well separated, with setation not arranged in whorls, genital capsule of male usually not rotated, with a pair of parameres, a pair of well developed gonocoxites, and long, bilobed epandrium, the sternite 8 of female with a pair of valvifers.

Taxonomic remarks. As pointed out by Amorim (1982) who lists a series of about 25 synapomorphies for Colobostema , this genus is one of the best characterized of the Scatopsidae . However, like several other Enderlein genera, it was very poorly characterized when it was originally established in 1926 for two European and one New Guinean species ( Enderlein 1926), with only trivial wing venation features, The type species designated by Enderlein (1926: 140) himself as « Colobostema oldenbergi n.sp. » is in fact a synonym of the well known European species Sccitopse tristis Zetterstedt , while the other included species - the European S. incompleta (Verrait, 1886) - is clearly not congeneric with the type species. Hence, other workers of the family could not properly recognize this genus for a long time, until Cook (1956) redescribed the type species and used the name Colobostema in a new concept to include a series of morphologically well characterized and clearly related species. It is worth mentioning that Duda (1928), in his for his time excellent key for the Palaearctic species, had already segregated these species on the basis of the same characters as the «nigripenne-G ruppe», but without giving a formal taxonomic status inside of genus Sccitopse . Three European species were included in this group by Duda (loc.cit.), but only two of them were recognized by Cook (1974), who accepted all the synonymies established by former authors on the base of comparison of descriptions only. On the other hand, many new species of Colobostema have been described and some older names revised. This includes mainly species from North America ( Cook 1956), South Africa ( Cook 1965), Australia ( Cook 1971), Nepal ( Cook 1978), Oriental Region ( Freeman 1990), Africa ( Haenni 1993a), China ( Yang 1995), Russia and adjacent countries ( Krivosheina 2000), Northern Europe ( Krivosheina 2001), Belize (Haenni & Rapp 2003) and Mexico ( Huerta & Ibânez-Bernal 2008, Huerta 2013). The number of described species in the world (including those in the present work) summs up to about 60, but I have seen material of about 15 additional undescribed species from several parts of the world ( North Korea, Taiwan, Nepal, New Guinea, East Africa, Australia, Panama), while Amorim (1982) reported seven undescribed Neotropical species. This would bring the total number to some 90 species worldwide. However, there is no doubt that many more remain undiscovered, not only in the tropical regions, where they might be very numerous, but even in the more intensively collected temperate regions.

The placement of Colobostema in the subfamily Scatopsinae proposed by Cook (1963) is well founded and generally accepted. Colobostema was first placed in the tribe Scatopsini by Cook (1963, 1974), but Amorim (1994) erected the tribe Colobostematini for this genus and the following more or less related genera: Holoplagia Enderlein, 1912 , Ferneiella Cook, 1985 , Efcookella Haenni, 1998 (- Cookella Freeman, 1985 ), Lumpuria Edwards, 1928 (- Villoscatopse Cook, 1978 ), Borneoscatopse Freeman, 1990 , and the fossil genus Procolobostema Cook, 1971 (Oligocène / Miocene). More recently Amorim (1998) elucidated the relationships of the genera within the tribe Colobostematini .

There has been much confusion concerning the grammatical gender of Colobostema , ihe name being sometimes treated as a feminine word, sometimes as a neutral one. Enderlein himself (1926) in the original description of the genus described C.fumipenne (neutral), but also included C. incompleta (feminine). In fact Colobostema is derived from the Greek words KoXoßocr Ccolobos’, truncate, shortened, uncomplete) and aTX|p, a d sterna’, standing piece, button). Etymologically, the name very probably refers to the truncate stem vein arising anteriorly from vein M,, a character pointed out by Enderlein (1926) in the original description. Sterna is a neutral substantive and the species included in this genus must thus end in -um or in -e.