New species of Hercostomus Loew, 1857 from Afrotropics (Diptera: Dolichopodidae) and key to Afrotropical fauna

Five new species of Hercostomus Loew, 1857 from Kenya, Namibia, Tanzania and South Africa are described and illustrated. They belong to the Hercostomus longiventris lineage, which also appears similar to the Palaearctic H. chetifer subgroup and the Oriental H. takagii and H. absimilis groups on the basis of the modified male fore tarsus. The male cercus of almost all Afrotropical species is remarkable in having ventral processes or projections and are conditionally divided into H. nectarophagus and H. perturbus subgroups on the basis of the presence of one or two ventral projections on the cercus, respectively. Hercostomus brandbergensis sp. nov. and H. fedotovae sp. nov. are associated with the H. nectarophagus subgroup; H. koshelevae sp. nov., H. vikhrevi sp. nov., and H. sanipass sp. nov. are associated with the H. perturbus subgroup. The new species differ by fine structures of the male fore tarsus, cercus and postgonite. An identification key to males of 23 Afrotropical species of Hercostomus is compiled for the first time. New records are given for some known species.


Introduction
Hercostomus Loew, 1857 is a mega-diverse dolichopodid genus comprising about 500 species worldwide .  divided the Afrotropical species of the genus into three groups, and  provided a key to the then known species. Later Grichanov (2010) separated one of those groups as a new genus, Afrohercostomus Grichanov, 2010, and another species group as a new genus, Neohercostomus Grichanov, 2011(Grichanov, 2011a. Hercostomus scharffi  was transferred to the genus Setihercostomus Zhang & Yang, 2005(Grichanov et al., 2014. Presently 23 (excluding three doubtful) species of Hercostomus, 14 species of Afrohercostomus, 21 species of Neohercostomus and one species of Setihercostomus are known from the Afrotropics (Grichanov 2018;this paper). A key to Afrotropical dolichopodid genera including all genera of the subfamily Dolichopodinae was recently published by Grichanov & Brooks (2017). Nevertheless, an identification key to Afrotropical species of Hercostomus does not exist.
Treatment of rich collections of the KwaZulu-Natal Museum (South Africa) and new material from other museums has yielded specimens of undescribed dolichopodine species, which can be associated with the nominotypical Hercostomus longiventris lineage (Brooks 2005). In this paper, five new species of Hercostomus from Kenya, Namibia, Tanzania and South Africa are described and illustrated, new records are given for some known species, and a key to 23 known species of the Afrotropical Region is provided for the first time.

Material and methods
The new Hercostomus species discovered were photographed with a ZEISS Discovery V-12 stereo microscope and an AxioCam MRc5 camera. Genitalia preparations were photographed with a ZEISS Axiostar stereo microscope and an AxioCam ICc3 camera. Morphological terminology and abbreviations follow Cumming & Wood (2017) and Grichanov & Brooks (2017). Body length is measured from the base of the antenna to the posterior tip of epandrium. Wing length is measured from the base to the wing apex.

Diagnosis
Having simple fore tarsus, the new species is close to H. nectarophagus Curran, 1924, differing distinctly in male mid and hind femora each with ventral row of erect cilia, about as long as diameter of femur. Hercostomus nectarophagus males have no long ventral cilia on femora . The hypopygia are rather species-specific in the two species.

Etymology
The species is named after the type collection locality: the Brandberg Massif. Paratype NAMIBIA • 1 ♂; same collection data as for the holotype; terminalia dissected, stored in glycerin in microvial pinned with source specimen; NMNW. Description Male ( Fig. 1) MeasureMents (in mm). Body length 3.6; antenna length 0.8; wing length 2.9; wing width 1 (Fig. 1A).

Female
Unknown.

Ecology
The Brandberg Massif is an isolated mountain range in western Namibia on the eastern edge of the Namib Desert, located in the Nama Karoo Biome. The type locality "Mason Shelter" (1800-1750 m a.s.l.) is a more or less flat open plain, dissected by some small riverbeds and fringed by rocky hills with huge boulders and rock slabs. It contains some single trees of Acacia hereroensis Engl., Ficus sycomorus L. and Ozoroa crassinervia (Engl.) R.Fern. & A.Fern., abundant small trees of Commiphora saxicola Engl. and scattered individuals of Sterculia quinqueloba (Garcke) K.Schum., Galenia africana L., Eriocephalus dinteri S.Moore and Cyphostemma currorii (Hook.f.) Desc. at the southern margin of the plain. In addition, low shrubs of Salsola sp. are evenly dispersed throughout (Koch 2006). The Hercostomus brandbergensis sp. nov. type specimens were collected by Malaise trap installed in one of the riverbeds.

Diagnosis
The new species belongs to the Hercostomus nectarophagus subgroup of species, differing distinctly by its small size, narrow face, fore tarsomere 3 simple, fore tarsomeres 4-5 flattened and widened, fore tarsomere 4 white and tarsomere 5 deep black. The hypopygium is similar to that in other species of the subgroup.

Etymology
The species is named for the Russian entomologist, Dr. Zoya Fedotova (VIZR: All-Russian Institute of Plant Protection, St. Petersburg), who has described over 1000 new gall midge species.

Female
Unknown.

Distribution
Tanzania.

Diagnosis
The new species is a sister species to H. koshelevae sp. nov., differing distinctly by its larger size, wider face, darker legs, strongly expanded fore tarsomere 3. The hypopygia are rather similar in the two species. Nevertheless, the proximal arm at the apex of ventral lobe of the postgonite in H. sanipass sp. nov. is thicker than that in H. koshelevae. The long basolateral cercal lobe in males of both species is very peculiar, being much shorter in males of close species with modified fore tarsus.

Etymology
The species is named for the well-known Sani Pass, a mountain pass located on the road between Underberg, KwaZulu-Natal and Mokhotlong, Lesotho, type locality for the new species. The species epithet "sanipass" is a noun in apposition. Head. Frons greenish-black, whitish pollinose; face black, densely white pollinose. One long, strong, vertical pair of ocellar setae, 1 short postvertical, pair of ocellar setae. Upper postocular setae black; lateral, lower ones white. Eye with short hairs; face glabrous. Face gradually narrowed towards palpus, 2.7 × as high as wide in middle, under antennae about 2 × as wide as width of postpedicel, at clypeus approximately as wide as width of postpedicel; clypeus not reaching lower margin of eyes. Antenna (Fig. 3B) slightly longer than height of head, entirely black; pedicel short and wide, internally convex anteriad, with short distal setulae; postpedicel asymmetrical, elongate, narrowed and angular apicodorsally, nearly 1.5 × longer than wide, covered with short pubescence; arista mid-dorsal, black, with short hairs. Length ratio of scape to pedicel to postpedicel to stylus (1 st -2 nd segments), 27/14/28/18/63. Palpus and proboscis moderately small, yellow, with short black setae; palpus with 1 black bristle.
Wings. Simple, greyish, veins brown. Costa simple. R 1 reaching to first third of wing length. R 2+3 and R 4+5 weakly divergent. Ratio of part of costa between R 2+3 and R 4+5 to between R 4+5 and M 1+2 , 7/3. R 4+5 and M 1+2 slightly convergent in distal part; M 1+2 joining costa before wing apex. Crossvein dm-m straight, almost perpendicular to longitudinal wing axis, forming right angle with M 1+2 and acute angle with M 4 longitudinal veins. Ratio of dm-m to distal part of M 4 , 45/82. Posterior wing margin almost evenly convex. Anal vein distinct, almost reaching wing margin; anal lobe pronounced; anal angle obtuse. Lower calypter yellow, brown anteriorly, with black setae. Halter yellow.
abdoMen. Greenish-black, weakly pollinose, with black hairs and long marginal setae. Segment 7 about as long as epandrium. Segment 8 large, covering more than half lateral side of epandrium, with numerous fine short dark cilia. Genitalia (Fig. 3D) with epandrium brownish black in proximal part and dirty yellow in distal part, rounded-oval, twice longer than high. Foramen positioned before middle of left lateral side. Hypandrium mid-ventral, with short base, 4 long thin lobes of different lengths and widths. Phallus thin, projected. Distoventral epandrial lobe as short rounded prominence, fused to epandrium, with 2 short and 1 long setae. Surstylus yellow, bilobate; ventral lobe broad, simple, ⅔ length of dorsal lobe, with 1 subapical seta; dorsal lobe of surstylus expanded in distal half, with short narrow process at apex, several subapical setulae and 1 strong mid-dorsal seta. Distal lobe of postgonite as long as ventral lobe of surstylus, narrow, broad and pointed at apex. Ventral lobe of postgonite (Fig. 3E) strongly sclerotized, with 2 long arms (anterior and posterior) at apex forming letter V, 2 short symmetrical processes between them, covered with denticles on ventral side. Cercus (Fig. 3F) broad, yellow, densely covered with short light hairs, longer at apex; cercus with basolateral lobe, longer than cercus, densely covered with long setae, and with distolateral narrow process bearing 3 thick hook-tipped setae at apex; 1 strong seta proximal to process, 3 strong setae at apex of cercus.

Female
Similar to male except lacking male secondary sexual characters.

Ecology
According to type specimen labels, imagos inhabit rocks in mountain streams and damp mossy rocks along roads.

Diagnosis
The new species is sister species to H. sanipass sp. nov., differing distinctly in its smaller size, narrower face, lighter colored legs, weakly widened fore tarsomere 3. The hypopygia are rather similar in the two species. Nevertheless, the proximal arm at apex of ventral lobe of postgonite in H. koshelevae sp. nov. is always thinner than that in H. sanipass. The long basolateral cercal lobe in males of both species is very peculiar, being much shorter in males of close species with modified fore tarsus.

Etymology
The species is named for the Russian entomologist, Dr. Oksana Kosheleva (VIZR, St. Petersburg).

Female
Similar to male except lacking male secondary sexual characters.

Ecology
According to type specimen labels, imagos inhabit rocks in mountain streams, being common in forests.

Distribution
South Africa.

Diagnosis
The new species is close to H. balensis H. kefaensis Grichanov, 2004, both known from Ethiopia, differing distinctly in its larger size, in morphology of the male fore tarsus, antenna, wing and hypopygium. In H. balensis, male fore tarsomeres 4-5 dark, with fringe of white erect hairs, 1.5-2 × longer than diameter of tarsomeres; wing with less deep postero-proximal emargination; basoventral lobe of cercus distinctly shorter than mid-ventral lobe; the latter lobe bearing three strong simple setae, half as long as the lobe. In H. kefaensis, the male postpedicel is 2.5-3 × longer than high; fore tarsomere 4-5 dark, with short semi-accumbent dorsal hairs, tarsomere 4 with black hairs and tarsomere 5 with black and white hairs; wing with less deep postero-proximal emargination; mid-ventral lobe of cercus with three strong simple setae, slightly longer than the lobe.
Wings. Simple, greyish, veins brown. Costa simple. R 1 reaching to first third of wing length. R 2+3 and R 4+5 weakly divergent. Ratio of part of costa between R 2+3 and R 4+5 to between R 4+5 and M 1+2 , 61/16. R 4+5 and M 1+2 slightly convergent in distal part; M 1+2 joining costa at wing apex. Crossvein dm-m straight, forming right angle with both M 1+2 and M 4 longitudinal veins. Ratio of dm-m to distal part of M 4 , 46/75. Wing anal lobe with broad and deep postero-proximal emargination. Anal vein fold-like; anal lobe pronounced. Lower calypter yellow, with black setae. Halter yellow.
abdoMen. Mostly greenish black, weakly pollinose, with segments 2-3 broadly reddish yellow laterally, segments 4-5 with brown lateral spots, with black hairs and long marginal setae. Segment 7 slightly longer than epandrium (93/84). Segment 8 large, covering more than half lateral side of epandrium, with fine short dark cilia. Genitalia (Fig. 5D) with epandrium orange yellow, rounded-oval, twice longer than high. Foramen positioned before middle of left lateral side. Hypandrium mid-ventral, with short base, 4 long thin lobes of different lengths and widths. Phallus thin, projected. Distoventral epandrial lobe as short rounded prominence, fused to epandrium, with 2 short, 1 very long setae. Surstylus yellow, bilobate; ventral lobe broad, simple, ⅔ length of dorsal lobe, with 1 subapical seta; dorsal lobe of surstylus widened in distal half, with short narrow process at apex, several subapical setulae, 1 strong mid-dorsal seta. Distal lobe of postgonite as long as ventral lobe of surstylus, narrow, broad, pointed at apex. Ventral lobe of postgonite (Fig. 5E) strongly sclerotized, simple, covered with microscopic denticles on proximal side. Cercus (Fig. 5F) broad, yellow, densely covered with short light hairs, longer at apex, long strong setae at apex of cercus; cercus with 2 ventral lobes; basolateral lobe of cercus nearly as long as cercus, with bunch of about 9 long, curved at apex apical setae; mid-ventral narrow lobe with 3 pedunculate setae, thick on basal half, filiform on distal half, 2 times longer than lobe; 1 short strong seta between ventral lobes.

Female
Unknown.

Distribution
Kenya.

Ecology
According to the label data of the above specimens, imagos inhabit forest paths and stream margins in indigenous forests.

Hercostomus wittei
There are some Afrotropical species of Hercostomus with practically unmodified fore tarsomeres. Nevertheless, males of H. nectarophagus have inconspicuously modified fore tarsomeres, but their cerci are similar in shape with those of other members of the H. nectarophagus subgroup . The male cercus of H. brandbergensis is also similar in shape with that of males of the H. nectarophagus subgroup. Hercostomus intercedens is an unassigned species, having simple legs and simple subtriangular cerci.