Hercostomus Loew, 1857

Grichanov, I. Ya., Nourti, M. & Kettani, K., 2020, The Hercostomus exarticulatus species group in the Palaearctic Region (Diptera: Dolichopodidae), Caucasian Entomological Bulletin (Caucas. entomol. bull.) 16 (1), pp. 27-34 : 27-28

Genus Hercostomus Loew, 1857

Hercostomus exarticulatus species group

Diagnosis. Body size 2–3 mm.

Male. Head about as wide as high; antenna black; postpedicel rounded-ovate, with distinct apex, about as long as high, with short hairs; arista-like stylus mid-dorsal, about 2 times longer than antennomeres combined; distal segment of arista with short hairs; frons grey pollinose, nearly parallel-sided, wider than high; eyes finely haired; face densely white pollinose, narrow; clypeus small, slightly bulging; palpus small, with few hairs and 1 seta; proboscis short, with hairs; upper postocular setae black, lower postoculars yellow.

Thorax with all setae black; pronotum pubescent, with black hairs; proepisternum with 1 long black bristle above fore coxa; mesonotum dark with metallic reflection, weakly grey pollinose; 6 dorsocentral setae, 8–10 well developed acrostichals, biserial, almost reaching 5 th pair of dorsocentrals; pleura dark, with whitish grey pruinosity, in front of posterior spiracle bare; metapleuron bare; scutellum black with bluish reflection, with 2 strong medial setae and 2 short lateral setae or hairs.

Legs mostly yellow, hairs and setae black; fore coxa yellow or blackish ( exarticulatus ); mid and hind coxae dark with yellow apex, tarsi simple except hind basitarsus; fore leg with coxa bearing black hairs anteriorly and 3 black setae apically, fore femur with preapical posterior seta, fore tibia with few short anterodorsal and posterodorsal setae, 2–3 short apicals, with anterodorsal comb-like row of setae distally, no long apicoventral seta; midleg with coxa bearing some black hairs and setae laterally and apically, mid femur with 1 strong anterior preapical seta and 1 posteroventral preapical seta, with more or less distinct glabrous ventral tubercle at base; mid tibia usually with 3 anterodorsal, 2 posterodorsal and 5 apical bristles; hind leg with coxa bearing 1 strong seta at middle and 1 fine seta at apex, hind femur with row of dorsal setae on basal half, 1 anterior preapical bristle at apical quarter, hind tibia with some strong anterodorsal, posterodorsal, 3 apical bristles, row of 3–5 short ventral setae, densely covered with elongate setulae posteroventrally on distal half, with apical posteroventral comb of about 10 setulae and rounded or triangular or ovate dorsolateral apical projection covering distal excavation; hind basitarsus distinctly shorter than next tarsomere, with 3–4 short ventral setae, usually slightly curved at base, slightly swollen and flattened and/or excavated at extreme base, bearing ventrolateral thick seta or spine basally; apical projection of hind tibia and basal spine of hind basitarsus forming peculiar hitching lock between tibia and basitarsus.

Wing about 3 times longer than wide; membrane almost hyaline or greyish; costa simple, with short black setae dorsally; R 1 and R 2 + 3 almost straight; R 4 + 5 slightly convex anteriorly; M

1 with week curvation towards R

4 + 5 in middle of distal half, almost straight in distal section; R 4 + 5 and M subparallel at apex of wing; M 1 joining costa at wing apex; distal part of M 4 about 2 times longer than dm-m; anal vein distinct; anal angle obtuse; lower calypter yellow with black cilia; halter yellow.

Abdomen entirely dark and shiny dorsally, whitish grey pollinose laterally, with black hairs and long marginal setae; 6 th and 7 th segments bare, 7 th segment with well developed tergum and sternum; 8 th segment pear-like, with black cilia dorsally. Epandrium slightly longer than high, ovate or cuboidal, flattened basally; hypandrium mostly free, forming 2 pairs of symmetrical lobes reaching apex of small distoventral epandrial lobe; phallus long, thin;anteroventral part of postgonite not developed; posterodorsal portion strongly developed, long, horn-like, curved ventrally; surstylus bilobed, with dorsal lobe larger and broader than ventral lobe; cercus brown ( exarticulatus ) or yellow, dark at apex, band-like, strongly curved and directed ventrally; one subtriangular and one semirounded projections at middle of cercus.

Female similar to male except lacking male secondary sexual characters. Face wider than that in male.

Included species. Hercostomus exarticulatus ( Loew, 1857) ; Hercostomus exarticulatoides Stackelberg, 1949 ; Hercostomus canariensis Santos Abreu, 1929 ; Hercostomus vodjanovi Negrobov, Maslova et Selivanova, 2016 .

Notes. According to Brooks [2005], species of the exarticulatus group key to the Hercostomus longiventris lineage. According to the old keys to the Palaearctic Hercostomus species, the exarticulatus group belongs to the traditional 2 nd group of species [ Negrobov et al., 2012], although H. exarticulatus itself with partly dark femora has been usually included in the 4 th group as well [ Negrobov, Nechay, 2009b]. According to Yang et al. [2011], species of the exarticulatus group come to H. curvus group differing from the former in wholly black postocular setae and hypopygium morphology. The two species of the curvus group are known only from Oriental China.