Orussus melanosoma Lee & Wei, sp. nov.

(Figs 1, 2 and 3)

Female. Color: Predominantly black. Antennomere 10 dark brown. Fore and hind femora with white distal spot, all tibiae with white stripe extending from base up to 0.25 dorsally (Fig. 2 C). Fore wing infuscate from base to apex except for a hyaline band distal of pterostigma. Pterostigma, vein C and R blackish brown, other veins brown to dark brown or spectral (Fig. 2 F). Hind wing slightly infuscate distally, hyaline towards base. Cenchrus yellowish brown (Fig. 2 B).

Size. Body length 6.7 mm, fore wing length 5.4 mm.

Head. Head, thorax and distal abdomen with fine silvery hairs, mouth parts with golden hairs. Antennomere 9 2.5 times longer than wide, swollen proximally, broadest proximal to the middle, lateral margin rounded and depressed in dorsal view; antennomere 10 2.1 times longer than wide. Scapus short and cylindrical; combined length of antennomeres 4+5 clearly shorter than length of antennomere 6 (Fig. 1 B). Distance between lateral ocelli 3.3 times diameter of median ocellus. Ocellar corona distinct around median ocellus (Fig. 1 C), corona narrow, distance between median ocellus and lateral coronal tooth approx. 1.5 times diameter of ocellus, ventral coronal tooth present. Face without dorsal transverse and longitudinal frontal carinae (Fig. 1 B). Ventral transverse frontal carina complete, with small notch medially. Distance between eyes on vertex 1.2 times wider than distance between lateral ocelli. Frons areolate-rugose. Face almost flat in lateral view (Fig. 2 A). Subantennal groove well developed. Postocular carina indistinct and polished, distance between eye and postocular carina 0.9 times as wide as diameter of medial ocellus. Vertex and gena areolate-punctate and with dense pilosity of short silvery hairs. Occiput areolate and occipital carina absent.

Thorax. Mesoscutum without tubercle medially, irregularly densely punctate-areolate, interspaces with microsculpture, with sparse silvery pilosity posteriorly. Mesoscutellar sulcus distinct and deep. Mesoscutellum less densely sculptured than mesoscutum, interspaces mostly smooth; mesoscutellum acute triangular posteriorly (Fig. 2 B), raised and separated from surrounding sclerites; lateral margin of mesoscutellum distinct. Mesepisternum punctate-areolate, mesepisternal carina absent; large posterior depression mostly smooth except for a few large punctures. Metanotum with median and lateral longitudinal carinae well developed. Metepisternum areolaterugose, evenly sculptured.

Wing. Discal cell rhomboid, basal part broader than distal part, not reaching vein R. Vein 1r-RS spectral.

Leg. Hind coxa with sparse, silvery pilosity. Fore femur with ventral carina. Lateral ventral part of hind femora smooth. Hind tibia with 9 distinct pegs (Fig. 2 C), with weak lateral longitudinal carina and without ventral longitudinal carina; apical flange not particularly developed distally. Apical spurs of hind tibia about equal length.

Abdomen. Abdominal tergum 1 densely and irregularly punctate-areolate; anterior margin of tergum 1 and 2 with distinct transverse groove. Middle of tergum 5 in anterior 0.2 completely imbricate with few punctures, up to 0.8 irregularly punctate-areolate. Subshining close to posterior margin of terga (Fig. 2 E). Tergum 8 coarsely punctate. Longitudinal carina of tergum 9 indistinct. Ovipositor very weakly upcurved distally (Fig. 2 D), with minute apical teeth.

Male. (only differences from female described). Body length 4.0 mm, fore wing length 3.3 mm. Fore wing less infuscated than in female (Fig. 3 C). All legs almost entirely black, small pale brown spot present on fore and mid femur.

Etymology. The specific epithet is derived from the entirely black body. It is a noun.

Distribution. South Korea.

Material examined. Holotype: female. TD: YNU. South Korea. [GB]: Cheongdo-gun, Unmun-myeon, Ssalbawi, Unmunsan, M.T., N 35˚38΄08˝ E 129˚01΄27˝, 23.iii–19.iv.2013, J.W. Lee. Paratype: 1 male. TD: YNU. South Korea. [JN]: Namwon-si, Sannae-myeon, Bamsagol, 11.v–14.vii.2008.

Remarks. In the key of Vilhelmsen et al. (2014), Orussus melanosoma keys to Orussus rufipes; the female has a combination of traits that is a mix of those of O. rufipes and the undescribed species in couplet 36. Orussus melanosoma can be distinguished from O. rufipes and O. zhui by the black femora and the presence of a ventral carina on the fore femur, from O. striatus by the absence of the mesepisternal carina and the infuscate wings, and from O. brunneus by the position of the lateral ocellus, the paler forewing bases, the more densely sculptured mesoscutellum, and the more extensive white marking on the hind tibia in the female. The larger Orussus species included in the key above differ from O. melanosoma in having white markings on the antennae, head (O. abietinus and O. coreanus) or abdomen (O. japonicus).

The phylogenetic analyses place the new species as a taxon within the genus Orussus. Despite the differences in e.g., leg coloration, the female and male are always retrieved as a monophylum when included as separate terminals, corroborating that they belong to the same species. When included as a single terminal, O. melanosoma is not always retrieved in the same position as when analysed as separate sexes, but there is no great divergence in the placement. Figure 5 shows O. melanosoma in a basal polytomy with O. striatus, O. zhui, and the remaining Orussus species. Orussus melanosoma displays several traits that are plesiomorphic for Orussus, e.g., distinct pegs on the hind tibia, no white markings on other body parts (antenna, frons, pronotum, abdominal tip) than the legs. The basal placement and distribution of O. melanosoma also fits well with the previously stated hypothesis that the common ancestor of Orussus originated in the Far East (Vilhelmsen 2004; Vilhelmsen et al. 2014), the genus subsequently expanding its range across the Holarctic and into the Afrotropical region.