Merostenus (Merostenus) distigma Gibson, 2017, n. sp.
Creators: name: Gibson, Gary A. P.
Publisher: name: Zenodo
Year: 2017
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Hymenoptera
Eupelmidae
Merostenus
Merostenus distigma

description: M. (Merostenus) distigma n. sp.
Figs 31–38
Type material. Holotype ♀ (CNC). “ TANZANIA, Mt. Meru, | above Miriakamba Huts | S3.22201° E36 78352° | 3178m, 2.xii.2012, sift | 0 6, V. Grebennikov leg. / HOLOTYPE ♀ | M. (Merostenus) | distigma | Gibson ”. Pointmounted by right acropleuron; entire; uncontorted.
Paratypes (2♀). Kenya. Mt Kenya, Teleki Valley, IV.1980, 10,000 ft, D. Levin, Bambo [sic] forest along stream (1♀ CNC, CNC Photo 2016-53). Mt. Kenya, 3700m, 18.I.1980, D. Westerberg (1♀ BMNH, NHMUK 010353722).
Etymology. A combination of the Greek prefix di - (two) and stigma (spot), in reference to the two pits on the mesoscutum that uniquely differentiate females of this species.
Description. FEMALE (habitus: Figs 32, 34). Length = 2.8–3.1 mm. Head (Fig. 31) dark brown with variably distinct bluish to bluish-green luster under some angles of light or all but frontovertex lighter orangish-brown; in frontal view subquadrate, about 1.2× as wide as high, and in lateral view lenticular, about 1.6× as high as long with anterior surface uniformly curved; face in smaller females mostly meshlike coriaceous with parascrobal regions and scrobal depression dorsolaterally somewhat more strongly sculptured, and in largest female frontovertex coriaceous-reticulate and parascrobal regions quite distinctly, though shallowly reticulate; entirely setose with dark setae except for bare scrobal depression, with setae on frons mostly separated by distance equal to or slightly greater than anterior ocellar diameter; scrobal depression transversely Π-shaped above convex dorsal surface of interantennal prominence, the lateral margin curved dorsally near lateral limit of torulus so distinct parascrobal region differentiated, and dorsomedially with shallow depression on either side of midline, the depressions sometimes delimited ventrally by transverse ridge or carina, and dorsally above depressions smoothly merged into frons so dorsal limit not distinct, but separated from anterior ocellus by distance greater than LOL; ratio of OOL: POL: LOL: MPOD = 1.1: 2.5: 1.6: 1.0. Antenna (Figs 31, 32, 34) dark brown or scape basally variably extensively lighter, yellowish; scape slender, about 4.7× as long as apical width, and slightly curved; flagellum clavate with fl1 longer than wide and at least fl2–fl5 obviously longer than wide, but fl6–fl8 shorter, slightly longer to slightly shorter than wide [length(width) of pedicel and flagellomeres = 16(9), 10(7), 19(8), 19(10), 17(13), 15(13), 15(14), 15(15), 14(15), 37(17)]. Labiomaxillary complex and mandibles same color as head.
Mesosoma (Figs 32, 34) dark brown except axillae sometimes distinctly lighter, yellowish (Fig. 36). Pronotum completely sclerotized (Figs 32, 33); collar meshlike coriaceous and with dark setae mostly in Π-like line from posterolateral angle across collar near middle. Mesoscutum (Fig. 33) meshlike coriaceous to coriaceous-reticulate; with anterior margin abruptly reflexed as strongly transverse band between posterior margin of pronotum, and with lateral lobes only slightly, convexly raised relative to comparatively broad and shallowly concave median region, the lateral lobes not longitudinally carinate but with deep, subcircular pit or opening in cuticle within anterior half (Fig. 33: arrows); with line of comparatively long, variably dark brown setae along inner and outer inclined surfaces of lateral lobe, but broadly bare dorsomedially. Scutellar-axillar complex (Fig. 36) with scutellum elongate-oval and uniformly convex, somewhat more highly than, and only slightly longer than, but conspicuously larger than axillae, with frenum meshlike coriaceous and bare, but coriaceous to coriaceous-imbricate anterior to frenum and with dark setae laterally; axillae elongate-slender, more finely sculptured than scutellum, with at most obscure carinae dorsomedially adjacent to scutellum, with dark setae on outer surface, and anterior to scutellum separated by deep, slightly longer than wide depression. Fore wing (Fig. 36) extending flat over mesosoma to base of gaster; disc elongate-slender, about 3.6× as long as greatest width, almost uniformly light brownish to more distinctly brown basally and subhyaline apically, smooth or at most only very slightly, transversely wrinkled, and mostly bare but with marginal fringe apically, and with line of setae along broader submarginal vein differentiating bare costal cell extending about two-thirds length of disc, and with line of 3 or 4 setae on venation apically (presumptive marginal vein) not quite extending to rounded apical margin. Mesopleurosternum with mesopectus meshlike reticulate anterior to acropleural sulcus below prepectus and more finely coriaceous posteroventrally, with long white setae ventrally and linearly along acropleural sulcus; acropleuron (Fig. 35) posteriorly broadly curved to level of anterior margin of mesocoxa, meshlike coriaceous-imbricate over about anterior one-third, but about posterior two-thirds virtually smooth or medially only very finely, longitudinally coriaceous-strigose and posteriorly with subeffaced, more meshlike sculpture. Metanotum (Fig. 36) with dorsellum vertically raised over apex of scutellum, with only single distinct carina medially. Metapleuron (Fig. 35) entirely setose with long, comparatively dense white setae; anterior margin curved slightly over posterodorsal margin of acropleuron at about midheight but not obviously flange-like reflexed, though anteroventral margin angled posteroventrally over posterodorsal angle of mesocoxa, and ventral margin only slightly reflexed such that ventral region between acropleuron and metacoxa not distinctly differentiated. Legs (Figs 32, 34) similar to or distinctly lighter in color than mesosoma, often yellowish beyond coxae; mesotibia (left) with 4 apical pegs (Fig. 37); metacoxa with two separate bands of white setae, one ventrolaterally and one dorsolongitudinally, and with 1–4 pits in line on outer surface basally. Propodeum (Fig. 36) long, medial length about 0.7× distance between transscutal articulation and posterior margin of dorsellum; posterior margin shallowly, broadly incurved, and anterior margin shallowly incurved medially behind dorsellum; with paramedial longitudinal ridges at about level of lateral margin of dorsellum delimiting slightly concave median plical region from slightly higher lateral callar regions, the paramedial ridge reflexed slightly toward median anteriorly; plical region with complete median carina or carina irregular to obsolete anteriorly, but otherwise finely, irregularly sculptured; callus similarly but more finely sculptured than plical region, with spiracle separated from lateral margin by distance much greater than own diameter and with angulation or ridge lateral to spiracle basally differentiating lateral setose band with long white setae extending length and becoming more numerous posteriorly in region between metapleuron and propodeal foramen.
Metasoma with petiole transverse-quadrangular (Fig. 36). Gaster (Figs 32, 34) entirely dark brown or with green to partly coppery lusters; tergites all similarly sculptured, shiny and variably distinctly meshlike coriaceous, and with comparatively inconspicuous dark setae dorsolaterally, Gt1 with only a couple of setae laterally but setae becoming increasingly more numerous and extensive posteriorly; syntergum in dorsal view with posterior margin transverse to slightly incurved (Fig. 38); supra-anal plate brown; ovipositor sheaths brown, projecting only slightly beyond syntergum.
MALE. Unknown.
Distribution. AFROTROPICAL: Kenya, Tanzania.
Hosts. Unknown.
Remarks. As discussed within the section on monophyly and relationships of the excavatus species-group, M. distigma undoubtedly forms a monophyletic group with M. micropterus, M. reticulatus and M. speculum based on metapleural structure and setation, similar propodeal structures, and similarly structured scutellar-axillar complexes. Females of M. distigma differ from those of all other known Merostenus, brachypterous or not, by the presence of two circular pits laterally on the mesoscutum, on the mesoscutal lateral lobe just within the anterior half (Fig. 33: arrows). I have not seen such pits in any other eupelmid, but presence in the three available females demonstrates it is not an aberration. All three females also have two variably distinct paramedial depressions dorsally within the scrobal depression (Fig. 31) and one or more depressions or pits in a line laterally on the metacoxa basally. The unique holotype of M. speculum also has paramedial depressions at the dorsal limit of the scrobal depression, but lack the mesoscutal and metacoxal pits. Females of M. distigma are intermediate in sculpture between M. reticulatus and those of M. micropterus and M. speculum, the head, mesoscutum and gaster of M. reticulatus being much more coarsely reticulate and those of the latter two species more smooth and shiny. The different sculpture patterns are also correlated with different setal patterns. Females of M. reticulatus are the most densely setose whereas those of M. micropterus and M. speculum the most sparsely setose. Although a relative feature, the difference is most easily quantifiable on the mesoscutum. Females of M. reticulatus have the dorsally concave part of the mesoscutum entirely, uniformly setose (Fig. 100), whereas the setae are reduced to only a single row laterally on the inclined surface of the lateral lobe of M. distigma (Fig. 33) and to just one or two setae laterally on the inclined surface of the lateral lobe in M. speculum (Fig. 118) and M. micropterus (Fig. 86), respectively. Females of M. distigma share comparatively long fore wings extending to the base of the gaster with all but M. micropterus, and a marginal fringe apically with all species except M. reticulatus.
description: Published as part of Gibson, Gary A. P., 2017, Synonymy of Reikosiella Yoshimoto under Merostenus Walker (Hymenoptera: Chalcidoidea: Eupelmidae), with a checklist of world species and a revision of those species with brachypterous females, pp. 1-65 in Zootaxa 4255 (1) on pages 25-28, DOI: 10.5281/zenodo.556479