Merostenus (Merostenus) mexicanus Gibson, 2017, n. sp.

M. (Merostenus) mexicanus n. sp. Figs 74–82 Type material. Holotype ♀ (TAMU). “ MEXICO: Guerrero | 7mi W. Chilparlingo | ca. 7000', 15.VII.1987 | J.B. Woolley, 84-033-13 / HOLOTYPE ♀ | M. (Merostenus) | mexicanus | Gibson”. Point-mounted by meso- and metacoxae; entire but left fore wing detached and glued separately to point; strongly contorted. Etymology. Named after the country of collection. Description. FEMALE (habitus: Figs 74, 75). Length about 2 mm. Head (Fig. 76) yellow to light brownishyellow under some angles of light; in frontal view subquadrate, about 1.2× as wide as high, and in lateral view about 1.6× as high as long with frontal surface convex; shiny and almost smooth but with obscure meshlike sculpture along inner orbits, lower face and vertex; with dark setae except scrobal depression and dorsal surface of interantennal prominence bare, with setae on frons mostly separated by distance greater than MPOD; scrobal depression comparatively shallow but Π-shaped above interantennal prominence with lateral margin directed dorsally at level of outer margin of torulus so distinct parascrobal region differentiated and broadly arched margin separated from anterior ocellus by distance similar to POL; ratio of OOL: POL: LOL: MPOD = 1.0: 2.4: 1.4: 1.0. Antenna (Fig. 77) with scape, pedicel, and fl1 and fl2 yellow (Fig. 76), the remainder dark brown except clava ventrally lighter brown; scape spindle-shaped, widest subbasally, with length about 4× greatest width; flagellum clavate with fl1 subquadrate, fl2–fl4 longer than wide, but fl5–fl8 quadrate to slightly transverse [length(width) of pedicel and flagellomeres = 15(8), 7(7), 10(7), 10(8), 12(10), 11(11), 11(12), 10(13), 14(14), 31(14)]. Labiomaxillary complex and mandibles same color as head except mandibles reddish-brown apically. Mesosoma (Figs 74, 75) yellow to light brownish-yellow under some angles of light. Pronotum completely sclerotized; neck meshlike coriaceous, dorsal view of collar concealed by mesoscutum but at least with scattered dark setae. Mesoscutum (Fig. 79) meshlike reticulate; anterior margin largely concealed by pronotum, but apparently narrowly reflexed; lateral lobes comparatively low angulate on either side of broad, shallowly concave median region, the lateral lobes abruptly but not carinately margined dorsolongitudinally; dorsally concave part setose with dark setae except posteromedially, and with line of similar setae along outer inclined surface of lateral lobe. Direct dorsal view of scutellar-axillar complex (Figs 78, 79) obscured by gaster but elongate-slender scutellum lowly convex posteriorly and tapered anteriorly to acute angle widely separated from transscutal articulation, with about anterior half carinately margined mediolongitudinally, and with line of 3 setae along length anterior to bare frenum; axillae elongate-slender, almost flat and below plane of scutellum, but dorsomedially with longitudinal carina extending from scutellum on either side of median, with 3 setae on outer surface, and anterior to scutellum separated by elongate depression. Fore wing (Fig. 77: insert) right-angle bent at about level of posterior margin of scutellar-axillar complex near apex of costal cell; with dark, setose, submarginal vein differentiating slender costal cell within about basal one-quarter, and vein continued along leading margin as apically tapered, dark, setose marginal vein; with membrane posterior to venation only within about basal half, the portion basal to the bend bare except for 1 seta basally on dorsal surface, but distally tapered apical portion of disc entirely setose dorsally. Mesopectus (Fig. 80) with white setae posteroventrally and narrowly along acropleural sulcus anteriorly; acropleuron (Fig. 80) broadly curved posteriorly to level of anterior margin of mesocoxa, transversely coriaceousalutaceous anteriorly, smooth and shiny medially and very finely and inconspicuously meshlike coriaceous posteriorly. Metanotum concealed by gaster. Metapleuron not visible from posterior view but bare, shiny and at most obscurely coriaceous, and with only ventral margin above base of metacoxa distinctly reflexed, the anterior margin directed horizontally rather than vertically behind acropleuron because mesonotum flexed, but triangular region below anterior margin with dark spots suggesting presence of setose ventral region between acropleuron and metacoxa (Fig. 80). Legs (Fig. 74) yellow to light brownish-yellow similar to rest of body; mesotibia with row of 3 or 4 apical pegs; metacoxa with outer surface setose basally, the setae continued apically along ventrolateral margin, but apparently bare dorsolongitudinally. Propodeum (Fig. 79) comparatively long (relative length not measureable) with posterior margin shallowly, broadly incurved, with plical region quite highly angulate so as to be differentiated by deep depression from convex callar regions, with median carina and at about mid-length with transverse carina between median carina and callar region, and shiny with at most obscure meshlike sculpture; callus with position of spiracle relative to lateral margin not clearly visible, but with slender band of white setae extending from convex surface mesal to inner margin at about level of posterior margin of spiracle to posterolateral margin of propodeal foramen. Metasoma with petiole transverse-quadrangular. Gaster (Figs 74, 75) light brownish-yellow or under some angles of light somewhat darker brown than mesosoma except for subbasal pale band dorsally consisting of Gt2 and about apical half of Gt1, and with most sternites similarly pale; tergites finely meshlike coriaceous and inconspicuously, sparsely setose; syntergum in lateral view (Fig. 81) curved up relative to dorsal plane of gaster beyond fine, dark, transverse carina connecting cerci, and in dorsal view tapered posteriorly as broadly rounded syntergal flange, the dorsal surface uniformly setose with setae along posterior margin but these not differentiated from other setae (Figs 81, 82); supra-anal plate not visible but with subanal plate appressed to ventral surface of syntergum above ovipositor sheaths (Fig. 82); ovipositor sheaths mostly yellow but brown apically, projecting only slightly beyond syntergum. MALE. Unknown. Distribution. NEARCTIC: Mexico (Guerrero). Hosts. Unknown. Remarks. Merostenus mexicanus is the only excavatus -group species in the New World excluding M. excavatus, which apparently was introduced accidentally into eastern Canada. Unfortunately, the holotype is strongly contorted so that not all body parts can be described accurately or confidently. However, the holotype differs from all other Merostenus females in having the syntergum tapered posteriorly and curved upwards relative to the dorsal plane of the gaster, i.e. developed into a syntergal flange. It is also the only brachypterous species of Merostenus with the fore wings right-angle bent (Fig. 77: insert) rather than held flat over the body, and the only excavatus -group species with a setose disc and with the gaster subbasally pale dorsally and extensively pale ventrally (Figs 74, 75), though M. congoensis (Fig. 29) and M. reticulatus (Fig. 99) have Gt2 hyaline.

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