Eusterinx (Eusterinx) apicicornis, Humala, 2025

Humala, A. E., 2025, A review of Mexican species of the genus Eusterinx (Hymenoptera: Ichneumonidae: Orthocentrinae), Zoosystematica Rossica (China) 34 (1), pp. 149-159 : 151-155

Eusterinx (Eusterinx) apicicornis sp. nov.

( Figs 1–9)

Holotype. Female, Mexico, Tlaxcala, Nanacamilpa, San Felipe Hidalgo, 19°27ʹ35.2ʺN 98°35ʹ46.9ʺW, 2831 m a.s.l., MT 6 , 3 May – 2 June 2016, A. Contreras & Y. Marquez leg. ( UNAM).

Paratypes. Mexico, Tlaxcala: same data as for holotype, 1 female ( NHMUK), 6 males ( UNAM), 3 males ( ZISP) ; same data but 19°27ʹ22.4ʺN 98°35ʹ39.8ʺW, MT 5 , 4 Apr. – 3 May 2016, 1 female ( ZISP) ; Nanacamilpa, Eejido Los Búfalos , 19°28ʹN 98°35ʹW, 2830–2900 m a.s.l., bosque pino-encino [pine–oak forest], MT, 4 Apr. – 3 May 2016, A. Contreras & Y. Marquez leg., 1 male ( NHMUK) ; same data but 3 May – 2 June 2016, 2 males ( UNAM) .

Description. Female ( Figs 1–6). Body length

4.1 mm; fore wing length 3.2 mm.

Head 1.2 times as wide as high in frontal view; face at level of antennal sockets 1.6 times as wide as high, 0.55 times as wide as head. Inner orbits nearly parallel; face reticulate coriaceous, with sparse long setae ( Fig. 3). Antenna with 20–21 flagellomeres; first flagellomere about 4.3 times as long as wide; second flagellomere 1.8 times as long as wide; subapical flagellomeres subquadrate ( Fig. 2). Occipital carina complete, well-developed; temple comparatively wide, 0.8 times as wide as eye in dorsal view. Ocelli of moderate size; oculo-ocellar line 1.4 times and postocellar line 1.1 times as long as maximum diameter of lateral ocellus ( Fig. 5). Anterior tentorial pits large, open. Clypeus twice as wide as high in anterior view, well separated from face by distinct groove, convex near base, otherwise almost flat, its lower edge arched. Malar space 1.8 times as long as basal mandibular width, with subocular sulcus as strip of strigose sculpture ( Fig. 3). Mandibles slender, bidentate, strongly twisted inwards; lower tooth small and invisible in frontal view. Clypeus, frons, vertex, and gena polished, with scattered fine setiferous punctures.

Mesosoma 1.45 times as long as high, subpolished. Mesoscutum polished, with abundant long setae; notauli strongly developed as crenulated furrows, deep and sharp anteriorly, extending to middle of mesoscutum (as in Fig. 9); epomia present; epicnemial carina complete, reaching middle of mesopleuron ( Fig. 1). Mesopleuron polished, with sparse setae at upper anterior corner, denser at lower part; metapleuron coriaceous. Sternaulus short but distinct, adjacent to epicnemial carina ventrolaterally. Propodeum coriaceous with all carinae complete; area superomedia hexagonal, well-defined, 1.9 times as long as wide, slightly narrowed posteriorly ( Fig. 4). Area basalis strongly transverse, weakly delineated from area superomedia. Dorsal surface of propodeum almost bare, densely setose laterally ( Figs 1, 4). Propodeal spiracle round, small.

Fore wing without areolet; second recurrent vein (2m-cu) with two bullae; nervulus (1cu-a) interstitial (opposite to base of basal vein M&Rs); hind wing with nervellus (Cu&cu-a) reclivous, not intercepted (distal abscissa of Cu absent). Legs slender; hind coxa coriaceous; hind femur 5.1 times as long as wide and 0.75 times as long as hind tibia; hind basitarsus 0.47 times as long as hind tibia; fifth tarsomere as long as second tarsomere. Tarsal claws simple.

First tergite of metasoma 2.4 times as long as wide posteriorly, arcuate in profile, with distinct dorsal carinae, row of long setae on each lateral side and scattered setiferous punctures; sternite fused with tergite; glymma absent; spiracle at 0.54 times and apex of sternite at 0.57 times of first tergite length. Second tergite 1.1 times as long as wide posteriorly, with distinct round thyridium which adjacent to anterior margin of tergite ( Fig. 6). First tergite and anterior half of second tergite coriaceous, remaining tergites subpolished; epipleurae of tergites 2–4 separated by crease. Tergites 2 to 6 with long sparse setae. Ovipositor slightly upcurved, its tip strongly tapered, needle-shaped. Ovipositor sheath 0.4 times as long as hind tibia, with fine setae on lateral margins.

Coloration. Predominantly black species; clypeus, mandible and tegula brown; scape, pedicel, mouthparts and legs yellow; hind coxa, apical tarsomeres, thyridium, posterior margin of second tergite, anterior half and posterior margin of third tergite light brown; apical 3–4 flagellomeres pale yellowish. Wings hyaline, veins and pterostigma brown.

Male ( Figs 7–9). Similar to female. Antenna with 20–22 flagellomeres; first flagellomere about 3.6 times as long as wide; tyloids not developed, but flagellomeres 9–11 with bare areas devoid of distinct sensilla laterally ( Fig. 8). Coloration as in female, excluding predominantly yellowish clypeus and mandible, and fuscous tip of antenna ( Fig. 7).

Comparison. Eusterinx apicicornis sp. nov. can be distinguished from its congeners by the combination of the following characters: inner orbits in female subparallel ( Fig. 3); apical flagellomeres in female pale yellowish ( Fig. 2); fore wing with areolet lacking (vein 3rs-m absent) and nervulus interstitial ( Fig. 1); notauli strong, extending to the middle of mesoscutum ( Fig. 9); propodeum with area superomedia elongate, 1.9 times as long as its maximum width ( Fig. 4); first tergite slender, 2.4 times as long as wide posteriorly; male flagellomeres without tyloids ( Fig. 8).

From the Nearctic E. georgiana Dasch, 1992 , known from a single male from the USA ( Georgia), the new species differs in the absence of longitudinal striae on tergites 1 and 2, slenderer hind femur, coriaceous propodeum and the absence of propodeal apophyses. From the Holarctic E. subdola Förster, 1871 , it differs in the longer first flagellomere (about 4.3 times as long as wide in E. apicicornis vs. 2.65–3.0times in E. subdola ), upcurved ovipositor (straight in E. subdola ), longer malar space( Fig. 3) (1.8times as long as basal mandibular width in E. apicicornis sp. nov. vs. 1.25– 1.5 times in E. subdola ) and yellow hind coxa (fuscous in E. subdola ). From E. australis , the new species differs in the upcurved ovipositor (straight in E. australis ), predominantly fuscous metasomal tergites (tergites 1–3 rufous in E. australis ), and coriaceous propodeum (polished in E. australis ). From E. subtilis Dasch, 1992 , known only from females, the new species can be distinguished by its larger size, shorter ovipositor sheath ( Fig. 1) (0.4 times as long as hind tibiain E. apicicornis sp. nov. vs. 0.9 times in E. subtilis ), flagellum with 20–22 flagellomeres (14–16 flagellomeres in E. subtilis ), and notaulus not margined anteriorly by a carina.

Etymology. The species name is an adjective derived from the Latin words “ apex ” (tip) and “ cornu ” (horn), referring to the pale yellowish apical flagellomeres of the female.

Distribution. Mexico (Tlaxcala).