Megalochus Khalaim & Broad

Khalaim, Andrey I. & Broad, Gavin R., 2013, Tersilochinae (Hymenoptera: Ichneumonidae) of Costa Rica, part 2. Genera Megalochus gen. nov. and Stethantyx Townes, Zootaxa 3693 (2), pp. 221-266 : 225-227

Megalochus Khalaim & Broad , gen. nov.

Type species: Megalochus grandis Khalaim et Broad , sp. nov.

Comparison. The new genus is related to Stethantyx , but differs from this genus by the slenderer first metasomal segment, lacking glymmae ( Fig. 21 ), shortened antennae ( Fig. 20 ), and propodeum and metapleuron with coarse irregular rugae ( Fig. 23 ). These two genera form a distinctive group of genera, which we call the Stethantyx genusgroup, an addition to the three groups, Diaparsis , Phradis and Tersilochus genus-groups, suggested for European tersilochines by Horstmann (1981).

The Stethantyx genus-group differs from the other tersilochine genera by the fore wing with veins Rs +2 r and Rs angled more than 90° ( Figs 1–10 ), vein 2 rs-m and abscissa of M between 2 rs-m and 2 m-cu not or rather weakly thickened, and hind wing with vein cu 1& cu-a more or less vertical (usually reclivous in other tersilochine genera), and predominantly larger body size (4.2–15.0 mm). The wing venation of both genera seems plesiomorphic with respect to the usual tersilochine wing venation, with the unmodified veins 2 rs-m and M, the obtuse angled veins Rs +2 r and Rs and the narrow pterostigma. Megalochus is particularly un-derived, with hind wing vein M+Cu almost straight (strongly curved in all other tersilochine genera) and entirely pigmented, although not tubular basally (largely unpigmented, basally absent in other genera); the sub-basal cell is thus long and narrow, uniquely in the Tersilochinae . The wing venation, together with the short flagellomeres and narrowed proboscidial fossa are similar to the character states found in many Brachyscleromatinae, which may be closely related (cf. Quicke et al. 2009). It is tempting to speculate that Megalochus is a basal tersilochine that may partly bridge the gap between these two subfamilies, although this requires a phylogenetic test.

Diagnosis. Large species with body length 10.5–15.0 mm. Head strongly rounded behind eyes in dorsal view. Upper tooth of mandible longer than lower tooth. Clypeus large, lenticular, coarsely and densely punctate except lower margin. Malar space 0.5–0.6× as long as basal width of mandible. Flagellum of antenna unusually short, narrowed towards apex, with 27–36 flagellomeres ( Fig. 20 ); all flagellomeres, except the basal and the apical ones, distinctly transverse. Occipital carina complete. Hypostomal carina absent. Mesoscutum flattened, low in lateral view ( Fig. 22 ). Notaulus weak. Prepectal carina not joining to anterior margin of mesopleuron, dorsally indistinct ( Fig. 22 ). Subtegular ridge strongly raised in frontal view, projecting laterally. Foveate groove of mesopleuron deep and long, coarsely crenulate, weakly curved, extending from anterior margin of mesopleuron to base of mid coxa ( Fig. 22 ). Propodeum and metapleuron coarsely and irregularly rugose ( Fig. 23 ). Distance between spiracle and pleural carina about half diameter of spiracle. Fore wing with vein 2 m-cu postfurcal. Veins Rs +2 r and Rs angled about 125°. Vein 2 rs-m twice longer than abscissa of M between 2 rs-m and 2 m-cu, both these veins not thickened.

Hind wing with vein cu 1& cu-a subvertical. Hind femur distinctly clavate ( Fig. 21 ). Spurs of hind tibia weakly curved at apex. Tarsal claws not pectinate. Metasomal segment 1 slender, without glymma, round in cross-section ( Fig. 21 ). Thyridial depression very long. Ovipositor upcurved, without teeth.

Etymology. From the Greece mega (large) and the latter part of the generic name Tersilochus , on account of the large body size. Gender masculine.

Composition. Only one species is known, M. grandis sp. nov., described below.

Figures

FIGURES 20 – 23. Megalochus grandis sp. nov., Ƥ: 20 — head with antennae, frontal; 21 — hind leg and base of metasoma, left; 22 — mesosoma, left; 23 — propodeum, posterolateral. Scale bars = 0.2 mm.

FIGURES 1 – 6. Wings of Stethantyx spp., Ƥ: 1 — S. ajajuela sp. nov.; 2 — S. curvator sp. nov.; 3 — S. guanacasteca sp. nov.; 4 — S. heredia sp. nov.; 5 — S. niger sp. nov.; 6 — S. notaulator sp. nov.

FIGURES 7 – 10. Wings of Stethantyx spp., Ƥ: 7 — S. orosia sp. nov.; 8 — S. propodeator sp. nov.; 9 — S. puntarenasa sp. nov.; 10 — S. sanjosea sp. nov.