Mexican species of the genus Stethantyx Townes (Hymenoptera, Ichneumonidae, Tersilochinae)

Abstract Six species of the genus Stethantyx Townes are found to occur in Mexico. One species, S. mexicana sp. n., is described as new, and four recently described Neotropical species, S. alajuela Khalaim & Broad, S. heredia Khalaim & Broad, S. osa Khalaim & Broad and S. sanjosea Khalaim & Broad, are new records from Mexico. A key to species of Stethantyx occurring in Mexico is provided.


Introduction
Stethantyx is a large predominantly Neotropical genus with 42 described and many undescribed species (Yu et al. 2012;Khalaim and Broad 2013;. Along with the Neotropical monotypic genus Megalochus Khalaim & Broad, it forms the Stethantyx genus-group, characterized by the fore wing with abscissae of the radius meeting at an obtuse angle (more than 90°), intercubitus and abscissa of cubitus between intercubitus and second recurrent vein not or very weakly thickened, hind wing with nervellus more or less vertical, and prepectal carina with upper end not reaching anterior margin of mesopleuron, continuing above and backwards to the subtegular ridge (Khalaim and Broad 2013). Stethantyx differs from Megalochus by the longer antennae, first metasomal segment stouter and trapeziform in cross-section, presence of glymmae, and smooth or granulate (not rugulose) propodeum and metapleuron.
Only two native species, S. crassa Horstmann and S. nearctica Townes, and S. parkeri (Blanchard), introduced from South America, are known to occur in the Nearctic region (Horstmann 2010). In the Neotropical region, 22 species were recently described from Costa Rica (Khalaim and Broad 2013); in South America, eight species (including S. parkeri) have been described from Argentina, Brazil and Uruguay (Blanchard 1945, Graf 1980, and 16 species (including ten new species), have been found to occur in Western Amazonia . Two unidentified species of Stethantyx were also reported from Cuba (Fernández-Triana et al. 2006). Some species of Stethantyx were reared from the beetle families Nitidulidae and Curculionidae (Coleoptera). In the Nearctic region, S. crassa was reared from Cryptarcha sp. and/or Lobiopa undulata Say (Nitidulidae) from sap spots on oak (Williams et al. 1984, Horstmann 2010, and S. nearctica was reared from Balaninus sp. (Curculionidae) on Quercus alba L. (Fagaceae), probably from acorns (Horstmann 2010). In South America, three species, S. argentiensis (Blanchard), S. parkeri and one unidentified species, all parasitizing vegetable weevils (Curculionidae: Listroderes spp.) (Parker et al. 1950), were introduced to the southern U.S.A. and eastern Australia for the control of Listroderes obliquus Klug, a pest of many cultivated vegetables (Kerrich 1961, Wilson and Wearne 1962, Clancy 1969, Gauld 1984. Only one species, S. nearctica, was previously known from northern Mexico (Horstmann 2010). In this paper we review six Mexican species of Stethantyx, including one new species and four new records. A key for identification of these species is given.

Methods
The ichneumonid collection of the Universidad Autónoma de Tamaulipas, Cd. Victoria, Mexico (further UAT) was studied. One specimen of Stethantyx was borrowed from the Essig Museum of Entomology, University of California, Berkeley, U.S.A. (further EMEC). Some specimens were deposited in the Zoological Institute of the Russian Academy of Sciences, St. Petersburg, Russia (further ZISP).
Morphological terminology predominantly follows Townes (1969Townes ( , 1971 with changes according to Khalaim (2011). Photographs were taken at ZISP with a DFC 290 digital camera attached to a Leica MZ16 stereomicroscope; the partialy focused photographs were assembled with Helicon Focus software. Photographs of wings of S. mexicana sp. n. (Fig. 16) were taken from a microscope slide prepared with Canada balsam.

Stethantyx Townes, 1971
http://species-id.net/wiki/Stethantyx Type species. Stethantyx nearctica Townes, 1971.  6,7,10,11,24,25). Propodeum not as above: with basal keel ( Propodeum with broad basal area (Fig. 26). Propodeal spiracle separated from pleural carina by 1.5-2.0 times diameter of spiracle (Fig. 25). Face black (Fig. 24) Mesoscutum, scutellum and propodeum black, strongly contrasting with remaining mesosoma (Fig. 17)  Comparison. Differs from its North and Central American congeners by the combination of brownish orange mesosoma with black mesoscutum, scutellum and propo-  (Fig. 17), and propodeum with basal keel (Fig. 18). In the key to Costa Rican species of Stethantyx (Khalaim and Broad 2013) it runs to couplet 7 but differs in this couplet from both species, S. tenoriosa Khalaim & Broad and S. mesoscutator Khalaim & Broad, by the propodeum with basal keel (basal area in two other species), and from S. mesoscutator also by the black propodeum. The new species is morphologically similar to S. heredia as both have propodeum with basal keel but differs (besides colour pattern of mesosoma) by the somewhat longer temple and longer second metasomal tergite. Stethantyx mexicana sp. n. is a very distinct species, and despite the fact that it is described only from males, it may easily be distinguished from all known species of Stethantyx.

Key to species of Stethantyx occurring in Mexico
Description. Male. Body length 4.8 mm. Fore wing length 3.45 mm. Head: Roundly narrowed behind eyes in dorsal view (Fig. 10); temple almost 0.6 times as long as eye width. Mandible with upper tooth much longer than lower tooth (Fig. 12). Clypeus lenticular, flat in lateral view, about 2.5 times as broad as long, smooth, punctate on upper 0.3 (Fig. 11). Malar space 0.2 times as long as basal width of mandible (Fig. 13). Flagellum of antenna with over 28 segments (tips of all antennae absent), distinctly tapered towards apex; all flagellomeres, except the basal one, 1.3-1.4 times as long as broad (Fig. 14); flagellomeres 4 to 14 bear finger-shaped subapical structures on outer surface. Face and frons finely and densely punctate on finely granulate dull background. Vertex finely and densely punctate (punctures distinct medially and indistinct laterally) on very finely granulate, weakly shining background. Temple with very fine, mostly indistinct punctures, weakly shining. Face with weak prominence centrally. Occipital carina complete.
Wings: Fore wing (Fig. 16) with first and second sections of radius angled about 130°. Intercubitus 1.5-2.0 times as long as abscissa of cubitus between intercubitus and second recurrent vein. Metacarp almost reaching apex of fore wing. Hind wing (Fig. 16) with nervellus distinctly inclivous.
Legs: Slender (Fig. 15). Hind femur slightly clavate, 4.7 times as long as broad and 0.8 times as long as tibia. Hind spurs slightly curved at apex. Tarsal claws rather long, not pectinate.

Metasoma:
First tergite slender, 4.6 times as long as posteriorly broad, entirely smooth. Glymma situated somewhat behind centre of tergite, moderately large, groove between glymma and ventral part of postpetiole weak but distinct in two paratypes and absent in the holotype. Second tergite almost 2.6 times as long as anteriorly broad (Fig. 19). Thyridial depression very long, more than 5.0 times as long as broad (Fig. 19). Coloration: Head black with lower part of face slightly reddish brown, clypeus and malar space yellow. Palpi and mandible (teeth reddish black) yellow. Scape and pedicel of antenna dark brown or brownish black; flagellum black, probably without pale band. Mesosoma brownish orange; propleuron and lower part of pronotum yellowish; mesoscutum, scutellum and propodeum dark brown or black, strongly contrasting with remaining mesosoma. Tegula fuscous. Pterostigma dark brown. Legs yellow to brownish yellow; hind leg with coxa with brown mark on extero-outer surface, femur brown to dark brown, and tibia and tarsus blackish. First tergite black. Metasoma behind first tergite predominantly dark brown (almost black dorsally), ventrally yellowish, second and following tergites with pale band posteriorly.
Female unknown. Variability. The three specimens are very uniform, with minor variation in structure and coloration. One paratype has the basal keel of the propodeum centrally indistinct.

Discussion
Four species of Stethantyx, previously known from Costa Rica and South America, were recorded mostly from central and southern parts of Mexico and, along with the new species, belong to the Neotropical complex of species. Only one species, S. nearctica, occurring in northern Mexico and U.S.A., belongs to the Nearctic complex of species. All Mexican species of the Neotropical complex were collected in summer (June to August), while the flight period of S. nearctica in Mexico is from October to January. In comparison with Costa Rica, where many species of Stethantyx are rather abundant through the year, in Mexico this genus seems to be rather rare because all Mexican species are represented by single or few specimens in available material.