Tersilochinae (Hymenoptera: Ichneumonidae) of Costa Rica, part 2. Genera Megalochus gen. nov. and Stethantyx Townes

Abstract

Two Costa Rican genera, Megalochus gen. nov. and Stethantyx Townes, are revised. These genera comprise a distinctive generic group that we refer to as the Stethantyx genus-group, veins Rs+2r and Rs angled more than 90°, vein 2rs-m and abscissa of M between 2rs-m and 2m-cu not or very weakly thickened, hind wing with vein cu1&cu-a (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. Both genera include medium sized to large species with body length 4.0 to 15.0 mm. Megalochus comprises only the type species, M. grandis sp. nov., occurring in Costa Rica, Ecuador and southern Brazil. It is the largest representative of the subfamily, with a body length of 10.5 to 15.0 mm. Megalochus differs from Stethantyx, besides the larger body size, by the slenderer first metasomal segment, which is round in cross-section and lacking glymmae, propodeum and metapleuron with coarse rugae, and shortened antennae with strongly transverse flagellomeres. Stethantyx is the dominant, most species-rich genus in the Costa Rican tersilochine fauna and probably in the Neotropical region. Twenty two species of this genus were discovered in

Contribution to the study of the genus Stethantyx Townes (Hymenoptera, Ichneumonidae, Tersilochinae), with the description of a new species from Brazil

“…This genus was considered to be related to the large Neotropical genus Stethantyx, forming with the latter and the monotypic Australian genus Australochus Khalaim (Khalaim 2015) a distinctive group of genera, the Stethantyx genus-group, and originally was distinguished from Stethantyx on the basis of the following features (Khalaim and Broad 2013): A new species from southern and southeast Brazil, Stethantyx durrelli, intermediate between the genera Megalochus and Stethantyx, was recently discovered. This species is apparently closely related to M. grandis as both are almost identical morphologically and in coloration, except (suprisingly!)…”

“…some species possess a right-angled radial cell, short and thick intercubitus and abscissa of cubitus between intercubitus and second recurrent vein, broad pterostigma, epicnemial (prepectal) carina with dorsal end obliterated and first metasomal segment without glymmae, and some undescribed species are not clearly distinguished from the genera Meggoleus, Probles Förster and Tersilochus Holmgren. Thus, most previously used diagnostic features of Stethantyx (Townes 1971, Khalaim andBroad 2013) do not work well for separating all Stethantyx species from other genera, and the limits of Stethantyx, as well as some other tersilochine genera, requires further investigation. Moreover, the generic status of Stethantyx must be confirmed by apomorphic features, while currently all diagnostic characters of this genus seem to be plesiomorphic.…”

“…Stethantyx Townes is a large New World genus comprising 48 described and many undescribed species, most of which are Neotropical (Khalaim and Broad 2013;Khalaim et al , 2015Khalaim and Ruíz-Cancino 2013;Khalaim 2016), as well as S. nearctica Townes which ranges from the northern US to Mexico and S. crassa Horstmann known from Canada to the southern United States (Horstmann 2010). Stethantyx is closely related to the small Neotropical genus Megalochus Khalaim & Broad, with only one widely distributed species, M. grandis Khalaim & Broad. The genera were thought to be related based on the following synapomorphies: 1) fore wing with obtusely angled first and second abscissae of radius; 2) slender and usually long intercubitus and abscissa of cubitus between intercubitus and second recurrent vein; 3) the narrow pterostigma; and 4) dorsal end of epicnemial (prepectal) carina not joining the anterior margin of mesopleuron, continuing dorsoposterior to the subtegular ridge, or evanescent dorsally (Khalaim and Broad 2013).…”

“…Stethantyx is closely related to the small Neotropical genus Megalochus Khalaim & Broad, with only one widely distributed species, M. grandis Khalaim & Broad. The genera were thought to be related based on the following synapomorphies: 1) fore wing with obtusely angled first and second abscissae of radius; 2) slender and usually long intercubitus and abscissa of cubitus between intercubitus and second recurrent vein; 3) the narrow pterostigma; and 4) dorsal end of epicnemial (prepectal) carina not joining the anterior margin of mesopleuron, continuing dorsoposterior to the subtegular ridge, or evanescent dorsally (Khalaim and Broad 2013). The Stethantyx genus-group was established for these two genera, comprising the largest and most conspicuous representatives of the subfamily, and recently the endemic Australian genus Australochus Khalaim was also included in this genus-group (Khalaim 2015).…”

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

“…Stethantyx is a large predominantly Neotropical genus with 42 described and many undescribed species (Yu et al 2012; Khalaim and Broad 2013; Khalaim et al 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).…”