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JHR 55: 129-138 (2017) JOURNAL OF *0errviewed opevaccers ural
doi: 10.3897/jhr.55.5322 (f-) Hymenoptera

http://jhr.pensoft.net The Inerational Society of ymenoptersts. RESEARCH

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

Andrey I. Khalaim'?

I Zoological Institute, Russian Academy of Sciences, St. Petersburg, Russia 2 Facultad de Ingenierta y Ciencias,
Universidad Auténoma de Tamaulipas, Cd. Victoria, Mexico

Corresponding author: Andrey I. Khalaim (ptera@mail.ru)

Academic editor: G. Broad | Received 19 May 2015 | Accepted 21 March 2017 | Published 28 April 2017
http://zoobank.org/1E275640-D5 C6-4048-ACBB-A1 7FFEC2D098

Citation: Khalaim AI (2017) Contribution to the study of the genus Stethantyx Townes (Hymenoptera, Ichneumonidae,
Tersilochinae), with the description of a new species from Brazil. Journal of Hymenoptera Research 55: 129-138. https://
doi.org/10.3897/jhr.55.5322

Abstract

A new species, Stethantyx durrelli sp. n. from Brazil, is described and illustrated. The recently described
genus Megalochus Khalaim & Broad is synonymized with Stethantyx. The new species is very similar to
S. grandis (Khalaim & Broad), comb. n. but differs by the first metasomal segment being trapeziform
in cross-section, the presence of a distinct glymma, and the metapleuron and dorsolateral area of the
propodeum being densely punctate, without coarse irregular rugae. These two species are the largest and
most conspicuous representatives of the subfamily Tersilochinae. A partial key to species of Stethantyx is

provided. Taxonomy and generic limits of Stethantyx are discussed.

Keywords

Neotropical region, South America, Megalochus, taxonomy, new species, new synonymy, key

Introduction

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. 2013, 2015; Khalaim and Ruiz-Cancino 2013; Khalaim 2016), as well

as S. nearctica Townes which ranges from the northern US to Mexico and S. crassa

Copyright Andrey I. Khalaim. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0),
which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

130 Andrey I. Khalaim / Journal of Hymenoptera Research 55: 129-138 (2017)

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). 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).

Nothing is known about the biology and host preferences of Megalochus but some
species of Stethantyx were recorded as parasitoids of the beetle families Nitidulidae and
Curculionidae (Parker et al. 1950, Williams et al. 1984, Horstmann 2010). Although
the genus Stethantyx has been extensively studied in recent years, a large number of
species is still undescribed.

The aim of this work is to describe a new species of Stethantyx from Brazil, recon-
sider the classification of Megalochus and provide a partial key to species of Stethantyx.
The taxonomy of the genus Stethantyx is also briefly discussed.

Materials and methods

Material of South American Tersilochinae from the Utah State University, Logan,
Utah, USA (EMUS, Townes collection) and the Florida State Collection of Arthro-
pods, Gainesville, Florida, U.S.A. (FSCA) was examined. In this material, a new spe-
cies of Stethantyx was found.

Morphological terminology generally follows Townes (1969) with changes ac-
cording to Khalaim (2011). Photographs were taken at the Instituto de Biologia,
Universidad Nacional Auté6noma de México, D.F., México (UNAM) with a Leica
DFC290 HD digital camera attached to a Leica Z6 APO stereoscopic microscope.

Partly focused images were combined using the Leica Application Suite program.

Results and taxonomy

The genus Megalochus was described for a single species, M. grandis, occurring from
Costa Rica to southern 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 Stethan-
tyx genus-group, and originally was distinguished from Stethantyx on the basis of the
following features (Khalaim and Broad 2013):

Contribution to the study of the genus Stethantyx Townes... 134

Megalochus Stethantyx
a shortened; flagellomeres strongly not shortened; flagellomeres weakly
transverse transverse to elongate
Propodeum and metapleuron with coarse irregular rugae without rugae
Sub-basal cell in hind wing unusually long and narrow not especially narrow

trapeziform centrally in cross-section,
3.3—5.0 times as long as posteriorly

broad
Glymma lacking present

; round in cross-section, very slender, about
First metasomal segment ;
6.6 times as long as posteriorly broad

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 morphologi-
cally and in coloration, except (suprisingly!) for two important diagnostic characters
of the genus Megalochus: in S. durrelli, the glymma is present (Figs 15, 16) and the
propodeum and metapleuron are without rugae (Figs 10, 11). In addition, some other
species of Stethantyx also have shortened antennae (though not as short as in M. gran-
dis and S. durrelli) and some recently discovered species of Stethantyx (Khalaim et al.
2013) also have the first tergite very slender, upto 5.5 times as long as anteriorly broad
in female (6.6 times in M. grandis and 5.4 times in S. durrelli). Only one of the previ-
ous five diagnostic features of Megalochus works well for both species: the hind wing
mediella (M+Cu) is very weakly arcuate and subparallel to the submediella (1A), thus
the sub-basal cell is unusually long, 5.0-6.0 times as long as broad (2.8—4.0 times in
Stethantyx; compare Fig. 14 and Khalaim and Broad 2013: Figs 1-10). Thus, most of
the diagnostic features of Megalochus do not distinguish the two genera with certainty
and therefore this genus is synonymized here with Stethantyx (syn. n.). Stethantyx dur-
relli and S. grandis (comb. n.) can be distinguished from each other, as well as from
other congeners using the key below.

Portion of the key to species of Stethantyx

1 Fore wing with first and second abscissae of radius meeting at obtuse angle
(Pig 13) + Srethaniye Nearcli Ed SPECHESHCLOUD -v.0 aeansue desde ceessbepitcesbstehesbsantia ves 2
— Fore wing with first and second abscissae of radius meeting at right angle. Stetha-
ntyx radiata SpeCies-LOUP .......eeeee See key to species by Khalaim et al. 2015
2 Hind wing with mediella (M+Cu) very weakly arcuate and subparallel to sub-
mediella (1A), thus the sub-basal cell is unusually long, 5.0-6.0 times as long
as broad (Fig. 14). Large species with body length 10.5 to 15.0 mm............. 3
= Hind wing with mediella (M+Cu) distinctly arcuate; sub-basal cell not unu-
sually long, 2.8—4.0 times as long as broad. Small to moderately large species
with body length usually 4.0 to 10.0 mm... See keys to species by Khalaim
and Broad 2013, Khalaim et al. 2013, Khalaim and Ruiz-Cancino 2013

132: Andrey I. Khalaim / Journal of Hymenoptera Research 55: 129-138 (2017)

3 First metasomal segment round in cross-section, without glymma. Metapleu-
ron and dorsolateral area of propodeum with coarse irregular rugae. Fore
wing with intercubitus about twice as long as abscissa of cubitus between
intercubitus and second recurrent vein. Hind wing with nervellus slightly
inclivous or vertical. Female with hind femur strongly clavate. Ovipositor
with shallow dorsal subapical depression; sheath about 1.4 times as long as
URI oldest Kong inl Minas ohn Aner he S. grandis (Khalaim & Broad), comb. n.

— First metasomal segment trapeziform in cross-section, with a deep glymma
(Figs 15, 16). Metapleuron and dorsolateral area of propodeum densely
punctate on finely granulate background, without coarse rugae, at most with
fine wrinkles peripherally (Figs 10, 11). Fore wing with interubitus about 5.0
times as long as abscissa of cubitus between intercubitus and second recurrent
vein (Fig. 13). Hind wing with nervellus strongly inclivous (Fig. 14). Female
with hind femur weakly clavate (Fig. 12). Ovipositor with a sharp dorsal sub-
apical notch, distal margin of this notch is almost vertical (Fig. 18); sheath
almost twice as; long :as-TiStiter Gite ve scceewesuceisleedicattsiitt- S. durrelli sp. n.

Stethantyx durrelli Khalaim, sp. n.
http://zoobank.org/8057ADFA-7E53-465E-A982-8CA6BC87316E
Figs 1-21

Comparative diagnosis. Stethantyx durrelli sp. n. is very similar to S. grandis but dif-
fers from it by the metapleuron and dorsolateral area of propodeum densely punctate
on a finely granulate background (Figs 10, 11, 20), without coarse, irregular rugae;
fore wing with intercubitus 5.0 times as long as abscissa of cubitus between intercu-
bitus and second recurrent vein (Fig. 13) (versus 2.0 times in S. grandis); hind wing
with nervellus strongly inclivous (Fig. 14) (slightly inclivous to vertical in S. grandis);
hind femur of female weakly clavate (Fig. 12); first metasomal segment trapeziform
in cross-section and with deep glymma (Figs 15, 16, 21); and ovipositor with a sharp
dorsal subapical notch (Fig. 18). Moreover, the new species is generally paler than S.
grandis and has a somewhat longer ovipositor. These two species are the largest known
Tersilochinae with body length 10.5 to 15.0 mm (the largest specimens of Barycnemis
and Stethantyx have body lengths up to 10.0 mm), and can be distinguished from their
congeners using a partial key to species of Stethantyx above.

Description. Female. Body length 13.0 mm. Fore wing length about 9.2 mm.

Head rounded posterior to eyes in dorsal view (Fig. 4); temple 0.7 times as long as
eye width. Mandible finely and densely punctate basally, upper tooth distinctly longer
than lower. Clypeus broad, lenticular, 3.2 times as long as broad (Fig. 3), separated
from face by shallow broad impression, densely and coarsely punctate in upper half,
smooth and impunctate in lower half, weakly convex in lateral view. Malar space half
as long as basal mandibular width. Maxillary and labial palpi short (Fig. 5). Flagellum
of antenna short, distinctly narrowed towards apex, with 36 flagellomeres (Fig. 1); all

Contribution to the study of the genus Stethantyx Townes... 155)

Figures |-7. Stethantyx durrelli sp. n., female, holotype: I antenna, lateral view 2 base of antenna,

lateral view 3 head, frontal view 4 head, dorsal view 5 head, ventro-postero-lateral view 6 mesoscutum,

dorsolateral view 7 head and scutellum, dorsolateral view.

flagellomeres, except basal and apical ones, distinctly transverse; flagellomeres 2 to 7—9
(weak and inconspicuous on flagellomeres 8 and 9) bearing finger-shaped subapical
structures on outer surface (Fig. 2). Inner eye orbits very weakly convergent ventrally
(Fig. 3). Face with rather dense and long brownish setae, centrally with blunt promi-
nence. Face and frons densely punctate (distance between punctures mostly shorter
than one puncture diameter), very finely granulate to almost smooth between punc-
tures, dull. Vertex and temple with moderately dense punctures, smooth and weakly
shining between punctures. Occipital carina complete. Hypostomal carina completely

absent (Fig. 5).

134 Andrey I. Khalaim / Journal of Hymenoptera Research 55: 129-138 (2017)

Notaulus rather long, weakly impressed, with a strong longitudinal wrinkle and
sometimes with weak adjacent wrinkles (Figs 6, 7). Mesoscutum densely punctate (dis-
tance between punctures shorter than one puncture diameter), dull, finely granulate
between punctures (Fig. 6). Scutellum with moderately dense punctures, dull, finely
granulate between punctures, with lateral longitudinal carinae strong, developed in its
anterior 0.7 (Fig. 9, arrow). Epicnemial carina not joining anterior margin of meso-
pleuron, evanescent above (Fig. 8). Foveate groove of mesopleuron long, moderately
broad, crenulate, extending almost entire length of mesopleuron, weak anteriorly (eva-
nescent near epicnemial carina) and very deep and sharp centrally and posteriorly (Fig.
8). Mesopleuron distinctly and densely punctate, with impunctate area above foveate
groove in its anterior part, smooth between punctures centrally and finely granulate
peripherally (Fig. 8). Dorsolateral area of propodeum and metapleuron very densely
punctate, dull (Figs 10, 11); lower part and periphery of dorsolateral area with shallow
irregular wrinkles. Basal area of propodeum slightly widened anteriorly, 1.6 times as
long as anteriorly broad and 0.65 times as long as apical area; basal longitudinal carinae
weak (Figs 10, 11). Propodeal spiracle separated from pleural carina by 1.0-1.5 times
diameter of spiracle (Fig. 8). Apical area anteriorly widely truncate, subrectangular
(apical longitudinal carinae parallel), almost twice as long as broad (Figs 10, 11), flat,
very densely punctate, dull.

Fore wing (Fig. 13) with second recurrent vein (2m-cu) weakly postfurcal. First
and second abscissae of radius (Rs+2r and Rs) angled about 120°. Intercubitus (2rs-m)
not thickened, very long, about 5.0 times as long as abscissa of cubitus (M) between
intercubitus and second recurrent vein. First abscissa of radius almost straight, 2.5
times as long as width of pterostigma. Metacarpus (R1) not reaching apex of fore wing.
Hind wing with nervellus (cul &cu-a) strongly inclivous (Fig. 14).

Hind femur slightly clavate (Fig. 12), 4.7 times as long as broad, and 0.75 times as
long as tibia. Hind basitarsus half as long as tibia. Spurs of hind tibia distinctly curved
at apex.

First metasomal segment very slender, 5.4 times as long as posteriorly broad, tra-
peziform in cross-section, arcuate in lateral view, smooth, with glymma situated some-
what behind its middle (Fig. 15). Glymma deep, joining ventral part of postpetiole
by weak groove (Fig. 16). Second tergite 2.3 times as long as anteriorly broad (Fig.
17). Thyridial depression long (Fig. 17); thyridium slightly elongate, separated from
anterior margin of second tergite by 3.5 times times maximum diameter of thyridium.
Ovipositor upcurved, with a deep dorsal subapical notch; sheath 1.9 times as long as
first tergite and 1.75 times as long as hind tibia.

Head black; palpi, lower half of clypeus and mandible (except black teeth) brown-
ish yellow. Antenna with scape and pedicel dark brown, flagellum black. Mesosoma
(including tegula) black. Pterostigma pale brown. Legs brownish yellow; all coxae
black; trochanters brown to brownish black; fore and mid femora brownish; hind
femur brown, on lower and inner sides brownish black. Metasomal tergite 1 black,
following tergites brown. Wings infumate with yellow-brown.

Contribution to the study of the genus Stethantyx Townes... 135

Figures 8-14. Stethantyx durrelli sp. n., female, holotype: 8 mesosoma, lateral view 9 mesoscutum and

scutellum, lateral view 10 propodeum, dorsal view || propodeum, dorso-postero-lateral view 12 hind

femur and tibia, lateral view 13 apex of fore wing 14 basal part of hind wing.

Male. Body length 10.5—13.0 mm, fore wing length 8.4—9.5 mm. Flagellum with
38 flagellomeres (Fig. 19); flagellomeres 3 to 8—10 (weak and inconspicuous on flagel-
lomeres 9 and 10) bearing finger-shaped subapical structures on outer surface. Malar
space 0.4 times as long as basal mandibular width. Propodeal spiracle separated from
pleural carina by 0.5—1.0 times diameter of spiracle. Basal area of propodeum 0.7—0.8
times as long as apical area (Fig. 20). First tergite very slender and almost straight in

136 Andrey I. Khalaim / Journal of Hymenoptera Research 55: 129-138 (2017)

Figures 15-21. Szethantyx durrelli sp. n., female, holotype (15=—18) and male, paratype (19=21): 15 first
tergite, lateral view 16 glymma, lateral view I7 first and second tergites, dorsal view (the arrow points to
the hind end of second tergite) 18 apex of ovipositor, lateral view 19 antenna, lateral view 20 propodeum,

dorsolateral view 21 propodeum and first tergite, lateral view.

lateral view (Fig. 21); groove between glymma and ventral part of postpetiole absent
or indistinct. Otherwise similar to female.

Variation. The male from Sao Paulo has metapleuron almost entirely covered with
fine vertical wrinkles; dorsolateral area of propodeum with punctures mostly indistinct
because of numerous fine wrinkles; basal area rather indistinct (basal longitudinal cari-
nae weak); apical area hexagonal (apical longitudinal carinae ending anteriorly far from
the posterior end of basal longitudinal carinae), impunctate; and nervellus less inclivous.

Type material. Holotype female (EMUS), Brazil, State of Rio de Janeiro, Teresdp-
olis, 13.III.1966, coll. H. & M. Townes.

Paratypes. 1 male (FSCA), Brazil, State of Sao Paulo, Boracéia Biological Station,
Sangre Grande, 18.XI.1976, coll. T. Rogers, 23KMPO93834. 1 male (EMUS), Bra-
zil, State of Parana, NE of Curitiba, Campina Grande do Sul, 16.11.1966, coll. H. &
M. Townes.

Distribution. Southern and southeast Brazil (Rio de Janeiro, Sao Paulo, Parana).

Etymology. ‘The new species is named in honour of Gerald Durrell (1925-1995),

a well-known British naturalist and author of many popular books about animals.

Contribution to the study of the genus Stethantyx Townes... 137

Discussion

Originally, Townes (1971) described Stethantyx with no differential diagnosis, but ac-
cording to the key to world genera (Townes 1971: 34) Stethantyx is similar to another
Neotropical genus described in the same paper, Meggoleus Townes, and differs from the
latter by small, unspecialized propodeal spiracles (strongly enlarged in Meggoleus) and
inclivous to weakly reclivous nervellus in the hind wing (distinctly reclivous in Meggole-
us). Later, one more species of Meggoleus with enlarged propodeal spiracles was described
from Central Africa (Khalaim 2007) and two species from Peru (Alvarado 2012). Be-
sides species of Meggoleus with enlarged spiracles seen many undescribed Neotropical
species with small to weakly enlarged propodeal spiracles and variable inclivation of the
nervellus have been examined. These taxa probably also belong to Meggoleus, although
the characters suggested by Townes for separation of these two genera do not work.

Extensive study of Stethantyx in the past decade demonstrated a considerable mor-
phological diversity of this genus, e.g. 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 oblit-
erated and first metasomal segment without glymmae, and some undescribed species
are not clearly distinguished from the genera Meggoleus, Probles Forster and Tersilo-
chus Holmgren. Thus, most previously used diagnostic features of Stethantyx (Townes
1971, Khalaim and Broad 2013) do not work well for separating all Stethantyx spe-
cies 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.

Acknowledgements

I am grateful to David Wahl (EMUS) and Kevin A. Williams (FSCA) for loan of
valuable material, and Andrew Bennett (Canadian National Collection of Insects,
Arachnids and Nematodes, Ottawa, Ontario, Canada) and Gavin Broad (The Natural
History Museum, London, UK) for their important suggestions and criticism. Also I
wish to thank Alejandro Zaldivar-River6n (UNAM) for his kind help with taking high
quality photographs. This work was supported by the Russian Foundation for Basic
Research, grant no. 16-04-00197.

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