A taxonomic review of the genus Exochus Gravenhorst (Hymenoptera: Ichneumonidae: Metopiinae) from South Korea with descriptions of ten new species

ABSTRACT The South Korean species of the genus Exochus are revised. Ten new species, Exochus acostulatus Lee & Choi, sp. nov., Exochus adentatus Lee & Choi, sp. nov., Exochus areolaris Lee & Choi, sp. nov., Exochus carinalis Lee & Choi, sp. nov., Exochus dentisternum Lee & Choi, sp. nov., Exochus depressus Lee & Choi, sp. nov., Exochus nigritulus Lee & Choi sp. nov., Exochus occipitalis Lee & Choi, sp. nov., Exochus orbitalis Lee & Choi, sp. nov. and Exochus propodealis Lee & Choi, sp. nov., are described. Also, 21 species of this genus are reviewed and newly recorded from South Korea, with diagnoses provided. A key to the South Korean species of Exochus and illustrations of external characters are provided. http://zoobank.org/urn:lsid:zoobank.org:pub:B28700A7-9CA7-4AE7-9816-9C8F4CD46160


Introduction
Metopiinae Förster, 1869 is a medium-sized ichneumonid subfamily comprising 24 genera and over 830 described species worldwide. Among them, genus Exochus is the largest group of Metopiinae. It is a cosmopolitan genus comprising approximately 280 described species (Yu et al. 2012).
This subfamily is easily distinguished from other ichneumonids by the following characters: clypeus not separated from face by groove (except in Metopius), dorsal margin of face produced into triangular process extending between bases of antennae, division between trochantellus and femur of fore and mid legs often obsolete or absent, ovipositor short, not extending beyond metasomal apex. The species of the subfamily Metopiinae are koinobiont endoparasitoids in lepidopterous larvae and the usual hosts are among the pyraloids and tortricoids. The parasitoids emerge from the host pupa (Baltazar 1964).
Head. Rather transverse and narrowed behind eyes. Temple shorter than transverse diameter of eye (13 : 20). Ocelli small, its diameter 0.7 times distance between lateral ocellus and eye. Frons smooth, with deep V-shaped groove behind base of antennae. Antenna with 30 flagellomeres. First flagellomere 2.0 times as long as wide. Apical half of flagellum with transverse segments. Face almost square, coarsely and densely punctate, distance between punctures less than their diameter. Clypeus not separated from face, weakly concave. Mandible tapered apically. Upper tooth much longer than lower tooth. Malar space 0.75 times as long as basal width of mandible. Occipital carina present only laterally, hypostomal carina rather strong, almost lamelliform.
Mesosoma. Epomia strong, notaulus short but deep. Mesopleuron moderately coarsely and densely punctate, distance between punctures longer than their diameter. Pro-and metapleuron smooth and lustrous, without punctures or setae. Epicnemial carina reaching subtegular ridge. Vein Rs originating from apical half of pterostigma. Vein Rs+M rather strongly curved. Vein Cu-a postfurcal of about 0.3 of its length. Vein cu-a of hindwing weakly inclivous, intercepted in lower third, vein 3Cu not pigmented, but distinct. Hindwing with eight distal hamuli. Legs moderately stout, hind femur 2.4 times as long as wide. Ratio between length of hind tarsal segments 30 : 12 : 10 : 7 : 13. Front spur of mid tibia less than half length of hind spur. Tarsal claws simple. Propodeum without costula. Area basalis not separated from area superomedia by carina. Combined area basalis and superomedia parallel. Area dentipara bare, with some setae in hind outer angle. Propodeal spiracle 2.0 times as long as wide, closer to pleural, than to lateral longitudinal carina.

Etymology
From the absence of the costula on the propodeum.

Distribution
South Korea.

Remarks
The species is close to Exochus convergens Kusigemati, 1971, but differs by its longer malar space, the presence of the occipital carina laterally, yellow spots between the tops of the eyes and lateral ocelli, longer flagellum, bare area dentipara of propodeum, elongate propodeal spiracles, weakly inclivous vein cu-a of hindwing, and in coloration.
Colour. Black. Scape and pedicel from below, face, clypeus, malar space, mandible, palpi, whole frontal orbita widely, greater part of outer orbita, a spot on middle of frons, upper margin of pronotum widely, tegula, subtegular edge, a spot on middle of mesoscutum, scutellum and postscutellum entirely, a longitudinal stripe below subtegular edge and legs, except basal two-thirds of hind coxa yellow; flagellum from below and apical light brown.
Head. Strongly narrowed behind eyes. Frons moderately concave behind base of antennae.  Figure 6b). Area dentipara with only a few setae. Area basalis confluent with area superomedia. Propodeal spiracle 2.0 times as long as wide, situated in equal distance between pleural and lateral longitudinal carina. Fore third of justacoxal carina widened and projected as a tooth.
Ovipositor sheath no longer than apical depth of metasoma. Ovipositor gradually pointed to apex.

Etymology
From indistinct lower tooth of mandible.

Distribution
South Korea.

Remarks
The species is close to Exochus firmus Kusigemati, 1971, but differs by its larger body, indistinct lower tooth of mandible, wider face, strongly curved vein Rs+M in forewing and colour pattern. Colour. Black. Scape from below, face and clypeus entirely, mandible, palpi, malar space, temple widely, frons except space between ocelli, upper third of pronotum, two spots on the notauli, a large spot behind middle of mesoscutum, scutellum and postscutellm, tegula, subtegular ridge, large longitudinal spot below it, upper 0.25 of metapleuron, pleural area of propodeum, area dentipara of propodeum and legs, except base of hind coxa and trochanter bright yellow; hind tarsal segments red orange; flagellum from below light brown.

Exochus areolaris
Head. Strongly narrowed behind eyes. Antenna with 24 flagellomeres, short. First flagellomere only 1.5 times as long as wide, most segments transverse. Frons concave above antennal sockets, prominent in the middle as a process, with longitudinal carina from tip of the process to median ocellus. The distance from the frons process to interantennal process 0.5 times as long as ocellus diameter. The distance between lateral ocellus and eye 1.2 times as long as lateral ocellus diameter. Male. Unknown.

Distribution
South Korea.

Remarks
The species is close to Exochus pictus Holmgren, 1858 and Exochus rufigaster Kusigemati, 1971, but differs by its developed above occipital carina, short flagellum and reduced number of flagellomeres, shorter first flagellomere, transverse area superomedia of propodeum, not developed costula, longer forespur of mid tibia, very stout legs and colour pattern. Metasoma. Median longitudinal carinae strong, extending little behind middle of tergite 1. Tergite 2 0.6 times as long as wide apically. Epipleuron of tergite 3 wedge-shaped, the basal three-quarters of edge slightly concave. Metasomal tergites with fine punctures basally.

Distribution
South Korea.
Colour. Black. Upper half of face, scape from below, a couple oflateral spots on clypeus, mandible, palpi, tegula, tip of scutellum, apex of femora, base of tibiae and tarsal segments except last one yellow; legs reddish; flagellum from below light brown.
Head. Moderately narrowed behind eyes. Frons weakly concave behind base of antennae. Antenna with 23 flagellomeres. First flagellomere 2.5 times as long as wide, second flagellomere square. All other flagellomeres elongated. Diameter of ocellus as long as distance between eye and lateral ocellus. Temple 0.7 times as long as transverse diameter of eye. Occipital carina present only laterally. Face rather strongly convex longitudinally ( Figure 3e). Front tentorial pits not visible. Combined face and clypeus 1.2 times as high as wide, coarsely and densely punctate, the distance between points shorter than their diameter. Malar space with not deep furrow, 0.62 times as long as basal width of mandible. Apical margin of clypeus straight. Lower tooth of mandible much shorter than upper tooth, but distinct.
Mesosoma. 1.6 times as long as high in lateral view. Epomia moderately strong, notaulus present as a small pit on front part of mesoscutum. Scutellum and mesopleuron rather swollen. Prepectal carina reaching subtegular ridge. Hind margin of mesosternum projected backward as a couple of teeth. Sternaulus distinct on front third of mesopleuron. Metapleuron without any setae. Radial vein of forewing originated from middle of pterostigma. Vein Rs+M gradually curved. Vein Cu-a postfurcal as 0.5 of its length. Hindwing with five distal hamuli. Vein cu-a of hindwing intercepted in lower 0.25, vein Cu1 of hindwing faint. Propodeum fully areolated. Area basalis confluent with area superomedia. Combined area superomedia and area basalis convergent in front ( Figure 6e). Area dentipara with few long setae on hind outer corner. Propodeal spiracle 2.0 times as long as wide, situated a little closer to pleural than to lateral longitudinal carina. Front half of justacoxal carina widened as a lamella. Legs moderately stout, hind femur 2.2 times as long as wide, ratio between length of hind tarsal segments as 22 : 10 : 8 : 5 : 10. Front spur of hind tibia 0.5 times as long as hind spur.
Metasoma. Median longitudinal carinae of tergite 1 extending to 0.6 of its length. Tergite 2 0.7 times as long as wide apically. Metasomal tergites moderately coarsely and densely punctate, the distance between points longer than their diameter. Epipleuron of tergite 3 semicircular, the basal three-quarters of edge moderately strongly curved.

Etymology
From mesosternum projected backward as couple of teeth.

Distribution
South Korea.

Remarks
The species is close to Exochus bicoloripes Kusigemati, 1971, but differs by its longer malar space, lower number of flagellar segments, presence of costula, elongated propodeal spiracle, metanotum without any setae and coloration of the body. Colour. Black. Antenna from below, interantennal process, two spots laterally of antennal base, two spots between top of eyes and lateral ocelli, palpi, front half of tegula, hind upper corner of pronotum, subtegular ridge, femora apically, tibiae except base and apex, tarsal segments except last one of hind legs and subgenital plate apically yellow; femora reddish.

Exochus depressus
Head. Roundly narrowed behind. Frons V-shaped concave behind antennal sockets, ocellar area convex. Interantennal process long, extending above base of antennae. Antenna with 24 flagellomeres, short. First flagellomere 1.8 times as long as wide, the reminder flagellomeres transverse. Occipital carina not developed. Hypostomal carina not high. Face strongly convex tranversely ( Figure 3f). Temple shorter than transverse diameter of eye (13 : 16), not narrowed down. Front tentorial pits not indicated. Combined face and clypeus square. Apical ridge of clypeus weakly arched, in the middle third almost truncate. Malar space with shallow furrow, 0.6 times as long as basal width of mandible. Lower tooth of mandible much shorter than upper tooth.
Mesosoma. Depressed, 2 times as long as high in lateral view ( Figure 1f). Epomia present, notaulus short but deep, extending on front 0.2 of mesocutum length. Scutellum flat. Mesopleuron strongly swollen below subtegular ridge, sternaulus not developed. Prepectal carina almost reaching subtegular ridge. Hind middle part of mesosternum projected as a couple of teeth each lateral of mesosternal suture. Metapleuron smooth and lustrous, with some setae in hind lower corner. Radial vein of forewing originated a little before middle of pterostigma. Vein Cu-a postfurcal as 0.5 of its length. Hindwing with six distal hamuli. Vein cu-a of hindwing inclivous, intercepted on its 0.25. Legs stout. Hind femur 2.1 times as long as wide. Ratio between length of hind tarsal segments as 19 : 9 : 7 : 5 : 11. Front spur of mid tibia 2 times shorter than hind spur. Tarsal claws simple. Propodeum without costula. Area superomedia weakly convergent basally. Area basalis not separated from area superomedia by carina ( Figure 6f). Area dentipara haired basally and with some setae laterally. Propodeal spiracle 2.0 times as long as wide, closer to pleural than to lateral longitudinal carina.
Metasoma. Tergite 1 with short median longitudinal carinae, not reaching its middle. Tergite 2 0.85 times as long as wide apically, with transverse depression basally. Epipleuron of tergite 3 semicircular with basal three-quarters of edge strongly convex.
Ovipositor not surpassing tip of metasoma, gradually tapered to apex.

Distribution
South Korea.

Remarks
The species is close to Exochus latifasciatus Kusigemati, 1971, but differs by body size, longer face, shorter antenna and first flagellomere, smaller number of flagellomeres, entirely absent costula and coloration of the body. darkened; hind tibia yellow on the middle, more intensively darkened apically; flagellum from below and tegula brown.

Exochus nigritulus
Head. Transverse, moderately narrowed behind eye. Antenna with 29 flagellomeres, first flagellomere 2.5 times as long as wide, apical segments except last one square. Frons polished, with sparse and fine punctures. Diameter of ocellus as long as distance between lateral ocellus and eye. Occipital carina weak, absent from above and from below. Temple weakly shorter than transverse diameter of eye (15 : 17). Face moderately convex transversally, coarsely and densely punctured, the distance between punctures shorter than their diameter. Clypeus not separated from the face, with straight apical edge. Mandible tapered to apex, lower tooth much shorter than upper tooth. Malar space 0.62 times as long as basal width of mandible.  (Figure 6g). Area superomedia weakly wider than area dentipara. Area dentipara with long setae on hind outer angle. Propodeal spiracle 2.0 times as long as wide, closer to pleural carina than to lateral longitudinal carina.

Etymology
The specific name is derived from black area (absence of yellow spots) between eye and lateral ocellus.

Distribution
South Korea.

Remarks
The species is similar to Exochus kusigematii Tolkanitz (= E. erythropus Kusigemati 1971), but it differs by the following characters: smaller number of flagellar segments, straight apical margin of clypeus, absence of yellow spots on the top of eyes, more slender hind femur and coloration of the body.  Figure 6h). Area basalis not separated from area superomedia by carina. Area dentipara haired in greater part. Propodeal spiracle 2.0 times as long as wide, much closer to pleural than to lateral longitudinal carina.
Metasoma. Tergite 1 with short median longitudinal carinae, extending on its basal 0.4. Tergite 2 0.75 times as long as wide. Epipleuron of tergite 3 semicircular, the basal threequarters of edge strongly convex. Ovipositor sheath as long as apical depth of metasoma.

Etymology
From entirely absent occipital carina.

Distribution
South Korea.

Remarks
The species is close to Exochus ventralis Holmgren, 1858, but differs by not widened flagellum and elongated flagellomeres, not widened backward metasoma, more slender legs and coloration of the body. Colour. Black. Interantennal process, two spots laterally of antennae base, two spots between top of eyes and lateral ocelli, palpi, a spot on front half of tegula, unclear spot before base of hind tibia and basal half of last tarsal segment of hind leg yellow; hind part of tegula, flagellum from below and apically brown; legs reddish, coxae basally and hind tibia except base infuscate.

Exochus orbitalis
Head. Transverse, distinctly narrowed behind eyes. Frons smooth and concave above antennal sockets. Antenna with 25 flagellomeres. First flagellomere as seen from above curved outside, thin in the base, widened apically, 2.0 times as long as apical width, all flagellomeres elongated. Ocellus small, its diameter 0.8 times as long as distance between eye and lateral ocellus.  (Figure 6i). Lateromedian longitudinal carinae subparallel, weakly convergent from costula to base of propodeum. Area superomedia narrower from area dentipara, the last with some setae on hind outer angle. Propodeal spiracle almost 2.0 times as long as wide, closer to pleural than to lateral longitudinal carina.
Metasoma. Median longitudinal carinae reaching middle of tergite 1. Tergite 2 0.9 times as long as wide apically. Metasomal tergites moderately densely and finely punctured, the distance between points longer than their diameter. Epipleuron of tergite 3 wedge-shaped with straight edge.

Etymology
From face orbits ventrally convergent.

Distribution
South Korea.

Remarks
The species is close to Exochus convergens Kusigemati, 1971, but differs by its clypeus with straight apical margin, longer malar space, presence of occipital carina laterally, number of flagellomeres, shorter first flagellomere, presence of costula, shorter hind femur and coloration of the body.  (Figure 6j). Apical transverse carina in the middle and lateromedian longitudinal carinae limiting area superomedia laterally obsolete. Apical and lateral part of area dentipara haired. Propodeal spiracle 2.0 times as long as wide, closer to pleural than to lateral longitudinal carina.

Exochus propodealis
Metasoma. Median longitudinal carinae on tergite 1 extending on its basal 0.4. Glymma deep. Second tergite concave in the base, 0.8 times as long as wide apically. Epipleuron of tergite 3 semicircular, the basal three-quarters of edge being regularly convex. Ovipositor shorter than apical depth of metasoma.

Etymology
From propodeum with obsolete lateromedian longitudinal carinae and middle part of apical transverse carina.

Distribution
South Korea.

Remarks
The species is close to Exochus bicoloripes Kusigemati, 1971

Diagnosis
Female. Forewing 5.5 mm, body 6.0 mm long. Face, mandible and malar space yellow (Figure 3k). Vertex with large triangular yellow marks. Yellow triangular marks and yellow inner orbits confluent. Antenna with 28 flagellomeres; antenna ventrally yellowish brown and dorsally dark blackish brown. Mesosoma black. Upper corner of pronotum and upper margin of mesopleuron yellow. Scutellum flat and mostly black, posterior margin yellow. Propodeum with lateromedian longitudinal carinae and costula; area basalis and area superomedia not separated by carina (Figure 6k). Fore and mid legs yellow. Hind coxa reddish yellow, hind leg yellow, hind tibia with black band apically. Forewing vein cu-a distad of Rs+M. 2rs-m shorter than abscissa of M between 2rs-m and 2 m-cu. Vein cu-a of hindwing intercepted at lower third, vein Cu1 of hindwing present. Area between median longitudinal carinae of tergite 1 glabrous. Median area of tergite 2 glabrous. Epipleuron of third metasomal tergite semicircular.     Head strongly convex, upper face with projection ( Figure 4a); between antennal sockets with vertical ridge; dorsal margin of eyes with triangular yellow spots. Malar space black. Pronotum glabrous except sub-upper area, strongly sunken; epomia absent. Scutellum and postscutellum black. Propodeum with area superomedia (Figure 7a); area externa with hair; area superomedia and area dentipara with sparse hairs; spiracle of propodeum oval; metapleuron glabrous. Vein cu-a of hindwing intercepted at lower 0.3, with vein Cu1. Tergite 1 with distinct dorsal longitudinal carina, reach central area of tergite 1, weak up-curve in basal area, median area of tergite 1 without hair. Tergite 3 with epipleuron wedge-shaped, the basal part straight or weakly convex.    Exochus guttatus Tolkanitz, 1999 (Figures 4i, 7i) Exochus guttatus Tolkanitz, 1999: 191-201

Diagnosis
Male. Body length 7.1 mm. Antenna with 31 flagellomeres. Head weak convex, upper face with long projection and recurved; between antennal sockets without vertical ridge; dorsal margin of eyes with triangular yellow spots, connected to margin between antennal socket and eye. Antennal scape, clypeus, mandible and malar space yellow (Figure 4i). Pronotum strongly sunken and glabrous.

Diagnosis
Female. Body length 9.0 mm. Antenna with 40 flagellomeres. Head strongly convex, upper face with short projection; between antennal sockets without vertical ridge; dorsal margin of eyes with small triangular yellow spots. Face, clypeus and malar space black (Figure 5b). Pronotum strongly sunken. Scutellum and postscutellum black. Propodeum without area superomedia ( Figure 5i); area externa with hairs; area dentipara with sparse hairs partly; spiracle of propodeum ellipse; lower area of metapleuron partly sparse hair. Vein cu-a of hindwing intercepted at lower 0.2, with vein Cu1 trace. Tergite 1 with broad dorsal longitudinal carina, reach central area of tergite 1, up-curved in basal area; between dorsal longitudinal carinae without hair. Tergite 3 with epipleuron wedge-shaped, the basal part not convex.

Distribution
South Korea (new record), Japan, Russia.

Distribution
South Korea (new record), Russia.
Key to species of the genus Exochus from South Korea

1.
Epipleuron of third tergite wedge-shaped, basal three-quarters of the edge straight or weakly convex (Figure 8a)