First description of the metopiine genus Trieces Townes, 1946 (Hymenoptera: Ichneumonidae) from the Indomalayan region with three new species from India

Trieces Townes, 1946 is one of the largest metopiine genera for which species have been described from all zoogeographical regions except the Indomalayan. The present study reports a major range extension of Trieces with the description of three new species from India. The described species are members of the onitis species group. An identifi cation key to the Palearctic and Indomalayan species of the onitis group is included with the revised generic diagnosis and a key to separate Trieces from its closest genus Chorinaeus. Distribution pattern and character plasticity of Trieces are also discussed.

Trieces can be separated from other metopiine genera by the absence of a mesopleural suture, the apomorphic character of the genus (Gauld et al. 2002). In addition to this, the absence of a pocket structure on the lower pronotum is found to be a possible synapomorphy to distinguish Trieces from related genera such as Chorinaeus Holmgren, 1858 and Hemimetopius Benoit, 1955. This genus is very similar to the genus Chorinaeus except for the following characters: mesopleuron without mesopleural suture; pronotum without dorso-lateral depression, and metasomal tergites 1-3 with a lateral carina (Townes & Townes 1959;Townes 1971;Aeschlimann 1973;Gauld et al. 2002;Tolkanitz 2010). Even though Trieces and Chorinaeus are distinguishable by several characters, these genera are morphologically not well separated as at least one species, T. ranjithi Mazón & Bordera, 2021, was found to be intermediate between them (Mazón & Bordera 2020). An examination of more material and application of molecular phylogeny need to be done to resolve the taxonomic complication between Trieces and Chorinaeus and to delimit the species groups. Townes & Townes (1959) divided Trieces into four diff erent species groups (dentatus, integer, onitis and texanus) based on morphology. The species of the onitis group can be defi ned by the presence of a posterior slit-like depression on the metapleuron (Townes & Townes 1959;Tolkanitz 2010). This species group includes fewer than 10 species which are mostly distributed in the Palearctic region (Yu et al. 2016;Choi et al. 2016). The new species described in the present study belong to the onitis species group. Gauld (1984) and Townes & Townes (1959) mentioned the occurrence of species of Trieces in the Australian and Indomalayan regions, respectively (but yet to be described taxonomically). The present study reports on the distribution of Trieces for the fi rst time from the Indomalayan region with the description of three new species, T. irwini sp. nov., T. isolatus sp. nov. and T. orientalis sp. nov. from India. Identifi cation keys for the separation of Trieces from Chorinaeus and identifi cation of Palearctic and Indomalayan species of the onitis group are provided along with illustrations of new species. The distribution pattern of species of Trieces and morphological delimitation of the onitis group are discussed.

Material and methods
Specimens for the present study were collected by Malaise traps from the dry deciduous and evergreen forests of Biligiri Rangaswamy Temple Tiger Reserve (BRT), Chamarajanagar District, Karnataka and secondary wet forest of Zapami Village, Phek District, Nagaland. The collected specimens were kept in 95% alcohol and later mounted on card points and identifi ed. Images were taken with a Keyence VHX-6000 digital microscope with a magnifi cation of 200 ×. Final images were edited in Adobe Photoshop CS8 for removing artifacts formed during stacking. Measurements of body parts were taken from the holotypes by AxioVision 4.8. The type material of the new species is deposited in the collection of ATREE Insect Museum, Bengaluru, India (AIMB). Later, holotypes of the new species will be moved to the national repository at NBAIR, Bangalore. For morphological terminology and wing venation we follow Broad et al. (2018). For body sculpture we follow Eady (1968

Diff erential diagnosis
The new species, Trieces irwini sp. nov. diff ers from the other species of the onitis group in having the following combination of characters: i) mandible has only upper tooth, ii) fi rst metasomal tergite with ventro-lateral carina. This new species is more or less similar to T. homonae in having yellow face, but diff ers from the latter based on the following characters: mesopleuron with distinct longitudinal wrinkles posteriorly (vs without longitudinal wrinkles posteriorly in T. homonae), propodeum sparsely setose (vs densely setose in T. homonae), scutellum sparsely setose (vs densely setose in T. homonae), epicnemial carina joining with subtegular ridge (vs not joining with subtegular ridge in T. homonae).

Etymology
This species is named after veteran dipterologist Prof. Michael Edward Irwin (emeritus professor, University of Illinois, Urbana-Champaign, USA), who is a well-wisher and supporter of ATREE Insect taxonomy and Conservation Laboratory. H . Head transverse in dorsal view, not narrowed posteriorly behind eyes, 1.8 × as wide as long medially; frons smooth, setose; occiput smooth, glabrous medially rest setose; temple smooth dorsally, not convex, length 0.6 × as long as transverse diameter of eye in lateral view. Occipital carina present. Eyes sparsely setose. Distance from lateral ocellus to eye equal to diameter of ocellus. Distance between lateral ocellus 2.0 × distance from lateral ocellus to eye. Face not convex in lateral view, 1.4 × as wide as long in anterior view, slightly narrowed posteriorly, smooth, setose. Clypeus separated from face by shallow depression, sculptured similar to face, with lower margin weakly convex in middle. Length of malar space equal to basal width of mandible. Mandible with only upper tooth. Antennae with 19 fl agellomeres; all fl agellomeres longer than wide; fi rst fl agellomere 1.6 × as long as maximum width, 1.2 × as long as second fl agellomere.

M
. Metasoma coarsely and densely punctate. First metasomal tergite 1.1 × as long as apical width, with distinct dorso-lateral, ventro-lateral and pair of mid longitudinal carinae. Second metasomal tergite 0.7 × as long as its apical width, with distinct dorso-lateral carina and midlongitudinal carinae. Third metasomal tergite 0.7 × as long as its apical width, with dorso-lateral and midlongitudinal carinae distinct in basal half. . Body mostly black; antennae, face, lateral temples posterior half, maxillary and labial palps, fore and mid legs, hind coxae apically, metasomal sternites and ovipositor sheath yellow to yellowish brown, hind tibiae, tarsi reddish brown.

Male
Same as female.

Diff erential diagnosis
The new species comes closer to T. orientalis sp. nov. but diff ers based on the characters listed in the taxonomic key. Additionally, T. isolatus sp. nov. diff ers from the latter in having the following characters: hind coxa yellowish brown (vs black in T. orientalis sp. nov.), pterostigma yellow (vs black in T. orientalis sp. nov.), fi rst metasomal tergite longer than wide (vs wider than long in T. orientalis sp. nov.), antenna with 20 fl agellomeres (vs 23 in T. orientalis sp. nov.).

Etymology
The species name refers to the isolated pit below the metapleural slit. H . Head transverse in dorsal view, not narrowed posteriorly behind eyes, 1.7 × as wide as long medially; frons smooth, setose; occiput smooth, glabrous medially rest setose; temples smooth dorsally, setose, not convex, their length 0.7 × as long as transverse eye diameter in lateral view. Occipital carina present. Eyes sparsely setose. Distance from lateral ocellus to eye equal to diameter of ocellus. Distance between lateral ocelli 2.0 × distance from lateral ocellus to eye. Face not convex in lateral view, 0.9 × as wide as long in anterior view, slightly narrowed posteriorly, punctate, setose. Clypeus separated from face by shallow indistinct depression, sculptured similarly to face, with lower margin weakly convex. Length of malar space equal to basal width of mandible. Mandible with upper and lower teeth. Antennae with 20 fl agellomeres; all fl agellomeres longer than wide; fi rst fl agellomere 1.3 × as long as maximum width, as long as second fl agellomere. elliptical, separated from pleural carinae. Metapleuron smooth only at extreme base rest distinctly longitudinally striate, setose medially rest glabrous, with distinct isolated, longitudinal slit. Fore wing 3.4 × as long as wide. Vein 1cu-a distinctly postfurcal. Hind femur 2.2 × as long as its maximum width in lateral view. Hind tibia 3.0 × as long as its maximum width. Ratio of length of hind tarsomeres 1-5, 3: 1.5: 1.3: 1: 1.8. . Metasoma coarsely and densely punctate. First metasomal tergite 1.1 × as long as apical width, with distinct dorso-lateral and pair of mid longitudinal carinae, ventro-lateral carina absent. Second metasomal tergite 0.8 × as long as its apical width, with distinct dorso-lateral carina and midlongitudinal carinae. Third metasomal tergite 0.8 × as long as its apical width, with dorso-lateral and midlongitudinal carinae distinct in basal half.

Male
Unknown.

Diff erential diagnosis
The new species comes closer to T. koreanus but diff ers based on the characters listed in the taxonomic key. Additionally, T. orientalis sp. nov. diff ers from the latter in having the following characters: temple distinctly and closely punctate (vs sparse and indistinctly punctate in T. koreanus), fi rst fl agellomeres 1.6 × as long as maximum width (vs fi rst fl agellomeres 1.9 × as long as maximum width in T. koreanus), fi rst metasomal tergite 0.8× as long as apical width (vs fi rst metasomal tergite 1.7 × as long as apical width in T. koreanus).

Etymology
The species is named after the distribution extension of the genus to the Indomalayan (= Oriental) region. H . Head transverse in dorsal view, not narrowed posteriorly behind eyes, 1.7 × as wide as long medially; frons smooth, setose; occiput smooth, glabrous medially rest setose; temples smooth dorsally, not convex, their length 0.5 × as long as transverse eye diameter in lateral view. Occipital carina present. Eyes sparsely setose. Distance from lateral ocellus to eye equal to diameter of ocellus. Distance between lateral ocellus 1.8 × distance from lateral ocellus to eye. Face not convex in lateral view, 0.8 × as wide as long in anterior view, slightly narrowed posteriorly, punctate, setose. Clypeus separated from face by shallow depression, sculptured similarly to face, with lower margin weakly convex in middle. Length of malar space equal to basal width of mandible. Mandible with upper and lower teeth. Antennae with 23 fl agellomeres; all fl agellomeres longer than wide; fi rst fl agellomere 1.6 × as long as maximum width, as long as second fl agellomere. . Mesosoma 1.6 × as long as high; mesonotum densely, closely punctate, interspace smooth, without notauli. Scutellum smooth, closely punctate with distinct lateral carina. Mesopleuron punctate with longitudinal wrinkles posteriorly, setose. Epicnemial carina distinct, reaching anterior margin of mesopleuron. Propodeum punctate with parallel longitudinal dorsal carinae; spiracles small, elliptical, separated from pleural carinae. Metapleuron smooth, setose anteriorly and posteriorly rest glabrous, with distinct longitudinal slit and several short longitudinal rugae ventrally. Fore wing 3.2 × as long as wide. Vein 1cu-a distinctly postfurcal. Hind femur 3.0 × as long as its maximum width in lateral view. Hind tibia 3.9 × as long as its maximum width. Ratio of length of hind tarsomeres 1-5, 3.8: 1.8: 1.5: 1: 1.7. M . Metasoma coarsely and densely punctate. First metasomal tergite 0.8 × as long as apical width, with distinct dorso-lateral and pair of mid longitudinal carinae, ventro-lateral carina absent. Second metasomal tergite 0.8 × as long as its apical width, with distinct dorso-lateral carina and midlongitudinal carinae. Third metasomal tergite 0.7 × as long as its apical width, with dorso-lateral and midlongitudinal carinae distinct in basal half.

Biology
Unknown.

Discussion
Redefi nition and character plasticity of onitis species group Townes & Townes (1959) defi ned the onitis species group of the genus Trieces based on the following morphological characters: head wide to very wide; eyes sparsely setose; metapleuron setose anteriorly, with longitudinal wrinkles on posterior half and a distinct posterior slit-like depression. Presence of the metapleural slit is considered an apomorphic character of the species group (Kusigemati 1967;Tolkanitz 2010). Earlier studies have suggested that the presence of an occipital carina is a character of generic importance (Townes & Townes 1959), but in some species this character is found to be very plastic as occipital carina is absent in some species such as T. hokkaidensis and T. mandiblaris. So, even though the occipital carina is absent in two Eastern Palearctic species, T. hokkaidensis and T. mandiblaris are included in the onitis species group based on the presence of the metapleural slit (Kusigemati 1967(Kusigemati , 1971Tolkanitz 2010). Moreover, the addition of T. homonae to this group is supported by the presence of a metapleural slit, irrespective of the absence of longitudinal wrinkles on mesopleuron. The new species described in the present study point to the metapleural slit being the only constant character for this group.
Species of this group exhibit a very wide face (1.5-2.25 × as wide as long) in general (Walley 1969). But in the new species T. orientalis sp. nov. and T. irwini sp. nov., the face is not as wide as in other species of the group (<1.5 × as wide as long). This leads to the notion that Indomalayan species of the onitis group diff er markedly and can form a diff erent clade within the group. Generally, in species of this group, the median and lateral longitudinal carinae extend to the anterior half of the third metasomal tergite (Walley 1969). It is noted that the midlongitudinal carina extends ¾ the length of the tergite in T. koreanus (Choi et al. 2016). By considering all these morphologically variable characters it is important to mention that the character boundaries of onitis group of Trieces are more extending than previously assumed. Considering the newly defi ned characters like longer face and reduced number of fl agellomeres suggest that Indomalayan fauna of Trieces of onitis group might form a diff erent clade among the other species. Species delimitation and sexual dimorphism in the onitis group can be identifi ed by the diff erence in number of fl agellomeres (Walley 1969). Species of this group have at least 24 fl agellomeres. In the Nearctic region the intraspecifi c variation based on the number of fl agellomeres ranges from 1 to 6 segments (Walley 1969). This trend in the diff erence of number of the fl agellomeres between males and females can also be expected in the Palearctic and Oriental faunas by studying the male of the new species described here.

Distribution of Trieces
Species of Trieces have been described from the Afrotropical, Nearctic, Neotropical and Palearctic regions so far, but the existence of undescribed species from other regions has been published (Townes & Townes 1959;Gauld 1984;Yu et al. 2016). Until now no species has been taxonomically described from the Indomalayan region. The present study confi rms the distribution of Trieces to this region. The discovery of species of Trieces from the Indomalayan region fairly supports the observation of Townes & Townes (1959), where they mentioned the occurrence of undescribed species from the Philippines. It is important to note that the distribution range of none of the known species overlaps two diff erent zoogeographical regions. Until now, most of the species have been collected from dry habitats (Gauld et al. 2002). The species described in this paper are collected from dry deciduous, evergreen and wet forests of the Biligiri Rangaswamy Hills, Karnataka and Zapami Village, Nagaland. This fairly supports the fact that species of Trieces can also withstand wet climates. Species of Trieces are more abundant in the Northern Hemisphere and only 15 species are known from the Southern Hemisphere (Benoit 1955;Gauld et al. 2002;Mazón & Bordera, 2016;Yu et al. 2016). Gauld (1984) pointed to the occurrence of undescribed species from Australian region. The present study fairly supports the increased abundance pattern in the Northern Hemisphere.