A new enigmatic genus of the ichneumonid subfamily Ctenopelmatinae (Hymenoptera, Ichneumonidae) from Thailand

The Ctenopelmatinae is one of the least explored groups of Ichneumonidae in South East Asia. We describe and illustrate an enigmatic new genus, Thaictenopelma Ranjith, Reshchikov & Quicke with the type species, T. splendida Ranjith, Reshchikov & Quicke, sp. nov. , from a moderately high altitude site in northern Thailand. The new genus shows a unique set of morphological characters that distinguishes it from all other ctenopelmatine genera. The presence of a pair of complete latero-median as well as complete dorso-lateral carinae on the T2 are considered autapomorphic characters of the new genus. Affinities of the new genus within the Ctenopelmatinae are discussed and a note on the taxonomic placement is provided.


Introduction
The ichneumonid subfamily Ctenopelmatinae consists of more than 1,500 species belonging to 113 genera (Yu et al. 2016;Broad et al. 2018;Li et al. 2022;Reshchikov et al. 2022).The subfamily is currently divided into nine tribes (Broad et al. 2018), but its tribal classification is not stable (Gauld et al. 1997;Bennett et al. 2019) and it has never been recovered as monophyletic in phylogenetic analyses (Quicke et al. 2009;Bennett et al. 2019), possibly being paraphyletic with respect to Mesochorinae, Metopiinae, Oxytorinae and Tatogastrinae (Quicke et al. 2009;Quicke 2015).The most important characters of ctenopelmatines are the presence of an acute dorsal tooth on the apex of the fore tibia and a dorsal, subapical notch on the ovipositor of most species, although it is needle-like and lacking the notch in its egg-larval parasitoid members (most Pionini) (Cameron et al. 2014) as well as in species of some other genera, for example, Lathrolestes Förster (Reshchikov et al. 2010).In other respects, ctenopelmatines exhibit a wide spectrum of morphological characters (Townes 1970;Gauld 1984, Gauld et al. 1997).Species of Ctenopelmatinae are koinobiont endoparasitoids of sawfly (Hymenoptera) larvae and exceptionally of Lepidoptera caterpillars (Seyrig 1928;Heath 1961) and Coleoptera larvae (Barron 1994;Broad et al. 2018).
The known Oriental fauna of Ctenopelmatinae comprises 84 species belonging to 29 genera (Yu et al. 2016;Reshchikov et al. 2017aReshchikov et al. , b, 2022;;Reshchikov and van Achterberg 2018;Li et al. 2022).However, since their host sawflies are a predominantly temperate group, it is unsurprising that they are particularly uncommon in tropical regions where they are predominantly restricted to montane areas (Malaise 1945;Gauld 1997;Reshchikov 2015;Reshchikov et al. 2018).The South East Asian fauna is particularly poorly known with the only published records being for Gilen Reshchikov & van Achterberg, 2018, Metopheltes Uchida, 1932, Neurogenia Roman, 1910, Rhytidaphora Reshchikov & Quicke, 2022and Rhorus Förster, 1869(Reshchikov et al. 2017a;Butcher and Quicke 2023), although we have seen specimens of Scolobates Gravenhorst, 1829 from Thailand.Of these, both Gilen and Rhytidaphora were described within the past decade, and the possibility that the recently described Chinese genus, Unicarinata Sheng, Li & Sun, 2022 might also occur in the region cannot be neglected.
Here we describe an enigmatic new genus and a species, Thaictenopelma Ranjith, Reshchikov & Quicke (type species: Thaictenopelma splendida Ranjith, Reshchikov & Quicke sp.nov.) from Doi Pha Hom Pok and Doi Phu Kha National Parks, both located in northern Thailand.In Thaictenopelma gen.nov., T2 has a pair of complete latero-median carinae as well as complete dorso-lateral carinae which is a unique combination not present in any other members of the subfamily.The new genus and species are described and comprehensively illustrated photographically, and taxonomic placement of the new genus is discussed.

Methods
All specimens were collected using Malaise traps set up as part of (i) two-year long sampling programme at Doi Phu Kha (2018 and 2022) (ii) from the two year long TIGER sampling programme 2007-2008 across Thailand (for habitat photo see Suppl.material 1), (iii) from Twin Peaks Project, and (iv) Tea Fauna Project (www.teafauna.com)sampling in northern Thailand.In total more than 600 trap months' worth of catches were sorted.

List of repositories
CUMZ Chulalongkorn University Museum of Natural History, Bangkok, Thailand QSBG Queen Sirikit Botanic Garden, Chiang Mai, Thailand Morphological terminology follows Broad et al. (2018) and for cuticular sculpture we follow Harris (1979) and is aligned with the Hymenoptera Anatomy Ontology (HAO) (Yoder et al. 2010).

F1
antennal flagellomere 1 OD the longest diameter of a posterior lateral ocellus OOL the shortest distance between a posterior lateral ocellus and a compound eye POL the shortest distance between the posterior lateral ocelli S1-7 refers to the metasomal sternites 1-7 T1-T7 refers to the metasomal tergites 1-7 Diagnosis.Thaictenopelma gen.nov.can be separated from all other ctenopelmatine genera by its putatively autapomorphic carination pattern of T1 and T2.In particular, the pairs of complete latero-median and dorso-lateral carinae on T2 are completely unknown for the subfamily (Townes 1970).Additionally, the new genus can be distinguished from other ctenopelmatines by a combination of characters viz., the lower tooth of mandible being longer than upper tooth, propodeum with distinct carination, fore wing with rhombic areolet, T2 and T3 with posteriorly diverging groove basally, and T3 with distinct medio-basal protuberances.
Etymology.The generic name derived from a combination of 'Thai' for Thailand and 'Ctenopelma', type genus of the subfamily Ctenopelmatinae.
Variation.In paratypes from Doi Pha Luang antenna with 39 flagellomeres, occiput more strongly concave, area superomedia with transverse carina more strongly arched posteriorly.Clypeus completely black except apically, metapleuron and anterior part of propodeum black, T2 baso-laterally black.

Biology. Unknown.
Etymology.The species is named after the magnificent combination of morphological characters which are completely unknown from the members of the subfamily. Distribution.Thailand.

Discussion
The complete lateral longitudinal cartina of T2 is one of the diagnostic characters used by Townes (1970) to recognise the Ctenopelmatini, although this character state is also present in several species in the genera Hadrodactylus Förster, 1869 (Euryproctini) and Rhorus (Pionini).However, in members of the Ctenopelmatini, T8 of the female is produced posteromedially between the base of the ovipositor sheath and the cercus whereas in Thaictenopelma gen.nov.T8 apical margin is normal.Further, the carination pattern of T1 and T2 disagrees with a placement in Ctenopelmatini as all carinae (dorso-lateral and latero-median) are extended up to the posterior margins of the tergites.The complete propodeal carination of Thaictenopelma gen.nov., including a completely defined area superomedia, is a putatively plesiomorphic character state found in the Pionini Smith & Shenefelt, 1955 (most genera) and Perilissini Thomson, 1883(Lathrolestes Förster, 1869and Perilissus Förster, 1855), and only a few ctenopelmatines (Austropion Gauld, 1984, Hodostates Förster, 1869, Glyptorhaestus Thomson, 1894, Phaestus Förster, 1869, Petilium Townes, 1970, Lathrolestes and Perilissus) (Townes 1970;Gauld 1984, Gauld et al. 1997).
The new genus appears most similar to the pionine, Austropion from Australia (Gauld 1984), but Thaictenopelma gen.nov., which also has the ovipositor with a distinct (albeit shallow) pre-apical dorsal notch (Suppl.material 2), but can be clearly distinguishable from Austropion by a combination of following characters; the lower tooth of the mandible longer than the upper tooth (upper tooth longer that lower tooth in Austropion), the occipital carina complete (obsolescent in Austropion), the fore wing areolet broad basally (petiolate in Austropion), T1 with complete dorso-lateral carina (carina absent in apical half in Austropion), T2 with a pair of complete latero-median and dorso-lateral carinae (smooth without carinae in Austropion), and the ovipositor without an acute dorsal process (with acute dorsal process in Austropion).Gauld (1984) placed Austropion in the Pionini based on carination but noted that it was rather aberrant.The only other genus tradionally placed in the Pionini with an ovipositor notch is Hodostates Foerster, 1869, and based on this character, Cameron et al. (2011) stated that they " ... are confident in rejecting Hodostates from Pionini", but the combined molecular and morphological analyses of Quicke et al. (2009) recovered Hodostates deeply nested among other Pionini genera and thus it appears that a notched ovipositor is likely to be homoplastic within the subfamily as noted by Cameron et al. (2011).
Thaictenopelma gen.nov. is also similar to the Priopoda group of genera (Perilissini) by having the occipital carina joining with hypostomal carina at base of mandible (Fig. 2B, Suppl.material 2).Within Gilen, Neurogenia, Priopoda Holmgren, 1856 and Lathrolestes, the new genus is most closely resemble Gilen by having T2-3 with a broad subapical transverse impression and T2 lateral longitudinal carina but readily discriminate by lacking produced mid-longitudinal facial projection and having distinct complete latero-median carina of T2.
Due to the presence of rather mixed combination of morphological characters displayed in different tribes (Ctenopelmatini, Perilissini and Pionini) we refrain from assigning the new genus to any of the extant tribes and we prefer to keep it as incertae sedis within the Ctenopelmatinae, although on balance it seems most probable that belongs to the Perilissini.Similar conditions have been found in a couple of genera like Labrossyta Förster, 1869 and Hodostates (Townes 1970).All these strongly point to the need for comprehensive analyses of the tribal classification of the Ctenopelmatinae.
Finally, at the only two known localities, the new species seems either to be very uncommon or not to get collected easily in Malaise traps, since we only found seven individuals from more than 600 Malaise trap months' (>50 years) of sampling.