Review of the mandibularis group of the genus Dolichomitus ( Hymenoptera , Ichneumonidae , Pimplinae )

The mandibularis group of the genus Dolichomitus is reviewed. Three species are recognized, including a new species, Dolichomitus flavicrus sp. n. from Japan. The new species is closely related to Dolichomitus khasianus Gupta & Tikar, in having an entirely blackish underside of the metasoma, but can be separated from the latter by the smooth antero-median part of the first metasomal tergite between the latero-median carinae and a short longitudinal dark stripe on the posterior surface of the fore femur. A key to species of the mandibularis group is provided. Mitochondrial COI gene sequences were generated for D. mandibularis (Uchida) and D. flavicrus sp. n. to permit future comparisons.


Introduction
Dolichomitus Smith is a relatively large genus containing more than seventy species predominantly distributed in the Holarctic region but also extending to the Oriental and Neotropical regions (Gauld 1990, Yu et al. 2011).The mandibularis group, first recognized by Gupta and Tikar (1976), is one of the 9 species groups of the genus (Townes and Townes 1960, Gupta and Tikar 1976, Gauld 1991), characterized by the medially strongly bent mandibles with a shorter lower tooth.Two species of this group have been known, viz., Dolichomitus khasianus Gupta & Tikar from India and Dolichomitus mandibularis (Uchida) from Japan.Recently an additional species was discovered in Honshu, Japan and it turned out to be new to science through comparison with the types of known species.

Materials and methods
Both the holotypes of Dolichomitus mandibularis and Dolichomitus khasianus were borrowed from the Laboratory of Systematic Entomology, Hokkaido University, Japan (SEHU), and Zoologische Staatssammlung München, Germany (ZSM), respectively.The type specimens of the new species and other specimens examined are preserved in the collection of Osaka Museum of Natural History (OMNH) except for one paratype in the Natural History Museum, London (BMNH).External structures of specimens were observed under a steremicroscope (Nikon SMZ-800) and KEYENCE VHX-1000 digital microscope.Figures were prepared using the focus stacking function (combining several partially focused images) of the latter and the high resolution shot function of an Olympus E-M5 Mark II digital camera with 60 mm macro lens.See Matsumoto (2016) for DNA extraction, PCR and sequencing protocols.The INSD accession numbers for each sequence are mentioned in the specimens examined section.Terminology of adult morphology follows Gauld (1991).

The mandibularis group of the genus Dolichomitus
The main recognition characters of the genus Dolichomitus are: tip of lower valve of ovipositor with a dorsal lobe that partially encloses tip of upper valve; dorsally complete occipital carina; T2 with basal oblique groove longitudinal rather than transverse; vein Rs+M of fore wing opposite vein cu-a; vein Cu1 of hind wing separated from M by less than 1.0× length of cu-a; upper tooth of mandible as long as lower tooth or longer (in mandibularis group and in some other species).
Wings (Fig. 3a).Fore wing with vein Rs+M opposite cu-a; 2rs-m as long as 3rs-m, slightly shorter than vein M between 2rs-m and 2m-cu; vein M between 3rs-m and 2m-cu about 0.2× length of M between 2rs-m and 2m-cu, vein Cu1a separated from 1m-cu by about 1.2× length of Cu1b; vein cu-a weakly inclivous.Hind wing with vein M+Cu almost straight; distal abscissa of Cu1 present, reaching wing margin; vein Cu1 separated from M by 0.5× length of cu-a; vein cu-a reclivous to vein 1A.
Legs.Fore femur moderately inflated, 4.3-4.4×as long as wide; hind femur moderately stout, about 4× as long as its maximum width; hind tibia about 10.5× as long as its apical width; first tarsal segment of hind leg slightly longer than second and third segments combined; fifth segment about as long as second.
Metasoma.First metasomal tergite (Fig. 1d) with median longitudinal carinae distinct, moderately convergent posteriorly in dorsal view, extending to 0.5 of T1; median part between median longitudinal carinae strongly raised posteriorly, with median basal depression nearly smooth, densely puncto-reticulate posteriorly, lateral surface rugose; posterior half of lateral longitudinal carina distinct; spiracle situated at basal 0.35 of T1, slightly below level of lateral carina, encircled by deep oblong groove; T2 with antero-lateral corners strongly impressed in front of pair of anterolateral oblique grooves; central area of T2 strongly raised, with punctures very dense on dorsal surface and rather sparse laterally.First metasomal tergite 2.0× as long as its apical width; T2 about 1.1× as long as T1 and about 1.5× as long as its apical width.Ovipositor very long, about 70 mm, projecting beyond apex of metasoma by 10.0× length of hind tibia; ovipositor with expanded area of lower valve bearing 5 grooves, the most proximal 4 of which are reclivous, followed by apical 7 teeth (Fig. 1h); ovipositor sheath bearing short setae which are about 1.1× as long as width of sheath.
Coloration.Head, mesosoma and metasoma including mesosternum and membranous area between sclerites black (Figs 1f, 3c); lower half of clypeus tinged with reddish brown (Fig. 1a); labrum, maxillary and labial palpi yellow.Tegula and parategula yellow.Wings weakly tinged with yellowish brown, slightly darkened along distal margin.Legs largely vivid yellow, except for black coxae, short longitudinal dark stripe on posterior surface of fore femur (Fig. 1c) and dark brown tip of tarsal claw.
Remarks.This species is closely related to D. khasianus, from which it can be separated by a short and longitudinal dark stripe on the posterior surface of the fore femur, less developed epomia and lack of fine transverse striations on the antero-median part of the first metasomal tergite between the latero-median carinae.
All known specimens were collected while flying around nearly dead Pterocarya rhoifolia Sieb.et Zucc trees (Juglandaceae).In several cases, females were observed investigating the trunk of the tree with their antennae and thrusting their ovipositors into it.A male was also observed flying around the trunk.
Etymology.The specific name refers to the golden yellow legs contrasting with the black mesosoma and metasoma.

Dolichomitus khasianus Gupta & Tikar Figs 1e, 4
Dolichomitus khasianus Gupta & Tikar, 1976: 64.Remarks.This species is closely related to Dolichomitus flavicrus sp.n.Fore and mid coxae black, femora, tibiae and tarsi of mid and hind legs entirely concolorous yellow to reddish yellow, underside of metasoma including mesosternum and membranous area between sclerites entirely blackish in these species.However this species can be distinguished from the latter by the lack of a dark stripe on the posterior surface of the fore femur and by fine and dense transverse striations on the antero-median part of the first metasomal tergite (Fig. 1e).
This species was described based on a single female from India.Sheng & Sun (2010) recorded D. khasianus from Yunnan in China.
Distribution.India, China.Remarks.Relatively small species among members of the mandibularis group, with fore wing length 15mm or less.This species differs from D. khasianus and D. flavicrus sp.n. by the underside of the metasoma being not entirely blackish (Fig. 1g), with whitish membranous areas adjacent to sternites, and by its reddish fore and mid coxae (Fig. 5) and brown hind femur which is obviously darker than fore and mid femora (in the latter two species almost entirely yellow to reddish yellow).
Remarks.All male specimens were collected while flying along a trunk of an unidentified dead deciduous tree.

Discussion
Because of their large bodies and long ovipositors, the genus Dolichomitus is one of the most conspicuous and well-known genera in the family Ichneumonidae.A considerable number of taxonomic and faunal studies have been published for several biogeographical regions (Townes and Townes 1960, Gupta and Tikar 1976, Gauld 1991, Sheng and Sun 2002, 2010, Zwakhals 2010, Choi et al. 2016) and plenty of distributional records are available.However, the mandibularis group is known only from the Himalayas, South-western China and Japan, and not recorded in other regions.This distribution suggests that the mandibularis group is one of the representatives of a Sino-Japanese element of insects and plants (Shirozu 1947).
The known hosts of the genus Dolichomitus are coleopteran borers of dead wood, mainly belonging to Cerambycidae, and species of Curculionidae and Melandryidae are also recorded as hosts (Townes and Townes 1960, Fitton et al. 1988, Gauld 1991).No host record is available for members of the mandibularis group.However, the observed oviposition behaviour of females of Dolichomitus flavicrus sp.n., thrusting their ovipositors into dead Pterocarya rhoifolia trees, suggests that the host of this species is a borer of this tree.A cerambycid, Chloridolum (Chloridolum) thaliodes Bates is one of the most abundant species infesting dead or nearly dead Pterocarya rhoifolia at the collecting site.No other borers with enough biomass as a host for the larval development of such a large parasitoid as D. flavicrus was found there, so C. thaliodes is the most plausible candidate for the host of D. flavicrus, although confirmation is needed.In such a case, DNA barcode sequences of D. flavicrus would be helpful in identification of larvae parasitizing the host.

Figure 1 .
Figure 1.Dolichomitus species of the mandibularis group: a-d, f, h D. flavicrus sp n. (paratype) e D. khasianus (Holotype) g D. mandibularis a head in frontal aspect b propodeum in dorsal aspect c fore femur in posterior aspect d, e first metasomal tergite in dorsal aspect f, g first to third metasomal segments in ventral aspect h ovipositor tip in lateral aspect.Scale bars: 0.5mm (a, b, c, h); 1mm (d, e, f, g).

Figure 3 .
Figure 3. Holotype female of D. flavicrus sp.n.: a dorsal aspect b lateral aspect c ventral aspect.Scale bar: 10 mm.

Figure 5 .
Figure 5. Holotype female of D. mandibularis: a lateral aspect b labels c underside of data label.Scale bar: 10 mm.