Revision of the genus Spilopteron Townes, 1965 (Hymenoptera: Ichneumonidae: Acaenitinae) from Japan

Ten Japanese species of the genus Spilopteron Townes, 1965 are recognized. Five new species, S. albiventre  sp. nov., S. brachyurum  sp. nov., S. nigrum  sp. nov., S. oblongulum  sp. nov. and S. pseudonigrum  sp. nov., are described from Japan. Morphological discrimination between most Japanese species is confirmed by sequence analysis of the mitochondrial COI gene, which indicates the following relationships: S. oblongulum sp. nov. + S. apicale (Matsumura, 1912), S. brachyurum sp. nov. + S. nigrum sp. nov. + S. pseudonigrum sp. nov., and S. tosaense (Uchida, 1934) + S. luteum (Uchida, 1930). A key to the Japanese species of Spilopteron is provided. This genus seems to have its center of diversity in the mid-latitude area of East Asia.


Systematic position
The genus used to belong to the tribe Acaenitini sensu Townes (1971), but Wahl & Gauld (1998) proposed the discontinuance of the use of tribes within the subfamily Acaenitinae; we follow their opinion here.This genus closely resembles Siphimedia Cameron, 1902, known from the Oriental region, and Metachorischizus Uchida, 1928 from the Palearctic and Oriental regions, but it can be distinguished from them by the maxillary palpus with short hairs (vs long hairs in Siphimedia), the propodeal spiracle not enclosed by an elliptical carina (vs enclosed in Siphimedia), the propodeum with distinct regular carinae (vs irregular carinae in Metachorischizus), and the bullae in 2m-cu a little distant from each other (vs very close in Metachorischizus).

Etymology
This specific epithet of this new species is derived from the yellowish white metasomal apex.

Differential diagnosis
The new species most resembles S. brachyurum sp.nov.and S. pyrrhonae, but it is distinguished from them by the long malar space, 1.3-1.4times as long as the basal mandibular width (0.9-1.2 times in S. brachyurum and S. pyrrhonae), and the yellowish white marking on the apex of the metasoma (entirely black in S. brachyurum and S. pyrrhonae).

Differential diagnosis
Until the revision by Ito et al. (2015), this species had been confused with S. tosaense due to color variation.However, it can be distinguished from S. tosaense by the following character states: fore wing with the apical dark mark rounded and not extending downward (extending downward in S. tosaense), and without a dark mark below the pterostigma (Fig. 4b); frons with a depression between eye and antennal socket (absent in S. tosaense); and clypeus with a very weak median projection and two strong lateral projections (Fig. 3b) (with three equal-sized projections in S. tosaense).

Etymology
The specific epithet of this new species is derived from the short ovipositor sheath.

Differential diagnosis
This new species most resembles S. albiventre sp.nov.and S. pyrrhonae, but it is easily distinguished from both by the rounded area superomedia on the propodeum (the area is square in S. albiventre and S. pyrrhonae).

Differential diagnosis
This species can easily be distinguished from other Japanese species of Spilopteron by the entirely yellowish brown body (largely black or at least with black areas in other Japanese species) (Ito et al. 2012).ML analysis indicates that this species is most closely related to S. tosaense (Fig. 9), and this is also supported by the morphological similarity (except for the body coloration).
Color.Body reddish yellow (Fig. 5d).Antennal flagellum brown, usually with a distinct white band, but sometimes band not clear.Apex of mandible black (Fig. 3d).Apical area of hind trochantellus and basal area of hind femur brown.Fore wing with an apical dark mark extending downwards (Fig. 4d).
Male (n = 15; genitalia, n = 2) Similar to female.Clypeus 0.6-0.7 times as long as wide.Antenna with 39-42 flagellomeres; first flagellomere 1.1-1.2times as long as second flagellomere.Hind femur 4.4 times as long as maximum depth in lateral view.Hind tibia 13.4-14.2times as long as maximum depth in lateral view.First hind tarsomere 2.1 times as long as second and 2.9-3.1 times as long as longer hind tibial spur.T1 3.1-3.2times as long as maximum width, 2.3-2.4 times as long as T2.T2 0.9 times as long as maximum width.Antennal flagellum black, without a white band.

Differential diagnosis
This species can easily be distinguished from other species of Spilopteron by the ventral convexity of the hind femur, and the distinct sharp projection on S1 (see Ito et al. 2012).
Color.Body black (Fig. 5e).Antennal flagellum without a white band, brown apically.Face and postscutellum yellow with black marking medially, but sometimes entirely black except for inner margin of eye.Clypeus, subalar prominence, propodeum, fore and mid legs, hind trochanter, hind trochantellus, apex of hind femur, and apex of T1 yellow.Fore wing with an apical dark mark extending downwards (Fig. 4e).

Bionomics
Host unknown.Adults mainly fly from May to July.

Differential diagnosis
This new species most resembles S. pseudonigrum sp.nov., but is easily distinguished from it by the distinct apical marking on the fore wing (the apical portion is only infuscate in S. pseudonigrum sp.nov.).

Male (n = 1).
Similar to female (Fig. 1f).Body length: 9.0 mm.Head 0.7 times as long as wide in dorsal view.Face 0.8 times as long as wide.Antenna with 36 flagellomeres; first flagellomere 1.1 times as long as second flagellomere.Fore wing length 8.0 mm.Hind femur 3.2 times as long as maximum depth in lateral view.First hind tarsomere 3.7 times as long as longer hind tibial spur.T1 2.5 times as long as maximum width, 2.3 times as long as T2.T2 1.0 times as long as maximum width.Antennal flagellum without a white band (Fig. 1f).Face, clypeus, basal area of mandible, apices of T1-3, and fore and middle legs yellowish white.
Male genitalia of this species were not examined due to the limited number of specimens.

Etymology
The specific epithet of this new species is derived from the long ovipositor sheath.

Differential diagnosis
This new species most resembles S. flavescutatum Wang, 2004 and S. longitubus Wang, 2004 from China, but is easily distinguished from the former by the long T1, which is 3.5-4.3times as long as wide (2.7 times in S. flavescutatum), and from the latter by the polished area petiolaris (rugose in S. longitubus); the female antenna has 35 flagellomeres (43 flagellomeres in S. longitubus), and the male S1 ends in front of the spiracles of T1 (a little behind in S. longitubus).ML analysis indicates that this species is most closely related to S. apicale.Morphologically, this species shares some unique character states with S. apicale, such as the shape of clypeus and the depression between the eye and antennal socket, but it has an obviously longer ovipositor.

Etymology
The specific epithet of this new species is derived from the similarity to S. nigrum sp.nov.

Differential diagnosis
This new species most resembles S. nigrum sp.nov., although it can be distinguished by the merely infuscate apical area of the fore wing (with a distinct apical mark in S. nigrum sp.nov.).Although S. pseudonigrum sp.nov.and S. nigrum sp.nov.are difficult to distinguish from each other, they are distinct by molecular analysis (Fig. 9); the genetic distance between them was about 9.8 %.This species also resembles S. brachyurum sp.nov., but it has a square area superomedia of the propodeum (the area is rounded in S. brachyurum sp.nov.).

Differential diagnosis
This species resembles S. brachyurum sp.nov.and S. nigrum sp.nov.; however, it can be distinguished from them by the rounded apical dark mark on the fore wing (extending downwards in S. brachyurum sp.nov.and S. nigrum sp.nov.), and turned up clypeus in lateral view (not turned up in S. brachyurum sp.nov.and S. nigrum sp.nov.).It is also easily distinguished from other Japanese Spilopteron by the above character states.
Color.Body black (Fig. 5i).Antennal flagellum with a white band.Inner margin of eye and hind tarsomeres 3-5 white to yellowish white.Fore and mid legs brown.Fore wing with a rounded apical dark mark (Fig. 4i).

Discussion
We recognize ten species of Spilopteron from Japan, of which six occur in Hokkaido, nine in Honshu, five in Shikoku, four in Kyushu and two in the Nansei Islands (Yakushima Is., Amami-oshima Is.).
In other countries, this genus is known from the U.S.A. (four species), Canada (three species), Far East Russia (one species), mainland China (22 species), Korea (one species), and Taiwan (two species) (Yu et al. 2012;Ito et al. 2012).Therefore, this genus seems to have its center of diversity in the midlatitude area of East Asia.
In terms of body color, female S. tosaense are known to show an increasing melanism from south to north in the Japanese Archipelago (Ito et al. 2015).Also, S. luteum, distributed in Taiwan and southern Japan, has an entirely yellowish body color, although most Japanese species are dark.Similarly, many Chinese species of Spilopteron in southern areas have a yellowish body color (Wang 2004).In another case from ichneumonids, species of Apechthis Förster, 1869 show two conspicuous body color patterns: black or yellow (Watanabe & Takasuka 2013).The black species are mainly distributed in the Holarctic and Himalayan regions, but the yellow species are mainly in the Oriental and Neotropical regions.Therefore, such geographical color variation within or among species, along a latitudinal gradient or related to ecology (open or closed environment), seems not to be uncommon in ichneumonid wasps.
EtymologyThe specific epithet of this new species is derived from the entirely black body.