Monoctenus nipponicus Takeuchi, 1940

(Figs 1B, 2A 1, B1, C1, D1, 3B 2a, C2, 4A1, 8A1, B1, 9A1, 19)

Monoctenus nipponicus Takeuchi, 1940: 187; Gussakovskij 1947: 134, 136, 221; Takeuchi 1949: 50; Takeuchi 1955: 124; Togashi 1965: 252; Okutani 1967: 48; Smith 1975: 410; Okutani 1984: 24; Abe & Togashi 1989: 545; Togashi 2001: 41, 42; Naito et al. 2004: 16; Yoshida 2006: 36; Yoshida 2010: 29; Taeger et al. 2010: 211; Sundukov 2017a: 5; Sundukov 2017b: 35; Hara 2019: 46; Hara 2020: 287.

Additional description. Female. Length 5.5–6.0 mm. Coloration as in Takeuchi (1940) (Fig. 19A, B), but labrum dark yellow to dark brown, palpi yellow, basally dark brown, pronotum often posterodorsally yellow to brown (Fig. 3B 2a), coxae usually apically yellow narrowly, trochanters and trochantelli sometimes partly yellowish.

Clypeus with median furrow throughout or dorsally (Fig. 19E) or without median furrow. Antenna with 19–20 antennomeres (Figs 4A 1, 19F); flagellomere 6 in lateral view with breadth including serration 1.5–1.8 × dorsal length. Valvula 3 in dorsal view with same width throughout and apex slightly concave (Figs 2C 1, 19G), in lateral view with apex nearly truncate (Figs 2D 1, 19H); apical groove rather wide (Fig. 19I). Lance in lateral view with dorsal edge concave near base, gently rounded from middle to apex (Fig. 19J). Lancet with 10 annuli, acute apically (Figs 3C 2, 19K, L); length from ventral end of ctenidium 1 to apex 3.4–3.6 × breadth; ctenidium 1 slightly converging with ctenidium 2; ctenidia 2–6 inclined anteriorly.

Male. Figs 8A 1, 19C, D. Length 5.2–6.4 mm. Pronotum sometimes posterodorsally yellow brown. Antenna with 25–26 rami (28–29 antennomeres) (Fig. 1B). Subgenital plate in ventral view truncate apically. Genitalia Fig. 17M. Penis valve with paravalva nearly straight on ventral edge (Figs 8B 1, 9A 1, 19N); inner sclerite widest near middle; valviceps 2.5–2.7 × as long as broad.

Larva. The trunk yellow green and the head pale brown according to Okutani (1984).

Material examined. Holotype (Fig. 19A, B, E–K): ♀, labelled “15, IV, 1920 Katayama Takeuchi” and “ Monoctenus nipponicus Tak. Holotype ”. Paratypes: 1♂, same data label as holotype and “ Monoctenus nipponicus Tak. Allotype ” (Figs 1B, 19C, D); 1♀ 2♂, same data as holotype (Fig. 8B 1, 9A 1); 1♀, “15, IV, 1920 Gifu Takeuchi ”; 1♀, “[Fuchu-mura](in Japanese) 1939.4.23. NAKANISHI”.

The males of M. nipponicus and M. kondoi are not distinguishable, so we inferred the species of males from females collected at the same site on the same day. We were unable to identify the three male paratypes of M. nipponicus (see Appendix).

Other material examined: JAPAN: HONSHU: 1♀, Nara Pref., Yamatokoriyama, Yata, 17. IV. 2013, F. Ito (Figs 3C 2, 4A1); 1♀, Hyogo Pref., Tamba-Sasayama, Juniperus rigida, 27. III. 1966, T. Okutani (probably material of Okutani, 1967, 1984); 1♀, Hyogo Pref., Kobe, Kita Ward, Dojo, 18. IV. 2012, H. Yoshida (Fig. 2A 1, B1); 1♀ 4♂, ditto but 8. IV. 2013 (Figs 2C 1, D1, 3B 2a, 8A1, 19M, N).

Distribution. Japan: Honshu (Takeuchi 1940), Awaji Island (Naito et al. 2004). Russia: Primorsky (Sundukov 2017a).

Host plant. Cupressaceae: Juniperus rigida Siebold et Zucc. (Takeuchi 1940, Okutani 1967).

Life history. The adults appear from March to May (Takeuchi 1955, Hara 2020). The male adults actively fly over the host plant (Okutani 1984).

Remarks. Monostenus nipponicus (Fig. 19A, B) has the same color as M. obscuratus hokkaidonis (Fig. 20A– B) and the pale specimens of M. obscuratus obscuratus (Hartig, 1937) (fig. 226 in Borowski & Stawski 2021). Monoctenus obscuratus obscuratus usually has a mostly blackish brown hind tibia and distinctly infuscated wings (images of the female and male syntypes in Taeger et al. 2018), but the pale specimens, just like M. nipponicus, have an entirely yellow hind tibia and slightly infuscated wings. Monoctenus nipponicus is distinguished from M. obscuratus by having a female antenna with 19–20 antennomeres (Figs 4A 1, 19F), a flagellomere 6 with the breadth including the serration 1.5–1.8 × the dorsal length (Figs 4A 1, 19F), a male antenna with 26–27 rami and a valviceps 2.5–2.7 × as long as broad in the lateral view (Figs 8B 1, 9A 1, 19N). The two subspecies of M. obscuratus has a female antenna with 18 antennomeres (Figs 4A 2, 20E; images 12885, 18571 in Taeger et al. 2018), a flagellomere 6 with the breadth including the serration 1.1–1.4 × the dorsal length (Figs 4A 2, 20E; images 3642 (syntype), 12885 in Taeger et al. 2018), a male antenna with 22–24 rami (Enslin 1917, Gussakovskij 1947, Viitasaari & Varama 1987, Mol & Aarsten 1994, our material) and a valviceps 2.9–3.5 × as long as broad (Figs 9A 2, 20O; fig. 12b in Viitasaari & Varama 1987, fig. 4 in Mol & Aarsten 1994).

Monostenus nipponicus is also similar to M. juniperi (Linné, 1758) from Europe. They are separated as follows: M. nipponicus has a female abdomen almost entirely black (Fig. 19A, B), a female antenna with 19–20 antennomeres, a flagellomere 6 with the breadth including the serration 1.5–1.8 × the dorsal length (Figs 4A 1, 19F) and a male antenna with 26–27 rami, but M. juniperi has a female abdomen laterally yellow (images in Taeger et al. 2018), a female antenna with 16–18 antennomeres, a flagellomere 6 with the breadth including the serration 1.1–1.2 × the dorsal length (Fig. 18A) and a male antenna with 17–21 rami (Gussakovskij 1947, Viitasaari & Varama 1987, Zhelokhovtsev & Zinovjev 1988, Mol & Aarsten 1994, our material). Their ovipositors slightly differ: M. nipponicus has a lance with the dorsal edge slightly concave basally (Fig. 19J) and the length of a lancet from the ventral end of the ctenidium 1 to the apex 3.4–3.6 × the breadth and the ctenidia 1 and 2 of a lancet very slightly converging dorsally (Fig. 19K, L), but M. juniperi has a lance with the dorsal edge not concave basally (Fig. 18B) and the length of a lancet from the ventral end of the ctenidium 1 to the apex 4.3–4.5 × the breadth and the ctenidia 1 and 2 distinctly converging dorsally (Fig. 18C, D). Takeuchi (1940) used the presence or absence of a median clypeal furrow to separate these two species (present in M. nipponicus but absent in M. juniperi according to him), but in our material, a median clypeal furrow is present or absent in M. nipponicus and absent in M. juniperi. This character is not very useful to distinguish them.

Monoctenus nipponicus is also similar to M. kondoi from Japan. Their females differs as mentioned in the key and the remarks of the latter. Their males are indistinguishable.

This species is separated from other species of Monoctenus by the coloration (compare with the descriptions of other species of the genus by Norton 1872, Cresson 1880, Marlatt 1888, Gussakovskij 1947, Smith 1975, Smith et al. 2010, De Lira-Ramos et al. 2022, Japoshvili & Haris 2022, this study).