Monoctenus itoi Okutani 1958
Creators: name: Hara, Hideho
name: Nagase, Hirohiko
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Hymenoptera
Diprionidae
Monoctenus
Monoctenus itoi

description: Monoctenus itoi Okutani, 1958
(Figs 2C2, D2, 5A 2a, 6A 2a, B2a, 7A1, B1, 8A 2, 10A 2b, 11A1a, b, 15, 16)
Monoctenus itoi Okutani, 1958: 144; Togashi 1965: 253; Okutani 1967: 48; Smith 1975: 410; Okutani 1984: 24; Abe & Togashi 1989: 545; Togashi 2001: 42 (part, male); Taeger et al. 2010: 211; Yoshida 2006: 36; Yoshida 2010: 28; Hara 2019: 46; Hara 2020: 287 (part, male).
Additional description. Female. Length 6.9–8.6 mm. Figs 5A 2a, 15A, B. Head capsule black, with supraclypeal area yellow red to red brown, anterior tentorial pit and its surroundings usually yellow red to red brown, clypeus often yellow red to red brown dorsomedially, and lateral furrow of postocellar area and its surroundings and dorsomedial part of occiput often yellow red to red brown (Fig. 15E–H). Labrum black. Prepectus brown to black. Postspiracular sclerite black, sometimes partly yellow to brown. Mesepisternum and abdomen without pale parts respectively (Fig. 5A 2a, 15A, B).
Clypeus without median furrow; ventral edge widely concave (Fig. 15G, H). Antenna with 19–21 antennomeres (Fig. 7A 1); flagellomere 6 in lateral view with breadth including serration 1.8–2.1 × dorsal length. Valvula 3 (Figs 2C2, D2, 15I) in dorsal view tapering and with apex nearly pointed or narrowly rounded, in lateral view with apex narrowly rounded and dorsal edge nearly straight. Lance in lateral view with dorsal edge gently rounded at basal two-fifths and almost straight from middle to near apex (Fig. 15J). Lancet with 10 annuli (Figs 7B 1, 15K); length from ventral end of ctenidium 1 to apex 4.1–4.6 × breadth; ctenidia 1 and 2 converging dorsally; ctenidia 2–7 parallel, inclined anteriorly.
Male. Length 6.6–7.7 mm. Fig. 15C, D). Labrum dark brown to black (Fig. 10A 2b). Pronotum black (Fig. 11A 1a), often narrowly brown posterodorsally (Fig. 11A 1b). Tegulae black, sometimes yellow laterally. Antenna with 25–30 rami (28–33 antennomeres). Subgenital plate in ventral view rounded apically. Genitalia Fig. 15L; in penis valve, paravalva with ventral edge roundly convex and inner sclerite narrow, broadest near apex (Fig. 15M); valviceps 2.7–2.8 × as long as broad.
Immature stages. Early instar larva (Fig. 16B): Head and thoracic legs black; trunk green yellow. Late instar larva (Fig. 16C): 16–20 mm long; head brown yellow with black markings; thoracic legs black; trunk green. Probably final feeding instar larva (Fig. 16D, E): As in late instar. Cocoon (Fig. 15F): 10 mm long; brown; double-walled, with outer wall very loosely spun and inner wall tightly spun.
Material examined. Japan, Honshu: 1♀ 2♂, Kanagawa Pref, “Ôyama”, V. 1935, K. Sato (Fig. 6B 2a, 7B1, 15L, M); 1♀, Kanagawa Pref, Yokohama, Ngatsuda, 4. V. 1933, K. Sato (Fig. 15F, H, K); 11♀ 10♂, Kanagawa Pref, Yokohama, Asahi Ward, Yasashi, 23. V. 2021, M. Ishii (Fig. 7A 1); 6♀, same locality, 26. V. 2022, H. Nagase, and their eggs (Fig. 15A, B, J, 16A); 7♀, same data but 26. V. 2023, and their progeny, eggs laid 28–31. V., hatched 10. VI., coc. 11. VII. (Fig. 16B–F); 37♀ 30♂, Kanagawa Pref, Yokohama, Seya Ward, Seya, 25. V. – 1. VI. 2002, M. Ishii (Figs 2C2, D2, 5A 2a, 6A 2a, 8A 2, 10A 2b, 11A1a, b, 15C, D, E, G, I); 14♀ 1♂, same data but 25. V. 2004; 1♂, Hyogo Pref., Mt. Oginosen, 9. VII. 2012, T. Naito (Fig. 10A 2a, 11A 2b). Part of the specimens from Yokohama are deposited in Kanagawa Prefectural Museum of Natural History, Odawara.
Okutani (1958) described this species based on two females and two males. In the National Museum of Nature and Science, Tsukuba, where Okutani’s collection is currently preserved, we did not find any of the type specimens.
Distribution. Japan (Honshu) (Okutani 1958).
Host plant. Cupressaceae: Chamaecyparis obtusa (Siebold et Zucc.) Endl. (Okutani 1967), C. pisifera (Siebold et Zucc.) Endl. (Okutani 1958).
Life history. This sawfly is univoltine. The adults occur in May in the lowlands. Under rearing conditions, the females laid eggs individually inside one year old needles (Fig. 16A); the early instar larvae ate current year needles, but the late instar larvae mainly ate old needles.
Remarks. Specimens from Kanagawa Prefecture, which include a good number of female and male specimens collected together, show no distinct differences between them, so they can be safely considered to be the same species. They agree with the original description of M. itoi better than descriptions of other similar species, M. cryptomeriae, M. decoratus and M. fujisanus, and their holotypes (all females). However, while Okutani (1958) wrote “Antennae with 25 rami” for the male paratypes of M. itoi, 43 males from Kanagawa have an antenna with 27–30 rami. This may suggest that the Kanagawa specimens are not M. itoi. If so, they belong to an undescribed species. Unfortunately, all the type specimens of M. itoi are most likely to have been lost. Based on our current material, it would be reasonable to consider that the Kanagawa specimens are M. itoi and that the difference in the number of antennal rami is included in intraspecific variation.
This species is separated from other species as stated in the key and the remarks of M. cryptomeriae. In addition to the characters in the key, this species is distinguished from M. cryptomeriae and M. decoratus by having a female antenna with 19–21 antennomeres and a flagellomere 6 in the lateral view with the breadth including the serration 1.8–2.1 × the dorsal length (Fig. 7A 1) (antennomeres less than 18 and a flagellomere 6 with the breadth less than 1.8 × the dorsal length in the latter two species, Figs 12G, H, 13E).
description: Published as part of Hara, Hideho & Nagase, Hirohiko, 2023, The Japanese species of Monoctenus (Hymenoptera: Diprionidae), pp. 541-561 in Zootaxa 5380 (6) on pages 550-552, DOI: 10.11646/zootaxa.5380.6.3, http://zenodo.org/record/10259644