Macrostemum okinawanum (Matsumura 1931)

(Figs 9 L–9Y)

Macronema okinawanum Matsumura 1931, 1133, male, Okinawa. Macrostemum okinawanum: Kuranishi and Kimura 2001, 17–18, figs 1, 2, male, Amami-o-shima, Toku-no-shima, Okinawajima.

Specimens. Holotype male (pinned, cleared abdomen was dried up in a small vial), labeled “ Japan Matsumura, v.1907, Type Matsumura, Macronema okinawanum ”, Okinawa-jima (HU). Amami-o-shima: 10 males, Mt. Yuwan-dake, 300 m a.s.l., 19.vi.1998, K. Mizota, L; 1 male, 1 female, Sumiyo-cho, 24.vi.2007, M. Takai (SCM); 2 females, Uken-son, 8.v.1998, H. Moriya; 1 male, Uken-son, 1.vii.2007, M. Takai (SCM); 6 males, 1 female, Yuwan-gama, 18–19.iv.2015, SI, P; 1 male, Yamato-son, Yuwan-gawa, small stream, 18–19.iv.2015, SI, P; 2 males, Yuwan-gama, headwater, 18–19.iv.2015, SI, P; 2 males, Amami-shi, Naze-Asato, small stream, 20– 21.iv.2015, SI, P; 1 female, Amami-shi, Sumiyo-son, Yakugachi-gawa, 29.iv.2017, N. Katsuma. Okinawa-jima: 1 male, Kunigami-son, Okuma, 3.vi.2003, M. Tanaka (MT); 1 male, 1 female, same locality, 24.ix, 2005, M. Tanaka (MT).

Distribution. Japan: Ryukyu (Amami-o-shima, Toku-no-shima, Okinawa-jima). Endemic to central Ryukyu.

Remarks. This species was originally described from Okinawa-jima by Matsumura (1931), and Kuranishi and Kimura (2001) recorded from Amami-o-shima and Toku-no-shima for the first time. The holotype male deposited in Hokkaido University is in poor condition (Fig. 9L), but general appearance is similar to that of M. formosicolum . The dark markings on the right forewing are similar to that of the latter, but dark spots on cross veins, r and m-cu, are absent in the holotype of M. okinawanum (Fig. 9M). One male specimen collected from Okinawa-jima also has similar markings as the holotype (Fig. 9P 1), but most dark spots of other specimens (1 male and 1 female) are indistinct or absent (Fig. 9P 2). Kuranishi and Kimura (2001) reported that markings of forewings were variable in the Okinawa-jima population. On the other hand, specimens collected from Amami-o-shima have large and distinct markings, and the central three dark spots often fuse into a large arched band (Kuranishi and Kimura 2001, fig. 2; Figs 9U 1, 9U 2). These Amami-o-shima specimens also lack spots on cross veins r and m-cu.

We could not observe the holotype genitalia in detail because the abdomen in the small vial was dried and shrunk. However, morphology of two males collected from Okinawa-jima is very similar to that of M. formosicolum, although dorsal aspects of segment X are variable (Figs 9R 1, 9R 2). Male genitalia of specimens collected from Amami-o-shima are also similar to those of M. formosicolum (Figs 9 V–9Y), but the apico-ventral lip of the phallotheca is slightly shorter than that of the latter (Figs 9X, 9Y).

Since populations of Okinawa-jima and Amami-o-shima may be a subspecies of M. formosicolum, further study with molecular data is needed to clarify the taxonomic status of this species. Macrostemum okinawanum has been listed in the Japanese Red List as a near-threatened species (Ministry of the Environment of Japan 2017).

Japanese name. Okinawa-hoshi-shima-tobikera.