Sejanus Distant 1910

Checklist of Sejanus species known in Japan and Taiwan Tribe Leucophoropterini Schuh, 1974 Subtribe Leucophoropterina Schuh, 1974 Genus Sejanus Distant, 1910 S. amami Yasunaga, 2001 — Distribution: Japan (Amami-Oshima Is.)— Host: Unknown. S. azumanus Yasunaga & Duwal, 2020 — Japan (northern Honshu)— Elaeagnus umbellata Thunb. (Elaeagnaceae). S. breviniger Yasunaga, 2001 — Japan (Okinawa Is.).— Mallotus spp. (Euphorbiaceae). S. epicurus Yasunaga & Duwal n. sp. — Taiwan (Pingtung).— Hibiscus taiwanensis S.Y. Hu (Malvaceae). S. juglandis Yasunaga, 2001 — Japan (Hokkaido, Honshu, Shikoku, Kyushu).— Juglans mandshurica Maxim. (Juglandaceae). S. komabanus Yasunaga, Ishikawa & Ito, 2013 — Japan (Honshu), Korea (Chungcheongmam-do, Gyeonggi-do).— Mallotus japonicus (Lf.) Müll.Arg. (Euphorbiaceae). S. neofunereus Schuh, 1984 — Japan (Ryukyus: Okinawa Pref.), Hong Kong, Philippines, Taiwan (Nantou).— Unknown. S. potanini (Reuter, 1906) — Japan (Hokkaido, Honshu, Shikoku, Kyushu), Russian Far East, Korea, China.— Various deciduous broadleaf trees, particularly on willows, Salix spp. (Salicaceae). S. ryujin Yasunaga & Duwal n. sp. — Japan (Kyushu: Nagasaki Pref.). — Hibiscus hamabo Sieb. et Zucc. (Malvaceae). S. vivaricolus Yasunaga & Ishikawa, 2013 — Japan (SW Honshu, Shikoku, Kyushu, and Nakadori, Wakamatsu and Yakushima Islands); Korea (Gyeonggi-do, Jeju Island).— Elaeocarpus zollingeri K.Koch (Elaeocarpaceae), Ligustrum japonicum Thunb. (Oleaceae), Mallotus japonicus, Triadica sebifera (L.) Small, (Euphorbiaceae), Myrica rubra Sieb. & Zucc. (Myricaceae), Zanthoxylum ailanthoides Sieb. & Zucc. (Rutaceae); this polyphagous species is considered predominantly predaceous. Taxonomy Genus Sejanus Distant Diagnosis: This genus was well defined by Schuh (1984) and Menard & Schuh (2014); distinguished from other genera of Leucophoropterini principally by the following characters: Body generally fuscous, small-sized (mostly 2–3 mm in total length); dorsum well-polished, shining, with uniformly distributed, simple setae; base of cuneus often with ivory (or occasionally orange-red) fascia (cf. Figs. 1H–J, 2F) that is interrupted at middle or divided into two spots in some species (Fig. 3I–J); C- or J-shaped vesica (endosoma) with secondary gonopore opening at apex; small, thin-rimmed female sclerotized ring; and relatively simple interramal sclerite with comb-shaped microstructures and narrow posterior margin sclerite. Discussion. Sejanus Distant is a typical Indo-Pacific group and more than a few undescribed species are present mainly in the Oriental Region (Yasunaga & Duwal, unpublished data). For temperate and cold temperate climatic zones of Japan and adjacent regions, the fauna was considered to have been almost perfectly clarified by a series of recent works (e.g., Yasunaga, 2001a; Yasunaga et al., 2013; Oh et al., 2020; Yasunaga & Duwal, 2021). Nonetheless, recent fieldworks have yielded two unique congeners that inhabit cryptic underside of hibiscus bracts and flower buds in southwestern Japan and Taiwan. Several species of phyline plant bugs, e.g. Campylomma astica Yasunaga, C. hibiscicola Yasunaga, C. seunghwani Yasunaga and Decomioides verecundus Yasunaga, were documented to prefer similarly concealed habitats on Hibiscus tiliaceus L. (Yasunaga, 2021) or Macarang a spp. (Euphorbiaceae) (Yasunaga, 2010; 2016). Within such niches, thrips (Thysanoptera), cicadellid leafhoppers(Auchenorrhyncha) and/or aphids (Sternorrhyncha) were observed to co-occur and are assumed to be prey of these phylines (e.g. Nakatani et al. 2017). Except for some Palearctic members (see above checklist), the breeding host plants of many Sejanus congeners are unknown (Menard & Schuh, 2014). In laboratory tests, both adult and immature forms of S. vivaricolus can be reared by brine-shrimp eggs (cf. Fig. 3F); we consider that most Sejanus species are principally predaceous. Key to Sejanus species from Japan and Taiwan 1. Hemelytron totally shiny fuscous; base of cuneus with faint, narrow, and indistinct pale (reddish or whitish) fascia or spots if present at all (cf. Fig. 2E, 3C–E)......................................................................... 2 - Hemelytron almost entirely fuscous, except for base of cuneus with defined, white or ivory spots (Fig. 3I–J), or a continuous creamy white fascia (Fig. 1H–J, 2F)...................................................................... 8 2. Apex of metafemur clearly yellow, yellowish brown or yellow-orange........................................... 3 - Metafemur entirely darkened, or its extreme apex only slightly pale............................................. 7 3. Antennal segment II pale brown with darkened apical 1/3–1/2 (♁)/ 1/4–1/6 (♀).................................... 4 - More than apical 2/3 (♁)/ 1/2 (♀) of antennal segment II darkened.............................................. 6 4. Male...................................................................................... S. azumanus - Female............................................................................................. 5 5. Labium as long as basal width of pronotum or metafemur; associated with Elaeagnus umbellata in northern Honshu................................................................................................. S. azumanus - Labium obviously longer than basal width of pronotum or metafemur; currently known to inhabit a halophyte, Hibiscus hamabo, in warm temperate climatic zone........................................................... S. ryujin n. sp. (♀) 6. Body larger; total body length more than 2.8 mm (♁)/ 2.7 mm (♀); length from apex of clypeus to cuneal fracture greater than 2.0 mm..................................................................................... S. potanini - Body smaller; total body length up to 2.6 mm (♁)/ 2.5 mm (♀); length from apex of clypeus to cuneal fracture less than 1.9 mm ...................................................................................... S. komabanus 7. Male antennal segment II shorter than basal width of pronotum; ventral cleft of scent efferent system elongate. S. vivaricolus - Male antennal segment II longer than basal width of pronotum; ventral cleft of scent efferent system rounded and shallow; currently known only from Okinawa Island........................................................ S. breviniger 8. All femora creamy yellow, not darkened (Fig. 2I–J)............................................. S. epicurus n. sp. - All femora, at least their basal parts, dark brown to fuscous.................................................... 9 9. Apex of metafemur yellow or creamy white............................................................... 10 - Metafemur almost totally darkened...................................................................... 11 10. Body larger; total body length greater than 3.0 mm; base of cuneus usually with two ivory spots; specialist of a Japanese walnut, inhabiting deciduous forest zone................................................................. S. juglandis - Body tiny; total body length up to 2.5 mm; base of cuneus with whitish brown fascia (Fig. 2F); inhabiting coastal Hibiscus hamabo ............................................................................... S. ryujin n. sp. (♁) 11. Antennal segment II longer than 0.88 mm (♁)/ 0.74 mm (♀); male antennal segment II wholly black; anterior ivory mark of cuneus usually continuous........................................................................ S. amami - Antennal segment II <0.72 mm; base of male antennal segment II pale; anterior ivory mark of cuneus usually divided into two spots or slightly interrupted medially (Fig. 3I–J).................................................. S. neofunereus

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