Ectamenogonus plebejus ( Candèze, 1873 )

Arimoto, Kôichi, 2022, Taxonomic revision of the genus Ectamenognonus Buysson (Coleoptera, Elateridae, Elaterinae) from Japan, Zootaxa 5087 (2), pp. 306-334 : 317-325

publication ID	https://doi.org/ 10.11646/zootaxa.5087.2.4
publication LSID	lsid:zoobank.org:pub:701019E0-F757-40E9-A54D-F936DBE0BCC7
DOI	https://doi.org/10.5281/zenodo.5828100
persistent identifier	https://treatment.plazi.org/id/03D1A92A-FFA4-FFDC-3085-137BFDC1E855
treatment provided by	Plazi
scientific name	Ectamenogonus plebejus ( Candèze, 1873 )
status

Treatment

Ectamenogonus plebejus ( Candèze, 1873)

( Figures 8 View FIGURE 8 , 9 View FIGURE 9 , 10B–D View FIGURE 10 , 11–13 View FIGURE 11 View FIGURE 12 View FIGURE 13 , 19G–K View FIGURE 19 )

Ludis plebejus Candèze, 1873: 28 (original description; type locality: Japan).

Crigmus plebejus ; Lewis, 1894: 266 (changed generic status).

Trichophorus plebejus ; Schwarz, 1907: 259 (changed generic status).

Neotrichophorus plebejus ; Schenkling, 1927: 432 (changed generic status).

Homotechnes plebejus ; Baba and Ôhira, 1956: 14 (changed generic status); Kishii and Ôhira, 1956: 76.

Penthelater plebejus ; Ôhira, 1970: 24 (changed generic status).

Ectamenogonus plebejus ; Kishii, 1998: 4 (used following treatment of Platia and Cate (1990)).

Caledonelater plebejus ; Jiang, 1993: 149 (treated as belonging to Caledonelater ).

Megapenthes fusconiger Kolbe, 1886: 199 (original description; type locality: Seoul, Korea); Miwa, 1934: 164 (suggested as junior synonym); Kishii, 1999: 56 (treated as synonym).

Penthelater yakuensis Ôhira, 1970: 9 (original description; type locality: Japan, Kagoshima Prefecture, Kumage District, Yakushima Town ( Yaku Island ), Miyanoura ). Syn. nov.

Ectamonogonus yakuensis ; Kishii, 1999: 56 (changed generic status).

Ectamenogonus takumii Kishii, 2006 : (original description; type locality: Japan, off Kyushu, Nagasaki Prefecture, Tsushima City ( Tsushima Island ), Mine Town , Mine , Nakazato ) [partim].

Notes. No details of the collection sites of the type specimens were given in the original description or on the collection labels ( Candèze, 1873). Lewis (1894) indicated that the collection sites of the types are Nagasaki, Ashiwo, and Sapporo. Ôhira (1999) examined the lectotype and thought that it was collected in Nagasaki, but there is no clear evidence of this.

Type material. Holotype of Penthelater yakuensis . Male [ GN. 1435], Japan, Kagoshima Prefecture, Kumage District, Yakushima Town ( Yaku Island ), Miyanoura , 11 VII 1968, K. Suga leg. Verbatim label data ( Fig. 2E View FIGURE 2 ). “ HOLOTYPE ”; “ 宮ノ浦 / 11 VII 1968 / K. Suga ”; “ fl真 ”; “ Penthelater / yakuensis/ Ôhira, 1970 / H. Ohira Det. 1970” . Paratype of Ectamenogonus takumii . Female, Japan, Nagasaki Prefecture, Tsushima City ( Tsushima Island ), Izuhara Town , Sasu Pass , 22–28 VII 1959, Takashi Kishii leg. Verbatim label data ( Fig. 18G View FIGURE 18 ). “female symbol”; “3055”; “ PARATYPE ”; “ SASU Pass/ Is. Tsushima / 22-28. VII, 1959”; “ Ectamenogonus / takumii/ Kishii, nov./ Det. T. KISHII, 2003” .

Non-type material. Japan. Honshu. Chiba Prefecture. 1 male [ KEP01 ], Chiba City, Miyako Town , 19 VIII 1993, J. Naito leg. Fukui Prefecture. 1 female [ KEP03 ], Takada-Betsuin , 8 VIII 1961, T. Hori leg. Shiga Prefecture. 1 female [ KEP04 ], Ôtsu City, Ômimaiko , 29 VIII 1959, I. K. leg .; 1 female [ KEP05 ], Ôtsu City , 10 VIII 1963, Shimizu leg. Kyoto Prefecture. 1 female [ KEP06 ], Kyoto City , VIII 1957, collector unknown ; 1 female [ KEP07 ], Kyoto City , 1 IX 1957, Y. Tanaka leg. ; 1 male [ GN. 2124], Kyoto City , 19 VIII 1957, S. Yoshida leg. ; 1 female [ KEP08 ], Kyoto City, Sakyô Ward , 27 VIII 1961, collector unknown ; 1 female [ KEP09 ], Kyoto City, Sakyô Ward, Syûgakuin , 27 VIII 1964, Shinzô Yoshida leg. ; 1 female [ KEP10 ], Kyoto City, Sakyô Ward, Shimogamo , VIII 1951, Y. Kakemi leg. ; 1 female [ KEP11 ], Kyoto City, Sakyô Ward, Ginkaku-ji Temple , 29 VIII1952, H. Ishida leg. ; 1 female [ KEP13 ], Kyoto City, Kita Ward, Murasakino , 16 VIII 1962, M. Hori leg. ; 1 female [ KEP14 ], Kyoto City, Nakagyô Ward, Nishinokyô , 3 VIII 1964, Masami Ogawa leg. ; 1 female [ KEP15 ], Kyoto City, Nakakyo Ward, Mibu , 23 VIII 1960, T. Koiike leg. ; 1 female [ KEP16 ], Kyoto City, Higashiyama , 27 VIII 1962, T. Arai leg. ; 1 male [ KEP17 ], Kyoto City, Higashiyama , 7 VIII 1963, H. Kawashima leg. ; 1 female [3056], Kyoto City, Higashiyama Ward, Izumiyama , 20 VIII 1956, O. Nimura leg. ; 1 male [3057], Kyoto City, Shimogyô Ward , 14 VIII 1964, Masao Inoue leg. ; 1 female [ KEP18 ], Kyoto City, Shimogyô Ward, Sichijô-Ômiya , 2 VIII 1963, Syôichi Kobayashi leg. ; 1 female [ KEP19 ], Kyoto City, Arashiyama , 10 VIII 1960, K. Ueda leg. ; 1 male [ KEP20 ], Kyoto City, Nishikyô Ward, Matsuo , 9 VIII 1962, H. Kojima leg. ; 1 female [ KEP21 ], Kyoto City, Nishikyô Ward, Katsura , 20 V 1946, T. Kishii leg. ; 1 female [ KEP22 ], Kyoto City, Fushimi Ward, Mt. Inari-yama , 20 VIII 1962, Imanishi leg. ; 1 female [ KEP23 ], Kyoto City, Fushimi Ward, Momoyama , 31 VII 1960, Y. Higuchi leg. ; 1 female [ KEP24 ], Uji City , 21 VIII 1962, H. Koyama leg. ; 1 male [ EPM01 ], Yawata City, Mt. Otoko-yama , 16 VIII 2013, Tateo Itô leg. ; 1 female [ EPF01 ], same place as the former, 5 VII 2012, Tateo Itô leg. ; 2 males, 4 females [ EPM02 , EPM03 , EPF02–05 ], same place as the former, 15 VIII 2015, by PET bottle traps containing ethanol ; 3 females [ EPF06–08 ], same place as the former, 29 VIII 2015, by PET bottle traps containing ethanol. Osaka Prefecture . 1 female [ KEP25 ], Hirakata City , 1 VIII 1957, T. Nakamura leg. (Nakamu in label) ; 1 female [ KEP26 ], Mishima District, Yamazaki , 17 VIII 1965, Hirofumi Ôta leg. ; 1 male [ KEP27 ], Kadoma City (once Kadoma Town ), 3 VIII 1958, Sasaki leg. Hyôgo Prefecture. 1 female [ EPF09 ], Takaraduka City, Mefu , 26 VIII 1986, K. Odanaka leg. ; 1 female [ KEP28 ], Kobe City, Tarumi , VIII 1951, M. Ishida leg. ; 1 female [ KEP29 ], Kobe City, Karasuhara , 30 VIII 1952, T. Takajashi leg. Hiroshima Prefecture. 1 male [ KEP30 ], Hatsukaichi City, Yoshiwa (once Saiki District , Yoshiwa Village ), Kanmuri Highland , 4 X 1997, Hiroaki Mukunoki leg. Kyushu. Miyazaki Prefecture. 1 male [ EPM04 ], Nobeoka City, Kitagawa Town, Nagai-Honmura ( Motomura in label), 26 VII 2000, Masato Mori leg. Gotô Islands. 1 male [ KEP31 ], Nagasaki Prefecture, Hira-shima Island , 3 VIII 1978, N. Koga leg. Koshiki Islands. 1 male [3052], Kagoshima Prefecture, Satsumasendai City, Kamikoshiki Town ( Kamikoshiki Island ), Satochôsato (once Sato ), 28 VII–VIII 1967, Hirayasu leg. ; 1 female [3053], Kagoshima Prefecture, Satsumasendai City, Kamikoshiki Town ( Nakakoshiki Island ), Taira , 1–4 VIII 1967, Hirayasu leg. ; 1 male [3054], Kagoshima Prefecture, Satsumasendai City, Shimokoshiki Town ( Shimokoshiki Island ), Aose , 4–14 VIII 1967, Hirayasu leg. Ryukyu. Yaku Island. 1 male [ EPM05 ], Kagoshima Prefecture, Kumage District, Yakushima Town, Anbô , 15–19 VII 1985, Isao Tanaka leg. ; 1 female [ KEP32 ], same place, 24 VII 1950, T. Shirozu leg. Okinawa Island. 1 female [ OEP01 ], Okinawa Prefecture, Kunigami District, Motobu Town, Nobaru ( Nohara in label), 31 VII 1975, Yoshihisa Kusui leg. ; 1 male [ EPM06 ], Okinawa Prefecture, Nakagami District, Nakagusuku Village, Deegusuku , 10 VIII 2011, Yoshihisa Kusui leg. ; 1 female [ EPF10 ], Okinawa Prefecture, Naha City, Syuri , 10 VII 1992, Masafumi Matsumura leg ; 1 male [ OEP02 ], same place, 6 VIII 1959, collector unknown ; 1 male [ OEP03 ], same place, 15 VII 1960, collector unknown ; 1 male [ EPM07 ], Okinawa Prefecture, Naha City, Syuri, Sakiyama , 10 VII 1992, Masafumi Matsumura leg. Tokashiki Island. 1 male [ EPM08 ], Okinawa Prefecture, Shimajiri District, Tokashiki Village, Tokashiki , 18 VI 2013, Yoshihisa Kusui leg. Kume Island. 1 male [2169], Okinawa Prefecture, Shimajiri District, Kumejima Town, Kanegusuku , 6 V 1973, K. Sugino leg.

Diagnosis. Antennae just reaching or extending beyond pronotum posterior lateral apices by apical antennomere in male. Antennomere IV 1.1–1.5 x longer than II–III combined. Prothorax 1.1–1.2 x longer than wide. Posterior edge of scutellar shield rounded but truncate in some. Elytra 2.4–2.6 x longer than wide, 2.0–2.3 x longer than pronotum length. Aedeagus 3.6–4.3 x longer than wide. Median lobe exceeding apices of parameres by apical 1/4 to 1/3. Paramere apex length 1.9–2.2 x width of parameres at expansions. Spiculum ventrale 3.6–4.2 x longer than sternite VIII. Ovipositor 1.2–1.3 x longer than length of midline of abdominal ventrites. Bursa copulatrix 1.7–2.3 x length of uterus, with two clusters of sclerotized spines.

Measurements. Holotype of P. yakuensis . BL: 9.44, BW: 2.53, MAE: 1.60, MBE: 0.962; OI: 166, PL: 2.90, PML: 2.49, PW: 2.53, PI: 115, EL: 6.39, EW: 2.45, EI: 260, BI: 220. Paratype of E. takumii . BL: 13.41, BW: 3.43, MAE: 2.01, MBE: 1.24; OI: 162, PL: 4.08, PML: 3.46, PW: 3.43, PI: 119, EL: 8.59, EW: 3.42, EI: 251, BI: 210. Non-type specimens. Male (21 specimens). BL: 9.18–12.3, BW: 2.44–3.35, MAE: 1.54–2.04, MBE: 0.93–1.22; OI: 163–179, PL: 2.95–3.79, PML: 2.50–3.20, PW: 2.44–3.31, PI: 110–121, EL: 6.04–8.12, EW: 2.42–3.35, EI: 242–254, BI: 204–224. Female (37 specimens). BL: 11.3–14.5, BW: 3.05–3.98, MAE: 1.81–2.29, MBE: 1.09– 1.43; OI: 152–170, PL: 3.49–4.51, PML: 3.00–3.74, PW: 2.94–3.94, PI: 109–120, EL: 7.44–9.71, EW: 3.05–3.98, EI: 239–255, BI: 202–229.

Redescription. Body widest near pronotum hind angles but posterior half of elytra in some; surface with microstructures; interspaces between punctures generally larger than puncture diameter but partly smaller than puncture diameter. Color. Body black-brown to red-brown ( Figs. 1D, 1E View FIGURE 1 , 2C View FIGURE 2 ). Labrum reddish ( Figs. 8C View FIGURE 8 , 9C View FIGURE 9 ). Antennae red-brown to orange ( Figs. 1D, 1E View FIGURE 1 , 2C View FIGURE 2 ). Mandible orange but apical parts black ( Fig. 8C View FIGURE 8 ). Maxillary palpomeres orange ( Fig. 4C View FIGURE 4 ). Posterior edge of pronotum, anterior lobe of prosternum and mesial margin and posterior part of hypomeron reddish ( Figs. 1D, 1E View FIGURE 1 , 2C View FIGURE 2 , 8C, 8H View FIGURE 8 , 9C, 9H View FIGURE 9 ). Elytra around striae blackish, reddish in posterior margin ( Figs. 1D, 1E View FIGURE 1 , 2C View FIGURE 2 ). Legs red-brown to orange ( Fig. 8A View FIGURE 8 ). Posterior margin of abdominal ventrites I‒V orange ( Fig. 8A View FIGURE 8 ). Male. Tergites and sternites VIII‒X and aedeagus yellow ( Fig. 11 View FIGURE 11 ). Female. Tergites and sternites VIII yellow to red-brown ( Fig. 13A View FIGURE 13 ). Body covered with yellow-brown to red-brown setae.

Head. Frons beyond eyes in anterior view 0.3 x longer than wide ( Figs. 8B View FIGURE 8 , 9B View FIGURE 9 ); supra-antennal carina in ventral view emarginate medially ( Fig. 4D View FIGURE 4 ). Male. Antennae just reaching ( Fig. 10B View FIGURE 10 ) or extending beyond ( Fig. 10C, D View FIGURE 10 ) pronotum posterior lateral apices by apical antennomere, extending beyond pronotum posterior margin excluding posterior angles by apical antennomere; antennomere II 0.9–1.1 x longer than wide; III 1.2–1.7 x longer than wide; IV 1.8–2.2 x longer than wide, 1.1–1.5 x longer than II–III combined ( Fig. 5D View FIGURE 5 ), 1.0–1.1 x longer than V; V 1.7–2.2 x longer than wide; XI 2.7–3.2 x longer than wide ( Fig. 5E View FIGURE 5 ). Female. Antennae not reaching pronotum posterior margin excluding posterior angles by apical antennomere ( Fig. 1F View FIGURE 1 ); antennomere II 0.9–1.3 x longer than wide; III 1.2–1.6 x longer than wide; IV 1.9–2.2 x longer than wide, 1.1–1.3 x longer than II–III combined, 1.0–1.2 x longer than V; V 1.7–2.0 x longer than wide; XI 2.3–2.6 x longer than wide.

Prothorax 1.1–1.2 x longer than wide, widening posteriad, widest just behind posterior lateral apices but at posterior lateral apices in few; side rounded in anterior 1/3, straight in posterior 2/3. Pronotum posteriorly without median longitudinal depression. Prosternum: ventral margin distinctly inclined in anterior 1/5 (at 17–23 degrees against prosternal horizontal line, Figs. 8F View FIGURE 8 , 9F View FIGURE 9 ); exceeding anterior angles of prothorax ( Figs. 8F View FIGURE 8 , 9F View FIGURE 9 ). Prosternal process depressed between procoxae ( Figs. 8F View FIGURE 8 , 9F View FIGURE 9 ), in profile distinctly inclined and then almost horizontal behind procoxae ( Figs. 8F View FIGURE 8 , 9F View FIGURE 9 ); sides of dorsal lobe almost straight and parallel ( Fig. 8A View FIGURE 8 ) or broadly rounded ( Fig. 9A View FIGURE 9 ) anteriorly and then narrowed to apex; ventral margin of ventral lobe in profile broadly rounded posteriorly; apex in ventral and lateral views rounded ( Fig. 8A, F View FIGURE 8 ). Hypomeron slightly grooved next to impunctate ridge ( Fig. 5H View FIGURE 5 : white arrow). Pronotosternal sutures moderately opened anteriorly ( Figs. 8H View FIGURE 8 , 9H View FIGURE 9 ). Scutellar shield 1.4–1.7 x longer than wide ( Figs. 8G View FIGURE 8 , 9G View FIGURE 9 ), widest before anterior half, convex, strongly inclined anterior-downwards, not visible in profile ( Figs. 8F View FIGURE 8 , 9F View FIGURE 9 ); anterior edge almost straight; sides almost straight or broadly rounded anteriorly; posterior edge rounded but truncate in some. Mesosternum: posterior edge 0.1 x longer than mesosternum width, triangularly emarginate ( Figs. 8I View FIGURE 8 , 9I View FIGURE 9 : arrow), with widely rounded angles; borders of mesosternal cavity in profile horizontal anteriorly and then roundly and gently inclined ( Figs. 8F View FIGURE 8 , 9F View FIGURE 9 ). Elytra 2.4–2.6 x longer than wide, 2.0–2.3 x longer than pronotum length; apex emarginate; apical outer edge of each elytron rounded; apical internal edge of each elytron slightly pointed or rounded (likely due to damage) ( Figs. 8J View FIGURE 8 , 9J View FIGURE 9 ).

Abdomen. Ventrite V 0.6–0.7 x longer than wide ( Fig. 10A View FIGURE 10 ). Male. Tergite VIII 1.1–1.3 x longer than wide, rounded apically ( Fig. 11A View FIGURE 11 ). Sternite VIII with posterior edge shallowly emarginate ( Fig. 11B View FIGURE 11 ). Tergite IX 1.1–1.2 x length of tergite X, with median notch rounded ( Fig. 11C View FIGURE 11 ). Tergite X 1.1–1.3 x longer than wide, rounded apically ( Fig. 11C View FIGURE 11 ). Sternite IX 2.8–3.3 x longer than wide, rounded apically ( Fig. 11D View FIGURE 11 ). Aedeagus 3.6–4.3 x longer than wide ( Fig. 11E, F View FIGURE 11 ). Phallobase 0.5 x total length of aedeagus, 1.8–2.2 x longer than wide. Median lobe exceeding apices of parameres by apical 1/4 to 1/3; basal struts 0.4 x total length of median lobe. Parameres fused ventrally; preapical expansions gently projecting laterally beyond side of apex; apex beyond preapical expansions blade-like shaped ( Fig. 11G View FIGURE 11 ), rounded laterally, with one to three setae dorsally and one or two setae and three to five sensilla ventrally; apex length 1.9–2.2 x width of parameres at expansions. Female. Tergite VIII 1.4–1.5 x longer than wide ( Fig. 12B View FIGURE 12 ). Sternite VIII 1.1–1.2 x longer than wide ( Fig. 12C View FIGURE 12 ); spiculum ventrale 3.6–4.2 x length of sternite VIII ( Fig. 12A View FIGURE 12 ). Ovipositor 1.2–1.3 x longer than length of midline of abdominal ventrites; coxites two segmented at ventral side ( Fig. 12H View FIGURE 12 ), with some setae; stylus with setae around apex ( Fig. 12H View FIGURE 12 ). Vagina long; uterus globular ( Fig. 12A View FIGURE 12 ); bursa copulatrix U-shaped ( Fig. 12A View FIGURE 12 ), long, 1.7–2.3 x length of uterus, with 56–86 or 117 sclerotized spines, of which 24–39 spines forming a cluster in first half ( Fig. 12D View FIGURE 12 ) and 23–53 or 88 spines forming rows in latter half ( Fig. 12E View FIGURE 12 ); long thin sac extending from apex of bursa copulatrix ( Fig. 12F View FIGURE 12 ), with thin coiled sac near apex of bursa copulatrix ( Fig. 12F, G View FIGURE 12 ).

Comparative notes. Two Ectamenogonus species , E. plebejus and E. robustus , are distributed in mainland Japan and might be confused with each other ( Ôhira, 1999). Ectamenogonus plebejus is distinguished from E. robustus by the following contrasting characters ( E. robustus in parentheses): antennae just reaching or extending beyond pronotum posterior lateral apices by apical antennomere in male (antennae just or not reaching pronotum posterior lateral apices by apical antennomere in male); antennomere IV 1.1–1.5 x longer than II–III combined (antennomere IV 1.8–2.1 x longer than II–III combined); prothorax 1.1–1.2 x longer than wide, PI: 109–121 (prothorax 1.0–1.1 x longer than wide, PI: 101–111); aedeagus 3.6–4.3 x longer than wide (aedeagus 3.3 x longer than wide); median lobe exceeding apices of parameres by apical 1/4 to 1/3 (median lobe exceeding apices of parameres by apical 1/5 to 1/4); paramere apex length 1.9–2.2 x width of parameres at expansions (paramere apex length 1.3–1.8 x width of parameres at expansions); bursa copulatrix long, 1.7–2.3 x length of uterus (bursa copulatrix short, 1.0–1.1 x length of uterus); bursa copulatrix with two clusters of sclerotized spines (bursa copulatrix with a cluster of sclerotized spines).

Discussion. Kishii (2006) separated the Tsushima Island population from E. plebejus by the width of the aedeagus and number of the sclerotized spines in the bursa copulatrix, and described the endemic species E. takumii , removing the record of E. plebejus by Miwa (1933) from the island. From my observations, the male holotype of E. takumii shares diagnostic characters with E. robustus in the proportions of the antennae, prothorax, and elytra and width of the aedeagus (see diagnosis of E. robustus ). The holotype is characterized only by preapical expansions of the parameres distinctly projecting laterally beyond the side of the apex ( Fig. 19F View FIGURE 19 ). However, it is though that this is within the variation found in E. robustus , which has variable preapical expansions of the parameres, ranging from not projecting ( Fig. 17F View FIGURE 17 ) to slightly projecting laterally beyond the side of apex ( Figs. 16G View FIGURE 16 ). This study found that the holotype is not distinguished from E. robustus only by the preapical expansions of the parameres and concluded that E. takumii should be a junior synonym of E. robustus . The female paratype of E. takumii shares diagnostic characters of E. plebejus in the proportions of the antennae, prothorax, and elytra and the length of the bursa copulatrix (see diagnosis of E. plebejus ) and is not distinguished from female E. plebejus . The number of the sclerotized spines of the paratype is also within the range of the variation in that of E. plebejus . The paratype was concluded to belong to E. robustus . Accordingly, the type specimens of E. takumii include a male E. robustus and female E. plebejus . Female of E. robustus from Tsushima Island was also collected (ERF14 and ERF15). The two Ectamenogonus species are distributed sympatrically on Tsushima Island.

Ectamenogonus yakuensis and E. plebejus are very similar to each other in the proportions of the antennomeres, prothorax, and elytra, and shape of the scutellar shield. Ectamenogonus yakuensis is known only from the male holotype from Yaku Island, which is characterized by a smaller body ( Fig. 2D View FIGURE 2 ) and antennae extending beyond the pronotum posterior lateral apices by the apical antennomere ( Fig. 10D View FIGURE 10 ). This study found that the antennae of male E. plebejus are variable, ranging from just reaching ( Fig. 10B View FIGURE 10 ) to extending beyond ( Fig. 10C View FIGURE 10 ) the pronotum posterior lateral apices by one apical antennomere. The antenna length versus pronotum length of the holotype is slightly longer than that of the other specimens of E. plebejus examined, although E. yakuensis is difficult to distinguish from E. plebejus by the slight difference in antenna length. The general structure of the aedeagus of the holotype is similar to that of E. plebejus , while the paramera apices of its aedeagus are lost ( Fig. 12E, G View FIGURE 12 ). The aedeagus of an additional specimen from Yaku Island (EPM05) is similar to that of E. plebejus , with paramera apices. Therefore, E. yakuensis was determined to be within the range of variation found in E. plebejus and should be a junior synonym of E. plebejus .

Newly collected specimens from the Okinawa Islands were examined: Okinawa (OEP01–03, EPM06, EPM07, and EPF10), Tokashiki Island (EPM08), which is between Okinawa and Kume Islands, and the specimen recorded by Kishii (1974) from Kume Island (2169). These specimens are similar to specimens from mainland Japan in antenna length, proportions of antennomeres and body, shape of scutellum and aedeagus, and length of the bursa copulatrix (see diagnosis of E. plebejus ) and is difficult to distinguish from E. plebejus from mainland Japan. The two populations were determined to belong to the same species, E. plebejus .

Species recorded as E. plebejus from Miyako Island belongs to E. miyakoensis (see discussion of E. miyakoensis ).

Distribution ( Fig. 20 View FIGURE 20 ). Japan: Hokkaido, Honshu, Awa Island (off Honshu), Sado Island (off Honshu), Miyake Island (off Honshu), Oki Islands (off Honshu), Shikoku, Kyushu, Tsushima Island (off Kyushu), Gotô Islands (off Kyushu), Koshiki Islands (off Kyushu), Ryukyu Islands (Yaku, Nakano, Okinawa, Tokashiki and Kume Islands); Korea: mainland, Cheju Island, Ulleung Island; Taiwan (doubtful) ( Kishii, 1999, 2006; Suzuki, 1999; Platia and Han, 2010; this study).

Ectamenogonus plebejus was recorded from many sites in Taiwan ( Miwa, 1930, 1931), but subsequent authors stated that they did not find E. plebejus in Taiwan ( Suzuki, 1999; Kishii, 2004) and suggested that the past records were based on misidentification ( Ôhira, 1994, 1999).

Ecology. This species is often collected by light traps at night ( Ôhira, 1994, 1999). Specimens (EPM02, EPM03, and EPF02–08) were attracted to trees with Platypus quercivorus ( Curculionidae , Coleoptera ) and collected by interception traps in laurel forest.