Stenichnus (Stenichnus) bellulus Jaloszynski 2004

Stenichnus (Stenichnus) bellulus Jałoszyński

(Figs 13, 15–21)

Stenichnus bellulus Jałoszyński, 2004: 158.

Material studied. TAIWAN: 1 ♁, Taipei County, Fushan Botanical Garden, 21– 28.04.2008, leg. J. Borowski (cPJ); 1 ♁, Taichung County, Anmashan, 2225 m, 02.05.1990, leg. A. Smetana (MHNG); 3 ♀♀, Pingtung County, Peitawushan, trail at 1500 m, 01.05.1992, leg. A. Smetana (MHNG, cPJ); 2 exx., Hsinchu County, Hsinkuang village env., 44 km on road 60, Jienshih township, 1600 m, mountain forest, leaf litter of ‘ Canacea ’ {misspelling of Cannaceae?}, 25.03.2008, leg. S. Vit (MHNG); JAPAN, Okinawa Prefecture: Ishigaki-jima: 8 exx., Kabira env., roadside in subtropical forest, 12 and 18.01.2017, leg. P. Jałoszyński (cPJ); Iriomote-jima: 1 ex., 8 km NW Ôhara, forest edge, leaf litter, 11.01.2017, leg. P. Jałoszyński (cPJ); 1 ex., 10 km NW Ôhara, forest, rotten hey, 13.01.2017, leg. P. Jałoszyński (cPJ); 1 ♁, 1 ♀, Funauki env., 21– 25.03.2007, leg. T. Lackner (cPH); 2 ♁♁, Ôtamirindô, 7– 11.04.2005, FIT, leg. T. Fukuzawa (cPJ); Yonaguni -jima: 3 exx. (incl. 1 ♁), Mantabaru-Shinrinkoen, 9– 11.09.2004, leg. K. & S. Arai (cPJ); 6 exx., Mt. Urabudake, 20.03.2005, leg. S. Nomura (NSMT).

Distribution. Japan: Ryukyus: Yaeyama Islands: Iriomote-jima, Ishigaki-jima and Yonaguni-jima; Taiwan.

Remarks. This common species is broadly distributed in forested areas of Iriomote-jima and Ishigaki-jima; here for the first time recorded from Yonaguni-jima, which is situated ~ 70 km west of Iriomote and ~ 100 km east of Taiwan. In Taiwan, it was collected mainly in mountainous areas, even at elevations exceeding 2000 m, whereas in Ishigaki and Iriomote it can be commonly found at foot of forested hills.

Populations of S. bellulus show some variability that may be an interesting subject for molecular studies, with slight external differences between beetles inhabiting Yonaguni and Iriomote + Ishigaki + Taiwan. The specimens from Yonaguni-jima are slightly slenderer than those from the remaining islands. However, the variability in male genital structures (Figs 15–21) in the studied sample does not seem to correspond with the disjunct distribution, and even beetles inhabiting one island show some differences in the shape of the median lobe, its apical margin, and especially in the shape of the median apical endophallic plate. The latter can be subtrapezoidal (Figs 15–19) or subtriangular (Fig. 20), and its distal margin can be rounded (Fig. 15), truncate (Figs 16, 18) or broadly subtriangular with rounded tip (Figs 17, 19). This plate during copulation is pushed distally and strongly flipped ventrally so that in ventral view it is inverted, with its broad base directed distally, and the narrow apex directed toward base of the aedeagus, while the membranous folds of the inner sack covered with dense minute cuticular projections are evaginated from the ostium and ‘inflated’ to anchor inside the female’s bursa copulatrix (Fig. 21). This great variability in the aedeagal structure is unusual in Stenichnus and will require further study when more specimens from the entire species range become available.

For notes on distinguishing S. bellulus from S. taiwanicus see the Remarks for the latter species.