Laccobius (Microlaccobius) roseiceps Régimbart, 1903 RẦflǿ 牙ḃ

(Figs 13, 17, 22, 25)

Laccobius (Microlaccobius) roseiceps Régimbart, 1903: 59 .

Material examined. TAIWAN: PINGTUNG: 3 males, 6 females (HCLC): Ligang Township [¶ffiė], Erchong River [二AEë], 22.7982°N 120.5011°E, 32m 26.IV.2019 . Hsing-Che Liu . KAOHSIUNG: 1 spec. (HCLC): Liouguei District [六AE區], Laonong River [Ž濃ë], 22.996017°N 120.638178°E, 229m, 24.VI.2020. Hsing-Che Liu & Uitsiann Ong leg. KINMEN: 2 males, 20 spec. (HCLC, NCHU): Main Island, 5-10. VII. 2020, Hsing-Che Liu leg.

Diagnosis. Small species, body length 1.7–2.2 mm, body width 1.0– 1.3 mm. Body elongate oval (Fig. 13), weakly convex. Head dark, with distinct preocular spots. Pronotum pale, with small dark oval spot in median, spot leaving large lateral portions of the pronotum yellow. (Figs. 22). Scutellar shield dark. Elytra pale, with densely arranged small dark spots, larger spots present medially and laterally. Leg pale or yellowish. Male genitalia (Fig. 17): Aedeagus 0.4 mm long. Median lobe wide, its apex rounded, with a pair of diverging lines running from apex; parameres slender, larger than median lobe, slightly bent inward.

Differential diagnosis. Laccobius roseiceps may be easily recognized by the pronotum with small oval dark spot. In this character, it may resemble L. hoi sp. nov. from which it mainly differs in smaller body size (1.7–2.2 mm in L. roseiceps, 2.5–2.7 mm in L. hoi sp. nov.). The structure of the median lobe (with the diverging lines) is very typical and hard-to-confuse with any other Laccobius species.

Distribution. China (Hong Kong), Japan (Honshu, Kyushu, Tanegashima), Taiwan (Kinmen islands) (Nakajima et al. 2020; Przewoźny, 2020, Liu et al. 2021). First record for Taiwan island (Fig. 27).

Bionomics. All specimens were collected from very slowly running streams. In southern Taiwan, the species co-occurred syntopically with L. hoi sp. nov. and L. formosus (Fig. 25).