Coelostoma stultum, (Walker, 1858)

Liu, Hsing-Che, Hu, Fang-Shuo & Fikáček, Martin, 2020, Review of the genus Coelostoma of Taiwan with description of a new species (Coleoptera: Hydrophilidae), Acta Entomologica Musei Nationalis Pragae 60 (1), pp. 155-162 : 159-160

stultum ( Walker, 1858)

( Figs 2F , 3A )

Hydrobius stultus Walker, 1858: 209.

Coelostoma stultum : ORCHYMONT (1928: 56) (recorded from ‘Formosaʼ without specified locality).

Coelostoma (Holocoelostoma) stultum : MOUCHAMPS (1958: 3).

For complete synonymy see HANSEN (1999).

Material examined. TAIWAN: HSINCHU: 1 1 ♀ ( HCLC): Zhudong [Űǥḃ], 28.viii.2018, 24.784950°N 121.036672°E, 83 m, Hsing-Che Liu leg. JAPAN: YAEYAMA ISL.: 1, 1 spec. ( NMPC): Iriomote Is., 28.vi.1981, S. Morita lgt.[this specimen was used to illustrate the genitalia of C. stultum in Fig. 2F ].

Diagnosis. Body size 5.4–5.7 mm, body width 3.0– 3.2 mm. Body oval. Labrum black with yellow edges, its front margin emarginate. Elytral surface densely punctate, without traces of series, sutural stria reaching basal half of elytra. Mesofemora with strong setae, but without dense pubescence. Abdominal ventrite V with row of stout setae situated in apical emargination.

Male genitalia ( Fig. 2F ): aedeagus 0.8–0.9 mm long. Median lobe shorter than parameres, wide basally, narrowing towards midlength, apical half narrowly parallelsided, rounded apically; gonopore wide, situated apically; parameres bent inwards in apical third, truncate apically. Differential diagnosis. This species differs from other Taiwanese species except C. bhutanicum in the following combination of characters: mesofemora without dense pubescence and the apical portion of abdominal ventrite 5 with a shallow emargination possessing stout setae (i.e. diagnostic characters of Holocoelostoma ). It can be distinguished from C. bhutanicum by having the median lobe wide in the basal half and not spoon-like in shape. In contrast to C. bhutanicum , specimens of C. stultum are slightly larger but with a relatively smaller and less sclerotized aedeagus.

Bionomics. Both examined specimens from Taiwan were found in rotten rice stems near a rice field ( Fig. 3A ).

Distribution. China (Chongqing, Fujian, Guangxi, Guangdong, Hainan, Jiangxi, Sichuan, Yunnan, Xizang), Andaman Is., India, Indonesia, Japan, Malaysia, Mascarene Is., Myanmar, Nicobar Is., Oman, Philippines, Saudi Arabia (south), South Korea, Sri Lanka, Taiwan, Thailand, United Arab Emirates, Vietnam ( JIA et al. 2014, 2017; this paper). Some of these records may actually refer to C. bhutanicum (see above under that species).

Figures

Fig. 2. male genitalia and front view of the head of Taiwanese Coelostoma species.A–F – genitals in dorsal view:A – C. fallaciosum Orchymont, 1936; B – C. vitalisi Orchymont, 1923; C – C. phallicum Orchymont, 1940; D – C. wui Orchymont, 1940; E – C. bhutanicum Jayaswal, 1972; F – C. stultum (Walker, 1858), specimen from Japan: Iriomote Island; G–H – front view of head with labrum: G – C. taiwanense sp. nov., paratype; H – C. fallaciosum.

Fig. 3. Habitat of Coelostoma species.A – Hsinchu County, Zhudong: habitat of C. stultum (Walker, 1858); B – Hsinchu County, Hengshan Township: habitat of C. wui Orchymont, 1940; C – Taichung City, Wufeng District:habitat of C. taiwanense sp.nov.and C. bhutanicum Jayaswal, 1972; D – Hsinchu County, Beipu Township: habitat of C. fallaciosum Orchymont, 1936; E – Yilan County, Jiaoxi Township: habitat of C. phallicum Orchymont, 1940; F – Taipei city, Neihu District: habitat of C. vitalisi Orchymont, 1923. Photos by H.-C. Liu (A–C, F), R. Matsushima (D) and F.-S. Hu (E).