Cercyon (Cercyon) divisus Hebauer, 2002

Ryndevich, Sergey K., Jia, Fenglong & Fikáček, Martin, 2017, A review of the Asian species of the Cercyon unipunctatus group (Coleoptera: Hydrophilidae: Sphaeridiinae), Acta Entomologica Musei Nationalis Pragae (Acta. Ent. Mus. Natl. Pragae) 57 (2), pp. 535-576 : 538-543

Cercyon (Cercyon) divisus Hebauer, 2002

( Figs 1–2 , 13 )

Cercyon (Cercyon) divisus Hebauer, 2002: 42 .

Type locality. Nepal, Karnali zone, Khari Lagna, 3500–3700 m a.s.l. [GPS 29°21’N 82°10’E: AHRENS 2004].

Type material examined. HOLOTYPE: ♂ ( SMTD): ‘ Nepal, Karnali zone Khari Lagna 35-3700 m N-Jumla, 23./24.6., 4.7.95 lg. Ahrens & Pommeranz’.

Additional material examined. CHINA: YUNNAN: 1 spec. ( NHMB): Habashan Mts., E slope , 3000–3600 m, 27º20’N 100º09’E, 13–17.vii.1992, David Král leg.; 9 spec. ( NHMB, CSR, NMPC): Yulongshan Mts. , 2900–3500 m, 27°01’N 100°12’E, 24–26.v.1993, Vit. Kubáň leg.; 1 spec. ( NHMB): Yulongshan , 3300 m, 27.07N 100.14E, 28.v.1993, V. Kubáň leg.; 1 spec. ( NHMB): Yulongshan Mts. , 3500–4000 m, 27.10N 100.13E, 16–19. vi.1993, V. Kubáň leg.; 1 spec. ( NHMB): Yulong Mt. , 3900 m, 27.10N 100.13E, 16–19.vi.1993, Bolm leg.; 1 spec. ( NHMB): Yulong Mt. , 3200 m, 27.00N 100.12E, 23–24.vi.1993, Bolm leg.; 3 spec. ( NMPC, CSR): 26 km N Lijiang, 15.vi.2007, Ganhaizi pass, individually collected under stones, on soil surface and on plants and dense shrubs, sparse coniferous forest (with dominante Pinus ), 27º07.1’N 100º14.9’E, 3000 m, J. Hájek & J. Růžička leg.; 3 spec. ( NMPC, CSR): 32 km N Lijiang, 16.vi.2007, Maoniuping, yak meadows (wet pasture), individually collected in and under fresh and older excrements of yak ( Bos mutus ), 27º09.9’N 100º14.5’E, 3540 m, J. Hájek & J. Růžička leg.; 9 spec. ( NHMB): Yulong Mts. , 3200 m, 24–26.v.1993, 27º01N 100º12E, Bolm lgt.; 1 spec. ( NMPC): Gaoligong Mts. NNR , Kongshu vill. env ., 2035 m, 25°43.5’N 98°38.4’E, 30.vi.–1.vii.2016, J. Hájek & J. Růžička leg.; 1 spec. ( NMPC): Gaoligong Mts. NNR, E of Kongshu, cow excrements, 2035–2230 m, 25°43.2’N 98°38.4’E, 1.vii.2016, J. Hájek & J. Růžička lgt.; 1 spec. ( CAPG): Nujiang, Lisu Pref., Gaoligong Shan, valley 21 km W of Gongshan, 27°47’03”N 98°27’39”E, 3320 m, moss, alder, bamboo, Rhododendron , sifted, 6.vi.2007, Pütz leg. SICHUAN: 1 spec. ( NHMB): Moxi-Hailougou , 1200–1900 m, 29°37’N 102°07’E, 1–7.vii.1994, D. Král & J. Farkač leg.; 1 spec. ( NHMB): 20 km N Sabdé , 3200 m, 10–16.vii.1998, J. Král leg.; 2 spec. ( CSR): pass N of Jiulong, 29°19’20”N 101°30’23”E, 4565 m, 22–23.vii.2009, Belousov & Kabak leg.; 3 spec. ( NMPC, SYSU): Moxi env., Hailuogou valley, above Cableway station, mixed forest with Abies , Betula , Rhododendron and broadleaf trees, baited pitfall trap (fish meat), 3100 m, 29°34’28’’N 101°59’24’’E, 18–21.vi.2014, J. Hájek, J. Růžička & M. Tkoč lgt. INDIA: WEST BENGAL: 5 spec. ( CAS, NMPC): Darjeeling, Tonglu, 19–23.v.1998, 2600–3000 m, Fabrizi & Ahrens leg. NEPAL: BAGMATI: 1 spec. ( SMTD): Mt. Panchase, 20 km W of Pokhara, sifting of forest leaf litter, 2300 m, 20.v.1997, O. Jäger leg . KARNALI: 1 spec. ( NMPC): Jumla, Churta, E Jagdula valley, 3800–4100 m, 3.vi.2007, 29º09’49N 82º31’09E, alpine mats, M. Hartmann leg. TAPLEJUNG: 1 spec. ( NMPC): upper Simbua Khola, near Tseram, 10–15.v.1988, 3250– 3350 m., Schawaller leg.

Published records. NEPAL: KARNALI: Lagna, N. Jumla ; Mabu Pass, N of Dailekh. Bagmati: Langtang, Chandan Bari env.; Helambu, Tharepathi; Helambu, Mulkharka-Chisapani ( HEBAUER 2002a).

Diagnosis. Head black; pronotum pale with central dark spot of variable size and shape (present only mesally, or large and laterally lobate, or covering nearly whole pronotum except pale lateral margins); elytra pale with variable pattern of dark spots (the following areas may be dark: sutural interval, bases of elytral intervals 1–4, humeral area, and subapical part of elytral intervals 7–9); last maxillary palpomere slightly darker; dorsal surface without hairs; elytral intervals flat; mesoventral plate 5.0–6.0× as long as wide; fifth abdominal ventrite without apical emargination; median projection of sternite 9 narrow to wide, base straight; paramere rather wide subapically, almost straight on outer margin, narrowly rounded apically, apex with setae. Median lobe widest near middle, slightly narrowing apically.

Redescription. Form and color. Body elongate oval ( Fig. 1 ), length 2.2–2.7 mm, width 1.4–1.6 mm. Head black with very small brownish preocular spots; pronotum reddish-brown with central black spot of variable extent: confined to central part, extended more laterally in anterior portion (i.e. unilobate laterally) or anteriorly and posteriorly (i.e. bilobate laterally), or extending laterally throughout its length and leaving only a rather wide pale pronotal margin; scutellum brown to black; elytron brownish-yellow or reddish-yellow, base of elytra darker (in some specimens with dark spot at bases of intervals 1–4), sutural interval pale to almost completely dark; humeral area pale or with dark spot; epipleura of elytra brownish-yellow to brown.Antennae yellowish except for darker club. Maxillary palpomeres yellowish, ultimate palpomere darker. Ventral surface black or dark brown, mesoventral plate and metaventral pentagon brown to dark brown, posterior margins of abdominal ventrites brownish. Legs brownish-yellow to brown.

Head. Clypeus with dense, moderately coarse punctures, interstices without microsculpture. Anterior margin of clypeus with narrow bead. Frontoclypeal suture undetectable. Frons without microsculpture on interstices. Eyes small, somewhat protruding, interocular distance ca. 6× of one eye in dorsal view. Mentum glabrous, ca. 1.8–2.1× as wide as long, densely and coarsely punctate. Antennae with 9 antennomeres, scapus ca. 1.3× as long as antennomeres 2–5 combined, club compact. Maxillary palpomere 2 strongly swollen, palpomere 4 almost symmetrical, equal to palpomere 3 in length.

Thorax. Elytra and pronotum without hairs. Pronotum ca. 2.4× as wide as long. Pronotal punctation similar to that on head. Lateral margins of pronotum with narrow bead, the bead overlapping anterior and posterior corners, anterior and central part of posterior margin of pronotum without bead. Prosternum with strong longitudinal carina medially; antennal groove distinct, moderately large, rounded laterally. Mesoventral plate very narrowly elongate, ca. 5.0–6.0× as long as wide, widest in medial part ( Figs 2I–J, M–N ). Metaventrite with raised, glabrous, sparsely punctate median pentagonal area; femoral lines absent ( Figs 2I, M ). Elytra with 10 punctate striae, striae 1–9 impressed, reaching base, stria 10 very short; intervals flat; ground punctures on intervals very fine; humeral bulge not distinct. Epipleuron flat, horizontal. Femora with sparse and shallow punctures ventrally, with distinct tibial groove. Tarsi with densely arranged whitish setae ventrally, first metatarsomere about as long as metatarsomeres 2–3 combined.

Abdomen. Abdomen with five exposed ventrites, first ventrite longer than other ventrites, ca. 2× as long as second ventrite, bearing distinct median longitudinal carina; fifth ventrite arcuate, not emarginate apically.

Male genitalia ( Figs 2A–H ). Phallobase slightly shorter than parameres, asymmetrical basally. Paramere gradually narrowing towards apex, rather wide subapically, almost straight on outer margin, narrowly rounded on lateral margin apically, apex and mesal edge with numerous setae subapically; apex of parameres membranous. Median lobe widest near mid-length, slightly narrowing apically, with short ароdemes basally; apex pointed, gonopore moderately large, situated subapically. Median projection of sternite 9 narrow to wide, apex with 2 short setae, pointed to rounded, median portion shorter than lateral struts or equally long as lateral struts, base almost direct.

Comments on variation and distribution. Cercyon divisus is a very variable species especially in dorsal coloration and in the shape of male sternite 9, and also slightly in the proportions of the mesoventral plate and male genitalia. Variability of dorsal coloration and of male sternite 9 does not seem to be geographically based, and specimens from the same locality (or adjacent localities) may differ largely in these characters (e.g., compare coloration of two specimens from the same locality on Figs 1C–D , and shape of the male sternite 9 of the specimens from Yunnan on Figs 2D,F,G ). Other characters vary geographically: Chinese specimens are slightly larger, having a slightly narrower mesoventral plate (6.0× as long as wide, Fig. 2N ). Specimens from India and Nepal have a slightly more robust medial lobe of the male genitalia and a larger gonopore, a slightly wider mentum (ca. 2.1× as wide as long; Fig. 2K ) and slightly deeper punctation of the median pentagonal area of the metaventrite ( Fig. 2I ).

We originally intended to regard the Chinese specimens as a separate species, but detailed examination of all available specimens revealed that the observed morphological differences are either too minute (shape of the median lobe and mesoventral plate), seem to vary in the same extent locally as well as across the whole range (dorsal coloration) and/or form a continual series of intermediate forms without clear limit between two morphotypes (male sternite 9). Unfortunately, the species is so far known only from western Himalaya and mountains in Yunnan and Sichuan, with a huge gap in the Eastern Himalaya from where no specimens are known ( Fig. 13 ). This fact further complicates the assessment to what extent the variability is continual and geographically correlated. Our decision to regard all examined specimens as representatives of one species is therefore preliminary and should be corroborated later by DNA markers and/or by examination of Eastern Himalaya specimens.

Biology. Specimens in which collecting circumstances are known were collected from yak and cow excrements, in pitfall traps baited by rotten fish, sifted from leaf litter or collected individually under stones in high altitude forests ( Alnus + Rhododendron + bamboo, mixed forests with Abies , Rhododendron and broad-leaf trees, and sparse coniferous forests with Pinus ).

Distribution. Cercyon divisus is known from western Himalaya ( Nepal and India: Darjeeling area) and from mountains of Yunnan and Sichuan in China; records from Eastern Himalaya are missing but its occurrence there is very probable. Newly recorded from India and China.

Figures

Fig. 1. Dorsal and lateral habitus of Cercyon divisus Hebauer, 2002. A, C–D – specimens from China: Yunnan, Yulongshan; B – specimen from Nepal: Taplejung Distr., upper Simbua Khola near Tseram.

Fig. 2. Cercyon divisus Hebauer, 2002. A–C – genitalia of specimen from Nepal: Taplejung Distr. (NMPC) (A – tergmen; B – median lobe; C – sternite 9). D–H – variability in the shape of male sternite 9 (D – China: Yunnan: Habashan; E – Nepal: Karnali Prov.; F – China: Yunnan: Maoniuping; G – China: Yunnan: Yulongshan; H – China: Sichuan: Moxi). I–P – ventral morphology (I–L – specimen from India: West Bengal: Darjeeling; M–P – specimen from China:Yunnan:Maoniuping):I, M – meso- and metaventrite; J, N – detail of mesoventral plate; K, O – mentum; L, P – prosternum and antennal groove.

Fig. 13. Known distribution of the species of C. unipunctatus species group in Asia.