Cercyon (Cercyon) unipunctatus ( Linnaeus, 1758 )

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 : 557-560

Cercyon (Cercyon) unipunctatus ( Linnaeus, 1758)

( Figs 8 , 11 , 13 )

Coccinella unipunctata Linnaeus, 1758: 364 . Transferred to Cercyon by LEACH (1817: 95). For complete synonymy see HANSEN (1999).

Type locality. Europe.

Type material examined. Coccinella unipunctata . The species was described from Europe based on an unspecified number of specimens. Based on the on-line catalogue of the Linnaeus collection, there is a single pinned specimen present in the collection, bearing the labels ‘unipunctata [hw] // 6 [p]’. We consider this specimen as the syntype. Based on the photographs available on-line, the specimen corresponds well with the European specimens treated under the name Cercyon unipunctatus by the body form and coloration (yellow elytra with central dark spot and darkened sutural interval, dark pronotum with pale lateral sides).

Additional material examined. KAZAKHSTAN: EAST KAZAKHSTAN REGION: 1 spec. ( SZMN): Vost. Kazakhstan, Markakolskiy r-n [Markakol district], s. [vill.] Urunkhayka, korov.n-z [cow dung], Markakolskiy rayon, 2.vii.1996, V. Zinchenko [leg.]. RUSSIA: YAMALO- NENETS AUTONOMOUS OKRUG: 2 spec. ( ZMMU): Salekhard, 19.vi.1955, Telishev leg. KEMEROVO OBLAST: 1 spec. ( ZISP):‘Kuznetsk, Tomsk g.’, Khvorov & Gorchakovskiy [leg.]. TYUMEN OBLAST: 1 spec. ( ZISP): okr. Tobolska [Tobolsk env.], 21.v.1925, Fridolin [leg.]. IRKUTSK OBLAST: 1 spec. ( ZISP): Irkutsk, Yakovlev [leg.]. SAKHA (YAKUTIA) REPUBLIC: 4 spec. ( ZISP): Yakutsk, 22.v.1911; 1 spec. ( ZISP): same locality, 22.vi.[19]25, Bianki [leg.]; 2 spec. ( ZISP): same data but 18.vi.[19]25. ALTAI REPUBLIC: 1 spec. ( ZISP): Uznezya on Katun, Altai, 25.vii. [1]909, [leg.] Gorchakovskiy; 1 spec. ( ZISP): same locality, 4.–6.viii.[1]909. SAKHALIN OBLAST: 1 spec. ( CSR): Kunashir, cordon Аlekhinskiy, 7.vii.2015, Yu. Sundukov & L. Sundukova leg.

Published records. RUSSIA: PRIMORSKY KRAI: Chernye Gory, Venedivnovo [likely misspelled form of “Venevitinovo”] ( HEBAUER 1995). MONGOLIA: KHENTII: Onon-Balj National Park, Bayan-Ovoo ( KORSUN et al. 2012). CHINA: HEILONGJIANG: Mishan ( JIA et al. 2011).

Diagnosis. Head black; pronotum black with widely pale lateral margins; elytra reddish-yellow with black central pentagonal spot, sutural interval black except basal part; maxillary palpi yellowish to reddish, last palpomere darker; elytral intervals flat; mesoventral plate narrowly elongate, ca. 3.7–5.0× as long as wide, metaventrite without femoral lines; pentagonal area of metaventrite with shallow and sparse punctation, distance between individual punctures in lateral parts as 4–6 diameters of puncture, fifth ventrite not emarginate apically; paramere rather narrow near base, slightly concave on outer margin, apex almost straight with some setae; median lobe nearly parallel-sided, triangularly narrowing apically; sternite 9 narrowly rounded apically, with 2 very short subapical setae, base strongly rounded.

Redescription. Form and color. Body elongate oval ( Fig. 8A ), length 2.0– 3.8 mm, width 1.0– 1.8 mm. Head black without paler preocular spots. Pronotum black, lateral margins narrowly pale, anterior margin very narrowly pale, base very narrowly pale only near posterolateral angles. Scutellum black. Elytra and epipleura reddish to yellowish, elytral disc with black pentagonal spot located in the middle of elytra; sutural interval black except basal part. Antennae yellowish except for darker club. Maxillary palpomeres yellowish to reddish, last palpomere darker. Ventral surface black or dark brown, posterior margins of abdominal ventrites yellowish or brownish. Legs brownish-yellow to reddish-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. 6.3–6.6× the width of one eye in dorsal view. Mentum glabrous, ca. 1.6× as wide as long, sparsely and finely punctate, with barely transverse wrinkles ( Fig. 8G ). Antennae with 9 antennomeres, scapus ca. 1.3–1.6× 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. 2.0–2.1× as wide as long. Pronotal punctation similar to that on head. Lateral margins of pronotum with narrow 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, medium large, rounded laterally. Mesoventral plate narrowly elongate, ca. 3.7–5.0× as long as wide, widest in medial part ( Fig. 8F ). Pentagonal area of metaventrite with shallow and sparse punctation, distance between individual punctures in lateral parts as 4–6 diameters of puncture ( Fig. 8E ). Metaventrite with raised glabrous sparsely punctate median pentagonal area; femoral lines absent. Elytra with ten punctate striae, striae 1–9 impressed and reaching base, stria 10 very short; intervals flat; ground punctures on intervals very fine, humeral bulge indistinct. Epipleura 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 ventrites, first ventrite distinctly longer than other ventrites, ca. 1.7–1.8× as long as second ventrite, with distinct median longitudinal carina, fifth ventrite arcuate, not emarginate apically.

Male genitalia ( Figs 8B–D ). Phallobase slightly longer than parameres, asymmetrical basally. Paramere rather narrow near base, slightly concave on outer margin, apex membranous, almost straight, with some setae. Median lobe nearly parallel-sided, lateral margins with very short setae in apical part, apex triangular, obtusely pointed; gonopore large, situated subapically; ароdemes long. Median projection of sternite 9 narrowly rounded apically, bearing 2 very short subapical setae, base strongly rounded, median portion shorter than lateral struts.

Variation. Some specimens of C. unipunctatus have almost black lateral margins of pronotum, with narrowly pale areas only near anterior angles of pronotum. Form and size of sutural spot are very variable ( Fig. 11 ) and extremely pale specimens have only weakly visible sutural spot. The dark morph of C. unipunctatus was described by NYHOLM (1952) as C. janssoni Nyholm, 1952 later recognized as belonging to C. unipunctatus ( LINDBERG 1955, SMETANA 1978). This rare morph only occurs in southern Sweden, and hence is not treated here in detail. The ratio of length to width of mesoventral plate may vary significantly even in specimens from the same location.

Biology. Polysaprophage; the species inhabits different organic rotting material ( SMETANA 1978, 1988; RYNDEVICH 2004с, 2007), mainly mammal excrements (especially cows, horses and sheep) and chicken manure. It frequently occurs in compost and rotting plant debris, and sometimes specimens can be found in decomposing remains near water. In Europe, specimens of C. unipunctatus were collected in the nests of different bird species: mute swan Cygnus olor (Gmelin, 1789) , tufted duck Aythya fuligula ( Linnaeus, 1758) , black-headed gull Larus ridibundus (Linnaeus, 1766) , marsh harrier Circus aeruginosus ( Linnaeus, 1758) , greater spotted eagle Aquila clanga Pallas, 1811 and song thrush Turdus philomelos Linnaeus, 1758 where they look for decaying organic remains (manure, plant debris etc.) ( RYNDEVICH & LUNDYSHEV 2005, LUNDYSHEV & RYNDEVICH 2010). Cercyon unipunctatus flies to light.

Distribution. Cercyon unipunctatus is a widespread Palaearctic species occurring throughout Europe except its southernmost parts ( FIKÁČEK et al. 2015), in Asia it is known from Kazakhstan, Russia, Mongolia, northernmost China (Nei Mongol) and northern Japan. In the middle of 19 th century the species was introduced to North America where it also became widespread ( SMETANA 1978).

Figures

Fig. 8. Cercyon unipunctatus (Linnaeus, 1758). A – dorsal and lateral habitus; B–D – male genitalia (B – tegmen; C – median lobe; D – sternite 9). E–H – ventral morphology (E – meso- and metaventrite; F – detail of mesoventral plate; G – mentum; H – prosternum and antennal groove).

Fig. 11. Cercyon unipunctatus (Linnaeus, 1758), variability of the elytral coloration.

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