Pachysternum apicatum Motschulsky, 1863

Fikáček, Martin, Jia, Fenglong & Prokin, Alexander, 2012, A review of the Asian species of the genus Pachysternum (Coleoptera: Hydrophilidae: Sphaeridiinae), Zootaxa 3219, pp. 1-53 : 15-20

Pachysternum apicatum Motschulsky, 1863

( Figs. 18 , 36, 50, 72)

Pachysternum apicatum Motschulsky, 1863: 448 .

Pachysternum apicatum: Knisch (1921: 88, faunistics) ; Knisch (1934: 158, catalogue); Orchymont (1926a: 224, identification key, distribution); Orchymont (1928: 83, catalogue), Hansen (1999: 306, catalogue).

Type locality. Sumatra. Motschulsky (1863: 448) indicated “le continent indien” as the type locality. This was interpreted as India by all subsequent authors, although Orchymont (1926a) most probably recognized the discordance between this interpretation of the type locality and the distributional area of the species, indicating the distribution as “ Tonkin, Malacca, Iles Mentawei, Java, Iles Lombok ( Inde d’après Motschulsky)”. Based on the label data of the types of P. nigrovittatum (see below), Motschulsky used the term “ India ” (or “ India orientalis”) in a very broad sense corresponding with the whole Oriental Region including the islands of Sundaland. This may be also the case of the expression “le continent indien” used in the original description of P. apicatum , even though it seems to refer rather to the continental part of the Oriental Region than to the islands. Taking into account the locality data of type specimens, we specify Sumatra as the type locality of this species and consider the type locality indicated by Motschulsky (1863) as ambiguous.

Type material. Lectotype (hereby designated): male ( ZMUM): “[small yellow triangular label] // Type [small white label, in handwritten] // Pachysternum / apicatum / Motsch / Ind. or. Sumatra [yellow label, in handwritten]”. Paralectotypes: 3 males ( ZMUM): same label data as lectotype. [Note: We received four syntypes glued on the same paper label bearing the label mentioned above from ZMUM. One additional specimen, originally glued on the same label according to the remnants of glue, was lost. All four specimens have large hole in the right elytron, indicating that they were pinned originally. The indices of re-mounting of the specimens as well as the discordance of their label data with the type locality given by Motschulsky (1863) impeach the type status of these specimens. However, other indices seem to support their type status: (i) label data, handwriting on the labels and the arrangement of labels corresponds with those attached to the types of Pachysternum nigrovittatum , whose type status is unambiguous; (ii) the specimens correspond with short diagnosis by Motschulsky (1863). For these reasons, we consider all four specimens as syntypes and designate the lectotype from this series. We have remounted each specimen on a separate label, with the lectotype bearing the original labels and paralectotypes bearing their copies.]

Additional material examined. BRUNEI: 42 spec. ( BMNH, NMPC): Kuala Belalung FSC, 4°34'N 115°07'E, i.1992, lgt. N. Mawdsley; 14 spec. ( BMNH): same locality and collector, ii.1992. CHINA: Hainan: 1 female ( NMPC): Jiangfengling Mts., Tiachi Lake env., Bishu villa, elev. 950 m, 18°44.7'N 108°50.7'E, lgt. Fikáček . INDONESIA: Bali: 3 spec. ( ZMUC): Lake Bratan , elev. 1200 m [8°17'S, 115°9'E], 27.i.1994. lgt. J. Pedersen. North Sumatra: 1 female ( NHMW): Prapat [= Parapat ] env., elev. 1000 m [2°39'46''N 98°56'7''E], 17.ii.1990, lgt. S. Schödl. Sulawesi [unspecified]: 2 spec. ( IRSNB): “ Celebes ”, without date and collector. West Java: 2 spec. ( IRSNB): Buitenzorg [= Bogor ], ii.1890, lgt. Kannegieter ; 1 spec. ( IRSNB): Tjigembong [= Cigembong , 7°9'S, 106°55'59.88''E], vi.1915, lgt. J. B. Corporaal. West Nusa Tenggara: 4 spec. ( IRSNB): Lombok , Sapit , elev. 610 m [8°39'S, 116°19'E], iv.1896, lgt. H. Fruhstorfer; 9 spec. ( SMNS): Lombok, Senaro , N slope of Rinjani , elev. 1100 m [8°19'53''S, 118°25'2''E], 2–5.ii.1994, lgt. Bolm . West Sumatra: 1 spec. ( IRSNB): Fort de Kock [= Bukittinggi ], elev. 920 m [0°18'20''S 100°22'9''E], viii.1894, lgt. E. Modiglian; 3 spec., 1 female ( IRSNB, NHMW): same locality, x.1922, lgt. E. Jacobson; 1 female ( NHMW): Lembah Anai, W Padang Panjang [0°29'2''S 100°20'19''E], 12.ii.1991, lgt. H. Schillhammer; 3 spec. ( IRSNB): Mentawei, Si Oban [= Mentawei Islands , Sipora Is. , Sioban , 2°11'S, 99°43'E], iv–viii.1894, lgt. Modigliani ; 2 spec. ( NHMW): Padang, Bungus beach [0°57'13''S, 100°21'7''E], 14.ii.1991, lgt. S. Schödl (17); 1 spec. ( IRSNB): Sipora [= Sipura Is. ], Sereinu [2°11'S, 99°40'E], v–vi.1894, lgt. Modigliani ; 4 spec. ( NHMW): Siberut, Madobak , W Muarasiberut [1°38'23''S 99°7'22''E], 19.ii.1991, lgt. S. Schödl (24). LAOS: Bolikhamxai: 11 males ( NHMB, NMPC): 8 km NE Ban Nape, elev. 600 m, 18°21'N, 105°8'E, 1–18.v.2001, lgt. V. Kubáň. Louangphabang: 1 spec. ( NHMB): 5 km W of Ban Song Cha, elev. 1200 m, 20°33'N 102°14'E, 10–16.v.1999, lgt. V. Kubáň; 11 spec. ( NHMB): Thong Khan , elev. 750 m, 19°35'N 101°58'E, 11–21.v.2002, lgt. V. Kubáň. Phongsali: 3 spec. ( NHMB, NMPC): Phongsali env ., elev. 1500 m, 21°41'N, 102°6'E, 6–17.v.2004, lgt. V. Kubáň. MALAYSIA: Johor: 3 spec. ( IRSNB): “ Johore ”, without date and collector. Melaka: 6 spec. ( BMNH): Malacca [2°11'53''N 102°14'59''E], without date, lgt. Wallace ; 1 spec. ( IRSNB): same locality, without date, lgt. Kirsch . Pahang: 1 spec. ( FHGC): 30 km NE Raub, Lala Lembik, elev. 200–400 m [3°56'N 101°38'E], 22.iv.–15.v.2002, lgt. E. Jendek & O. Šauša ; 3 spec. ( BMNH): Taman Negara [= Taman Negara National Park , ca. 4°41'N, 102°34'E], 1–13.iii.1984, lgt. L. Jessop; 1 female ( NHMW): same locality, 12–14.vii.1993, lgt. H. Forster; 5 spec. ( NHMW): Tioman Is., E. Kg. Tekek , elev. 30 m [2°48'56''N 104°9'18''E], 30.i.1992, lgt. H. Schillhammer (11); 1 female ( NHMW): same locality, 15–24.vii.1993, lgt. Schuh ; 2 spec. ( FHGC): Tekek [2°48'56''N 104°9'18''E], 5.iv.1987, lgt. Leller . Perak: 6 spec. ( NMPC): Cameron Highlands, Batu 19 village env., elev. 590 m, 4°22.2'N 101°20.0'E, 5–15.v.2009, lgt. J. Hájek. Sabah: 1 spec. ( BMNH): 5 miles S of Mt. Trus Madi , elev. 549 m [5°28'29''N 116°31'6''E], 18–28.viii.1977, lgt. M. E. Bacchus; 17 spec. ( BMNH, NMPC): same locality, 18–28.viii.1977, lgt. M. E. Bacchus; 1 spec. ( NHMW): 50 km E Kota Kinabalu, Crocker Mts. , Gunung Emas [5°49'41''N 116°20'1''E], 16–27.iv.1993, lgt. I. Jeniš; 15 spec. ( BMNH): R. Karamuak, 7 miles SSE Telupid , elev. 61 m [6°5'13''N 117°15'17''E], 1–7.ix.1977, lgt. M. E. Bacchus; 2 spec. ( BMNH): same locality, 1–7.ix.1977, lgt. M. E. Bacchus; 3 spec. ( BMNH): 30 miles, Sandakan-Keningau Rd. , alt. 76 m, leaf litter, lgt. M. E. Bacchus; 1 spec. ( BMNH): “Sandakan, S. Lokan” [= Sandakan, Sungai Lokan, ca. 5°25'58''N 117°43'58''E], ix.1996, lgt. A. Y. C. Chung. Sarawak: 9 spec. ( BMNH, NMPC): 4th Division, Gn. Mulu NP, nr. base camp, aluvial forest litter, elev. 50–100 m [4°2'55''N 114°49'17''E], v–viii.1978, lgt. P. M. Hammond & J. E. Marshall; 3 spec. ( BMNH): same data, rotting fruit; 3 spec. ( BMNH): same data, pitfall trap, fish bait; 1 spec. ( BMNH): same data, cut grass; 1 spec. ( BMNH): same locality, pitfall trap, fish bait, alluvial forest, iii–v.1978, lgt. I. Hanski; 1 spec. ( BMNH): same locality, pitfall trap, iii–v.1978, lgt. I. Hanski; 3 spec. ( BMNH): 4th Division, Gn. Mulu NP, nr. Camp I, elev. 150–200 m [ca. 4°03'N 114°50'E], v–viii.1978, lgt. P. M. Hammond & J. E. Marshall; 3 spec. ( BMNH): Kuching , [1°31'52''N 110°20'54''E], 1910, lgt. J. E. A. Lewis; 2 spec. ( NMPC): Kapit, Sebong , Baleh river [2°9'N 113°25'E], 6–21.iii.1994, lgt. S. Bílý. Selangor: 3 spec. ( FHGC): Ulu Gombak Field Studies Centre (22 km NE Kuala Lumpur ), elev. 300 m [3°19'32''N 101°45'16''E], 17–22.xi.1988, lgt. W. Rohe; 13 spec. ( SMF): same locality, felled young bamboo shoot ( Gigantochloa scortechinii ) laying on the ground, 21.vii.2007, lgt. D. Kovac ( BS 31/07); 11 spec. ( SMF): same locality, felled young bamboo shoot ( Gigantochloa scortechinii ), 21.viii.2007, lgt. D. Kovac ( BS 30/07); 8 spec. ( SMF): same locality, in decaying Arthrocarpus fruit, 24.viii.2007, lgt. D. Kovac (V5/07 /2); 3 spec. ( SMF): same locality, felled young bamboo shoot ( Gigantochloa scortechinii ) laying on the ground, 24.viii.2007, lgt. D. Kovac ( BS 50/07); 9 spec. ( SMF): same locality, decaying Arthrocarpus fruit, 25.viii.2007, lgt. D. Kovac (V7/07 /02). SINGAPORE: 4 spec. ( IRSNB): Singapore [1°21'N 103°50'E], without date, lgt. Saunders ; 3 spec. ( IRSNB): same locality, without date, lgt. Baker; 1 spec. ( IRSNB): same locality, 1921, lgt. J. C. Maulton; 4 spec. ( ANIC): Yishun , 3.vii.1997, lgt. T. Gush. THAILAND: Chiang Mai: 1 male ( NHMW): Doi Inthanon , Bang Khun Klang , elev. 1200 m [18°32'N, 98°32'E], 16–23.i.1990, lgt. Malicky & Chantaramongkol ; 28 spec. ( BMNH): Chang Dao Hill Resort , 19°33.54'N 99°4.605'E, 27.vi.2006, lgt. M. V. L. Barclay & H. Mendel. Loei: 1 spec. ( ASKC): ca. 8 km S Khao Lak , Merlin resort env. [8°36'36''N 98°14'31''E], 30.vii.–11.viii.2007, lgt. A. Skale. Mae Hong Son: 2 spec. ( SMF): Pang Mapha , 5 km SE of Soppong [= Pang Mapha ], Ban Pha Mon env. [19°30'2''N 98°16'41''E], 1.viii.2006, lgt. D. Kovac ( B 195/06); 1 spec. ( SMF): same locality, 14.viii.2006, lgt. D. Kovac ( B 105/06). Yala: 1 male ( NHMW): Betong , Gunung Cang dun village [5°52'N 101°7'E], 26.iii.-22.iv.1993, lgt. Horák & Strnad . VIETNAM: Bac Thai: 1 male ( NHMW): Tam Dao [ National Park ], 75 km NW Hanoi [21°38'N, 105°30'E], 16–23.v.1991, lgt. Strnad . Nghe An: 26 spec. ( IRSNB): Lactho [= Lac Tho , 21°4'N, 106°6'E], without date, lgt. de Cooman .

Differential diagnosis. Because of the polymorphism of the dorsal coloration and shape of the anterior tibiae (but not the male genitalia), the correct identification of this species may be rather difficult. Generally, all specimens lacking sharply limited subbasal pale spots of elytra, alternating longitudinal pale and dark stripes on elytra, and/or pale submedian spots at posterior margin of pronotum should be checked for their possible assignment to P. apicatum . Among those, P. haemorrhoum may be easily distinguished by the lateral portions of metaventrite lacking microsculpture on interstices and therefore shiny in appearance ( Fig. 21 ), as well as by its distribution in Palaearctic Region and its completely different male genitalia ( Fig. 31 ). In continental SE Asia and southern and central China, similar species may be distinguished as follows: dark specimens of Pachysternum kubani differ from mainland forms of P. apicatum by the uniformly dark frons (the frons entirely or at least medially pale reddish in mainland P. apicatum ) and by the different shape of the apical portion of the median lobe (widely rounded in P. kubani , triangular in P. apicatum ; compare Figs. 33c, e and 36c). Pachysternum coomani differs from continental P. ap ic a - tum by more or less entirely pale reddish dorsal body surface (body dark brown to black, with small to large yellow apical elytral spot in continental P. apicatum , Figs. 50 d–g) and by the wide and parallel-sided median lobe of the aedeagus. In the islands of SE Asia, Pachysternum apicatum is very similar to P. curvatum from the Philippines, but is for one thing missing from Philippines, and for another differs in at least very weakly bisinuate or angular outer margin of anterior tibia ( Figs. 39 a–b, this character should be checked in other than strict dorsal views as well), by the morphology of the median lobe ( Fig. 36), and partly also by the coloration (see P. c u r v a t u m for details). The only species without basal spots on elytra with which P. apicatum co-occurs on the islands of SE Asia is P. sandacanum in northern Borneo; the Bornean form of P. a p i c a t u m ( Figs. 50 h–j) may be, however, very easily distinguished from it according to the coloration and shape of anterior tibia (see under P. sandacanum for details).

Redescription (based on a typical specimen from Lombok Is. corresponding with the lectotype, Figs. 50 a–b). Body widely oval, shape of elytra sexually dimorphic, female with distinctly pronounced humeral portion of elytra. Body length 2.2–3.6 mm (lectotype: 3.1 mm); body width 1.6–2.2 mm (lectotype 2.0 mm).

Coloration. Head dark brown with pale median portion of frons and clypeus. Pronotum dark brown, with large vaguely limited reddish spot in each anterolateral corner and vague slightly paler spot medially at anterior margin. Elytra black except for pale reddish spot on apex of each elytron extending up to posterior third on intervals 2–6 and along lateral margin. Ventral surface of head and prothorax brown, meso- and metathoracic sclerites black to dark brown; abdominal ventrites 1–4 dark brown with pale lateral portions, ventrite 5 entirely pale. Legs reddish brown, posterior portions of femora darker, brown.

External morphology. Clypeus with coarse and dense punctation consisting of punctures of two slightly different sizes. Frons with similar but sparser punctation as on clypeus, punctures separated ca. 2–3× puncture diameter. Interstices without microsculpture. Larger punctures on pronotum rounded, much larger than small punctures, small punctures minute, scar-like, divided by 2–3× puncture width. Pronotal interstices without microsculpture. Prosternum with very distinct median carina. Elytral series consisting of large, shallow punctures; interval punctation with minute semicircular punctures much smaller than serial ones, interval punctation consisting of two slightly different sizes of punctures, larger punctures setiferous; interstices without any trace of microsculpture. Elytral series distinctly impressed. Preepisternal elevation of mesothorax with deep posterolateral pits. Femoral lines on metaventrite slightly angulate, median portion of metaventrite bearing moderately large and rather dense setiferous punctation, interstices without microsculpture; lateral portions with very coarse and dense, densely pubescent punctation. Outer margin of anterior tibia very weakly bisinuate, outer series of spines slightly interrupted at the place of the sinuation.

Male genitalia ( Fig. 36). Tegmen 1.5–1.6 mm long, median lobe 1.5 mm long. Phallobase ca. twice as long as parameres, bearing small, slightly asymmetrical basal manubrium. Median lobe widest at midlength, gradually narrowing apicad, apical portion triangular, stump at very apex; gonopore subapical, rather indistinct; lateral pubescent lobes narrow. Sternite 9 with widely rounded median projection, without apical emargination.

Variation. Extremely variable species, varying especially in coloration and the shape of anterior tibiae, but rather constant in genital morphology. General coloration varies from very dark brown (typical form and majority of mainland forms, Figs. 50 a–f) to pale brown (some mainland forms and the Bornean form, Figs. 50 g–j). Wide variability concerns the color patterns of elytra, the extent of apical elytral pale spot varies from totally absent ( Figs. 50 i–j) through very small and confined to very apex only ( Figs. 50 d–h, these specimens are very similar to dark specimens of P. kubani sp. nov.) to specimens with large apical spot corresponding with the redescription above ( Figs. 50 a–c, this coloration is also present in the lectotype). Very rarely, there is also a vaguely defined pale humeral spot (these specimens resemble P. sulawesicum and may be distinguished by the morphology of male genitalia). Uniformly colored specimens or those with very small and rather indistinct apical elytral spot occur in Borneo and predominate also in the southern part of the Malayan peninsula. On the other hand, specimens from the chain of islands between Sumatra and Lombok and in Sulawesi usually have very distinct and large apical spot, which is also the case of the specimens from northern parts of the continental Asia.

The shape of anterior tibia varies highly from nearly continually arcuate (in specimens from Java, which are therefore very similar to allied P. c u r v a t u m and P. sandacanum sp. nov.) through weakly angular to indistinctly bisinuate (the most usual form, Fig. 39 a) to deeply emarginate and therefore resembling P. kubani sp. nov. ( Fig. 39 b). Deeply excised tibiae occur especially in all examined specimens from Borneo (where P. apicatum is therefore easily recognizable from similar P. sandacanum with continually arcuate outer margin of anterior tibiae) and with higher frequency also in the specimens from continental Asia. In continental specimens we have also found few specimens (from northern Laos and Vietnam) in which the series of spines on outer margin of the tibiae is not interrupted by a gap, as it is usual for the majority of the examined specimens of P. apicatum .

The wide variability mentioned above makes P. apicatum rather difficult to recognize in many cases. In contrast, the local populations are rather constant in all these characters in most cases ( Fig. 72 ). For example, all specimens from Borneo are rather pale brown, lack the apical elytral spot and have rather deeply bisinuate anterior tibiae; specimens from Malayan peninsula are similar to those from Borneo, but usually much darker; specimens from the island chain from Sumatra to Lombok are most frequently very dark brown, with large and very apparent apical elytral spot and only slightly angular anterior tibiae; and specimens from northern Thailand and northern Vietnam are similar to those from Sumatra in coloration, but have rather deeply bisinuate anterior tibiae. This may suggest that P. apicatum as it is understood here may be in fact a cluster of very similar sibling species. Further studies on wider material and possibly using other than morphological characters would be desirable for complete understanding of the problem which is left unresolved here. The lectotype designated above corresponds with the form with large apical elytral spot and only indistinctly sinuate/angulate outer margin of anterior tibiae, and in the case of splitting into more species, the name P. apicatum had to be therefore applied for that form occurring from Sumatra and adjacent islands through Java to Lombok Is.

Biology. Based on label data and personal experience, the specimens were collected from various kinds of decaying organic matter, most frequently from decaying plant remains (rotten manihot skins, rotten durian, native vegetable garden refuse, rotting fruit, leaf litter, felled young bamboo shoots), sometimes also collected in baited pitfall traps (with dead fish or dung as the bait) or on carcasses (“dead pig”). No specimen was collected from mammal excrements, which suggests that the biology of P. apicatum probably differs from most other Asian Pachysternum except from P. curvatum and P. sandacanum .

Distribution. Widely distributed in the whole southeastern Asia, reaching from southern China (Hainan) and northern Thailand, Laos and Vietnam through Malayan peninsula to the islands of Sundaland (Sumatra, Java, Bali Lombok, Sulawesi, Borneo).

Figures

FIGURE 72. Distribution and geography-based color variation of the species of the Pachysternum apicatum complex.

FIGURES 12 – 25. General morphology of the Asian Pachysternum. 12 – 14: pronotal punctation (12: P. nigrovittatum, 13: P. haemorrhoum, 14: P. r u g o s u m); 15: meso- and metathorax of P. nigrovittatum, ventral view; 16 – 19: preepisternal elevation of mesothorax (16: P. haemorrhoum, 17: P. s u l a w e s i c u m, 18: P. apicatum, 19: P. rugosum); 20 – 21: surface sculpture of metaventrite mesally and laterally of femoral line (20: P. nigrovittatum, 21: P. haemorrhoum); 22: elytral punctation of P. nigrovittatum; 23: scutellum of P. nigrovittatum; 24: anterior leg of P. nigrovittatum; 25: abdomen of P. nigrovitattum.

FIGURES 29 – 32. Male genitalia of Asian Pachysternum (a: tegmen, b: median lobe, c: apical portionof median lobe, d: sternite 9). 29: P. c a rd o n i, 30: P. coomani, 31: P. haemorrhoum; 32: P. nigrovitattum.

FIGURES 39 – 50. Anterior tibia of Asian Pachysternum species. 39: P. apicatum (a: lectotype, b: specimen from Borneo, Sabah); 40: P. c u r v a t u m, 41: P. sandacanum; 42: P. c a rd o n i; 43: P. coomani, 44: P. haemorrhoum, 45: P. kubani, 46: P. nigrovittatum, 47: P. rugosum, 48: P. stevensi, 49: P. s u l a w e s i c u m.