Scopaeus decipiens, , Kraatz, 1859

Frisch, Johannes, 2025, The Scopaeus decipiens species group from the East Palaearctic and the Oriental Regions, with redescription of S. velutinus Motschulsky, 1858 (Coleoptera: Staphylinidae: Paederinae: Lathrobiini), Zootaxa 5693 (2), pp. 179-200 : 180-184

1. The Scopaeus decipiens species group

The Scopaeus decipiens species group is diagnosed below, followed by a key and descriptions and redescriptions of the associated species. The species group characters are not repeated in the species descriptions. As the species cannot be distinguished by exoskeletal features, the descriptions are only based on the primary and secondary sexual characters.

1.1. Description of the Scopaeus decipiens group

Description: Macrophthalmous, macropterous species of uniform habitus capable of flight with palisade fringe of abdominal tergite VIII ( Fig. 1 ).

Body color reddish light brown (teneral specimens?) to medium brown, usually with lighter reddish brown or orange brown pronotum; elytra gradually lighter brown lateroposteriorly; tip of abdomen, antennae, mouthparts, and legs light brown to medium brown in darker colored specimens.

Exoskeleton very finely microsculptured with subnitid, finely punctate forebody surface; head with indistinct or notable, flat microreticulation ( Fig. 2 ); pronotum and elytra polished without microreticulation ( Figs 3, 4 ); head with simple punctation with puncture interspaces usually about two times as wide as puncture diameters ( Fig. 2 ); pronotal punctation moderately wider than cephalic punctation, slightly granular ( Fig. 3 ); elytral punctation coarser and denser than cephalic and pronotal punctation, granular ( Fig. 4 ); abdomen with dense, setiferous, posteriad extended, irregular granules ( Fig. 5 ).

Head about 1.1 times as long as wide, widest across parallel or slightly posteriorly widened tempora; eyes about 0.8 times as long as tempora; pronotum about 1.2 times as long as wide; elytral sutural length about as long as pronotal length; submedial labral denticles pointed, longer than pointed sublateral labral denticles; penultimate antennal segments quadrate; mesotibia slender, about 6 times longer than wide.

Stridular file very finely notched, comprised of about 60–70 clear denticles, contiguous with submarginal ridge of metaventrite, occupying about anterior half of submarginal ridge and slightly curved dorsad at posterior end ( Figs 6–8 ); cluster of feebly curved, subparallel plectral ridges situated in dorsal half of posterior surface of mesofemur; cluster made up of about three dorsal, clear plectral ridges followed ventrally by approximately three indistinct, shorter plectral ridges ( Fig. 9 ).

Metakatepisternal processes about 2.0 times as long as wide, tapered towards thin, acute apices ( Fig. 7 ).

Total body length 2.6–3.3 mm (Ø 2.9 mm); forebody length 1.4–1.8 mm (Ø 1.6 mm).

Male: Protarsomeres 1–4 dilated, about three times as wide as long.

Abdominal sternite VII (e.g. Fig. 10 ) with subtriangular emargination in about posterior third of sternite width with lateroposterior angles strongly, triangularly extended beyond posterior sternite margin; emargination narrowly truncate anteriorly and laterally bordered with conspicuous comb made up of long, black, medioposteriad pointing macrosetae; emargination anteriorly surrounded by semicircular crown of black macrosetae in median third of sternite width.

Abdominal stenite VIII (e.g. Fig. 11 ) with short, wide emargination occupying about posterior fifth of sternite length; posterior margin of emargination in about median third shortly, convexly extended posteriorly with extension slightly, concavely curved medially; sternite in median third or median half with large, medially divided field of black macrosetae occupying median third or posterior two-thirds of sternite length.

Aedeagus ( Figs 27–53 ) with short apical lobes occupying about apical 0.15 of aedeagal length. Apical lobes in dorsal view triangular (e.g. Fig. 29 ), in lateral view (e.g. Fig. 27 ) evenly curved ventrad toward obtuse or extended, ventrolaterad curved, pointed apical ends; ventral margin of apical lobes divided into obtuse or acute, more or less ventrolaterad curved, subapical tooth, membranous median lobe, and long, proximal portion with ventral margin running more or less parallel to dorsal margin of apical lobes toward obtuse or subacutely projecting, ventroproximal end (e.g. Figs 27, 28 ). Dorsal lobe inconspicuous, triangular in dorsal view (e.g. Figs 29 ). Flagellum short, strongly curved ventrad, not projecting from ventral margin of apical lobes. Ventral lobe short, not much projecting ventrally, in lateral view obtuse or shortly pointed apically (e.g. Fig. 27 ), in ventral view wide with distal margin triangularly incised medially (e.g. Fig. 28 ). Lateral lobes shortly convex, not much projecting laterally (e.g. Figs 28, 29 ), bearing long brush of ventrodistad pointing setae (e.g. Fig. 27 ). Phallobase strongly enlarged proximally, about as long as apical portion of aedeagus, median foramen thus situated in about middle of aedeagal length (e.g. Fig. 28 ). Postforamen and circoforamen weakly sclerotized (e.g. Fig. 28 ). Length of aedeagus 0.54–0.67 mm.

Female: Protarsomeres 1–4 narrow, about twice as wide as long.

Laterotergites IX with strong, convex, subapical, lateral enlargement clearly set off from narrow, acute apical ends ( Fig. 54 , arrow).

Female primary genitals made up of strongly sclerotized bursa ( Figs 54–56, 58–61 ), short bursal duct not much longer than bursa ( Fig. 56 ), and two-piece sperm pump with slender apical ends ( Figs 54, 56 ). Bursa with ends curved dorsad ( Figs 55, 58–61 ); anterior end of bursa widened dorsoventrally ( Figs 58, 59 ) or laterally ( Figs 60, 61 ).

Differential diagnosis: The Scopaeus decipiens species group does not have a specific external appearance which defines it within the genus. For example, it strongly resembles the Scopaeus limbatus species group, that is distributed in the Oriental Region as well ( Frisch 2005). The S. decipiens group can, however, easily be identified according to primary and secondary sexual features.

Males are clearly distinguished from all other species of Scopaeus by the characteristic shape and setation of the abdominal sternites VII and VIII ( Figs 10–25 ) and the unique aedeagus ( Figs 27–53 ) with a ventral, subapical tooth of the apical lobes followed proximally by a membranous lobe.

Females are unique within Scopaeus by the clear, lateral, subapical enlargement of laterotergite IX ( Fig. 54 ). They are also distinguished from nearly all Scopaeus by the sclerotized bursa ( Figs 58–61 ), while the bursa is usually membranous in Scopaeus . As far as is currently known, among the Oriental Scopaeus only the S. laevigatus group also has a sclerotized bursa which, in contrast to the narrow, highly sclerotized bursa of the S. decipiens group, is less sclerotized and broader, more or less pocket-shaped (e.g. Frisch 2003: Figs 137–145).

Distribution: The Scopaeus decipiens species group is an Oriental faunal element, which reaches the southeastern Palaearctic ( Fig. 62 ). Northernmost records are known from northern Vietnam ( Ninh Binh), central ( Guizhou) and eastern ( Jiangsu) China, and central Honshu ( Chiba) in Japan. The species group is also recorded from southern China, Taiwan, and South Korea. Further to the south only scattered localities are known in Sri Lanka, Cambodia, Laos, the Malay Peninsula, and southeastern Borneo, but the species group is probably more widespread in South and Southeast Asia.

Bionomics: Even though I never collected specimens of the Scopaeus decipiens species group myself, I suspect that the associated species are no ecological exception within the genus and inhabit moist, sparsely vegetated, sandy or gravelly soils, preferably on the banks of running waters (cf. Frisch et al. 2002: 28). In fact, label data („under stones near stream“, „lake shore“, etc.) indicate riparian habitats. The species are good flyers, as a large proportion of the studied specimens was captured with light traps.

1.2. Species of the Scopaeus decipiens group

1.2.1. Key to the species of the Scopaeus decipiens group

The following key was created in the interest of a secure identification and does not reflect the phylogenetic relationships of the species included.

1 Male: Abdominal sternite VIII with medially divided field of black macrosetae long, occupying posterior two-thirds of sternite length (e.g. Fig. 13 ). Aedeagus with end of apical lobes truncate (e.g. Figs 31 ), and ventral lobe distally projected and pointed (e.g. Fig. 30 ). Female: Proximal end of bursa in lateral view subtruncate, in ventral view narrow and parallel ( Figs 56, 59 )…............................................................................................. .. complex

- Male: Abdominal sternite VIII with medially divided field of black macrosetae short, occupying only median third of sternite length ( Figs 11, 23, 25 ), or seemingly absent, reduced to few, indistinct setae ( Fig. 21 ). Aedeagus with end of apical lobes each extended into ventrolaterad pointing tooth (e.g. Figs 27, 28 , 42, 43 , 48, 49 ), and ventral lobe distally not projected (e.g. Figs 27 , 42 , 48 ). Female: Proximal end of bursa dorsally convexly widened ( Fig. 58 ), in ventral view narrow and parallel ( Fig. 58 ) or strongly dilated ( Figs 60, 61 )............................................................................ 2

2 Male: Abdominal sternite VIII with field of black macrosetae seemingly absent, reduced to few, indistinct setae ( Fig. 21 ). Female: Bursa with ends curved dorsad with distinct, median angle, in distal half less dilated dorsad, in proximal portion less widened laterally ( Fig. 60 )........................................................................ saaberae

- Male: Abdominal sternite VIII with medially divided field of black macrosetae present, occupying median third of sternite length ( Figs 11, 23, 25 ). Female: Bursa in ventral view with narrow or strongly dilated proximal end ( Figs 58, 61 )........ 3

3 Male: Apical lobes of aedeagus moderately narrowed and not extended apically ( Figs 28, 29 ), with short ventrolaterad pointing apical teeth ( Fig. 27 ), and truncate subapical teeth ( Fig. 27 ) not projecting from apical lobes laterally ( Fig. 28 ). Female: Proximal end of bursa dorsally convexly widened, but narrow and parallel in ventral view ( Fig. 58 ).............. decipiens

- Male: Apical lobes of aedeagus strongly narrowed and extended apically, with long ventrolaterad pointing apical teeth ( Figs 48–53 ), and pointed subapical teeth ( Figs 49, 52 ) projecting from apical lobes laterally ( Figs 50, 53 ). Female: Proximal end of bursa narrow, but strongly dilated in ventral view ( Fig. 61 )............................................... kritschi

Figures

Figure 62. Distribution of the Scopaeus decipiens species group: °—S. decipiens, ⬡—S. complex, D—S. saaberae,▲—S. kritschi.

FIGURES 1–5. Habitus (1) and microsculpture of head (2), pronotum (3), elytra (4), and abdomen (5) of Scopaeus decipiens species group with example of S. kritschi, Cambodia, Angkor.

FIGURES 6–9. Stridular file of metaventrite in lateral view (6), stridular files of metaventrite (in sublateral position) in ventral view (7), excerpt of metaventrite with left stridular file (8), mesothoracal leg with plectral ridges (9) of Scopaeus kritschi, Cambodia, Angkor (6–8); S. decipiens, Sri Lanka, Galle (9). Abbreviation: mkp—metakatepisternal process. Scale bars: A— Fig. 9 (excerpt of leg with plectral ridges), B—Fig. 8, C—Fig. 7.

FIGURES 10–26. Male abdominal sternite VII (10, 12, 14, 16, 18, 20, 22, 24) and male abdominal sternite VIII (11, 13, 15, 17, 19, 21, 23, 25, 26) of Scopaeus decipiens, lectotype, Sri Lanka (10, 11); S. complex, lectotype, Japan (12, 13); S. complex, China, Zhejiang, Siming Mts (14, 15); S. complex, Taiwan, Kaohsiung (16, 17); S. complex, Vietnam, Cuc Phuong, Ninh Binh (18, 19); S. saaberae, paratype, Indonesia, Borneo, Pagate (20, 21); S. kritschi, holotype, Cambodia, Angkor (22, 23); S. kritschi, paratype, Laos, Khammouane, Nakai (24, 25); S. velutinus, lectotype, „India Orientales“ (26).

FIGURES 27–32. Aedeagus in lateral (27, 30), ventral (28, 31), dorsal view of (29, 32) of Scopaeus decipiens, lectotype, Sri Lanka (27–29); S. complex, lectoype, Japan (30–32). Abbreviations: al—apical lobes, cf—circoforamen, dl—dorsal lobe, f— flagellum, ll—lateral lobes, mf—median foramen, pf—postforamen, vl—ventral lobe. Arrows: a—apical tooth of apical lobe, b—subapical tooth of apical lobe, c—membranous ventral lobe of apical lobe, d—ventroproximal end of apical lobe, e—distal margin of ventral lobe.

FIGURES 33–41. Aedeagus of Scopaeus complex in lateral (33, 36, 39), ventral (34, 37, 40), dorsal view (35, 38, 41) from Taiwan, Kaohsiung (33–35); Vietnam, Cuc Phuong, Ninh Binh (36–38); China, Zhejiang, Siming Mts (39–41). Abbreviation: vl—ventral lobe. Arrows: a—apical tooth of apical lobe, b—subapical tooth of apical lobe, c—membranous ventral lobe of apical lobe, d—ventroproximal end of apical lobe, e—distal margin of ventral lobe.

FIGURES 42–47. Aedeagus of Scopaeus saaberae in lateral (42, 45), ventral (43, 46), dorsal view (44, 47); holotype, Malaysia, Selangor, Kuala Lumpur (42–44); paratype, Indonesia, Borneo, Pagate (45–47). Abbreviation: vl—ventral lobe. Arrows: a— apical tooth of apical lobe, b—subapical tooth of apical lobe, c—membranous ventral lobe of apical lobe, d—ventroproximal end of apical lobe, e—distal margin of ventral lobe.

FIGURES 48–53. Aedeagus of Scopaeus kritschi in lateral (48, 51), ventral (49, 52), dorsal view (50, 53); holotype, Cambodia, Angkor (48–50); paratype, Laos, Khammouane, Nakai (51–53). Abbreviation: vl—ventral lobe. Arrows: a—apical tooth of apical lobe, b—subapical tooth of apical lobe, c—membranous ventral lobe of apical lobe, d—ventroproximal end of apical lobe, e—distal margin of ventral lobe.

FIGURES 54–61. Female abdominal segment IX in ventral (54) and lateral view (55); gonocoxites with bursa, bursal duct and sperm pump in ventral view (56); sperm pump (57); bursa (58–61) of Scopaeus kritschi, paratype, Cambodia,Angkor (54, 55, 57, 61); S. decipiens, Sri Lanka, Kitulgala (58); S. complex, Japan, Okayama (56, 59); S. saaberae, paratype, Indonesia, Kalimantan Tengah, Telang Baru (60). Abbreviations: b—bursa, bd—bursal duct, lgp—lateral gonocoxal plate, lt IX—laterotergite IX, sp—sperm pump. Arrow: subapical, lateral enlargement of laterotergite IX. Scale bars: A—Figs 53–55, B—Figs 56–61.