Introduction

The genus Hydnobius Schmidt, 1841 is distributed throughout the Holarctic region with 16 Palaearctic and 7 Nearctic species (Peck and Cook 2009; Perreau 2015). Species diversity is concentrated and rather high in Europe, while only four species are recorded exclusively from Asia. Some of the species show wide distributional patterns (e.g. H. spinipes Gyllenhall, 1813; Hydnobius longidens LeConte, 1879), however, there are also a few endemic species, e. g. H. enomotoi Hoshina, 2012 and H. akitsuensis Hoshina & Sunada, 2003 from the Kuril Islands and Japan (Honshu). The taxonomy of the Palaearctic species was studied by Daffner (1983) who revised material of more than 12,000 specimens of 320 Leiodidae species including the types of 234 species.

Figs. 1–2
figure 1

Hydnobius punctulatus, lectotype. 1 Habitus, dorsal view. 2 Habitus, ventral view

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Figs. 3–5
figure 2

Hydnobius punctulatus. 3 Head and pronotum, paralectotype, dorsal view. 4 Male left hind-leg, lectotype, ventral view. 5 Aedeagus, lectotype, dorsal view

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Figs. 6–9
figure 3

Hydnobius punctulatus, specimens from Virt env. 6 Aedeagus, dorsal view. 7 Aedeagus, same specimen, lateral view, part of internal sac omitted. 8 Female sternite VIII, ventral view. 9 Female coxite and styli (some setae broken), ventral view

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All Hydnobius species are small, reddish brown to dark brown and rather inconspicuous beetles usually difficult to collect. The number of preserved specimens in European Museums is usually low. The bionomics and larval stages are still unknown; however, both larvae and adults seem to feed on subterranean fungi or grass roots infested by fungi (Daffner 1983; Peck and Cook 2009). Some species prefer well-drained sandy soils at margins of different types of forests, steppes or sandy-gravel banks of streams (Daffner 1983).

Use of flight intercept traps in a remnant of mixed riverine forest near the Danube River in proximity of Comenius university campus in Bratislava (Slovakia) and evening sweeping of grass near forest margin in the village of Virt (southern Slovakia) revealed several Hydnobius specimens. They were identified using the revision of the Palaearctic Leiodini (Daffner 1983), resulting in identification of Hydnobius punctulatus Hampe, 1861. This species is recorded rarely and is yet known from four European and two Asian countries (Perreau 2015), although Hoshina (2012) mentioned distribution in Russia including Far East. The previous schematic drawings of diagnostic characters based on limited sources of material showed need to re-examine the type specimens of H. punctulatus and to redescribe the species. Technical possibilities and progress in digital technologies enables us to newly illustrate all diagnostic characters in a more precise way, add comments on variability and new distribution data. Examination of Hydnobius specimens from different collections and samples surprisingly resulted in another new record of Hydnobius claviger Strand, 1943 for Slovakia.

Material and methods

The material used for the study was collected by the senior author and borrowed from the following collections (abbreviations used refer to collections in the text).

CKB :

Ján Kodada Collection, Bratislava, Slovakia

CMB :

Oto Majzlan Collection, Bratislava, Slovakia (O. Majzlan)

NMW :

Naturhistorisches Museum, Wien, Austria (H. Schillhammer)

SNM :

Natural History Museum of Slovak National Museum, Bratislava, Slovakia (V. Janský)

In addition to Hydnobius punctulatus, the following species were studied:

Hydnobius punctatus Sturm, 1807: 1 ♂, (SNM): “Čechoslovakia Trenč. Teplice Kočí, coll J. Laco”; 1 ♂ (SNM): “Čechoslovakia Trenčín, Selec Kočí, coll J. Laco “.

Hydnobius spinipes (Gyllenhal, 1813): 1 ♂ 2 ♀♀ (SNM): “M. Tatry 10. III Roubal 1927”; 2 ♂♂ 1 ♀ (CMB): “Slovakia bor. 6887 d Stará Lesná 2011, O. Majzlan lgt. 9.8.”

Hydnobius multistriatus (Gyllenhall, 1813): 2 ♂♂ (SNM): “Slov. Parkan Belá Roubal”.

Hydnobius claviger A. Strand, 1943: 1 ♂ (CKB): “Slovakia, 1988, 28.9. Suchý Vrch [eastern Slovakia, Lipovce village env.], J. Kodada lgt.”

Specimens studied were relaxed in warm water with several drops of concentrated acetic acid, cleaned and dissected; male genitalia and whole female abdomens were cleared subsequently for several days in lactic acid.

The external characters were examined with a stereomicroscope Leica M205C at magnifications from 10× to 160×. The metric characters were measured with an eyepiece graticule to the nearest 0.05 mm, or using LAS microscope software and Leica MC190 HD camera attached to a stereomicroscope.

The specimens as well as the aedeagus of the lectotype were photographed with a Zeiss Axio-Zoom V-16 stereomicroscope using diffuse LED lighting at magnifications up to 168× with a Canon 5D mark IV attached. Dissected male, female genitalia and pregenital segments were studied in a temporary microscope cavity slide covered with micro-glass slide at magnifications up to 640× with a Leica DM 1000 microscope. All drawings were made using a Leica drawing device.

The abbreviations for the measured characters used in the text [the characters were selected to be consistent with the reviews of Daffner 1983, Peck and Cook 2009 and Hoshina 2012]:

ACL :

antennal club length, combined length of antennomere 7–11 forming antennal club

ACW :

antennal club width, maximum width of widest antennomere

BL :

body length without head, length of pronotum and elytra measured along midline

EL :

elytral length along suture from the most anterior to the most posterior point

EW :

elytral width, maximum width combined

PL :

pronotal length along midline

PW :

maximum pronotal width

Hydnobius punctulatus Hampe, 1861

Hydnobius punctulatus Hampe, 1861: 66–67.

Hydnobius kaszabi Hlisnikovský, 1965: 57–59. The species was synonymised by Daffner (1983: 34).

Redescription of the Lectotype male

(Figs. 1, 2, 4, 5). Body form elongately obovate and moderately convex dorsally. Dorsum shining, unicoloured reddish brown; head and pronotum, antennae and legs reddish brown like the dorsum of body, only terminal tarsomeres slightly paler; entire ventral side reddish brown.

Length of pronotum and elytra (BL) 2.26 mm, body ca 1.8× as long as wide (BL/EW), moderately convex and almost glabrous except for sparse and very fine, short pubescence. Pubescence best visible along lateral margins and near apices of elytra. Head 0.83 mm wide, sparsely minutely punctate, ca 0.69× as wide as pronotum; right mandible tridentate, bearing one apical and one subapical small tooth and one large tooth near middle; left mandible bidentate with one apical and one subapical tooth [mandible description based on a male paralectotype (Fig. 3)].

Antennal club broad, ratio width: length = 1:2.47 (0.17:0.42 mm). Antennomeres 1–3 each longer than wide; remaining antennomeres wider than long; terminal antennomere large; lengths ratio of antennomeres 2–11 = 1.71:1.60:1.28:1.31:1.26:1.83:1.00:2.34:2.57:2.94; width ratio of antennomeres 2–11 = 0.56:0.64:0.75:0.81:0.90:1.41:1.00:1.94:2.03:1.27.

Pronotum ca 1.47× as wide as long, widest slightly posteriad of middle; sides rounded, basal angles obtuse; surface sparsely minutely irregularly punctate, puncture diameters moderately smaller than diameters of facets, transverse basal groove fine, distinct. Scutellum impunctate. Elytra ca 1.16× as long as wide, subequal in width with pronotum, widest ca at anterior 2/5, transversely and shortly strigose, punctate; EL = 1.45 mm, EW = 1.25 mm; punctures of elytra larger than those on head and pronotum; sutural stria distinct, arising from anterior third of elytral length and reaching apex, clearly impressed; remaining striae punctate, confused; puncture intervals slightly smaller than strial punctures.

Mesoventrite microsculptured, impunctate and almost glabrous; disc of metaventrite shiny with very sparse fine punctures, punctures with moderately long setae. Profemur and mesofemur simple (unarmed), metafemur with large tooth on posterior margin before apex (Fig. 4), middle one-third of posterior margin to apex of tooth serrulate. Protibia and mesotibia weakly widened apically, metatibia slender, weakly sinuate on inner margin; all tibiae spinose on outer margin.

Aedeagus (Figs. 5–7) robust; median lobe ca 2.3× as long as wide, widest near middle, gradually arcuately narrowing anteriad to apical 0.15, then abruptly narrowed to sub-triangular apex; apex rounded, not protruding. Posterior portion gradually narrowed, base narrow and bent (lateral view). Parameres broad at base, ca 1.5× as long as median lobe; sinuate, apex rounded with two setae. Internal sac with numerous short setae and small spines, distinct sclerites absent. [Fig. 5 shows aedeagus of the lectotype, Figs. 6 and 7 illustrate aedeagus of well-preserved male from Slovakia.]

Female

Externally similar to male except for simple metafemur lacking tooth. Coxites elongate, cylindrical, with apical setae; styli very short with long terminal seta (Fig. 9). Sternite VIII rounded apically; anterior apophysis moderately wide, apex rounded (Fig. 8).

Variability

In addition to the variability in metric characters, specimens show also slight variability in the size of the punctures on the dorsal side of the body, even within the type specimens. Tooth on male metafemur slightly varies in size within small and large males. However, the form of the aedeagi and the sinuate parameres show almost no differences within examined specimens (Fig. 9).

Metric characters show following variability. Males: BL: 1.72–2.21 mm; BL/EW: 1.67–1.79; PL: 0.61–0.82 mm; PW: 0.91–1.17 mm; PW/PL: 1.42–1.54; EL: 1.07–1.43 mm; EW: 1.00–1.29 mm; EL/EW: 1.05–1.17; HW: 0.63–0.83 mm; PW/HW: 1.38–1.49; ACL/ACW: 1:2.31–1:2.59. Lengths ratio of antennomere 2–11: 1.62–2.00:1.57–1.98:1.28–1.60:1.23–1.52:1.17–1.38:1.75–2.45:1.00:2.29–2.91:2.22–2.80:2.94–3.48 (n = 7). Width ratio of antennomere 2–11: 0.56–0.65:0.52–0.64:0.61–0.75:0.70–0.81:0.82–0.88:1.39–1.47:1.00:1.82–2.00:1.89–2.09:1.27–1.44 (n = 7).

Females

BL: 1.85–2.23 mm; BL/EW: 1.71–1.77; PL: 0.63–0.75 mm; PW: 0.96–1.15 mm; PW/PL: 1.49–1.52; EL: 1.20–1.51 mm; EW: 1.04–1.25 mm; EL/EW: 1.14–1.21; HW: 0.52–0.80 mm; PW/HW: 1.43–1.84; ACL/ACW: 1:1.97–1:2.34. Length ratio of antennomere 2–11 = 2.06:2.00:1.59:1.52:2.32:1.00:2.77:2.79:3.04 (n = 1). Width ratio of antennomere 2–11 = 0.56:0.55:0.63:0.75:0.82:1.49:1.00:2.05:2.03:1.40 (n = 1).

Material examined. Type material

Five original specimens (2 ♂♂, 3 ♀♀ all deposited in NHM) were available for study, one of them, a male bearing an original identification label with the mention “type”, was designated by Daffner (1983: 34) as the holotype being in fact a lectotype, fixed by inference (ICZN, Art. 74.6). Lectotype male bearing white handwritten label “Hydnobius punctulatus Hmpe Typ.”; red label “Holotypus / Hydnobius / punctulatus / Hampe and male symbol / det. Daffner XI. 1980”; larger white handwritten label “punctulatus /Hpe Croat”. Aedeagus of lectotype was dissected and mounted on a celluloid card in Canada balsam by Daffner, this label is pinned below the lectotype specimen. Paralectotypes (1 ♂ and 3 ♀♀) each bear only a single red label “Paratypus / Hydnobius / punctulatus / Hampe and male or female symbol / det. Daffner XI. 1980”. All paralectotypes were originally glued on a small narrow triangular card, one female and one male specimen were remounted on larger cards and the female was dissected.

Additional material examined

1 ♂, 2 ♀♀ (CKB): “Slovakia, Bratislava, Petržalka, Pečniansky les, FIT [Flight Intercept Trap], 28.5.-6.7.2015, J. Kodada leg.”; 9 ♂♂, 1 ♀ (CKB, NMW): “Slovakia, Virt env. 28.5.2017 ca 47°45’43.6” N, 18°20′21.5″ E, J. Kodada & K. Goffová Lgt.”; 1 ♂ (NMW): “Ganglb. 95 Herkulesbad”.

Type locality

Agram [Agram is the historic German name for Zagreb], Croatia.

Distribution

The species was recorded from Bosnia and Hercegovina, Croatia, Hungary, Romania, Slovakia (new record), Turkey and Mongolia (Hampe 1861; Hlisnikovský 1965; Merkl 2006; Perreau 2015).

Hydnobius claviger Strand, 1943

Material examined

1 ♂ (CKB): “Slovakia, 1988, 28.9. Suchý Vrch [eastern Slovakia, Lipovce village env.], J. Kodada lgt.”

Widely distributed species H. claviger described from Norway [Gran-Hadeland, Daffner 1983], reported so far also from Austria, Germany, Hungary, Italy and Sweden (Merkl 2006; Perreau 2015). Generally, it is considered a rare species (Lompe 2002); the male specimen represents the first record for Slovakia.

Discussion

For correct species identifications it is necessary to examine the aedeagus; generally, the form of the aedeagus and the armature of the internal sac in everted position is very useful in defining taxa (Peck and Cook 2009). Unfortunately, it is not possible to evert the internal sac in all specimens, so often the structure appears as rather uninformative cluster of small spines. This was also probably the reason, why Daffner (1983) has not illustrated those structures. For most species the form of the parameres represents another, very useful identification character. The identification of single females may be difficult, even if the illustrations of coxites with styli and of sternite VIII are available. Width ratio of the terminal antennomere to the preterminal one used in the key by Daffner (1983) is rather less applicable due to the small size of these segments (e.g. 0.108:0.169 mm). Except for their small size, the club segments are elliptical in cross section so it is very difficult to compare different antennae at the same position.

The description of H. kaszabi is based on a unique female from Central Aimak in Mongolia (Hlisnikovský 1965); it is questionable if this specimen is truly conspecific with H. punctulatus because the distribution of both taxa is poorly known and the material from Mongolia is scarce.

Hydnobius punctulatus resembles the widely distributed North American H. longidens in having distinctly sinuate parameres. In contrast, the internal sac of the aedeagus of H. longidens possesses a pair of sclerotised oblong lobes (Peck and Cook 2009).

Hydnobius punctulatus is keyed by Daffner (1983) with H. claviger Strand, 1943, based on the very large and wide antennal club with the terminal antennomere one-third narrower than the preterminal segment. H. claviger can be distinguished by the elongate aedeagus with nearly straight, not sinuated parameres, the larger size and the darker or black antennal club.

Another externally similar species is the widely distributed and variable Hydnobius spinipes (Gyllenhall, 1813), differing in the form of the aedeagus and the not sinuate parameres, in darker/black colour of the antennal club and, in some specimens, in darker head and pronotum (see Daffner 1983).

Hoshina (2012) considered Hydnobius enomotoi Hoshina, 2012 (Kuril Islands) similar to H. punctulatus based on a small tooth projection of the male metafemur. In fact, even the smallest males examined possess a larger metatibial tooth of different shapes.