Neosclerus CAMERON

Assing, Volker, 2011, A revision of the genus Neosclerus C (Coleoptera: Staphylinidae: Paederinae), Beiträge Zur Entomologie = Contributions to Entomology 6 (1), pp. 89-148 : 91-94

The genus Neosclerus CAMERON

Neosclerus CAMERON, 1924: 188 f. [type species: N .. fortepunctatus CAMERON, 1924 ]

Lobochilus BERNHAUER ,, 1920: 179 [preocc.; type species: L. javanus BERNHAUER ,, 1920]

Redescription:

Species of rather small and uniform size, body length 2.8-4.1 mm; habitus similar to that of SuniusSunius (e.g., Figs 1, 7, 15, 21). Body in most species of dark (dark-brown to black) coloration, rarely partly or completely reddish; legs and antennae yellowish to reddish.

Head (e.g., Figs 2, 8, 16, 22) across eyes distinctly transverse, 1.1-1.3 times as broad as long; eyes enormous and strongly bulging, similar to those of Stenus LATREILLE , occupying the whole side of the head, and with relatively long pubescence; postocular region obsolete or extremely short, at most approximately as long as width of antennomere I; punctation of dorsal surface usually rather coarse and moderately to extremely dense, often distinctly sparser in posterior portion; interstices with or without microsculpture; neck not conspicuously slender, similar to that of Sunius . Antenna 0.7-1.2 mm long, slender, of similar morphology as in Sunius . Gular sutures rather widely separated. Mouthparts: labrum with anterior margin notched in the middle, but not dentate ( Fig. 83); ligula truncate and with approximately six short stout setae; maxilla and mandible similar to those of SuniusSunius ( Figs 82, 84).

Pronotum (e.g., Figs 2, 8, 16) distinctly narrower than head (including eyes), weakly oblong to weakly transverse; of similar shape as in Sunius ; punctation usually coarse, rarely fine and granulose, moderately dense to dense; impunctate midline of variable width, often weakly defined; interstices without microsculpture and glossy.

Elytra of variable length and width, in some species di- or polymorphic; in micropterous species distinctly shorter than pronotum (e.g., Figs 74, 81); in macropterous species usually approximately as long as or longer than pronotum (e.g., Fig. 2), rarely shorter than pronotum (e.g., Figs 28, 134); humeral angles in micropterous species often weakly marked; punctation usually moderately fine and very dense, often shallow and weakly defined. Hind wings completely reduced (micropterous species), fully developed (macropterous species), or of reduced length (di- and polymorphic species). Legs similar to those of Sunius ; protarsi without sexual dimorphism; all tarsi slender, not dilated; metatarsomere I somewhat longer than II.

Abdomen subparallel, widest at segment VI; punctation fine and moderately dense, usually more or less distinctly sparser on posterior than on anterior tergites; interstices with more or less distinct microsculpture; posterior margin of tergite VII with or without palisade fringe; tergite VIII usually with sexual dimorphism.

: tergite VIII usually with broadly and weakly convex posterior margin; sternite VII often with more or less distinctly concave posterior margin, in one species dentate on either side of the median concavity, and often with a cluster of dense setae posteriorly (e.g. Fig. 10); sternite VIII with moderately deep to deep, V-shaped to U-shaped posterior excision and often with additional modifications (anteriorly elevated in the middle, with median carina posteriorly extending into an acute and apically bifid process, or with pair of carinae; posteriorly with extensive impression or depression without pubescence); aedeagus of similar general morphology as in Sunius , ventral process often dorso-ventrally (e.g., Figs 5-6) or laterally (e.g., Figs 32-33) compressed, often subapically notched and/or dentate; internal sac with long series of spines (e.g., Figs 5-6), or with pairs of sclerotized structures basally (e.g., Figs 78-79), in median, or in apical portion (e.g., Figs 138-139).

: tergite VIII usually with more strongly convex posterior margin than in  ( Fig. 91); sternite VIII with broadly convex posterior margin.

Systematics:

Based on external characters, the mouthparts, and the male sexual characters, NeosclerusNeosclerus undoubtedly belongs to the subtribe Medonina . As can be inferred from the description above, Neosclerus is highly similar to Sunius , not only in external morphology, but also in the male primary and secondary sexual characters. In fact the only constant morphological differences found between the two genera are the shape of the anterior margin of the labrum ( Sunius : dentate on either side of median notch) and the size of the eyes. Even in micropterous species they are enormous and not smaller than in macropterous ones. There are SuniusSunius species with rather large eyes, too, but these are always distinctly smaller and much less bulging than in Neosclerus (see Fig. 159). These observations suggest that the derived morphology of the eyes is a synapomorphy shared by all Neosclerus species , so that there is little doubt that the taxon is monophyletic. Nevertheless, an external character such as eye size, which is often subject to considerable intrageneric variation in Paederinae , is by itself a rather weak argument for the hypothesis that NeosclerusNeosclerus should be distinct at the genus level and not placed within Sunius . However, further evidence comes from biogeography. Sunius probably has a Holarctic distribution; the Nearctic species have not been revised, but it seems likely that at least some of them actually belong to this genus. In the Old World, Sunius is strictly confined to the Palaearctic region with few scattered species distributed as far south as Yunnan, where they inhabit high-altitude habitats (( ASSING 2010); true Sunius from the Oriental region are unknown. The distribution of Neosclerus , in contrast, is predominantly Oriental, with some species reaching the extreme south of the Eastern Palaearctic region. In consequence, based on both morphological and biographic evidence, Neosclerus appears to represent as distinct genus, possibly the adelphotaxon of Sunius .

Intrageneric affiliations:

Within the genus, several species groups may be distinguished, but the affiliations of some species remain uncertain, either because the male sexual characters are unknown (N .. javanus , N .. granulicollis , N .. assamensis )) or because it is difficult to identify clear synapomorphies (N .. nigerrimus )). Based on the internal structures of the aedeagus, the genus falls into two groups. One of them has long series of small spines in the internal sac and is additionally characterized by the following characters: modified pubescence of the male sternite VII (exception: N .. erubescens )); sternite VIII without modifications besides the posterior excision; ventral process of aedeagus slender and subapically neither notched nor acutely dentate. This group is here referred to as the fortepunctatusfortepunctatus group and includes N .. fortepunctatus , N .. dupleseriatus , N .. barbatus , and N .. erubescens . The remainder of the genus has a pair of larger internal structures (plus additional membranous structures) in the basal, median, or apical portion of the internal sac. Among these species N .. glaberglaber and N .. bicarinatusbicarinatus form an isolated group (( glaberglaber group) which is distinguished from other groups by the following characters: ventral process curved, subapically neither dentate nor notched, dorso-ventrally more or less compressed, and apically abruptly narrowed towards the acute apex (ventral aspect). The brevipennis group, which includes nine species (N .. brevipennis , N .. schillhammeri , N .. praeacutus , N .. inarmatus , N .. rougemonti , N .. barbatulus , N .. rimatus , N .. incisus , N .. schuelkei )), is characterized as follows: ventral process of aedeagus somewhat spear-shaped (straight, apically very acute, subapically acutely dentate); sclerotized internal structures situated in basal or median portion of internal sac; male sternite VII with modified pubescence posteriorly; male sternite VII anteriorly with median elevation or pair of carinae (exception: N .. praeacutus )), posteriorly depressed or impressed and extensively devoid of pubescence. Finally, the hlavacihlavaci group, which exclusively includes micropterous species from southern China and Taiwan (N .. hlavaci , N .. atsushii , N .. armatus , N .. smetanai , N .. configens , N .. carinatus , N .. bifidus )), shares two obvious synapomorphies: the male sternite VIII has a median carina with a bifid posterior extension anteriorly and the ventral process of the aedeagus is obliquely notched and very finely acutely dentate at some distance from apex (best visible in lateral view).

Distribution and diversity:

The genus is widespread in the Oriental and the southern East Palaearctic regions, its distribution ranging from the southern slopes of the Himalaya southwards to Sri Lanka, Malaysia and Indonesia. Owing to the scarcity of material available from these regions, the distributions of individual species are poorly known. Two species (N .. brevipennis , N .. dupleseriatus )) are evidently widespread in the southern Himalaya and adjacent regions. The range of N .. glaberglaber extends from southern China to Malaysia, thus spanning almost 24 degrees of latitude. Neosclerus barbatulusbarbatulus is known from Myanmar, Thailand, and southern China. Several additional species may be widespread, too, as can be inferred from their fully developed hind wings and their collection data (some caught in interception traps), but are currently known only from one or two localities.

At least ten micropterous species without a palisade fringe at the posterior margin of the abdominal tergite VII undoubtedly have very restricted distributions, seven of them in Taiwan (N .. atsushii , N .. armatus , N .. smetanai , N .. configens , N .. carinatus , N .. bifidus , N .. inarmatus )) and three in southern China (N .. hlavaci , N .. incisus , N .. rimatus )). The same may be true of N .. praeacutus (southern China), whose hind wings are apparently of reduced length, but which still has a palisade fringe at the posterior margin of tergite VII.

The regions with the highest diversity are southern China (7 species), Taiwan (7), northern India (5), and Thailand (5). The fact that the NeosclerusNeosclerus fauna of Taiwan is composed of representatives of two species groups (N .. inarmatus of the brevipennisbrevipennis group and six species of the hlavaci group) suggests that it has originated from two colonization events.

Natural history:

As can be inferred from the collection data, Neosclerus species live in - usually moist - leaf litter, moss, and other debris of forests, shrub habitats, and on banks of streams. The altitudes range from near sea-level to almost 2600 m. Due to lack of material, little is known about the phenology of the species. Teneral adults were collected in May and August. Some species were repeatedly collected with flight interception traps, suggesting that they are active flyers.

Remarkably, several males of different species dissected in the course of the present study had teratologically deformed aedeagi. In one male the aedeagus was completely missing and one additionally had a sternite VIII without posterior excision. Teratologically deformed aedeagi are quite common in Medonina (( ASSING 2006), a phenomenon that is difficult to explain in view of the high selective pressure that should work against conditions that impair reproduction.

The species of Neosclerus 1