Histeridae of Socotra ( Coleoptera : Histeroidea )

The histerid beetles (Coleoptera: Histeridae) of Socotra Island (Yemen) are reviewed based on the material collected during the Czech expeditions undertaken between 2000 and 2012. A total of 20 species are recorded, three of which are described herein: Pachycraerus socotrensis sp. nov., Liopygus occidentalis sp. nov., and Teretrius (Neoteretrius) dispar sp. nov. Hypocaccus virescens Thérond, 1963 is transferred from the subgenus Baeckmanniolus Reichardt, 1926 to Hypocaccus s. str. Thomson, 1867 based on external morphology. Most taxa, albeit determined only up to their (sub)generic rank, are recorded from Socotra for the fi rst time. Due to poor understanding of their taxonomy, or lack of determination keys to the following (sub)genera: Tribalus Erichson, 1834, Plegaderus (Plegaderus) Erichson, 1834, Acritus (Acritus) LeConte, 1853, and Teretrius (Teretrius) Erichson, 1834, their representatives from Socotra are left without identifi cation pending revisions. The Socotran histerid fauna has been found to consist mainly of widely distributed African, Arabian/Near Eastern taxa, as well as local endemics. The occurrence of the (predominantly Holarctic) genus Plegaderus and the exclusively southeast Asian genus Liopygus Lewis, 1891 in Socotra is highly interesting.


Introduction
The fauna of histerid beetles of the Arabian Peninsula has been studied in detail in the past sixty to ten years (e.g. MÜLLER 1954, KRYZHANOVSKIJ 1979, MAZUR 1994, KANAAR 2008, with the efforts culminating in the publication of a comprehensive catalogue of the local histerid fauna by PENATI & VIENNA (2006). Regarding the fauna of the Socotra Archipelago, which is known to harbour high proportion of endemic fl ora and fauna (including insects), there have been only scant published records: several histerids were mentioned in the works of TASCHENBERG (1883), GAHAN (1903), WRANIK (2003), andTHÉRY et al. (2009). LACKNER & KAPLER (2007) described the fi rst Socotran endemic, Eutriptus jirinae. BATELKA (2012) published an interesting and highly readable summary of the geological history, climate and biodiversity of the Socotra Archipelago. Socotra Archipelago has not been subjected to many recent entomological surveys and that is the main reason why there have not been more published records, especially on the Histeridae. However, a recent series of expeditions of (chiefl y) Czech entomologists undertaken between 2000-2012 have yielded several interesting histerid beetles, and their detailed account is given below.

Material and methods
All dry-mounted specimens were relaxed in warm water for several hours. After removal from original cards, beetles were side-mounted on triangular points and examined under Nikon 102 binocular microscope with diffuse light. Male genitalia were fi rst macerated in 10% KOH solution for about 3 hours, cleared in 80% alcohol and macerated in lactic acid with fuchsine, incubated at 60°C for another 30 minutes, and subsequently cleared in 80% ethanol, and transferred and then observed in α-terpineol in a small dish.
Digital photographs of male genitalia were taken by a Nikon 4500 Coolpix camera and edited in Adobe Photoshop CS5. SEM micrographs were taken at the Laboratory of the Electron Microscopy at the Faculty of Science, Charles University, Prague, Czech Republic. Habitus photographs were made by F. Slamka (Bratislava, Slovakia). Figures were drawn based on the photographs or direct observations, using a Hakuba klv-7000 light box. All specimens were measured with an ocular micrometer. Body part terminology follows that of ÔHARA (1994) and LACKNER (2010). BEZDĚK et al. (2012) summarised "Socotran geographica l names used in entomological literature", including their visualisation on maps; we refer our readers to that paper for the geographic distribution of species presented here on the island.
Exact label data are cited and given in quotation marks for the type material. Authors' additional remarks are provided in square brackets. Separate label lines are indicated by a slash (/).
Abbreviations of morphological measurements follow ÔHARA (1994) and are used throughout the text as follows: APW width between anterior angles of pronotum; EL length of elytron along elytral suture; EW maximum width between outer margins of elytra; PEL length between anterior angles of pronotum and apices of elytra; PPW width between posterior angles of pronotum. Comments. Subgenus Tribalus s. str. of the genus Tribalus Erichson, 1834, with 65 described species is a species-rich genus with bulk of its representatives occurring in Africa, while a smaller number of taxa are present in the Palaearctic and Oriental realms (MAZUR 2011). Its representatives are found mostly under stones in wetter areas near streams, occasionally they are collected by sifting forest detritus as well. The subgenus contains numerous undescribed species; furthermore, its representatives are rather uniform in general outlook and the most reliable taxonomic characters are found on the male genitalia (T. Lackner, unpublished data). Due to these factors as well as absence of any contemporary or reliable identifi cation keys, we were unable to determine its exact taxonomic identity and we advocate its revision. New taxon for the Socotra archipelago.
Pronotum approximately 1.3 times broader than long across median line, with microscopic punctation, punctures separated by several times their diameter, laterally larger scattered punctures appear intermingled with fi ne punctation. Lateral pronotal stria well developed laterally, absent behind head; along posterior pronotal margin present irregular row of deep ocellate punctures. Anterior pronotal angles acute; hypomeron asetose.
Abdominal ventrite I even, with scattered microscopic punctation becoming more prominent apically. Lateral stria of abdominal ventrite I slightly costate; laterad to it present another much fi ner shortened stria parallel to it.
Female genitalia (Fig. 13). Median sclerite small, heart-shaped; gonocoxite setose, dentate apically; gonostylus bisetose. Variability. In some specimens the thin stria next to lateral stria of abdominal ventrite I can be absent, punctures of lateral disc of metaventrite can be sparser, elytral stria 3 can be intermittent and almost complete. Differential diagnosis. This Socotran species cannot be incorporated into the key of DESBORDES (1922: 384) due to the presence of the following characters: cuticle dark brown to lustrous pitch-black, elytra with only two complete dorsal striae (although in several specimens dorsal elytral stria 3 is complete, see below); dorsal elytral stria 1 does not reach elytral apex. Based on these particular characters alone, this species occupies an isolated position within the genus Pachycraerus. However, several specimens (where dorsal elytral stria 3 is complete) would key out in the aforementioned key near P. laticeps Lewis, 1906 described from Tanzania (Kilimanjaro), but do not correspond with it due to smaller body size and more cylindrical body shape. The cylindrical body shape of the Socotran species resembles P. desidiosus Marseul, 1854 from tropical Africa and Saudi Arabia, yet there are many differences between these two taxa, apart from different body sizes, dorsal elytral striae (more complete in P. desidiosus) and several other characters that separate the two species as well. Comments. The genus Pachycraerus Marseul, 1854, with 63 currently described species, is almost exclusively African in its distribution, with a single undescribed species collected from southern Oman (MAZUR 2011; T. Lackner, unpublished data). Its taxonomy is in fl ux, and a comprehensive revision of this rather large genus is highly necessary. New genus for the Socotra Archipelago. Etymology. Patronymic adjective, given after the Socotra archipelago. Collection circumstances. Found under bark of various trees. Distribution. Endemic to Socotra Island.

Description. Body
Head. Eyes strongly fl attened, not visible from above. Frontoclypeal area fi nely punctate, slightly depressed, traces of supraorbital striae visible above eye, other striae absent. Labrum fl attened, rectangular, each mandible with large triangular subapical tooth. Maxillary palpi very prominent, terminal maxillary palpomere longer than mandible itself, visible from dorsal view. Mentum large, quadrate, labial palpi thick, terminal labial palpomere rather thick, its width approximately half its length. Submentum considerably smaller than mentum, triangular. Antennal scape massive, its length approximately equals to that of antennal funicle. Pedicel thickened, approximately as long as antennomeres III and IV together; club large, oval, setose, intersegmental sutures visible.
Pronotum almost quadrate, along midline slightly broader than long, anterior angles strongly projected, acute. Marginal pronotal stria very thin, present only on apical angles and behind head; lateral pronotal stria slightly distanced from pronotal margin, parallel to it, terminating anteriorly on anterior pronotal margin. Pronotal disc impunctate; pronotal hypomeron asetose.
Propygidium broad, approximately 2.5 times as broad as long, with scattered deep ocellate punctures, separated by approximately 1.5-2.0 times their diameter. Pygidium in basolateral angles with two shallow depressions, each with deep fossa; pygidial surface basally with several vague shallow punctures, otherwise impunctate.
Legs. Protibial spur prominent; protarsal groove deep; outer protibial margin with 5 rather prominent teeth topped by tiny denticle; teeth 2-3 widely separated; mesotibia on outer margin with two widely spaced short denticles, two additional longer denticles situated near tarsal insertion; outer margin ventrally with sparse row of tiny widely spaced denticles. Metatibia slightly longer than mesotibia, otherwise similar to it, except for there is only a single denticle on outer margin medially instead of two.
Male genitalia. Sternite VIII (Figs 16-17) divided into two parts; tergite VIII and sternite VIII not fused (Fig. 18). Tergite IX (Fig. 19) divided into two parts; tergite X (Figs 19-20) small, its basal part wedged between the divided parts of tergite IX; sternite IX  or spiculum gastrale apically divided into two 'tails', pointed basally. Aedeagus (Fig. 21) tube-like, median lobe protruding from tegmen; phallobase (Fig. 22) approximately 1.5 times shorter than fused parameres. Differential diagnosis. The Socotran species strongly resembles the species Liopygus decemstriatus (Motschulsky, 1863) from Sri Lanka. It can, however, be readily distinguished from it based on the following characters: both dorsal elytral striae 2 and 4 are complete in the Socotran species (incomplete in L. decemstriatus); dorsal elytral stria 5 reaches even further basally in the Socotran species; propygidium of the Socotran species is entirely punctate (only partly punctate in L. decemstriatus); pygidium of the Socotran species is punctate only in its proximal part between the two fossa (pygidium of L. decemstriatus is punctate entirely). Comments. The genus Liopygus Lewis, 1891 contains 16 described species distributed exclusively in southeast Asia (MAZUR 2011). All Liopygus species, as far as known, live under bark, preying on small arthropods (DESBORDES 1919). Although DESBORDES (1919) published a key to the species of the genus, diffi culties using it for species determination were voiced by GOMY (2006), who described the only species of Liopygus after the World War II. The discovery of a member of Liopygus in Socotra Archipelago, considerably far from the distribution area of the genus is highly interesting, and we advocate a revision of the genus. Etymology. Specifi c epithet, the Latin adjective 'occidentalis' (= western), refers to the disjunct geographical location of the new species. Distribution. Endemic to Socotra Island, so far known only from the highest part of Hagher mountains. Comments. This species, described from 'Europe' is nearly cosmopolitan (MAZUR 2011). It occurs both on mammal faeces and carcasses. Reported from Socotra already by WRANIK (2003). Comments. This species was described from the Cape Verde Archipelago, but it occurs in the entire region of tropical Africa (MAZUR 2011). Recently KANAAR (2008) reported it also from the United Arab Emirates. In the light of its UAE discovery, its occurrence in Socotra, an island between the continent of Africa and the Arabian Peninsula, is not surprising.

Abraeinae: Plegaderini
Plegaderus (Plegaderus) sp. Comments. Genus Plegaderus Erichson, 1834 contains two subgenera: monotypic Hemitrichoderus Reichardt, 1941 with a single species P. (H.) adonis Marseul, 1876 described from Cyprus and also occurring in Turkey, and the nominotypical subgenus, which contains 27 species spread mostly in the Holarctic Region (MAZUR 2011). The species from Socotra belongs to the group of species with deeply impressed median stria on pronotum, dividing it into two convex parts (Fig. 8). Other species of this group are: P. (P.) caesus (Herbst, 1791), spread across Europe, Turkey, Azerbaijan and north Iran; P. (P.) dissectus Erichson, 1839 spread across southern England, central and south Europe, Turkey and north Iran; and the extremely rare P. (P.) fortesculptus Reitter, 1897 described from Azerbaijan and occurring also in Iran (MAZUR 2011). In fact, the type specimen of P. (P.) fortesculptus was discovered only recently (LACKNER, unpublished). SECQ & SECQ (1991) beautifully depicted the two former species in their key to French Plegaderini. Of the three, the species from Socotra most resembles Plegaderus (P.) caesus, which likewise possesses a string of tiny, equally distanced granules along lateral pronotal margins. The Socotran species differs, however, from P. (P.) caesus, in its smaller size, anteriorly narrowed pronotum; less impressed punctation of the elytra, in more dilated apices of protibia, body shape more rounded; the shape of prosternum, as well as in other characters. The herein depicted specimen from Socotra (Fig. 8) most likely belongs to a new species, we are, however, reluctant to describe it based on a single female. This is the fi rst record of the genus Plegaderus from the Afrotropical Region, to which the Socotran Archipelago biogeographically belongs. Comments. The genus Acritus LeConte, 1853 contains two subgenera: Pycnacritus Casey, 1916 with 9 described species found across the globe, and the nominotypical subgenus containing 118 currently recognized species with vast circumglobal distribution (MAZUR 2011). Acritus belongs to the so-called 'micro-histeridae' -a group of poorly studied and species-rich taxa that most likely feed on acarids. We were unable to identify the sole specimen from Socotra even after having consulted the matter with Y. Gomy (Nevers, France), who is a specialist on the 'micro-histerids'.
Anterior margin of prosternum (Fig. 29) slightly inwardly arcuate; marginal prosternal stria present anteriorly, complete; lateral prosternal striae strongly carinate, apically almost reaching marginal prosternal stria. Carinal prosternal striae subparallel to slightly divergent apically, not reaching anterior margin of prosternum (stopping just short of it). Entire disc of prosternum with scattered deep punctures separated by several times their diameter. Anterior margin of mesoventrite (Fig. 29) strongly projected; marginal mesoventral stria almost complete, not reaching mesoventral base laterally; disc of mesoventrite with sparse punctures; meso-metaventral stria absent. Metaventrite sparsely punctate, punctures most prominent along basal margin; lateral metaventral stria well developed, slightly carinate, curved outwardly and reaching mesepimeron. Metanepisternum narrow, with scattered punctures. Abdominal ventrite I without lateral striae; disc with denser and more prominent punctation than that of metaventrite. Protibia (Fig. 30) on outer margin with approximately ten densely set denticles; denticle 2 and 3 separated by a 'gap'; protibial spur long and thick; protibial groove deep; terminal protarsomere approximately as long as protarsomeres I-IV together. Mesotibia on outer margin with six denticles, denticles 3-6 situated atop triangular 'teeth'; metatibia (Fig. 31)  and more slender than mesotibia, outer margin adorned with three shorter, widely spaced denticles; both terminal tarsomeres approximately as long as the preceding four together.
Variability. Elytra in several specimens dark brown.
Female. Similar to male in habitus; mandibles simple, stout. Genitalia: disc of gonocoxite (Fig. 38) densely setose; apex quadrilobed; gonostylus short, narrow, bearing two long setae apically. Median sclerite (Fig. 38) triangular, resembling bull's skull; spermatheca (Fig. 39) globular. Differential diagnosis. This new species is rather large for the subgenus Neoteretrius and can be characterised by the following: mesoventrite without meso-metaventral stria, anterior margin of prosternum almost straight, weakly inwardly arcuate; carinal prosternal striae subparallel to weakly divergent anteriorly, outer margin of protibia with approximately 10 denticles. Teretrius dispar sp. nov. can be placed in the key of BICKHARDT (1921) (the only existing key to identify the members of Teretrius Erichson, 1834, which according to KANAAR (2008) requires revision) before species T. (N.) antelatus Lewis, 1914 from the Democratic Republic of Congo and Nigeria. Although we are not familiar with this species, it appears to differ from the newly described T. (N.) dispar in the dorsal punctation, smaller body size, the structure of the prosternal striae, as well as in other, minor characters. However, the most distinctive character of the newly described species is found on the mandibles, which are unusually large, strongly bent, wide at base and in  furnished with a well developed, inwardly turned acute horn. A sexually dimorphic species, the  are devoid of such a horn.
Etymology. The specifi c epithet of the new species is Latin adjective meaning 'different'. We chose this name to point out the sexual dimorphism between the two sexes, where the male is adorned with mandibular 'horns' whereas the female is without them. Collection circumstances. The specimens of the type series were mostly collected under bark of dead Boswellia elongata Balf. f. trees (J. Hájek, pers. comm.), see also KNÍŽEK (2012a,b). Distribution. Endemic to Socotra Island. Comments. The nominotypical subgenus Teretrius is a taxonomically complicated unit currently containing 76 described species spread across the entire world, with the bulk of species known from tropical Africa (MAZUR 2011). Its members live subcortically on various kinds of deciduous trees (mainly acacias in tropical Africa), hunting the larvae of coleopteran (sub) families Bostrichidae and Curuclionidae: Scolytinae. Several species of Teretrius have been even used in the pest control (see e.g. HOLST & MEIKLE 2003). Identifi cation of the species of both subgenera Neoteretrius and Teretrius s. str. is complicated by the fact that the taxa are generally uniform in outlook, their descriptions are often very concise and lack depiction of the diagnostic characters. In fact, the male genitalia of members of both subgenera were fi rst correctly illustrated by ÔHARA (2008). The presence of misidentifi ed or doubtfully identifi ed specimens in the collections that could be used as the reference specimens creates further confusion in the determination (KANAAR 2008). Given the above facts, we refrain from describing new taxa and record the above and the following species under a number pending an urgently needed revision of this genus. Comment. Saprinus (S.) bicolor is an attractive large species, mostly found on carrion, with distribution across tropical Africa and the Arabian Peninsula, with records also from the British Overseas Territory of Saint Helena (MAZUR 2011). Its occurrence in Socotra is in line with its general distribution. First record from Socotra.

Saprinus (Saprinus) caerulescens caerulescens (Hoffmann, 1803)
Comment. Saprinus (S.) caerulescens caerulescens is a large, free-living volant predator, found mostly on larger carrion where it preys on larvae of smaller arthropods, especially cyclorrhaphan fl ies (T. Lackner, pers. observ.). According to MAZUR (2011), it is distributed in southern Europe, Mediterranean subregion, the Azores and Cape Verde Archipelago, and Middle Asia. It has been introduced into Peru. From Socotra already reported by WRANIK (2003). Comment. The distribution of Saprinus (S.) chalcites covers a vast territory and is comparable with the following species. It is found in the entire Mediterranean subregion, Africa, in the Arabian Peninsula and in Middle Asia, India, Burma and it has also been introduced into Australia (MAZUR 2011). It is another typical saprobiont found on carrion and mammal excrements. First record from Socotra.
Comments. This species is widespread in Africa with records from southern Yemen (PENATI & VIENNA 2006). Reported from Socotra already by WRANIK (2003)  Comments. LACKNER (2013) examined the type series of the sand-dwelling H. virescens, and commented on the dubious subgeneric placement of this species, placed since its description in the subgenus Baeckmanniolus Reichardt, 1926. Members of Baeckmanniolus are (sensu BOUSQUET & LAPLANTE 2006) defi ned by the completely glabrous pronotum and possession of three rows of denticles on outer metatibial margin. In several Socotran specimens, the pronotal punctation is limited to 'a small cluster of scattered and fi ne punctures near anterior angles' as observed by LACKNER (2013) among the members of the type series. Other examined specimens from Socotra, however, have the pronotal punctation more prominent, covering lateral pronotal sides, anterior angles as well as postocular area of pronotum. Based on the punctate pronotum, as well as presence of only two rows of denticles on outer metatibial margin, the species Hypocaccus virescens is removed from the subgenus Baeckmanniolus and placed into the nominotypical subgenus.
Originally described from Somalia, reported also from Bahrain (MAZUR 2011). First record from Socotra.

Hypocacculus (Colpellus) praecox (Erichson, 1834)
Comments. This species is widespread in the entire Mediterranean Subregion, with records from the Canary and Cape Verde Islands, furthermore it occurs in the region of Sahel, Ethiopia, the Arabian Peninsula and Afghanistan (MAZUR 2011). It belongs to the group of typical freeliving volant saprobionts and is most commonly found on carrion or on mammal excrements. First record from Socotra. Comments. This species is known from Djibouti and north Yemen (MAZUR 2011). It occurs on the seashores, chiefl y under wrack or decomposing fi sh. First record from Socotra.

Discussion
Based on our study, the histerid fauna of Socotra Island contains 20 species, a considerable number of which (seven species, i.e. more than a third) could not, due to the poor knowledge of their taxonomy, be identifi ed to species and are only given generic, or subgeneric rank. Based on their biology, the identifi ed species belong to three distinct groups: a) psammophilous species spread chiefl y on the beaches of the Horn of Africa and the Arabian Peninsula (Neopachylopus secqi, Hypocaccus (H.) virescens); b) endemic saproxylic species (Eutriptus jirinae, Teretrius (Neoteretrius) dispar sp. nov., Pachycraerus socotrensis sp. nov., and Liopygus occidentalis sp. nov.; and c) widely spread, mainly saprobiont species (Hypocacculus (Colpellus) praecox, Saprinus (S.) bicolor, S. (S.) caerulescens, S. (S.) chalcites, S. (S.) splendens, Atholus bicolor, and Platylomalus digitatus). Higher taxa of the unidentifi ed species can be likewise divided into two groups: a) widely spread taxa (Teretrius, Acritus, and Tribalus) and taxa with limited distribution whose occurrence in Socotra is rather surprising (Plegaderus).
Although members of saproxylic Liopygus are distributed chiefl y in southeast Asia, there are Liopygus species found also in south or north India, respectively (see MAZUR 2011). The presence of Liopygus on the island of Socotra is of biogeographic signifi cance as it considerably broadens the distribution of the genus.
Arguably, the most interesting is the discovery of a member of the genus Plegaderus on the island. Plegaderus belongs to the subclass of subcortical 'micro-histerids' found mostly in the forested zone of both the Palaearctic and Nearctic Regions. None species is known from the Arabian Peninsula or Africa for that matter, with the exception of P. (P.) sanatus sanatus Truqui, 1852 reported from Algeria and Morocco (MAZUR 2011). This taxon must have colonized the island from the north, and its puzzling presence on the island of Socotra raises the probability of discovering additional species in the Arabian Peninsula.