Genus Microsternus Lewis (1887) from China, with description of a new genus Neosternus from Asia (Coleoptera, Erotylidae, Dacnini)

Abstract This work treats species of the genus Microsternus Lewis, 1887 from Asia and North America. A new genus is described: Neosternus (type species Microsternus higonius Lewis, 1887). A new species is described: Microsternus pengzhongi. A new synonym is provided: Microsternus tricolor taiwanicus Nakane (=Microsternus tricolor Lewis). Three species previously placed in Microsternus Lewis, 1887 are transferred to Neosternus resulting in the following three new combinations: Neosternus higonius (Lewis, 1887), Neosternus taiwanus (Chûjô, 1976), and Neosternus hisamatsui (Nakane, 1981).


General introduction
The family Erotylidae is composed of fungus feeding beetles which vary greatly in body size and color; many are elaborately patterned. Crotch's (1876) world revision of the Erotylidae was the last study to cover the entire Old World fauna at the species level, but it provided no keys nor illustrations, and only a few short descriptions. In the time between Chûjô and Chûjô 's (1988) catalog of the Old World erotylids and Wegrzynowicz's (2006) catalog of the Palaearctic erotylids, the China erotylid fauna had been studied intermittently, with scattered regional studies, checklists, and species descriptions. Most Chinese erotylid genera have no modern revisions. Wegrzynowicz (2002) formally synonymized the tribes Megalodacnini and Encaustini. More recent phylogenetic work by Leschen (2003), Robertson et al. (2004), and Leschen and Buckley (2007) were either inconclusive or resulted in different tree topologies that indicate more work is needed to better establish relationships of all tribes before making further taxonomic changes.

History
The first described member of the genus Microsternus Lewis is Megalodacne ulkei Crotch (1873). In studying the Japanese erotylid specimens, Lewis (1883) described Episcapha perforata, but on further study of these group, Lewis (1887a) found three similar Japanese species required a genus to be formed for their reception. Together with Episcapha perforata, Lewis thought these four species were congeneric with American species Megalodacne ulkei and established the genus Microsternus. Lewis (1887b) transferred Episcapha perforata into Microsternus becoming Microsternus perforatus (Lewis, 1883) and described three other species as Microsternus higonius Lewis (1887b), Microsternus crotchi Lewis (1887b) and Microsternus tricolor Lewis (1887b).
In this work, while examining the specimens of Microsternus from China, we described a new species Microsternus pengzhongi sp. n. from Hainan Prov. and reduce Microsternus tricolor taiwanicus Nakane to a synonym of Microsternus tricolor Lewis. After genitalic dissections and comparisons of head and pronotum structures, we recognized that the genus Microsternus can be divided in two species-groups. Microsternus higonius Lewis (1887b), Microsternus taiwanus Chûjô (1976) and Microsternus hisamatsui Nakane (1982) are not congeneric with the type species of Microsternus Lewis, Microsternus ulkei Crotch (1873). Unlike typical Microsternus, the species, M. higonius, M. taiwanus and M. hisamatsui do not have the pit posterior to the postmandibular lobes; pronotum has a deep sulcus along each side, which is broadly margined and formed thicken lines in lateral view; male genitalia with flagellum curved, bearing a dorsal, arched, cartilaginous mass on apical quarter, along with prosternum and mesosternum characters not present in other members of Dacnini. Here we describe a new genus Neosternus for these three species.

Male genitalia
The internal sac of the male genitalia is held invaginated within the median lobe. During copulation, the internal sac is everted; exposing any microstructure and extending the flagellum. The median lobe, internal sac, and flagellum are the true copulatory organs and show the majority of species specific characters. For additional insight into the genitalia of Erotylidae see Skelley (1998) and Skelley and Leschen (2007).
In this work, after dissection of the internal sac, we found the dorsal lobe of Microsternus has obvious differences that are important characters in species recognition.

Female genitalia
Female genitalia seemed to vary little from species to species. Structures varied in proportions, but species recognition based on female genitalia was not possible with any degree of confidence. The sclerotized spermatheca showed some variation in shape which could be useful to determine relationships within the genus. See Skelley (1998).

Material and methods
In addition to extensive collecting by the authors and their colleagues, Chinese specimens of the tribe Dacnini were borrowed from Wen-xuan Bi's private collections. North America specimens of the genus Microsternus were provided for study from Florida State Collection of Arthropods, USA [Paul E. Skelley]. The photos of type specimens were taken from The Natural History Museum, London, England.
Erotylids were collected in a wide variety of woodland fungi, in crevices under bark or in other retreats by splitting and sifting, and in light traps. For an examination of the male genitalia, the abdominal segments were detached from the body after softening in hot water. The genitalia, together with other dissected parts, were mounted in Euparal (Chroma Gesellschaft Schmidt, Koengen, Germany) on plastic slides. Photos of sexual characters were taken with a FUJIFILM X10 camera attached to an Olympus SZX 16 stereoscope; habitus photos were taken with a Canon macro photo lens MP-E 65 mm attached to a Canon EOS7D camera.
Diagnosis. Defining characters for Microsternus are body elongate, head with the pit posterior to the postmandibular lobes, pronotum without a deep sulcus along each side and narrowed margin in lateral view, mesosternum almost concealed by prosternal process, male genitalia with flagellum (Figs 59-64) bearing a straight mass on apical quarter.  Head width between eyes = 4 times eye diameter in dorsal view; punctation fine, spare, separated by two to four puncture diameters; epistome truncate, lacking marginal line on anterior margin; stridulatory files not evident. Eyes coarsely facetted. Antennomere III about 1.2 times as long as IV; antennomere VIII slightly wider than VII, about 1.3 times as wide as long; antennomere IX trapezoidal; antennomere X transverse; antennomere XI almost elliptic. Gular area with pit posterior to the postmandibular lobes. Maxillary and labial terminal palpomeres acuminate, sensory area restricted to apex. Mentum broad with anterior projection, almost triangular, slightly more than 2.3 times wider than long.

Key to Chinese species of genus Microsternus
Pronotum arched, widest at base (pl/pw = 0.65); narrowed from base to apex, with formed thinned lines in lateral view; disk finely and spare punctured, except the impunctate medio-basal area, which is limited by an arched transverse row of fine punctures.
Prosternum with median area including its process elevated in an elongate triangular plane, which is distinctly bordered by a ridge on both sides and shortly rounded-subtrun- cate in front, bearing a few fine punctures; sides rugose, coarsely and densely punctured. Mesosternum almost conceled by prosternal process, impunctate as the mesepisterna, which is somewhat concave. Metasternum rather sparsely and strongly punctured on lateral areas, some finer punctures on median area, with a pair of mesocoxal lines strongly divergent posteriorly. Abdomen rather strongly and closely punctured, but median areas of four basal visible sternites and medio-basal area of last visible sternite with few punctures respectively; without metacoxal lines on basal visible sternite. Legs rather robust.
Scutellum pentagonal, finely and sparely punctured. Elytra convex, with eight striae of distinct punctures on each elytron and each interstice with a row of extremely fine punctures.
Male genitalia (Figs 9-10) with flagellum bearing a straight mass on apical; flagellar apex acute with a well-separated ventral process; dorsal lobe of internal sac with long and tweezer-like structure in dorsal view (Figs 11-12).
Distribution. China (Hainan Province). Diagnosis. Characterized by its shining body, spare punctured pronotum and dorsal lobe's unique structure of internal sac.
Etymology. This species is named in honor of Mr. Zhong Peng, one of the collectors of this new species. Head width between eyes = 7 times eye diameter in dorsal view; punctation coarse, close, separated by half to two puncture diameters; epistome truncate, lacking marginal line on anterior margin; stridulatory files not evident. Eyes coarsely facetted. Antennomere III about 1.4 times as long as IV; antennomere VIII slightly wider than VII, about 1.2 times as wide as long; antennomere IX trapezoidal; antennomere X transverse; antennomere XI almost elliptic. Gular area with pit posterior to the postmandibular lobes (Fig. 42). Maxillary and labial terminal palpomeres acuminate, sensory area restricted to apex. Mentum broad with anterior projection, almost triangular, slightly more than 3.7 times wider than long.

Microsternus perforatus
Pronotum (Fig. 47) arched, widest at base (pl/pw = 0.63); narrowed from base to apex, with formed thinned lines in lateral view (Fig. 52); disk coarsely and close punctured, except the impunctate medio-basal area, which is limited by an arched transverse row of coarse punctures.
Prosternum with median area including its process elevated in an elongate triangular plane, which is distinctly bordered by a ridge on both sides and shortly rounded-subtruncate in front, bearing a few fine punctures; sides rugose, coarsely and densely punctured. Mesosternum almost conceled by prosternal process, impunctate as the mesepisterna, which is somewhat concave. Metasternum rather sparsely and strongly punctured on lateral areas, some finer punctures on median area, with a pair of mesocoxal lines strongly divergent posteriorly. Abdomen rather strongly and closely punctured, but median areas of four basal visible sternites and medio-basal area of last visible sternite with few punctures respectively; without metacoxal lines on basal visible sternite. Legs rather robust.
Scutellum pentagonal, with each corner rounded, flattish and almost impunctate on surface.
Elytra convex, with eight striae of distinct punctures on each elytron and each interstice with a row of extremely fine punctures.

Microsternus tricolor Lewis, 1887
http://species-id.net/wiki [24][25][26][27][28][29][30][31][32][33]41,46,51,[61][62]73,77 Microsternus tricolor taiwanicus Nakane, 1966, syn Head width between eyes = 8 times eye diameter in dorsal view; punctation coarse, close, separated by half to two puncture diameters; epistome truncate, lacking marginal line on anterior margin; stridulatory files not evident. Eyes coarsely facetted. Antennomere III about 1.7 times as long as IV; antennomere VIII slightly wider than VII, about 1.2 times as wide as long; antennomere IX trapezoidal; antennomere X transverse; antennomere XI almost elliptic. Gular area with pit posterior to the postmandibular lobes (Fig. 41). Maxillary and labial terminal palpomeres acuminate, sensory area restricted to apex. Mentum broad with anterior projection, almost triangular, slightly more than 4.0 times wider than long. Pronotum (Fig. 46) arched, widest at base (pl/pw = 0.58); narrowed from base to apex, with formed thinned lines in lateral view (Fig. 51); disk coarsely and close punctured, except the impunctate medio-basal area, which is limited by an arched transverse row of coarse punctures. Prosternum with median area including its process elevated in an elongate triangular plane, which is distinctly bordered by a ridge on both sides and shortly roundedsubtruncate in front, bearing a few fine punctures; sides rugose, coarsely and densely punctured. Mesosternum almost conceled by prosternal process, impunctate as the mesepisterna, which is somewhat concave. Metasternum rather sparsely and strongly punctured on lateral areas, some finer punctures on median area, with a pair of mesocoxal lines strongly divergent posteriorly. Abdomen rather strongly and closely punctured, but median areas of four basal visible sternites and medio-basal area of last visible sternite with few punctures respectively; without metacoxal lines on basal visible sternite. Legs rather robust.
Scutellum pentagonal, with each corner rounded, flattish and almost impunctate on surface.
Elytra convex, with eight striae of distinct punctures on each elytron and each interstice with a row of extremely fine punctures.
Male genitalia (Figs 24-25) with flagellum bearing a straight mass on apical quarter; flagellar (Figs 61-62) apex acute with a well-separated ventral process; dorsal lobe of internal sac with spade -like structure in dorsal view (Figs 26-27).
Comment. Nakane described 'taiwanicus' for a single female specimen, according his description, Microsternus tricolor taiwanicus can be distinguished from Microsternus tricolor by a difference in the elytral bands: Microsternus tricolor taiwanicus has the median black patch on each side is nearly quadrate, not triangular and more extended inwards, with the inner margin more longitudinal and the front angle nearly rectangular; the posterior yellow fascia is much broader and nearly as wide as the black band before the apex. On studying the specimens of Microsternus tricolor, we find the bands of elytra are variable in different specimens (Figs 30-33), after compare the photos about Microsternus tricolor from Taiwan and Japan, we think the differences Nakane mentioned in his paper are not unique to Taiwan.
Based on the information outlined above, we considered Microsternus tricolor taiwanicus is a new synonym of Microsternus tricolor.
Description. Body small, elongate oval (Figs 34-37, 76), with legs short and robust, the tarsi cylindrical, 5-jointed, the four basal joints short, nearly equal in size and not at all dilated, the last joint long. Antennae not very long, the latter with a broad 3-jointed club. Eyes coarsely facetted. Maxillary and labial terminal palpomeres (Figs 43,44) acuminate, sensory area restricted to apex. Pronotum (Figs 48,49) arched, widest at base; narrowed from base to apex, with a deep sulcus along each side, which is broadly margined and the bordering gradually widened anteriorly, which formed thicken lines in lateral view (Figs 53, 54); disk coarsely and sparsely punctured, except the impunctate medio-basal area, which is limited by an arched transverse row of coarse punctures. Prosternum (Figs 38, 39) with median area including its process elevated in an elongate triangular plane, which is distinctly bordered by a ridge on both sides and shortly rounded-subtruncate in front. Mesosternum almost concealed by prosternal process. Metasternum with a pair of mesocoxal lines strongly divergent posteriorly. Abdomen without metacoxal lines on basal visible sternite. Elytra strongly convex.
Distribution. China, Japan. Diagnosis. This new genus can be distinguished from Microsternus by body elongate oval, head without the pit posterior to the postmandibular lobes, pronotum with a deep sulcus along each side, which is broadly margined in lateral view, male genitalia with flagellum bearing a arched mass on apical quarter (Figs 55-58). Microsternus body elongate, head with the pit posterior to the postmandibular lobes, pronotum without a deep sulcus along each side and narrowly margined in lateral view, male genitalia with flagellum bearing a straight mass on apical quarter (Figs 59-64).
Etymology. As a uniquely new group within Dacnini, the generic name is derived from Microsternus, it is appropriate to call the genus "New sternus", and to abbreviate and combine the roots into a single word. The gender is masculine.  Head width between eyes = 8 times eye diameter in dorsal view; punctation coarse, sparse, separated by 3-4 puncture diameters; epistome truncate, lacking marginal line on anterior margin; stridulatory files not evident. Eyes coarsely facetted. Antennomere III about 1.8 times as long as IV; antennomere VIII slightly wider than VII, about 1.2 times as wide as long; antennomere IX trapezoidal; antennomere X transverse; antennomere XI almost elliptic; relative lengths of antennomeres II-XI: 15: 18: 10: 10: 10: 10: 10: 14: 15: 17. Maxillary and labial terminal palpomeres acuminate, sensory area restricted to apex. Mentum broad with anterior projection, almost triangular, slightly more than 3.5 times wider than long.

Key to species of genus
Pronotum arched, widest at base (pl/pw = 0.55); narrowed from base to apex, with a deep sulcus along each side, which is broadly margined and the bordering gradually widened anteriorly (Fig. 48), which formed thicken lines in lateral view (Fig. 53); disk coarsely and sparsely punctured, except the impunctate medio-basal area, which is limited by an arched transverse row of coarse punctures. Prosternum (Fig. 38) with median area including its process elevated in an elongate triangular plane, which is distinctly bordered by a ridge on both sides and shortly rounded-subtruncate in front, bearing a few fine punctures; sides rugose, coarsely and densely punctured. Mesosternum almost concealed by prosternal process, impunctate as the mesepisterna, which is somewhat concave. Metasternum rather sparsely and strongly punctured on lateral areas, some finer punctures on median area, with a pair of mesocoxal lines strongly divergent posteriorly. Abdomen rather strongly and closely punctured, but median areas of four basal visible sternites and medio-basal area of last visible sternite with few punctures respectively; without metacoxal lines on basal visible sternite. Legs rather robust. Scutellum pentagonal, with each corner rounded, flattish and almost impunctate on surface.
Elytra strongly convex, with eight striae of distinct punctures on each elytron and each interstice with a row of extremely fine punctures. Male genitalia (Fig. 65) with flagellum ( Fig. 66) curved, bearing a dorsal, arched, cartilaginous mass on apical quarter; flagellar apex acute with a well-separated ventral process; dorsal lobe of internal sac with separated front and triangular end (Fig. 67); ventral lobe of internal sac trident-like (Fig. 68).
Distribution. China, Japan. Diagnosis. Characterized by its small body and black pronotum. Head width between eyes = 8 times eye diameter in dorsal view; punctation coarse, sparse, separated by 3-4 puncture diameters; epistome truncate, lacking marginal line on anterior margin; stridulatory files not evident. Eyes coarsely facetted. Antennomere III about 1.8 times as long as IV; antennomere VIII slightly wider than VII, about 1.2 times as wide as long; antennomere IX trapezoidal; antennomere X transverse; antennomere XI almost elliptic; relative lengths of antennomeres II-XI: 15: 18: 10: 10: 10: 10: 10: 14: 15: 17. Maxillary and labial terminal palpomeres acuminate, sensory area restricted to apex. Mentum broad with anterior projection, almost triangular, slightly more than 3.5 times wider than long.  Pronotum arched, widest at base (pl/pw = 0.55); narrowed from base to apex, with a deep sulcus along each side, which is broadly margined and the bordering gradually widened anteriorly (Fig. 49), which formed thicken lines in lateral view (Fig. 54); disk coarsely and sparsely punctured, except the impunctate medio-basal area, which is limited by an arched transverse row of coarse punctures. Prosternum ( Fig. 39) with median area including its process elevated in an elongate triangular plane, which is distinctly bordered by a ridge on both sides and shortly rounded-subtruncate in front, bearing a few fine punctures; sides rugose, coarsely and densely punctured. Mesosternum almost conceled by prosternal process, impunctate as the mesepisterna, which is somewhat concave. Metasternum rather sparsely and strongly punctured on lateral areas, some finer punctures on median area, with a pair of mesocoxal lines strongly divergent posteriorly. Abdomen rather strongly and closely punctured, but median areas of four basal visible sternites and medio-basal area of last visible sternite with few punctures respectively; without metacoxal lines on basal visible sternite. Legs rather robust.
Scutellum pentagonal, with each corner rounded, flattish and almost impunctate on surface.
Elytra strongly convex, with eight striae of distinct punctures on each elytron and each interstice with a row of extremely fine punctures.
Male genitalia (Fig. 69) with flagellum (Figs 57-58) curved, bearing a dorsal, arched, cartilaginous mass on apical quarter; flagellar apex acute with a well-separated ventral process; dorsal lobe ( Fig. 70) of internal sac with separated front and triangular end; ventral lobe of internal sac trident-like.

Comment.
Neosternus hisamatsui Nakane is similar to Neosternus higonius Lewis in the form and color pattern of the body. Neosternus hisamatsui can be distinguished from N. higonius by the pronotum entirely reddish-brown. Neosternus higonius has pronotum black with reddish-brown sides. Though the male genitalia and dorsal lobe of internal sac of N. higonius is similar to N. hisamatsui, with only one specimen of N. higonius available and no Japanese specimens, we can't consider N. hisamatsui as a synonym of N. higonius. This should be considered after maor materials are available for study. (Chûjô, 1976), comb. n. http://species-id.net/wiki/Neosternus_taiwanus Chûjô, 1976.

Distribution. China (Taiwan).
Diagnosis. Characterized by its small body and markings of pronotum. Comment. Chûjô described Microsternus taiwanus from Taiwan. According Chûjô's description, Neosternus taiwanus is very similar to Neosternus higonius. The only difference between these two species were the bands of pronotum and elytra as noted in the key to species. No specimens are available for study.