On the genus Stephostethus LeConte, 1878 (Coleoptera: Latridiidae: Latridiinae) from Taiwan, with descriptions of two new species

The genus Stephostethus LeConte, 1878 of minute brown scavenger beetles (Coleoptera: Latridiidae: Latridiinae) is recorded from Taiwan for the first time, which extends the southernmost boundary of this genus in the Palaearctic realm. Two new species, S. taiwanus sp. nov. and S. yuanfengensis sp. nov., and one new record, S. chinensis (Reitter, 1877), are described in this study. A taxonomic key to the three species of this genus in Taiwan is also provided. The distributions, habitats and collecting methods of these three species, as well as the structure of the genital segments of this genus are discussed.


Introduction
The genus Stephostethus LeConte, 1878, consisting of 37 species worldwide, belongs to the subfamily Latridiinae Erichson, 1842. Most of the species are distributed in the Palaearctic and Nearctic realms, and seem to be restricted to temperate regions; in Asia there are records from areas such as China, Nepal and the mountainous areas of India (Rücker 2015(Rücker , 2018(Rücker , 2020. genital segments are the best diagnostic characters for species identifi cation, and the aedeagus is often weakly chitinized, limiting its use as a diagnostic character. However, the genital segments were termed "7 th tergite" in Muona (1983) and "fusion of last tergite and sternite" in Rücker (2018Rücker ( , 2020. Sen Gupta (1976) redefi ned the genus Stephostethus, added three species from India, and subsequently revised this genus and described nine new species from India (Sen Gupta 1983). Rücker (2004) described a new species from China, and since then, no further Stephostethus species have been added.
To date, in Taiwan, only three genera of Latridiinae have been recorded (Chan & Lee 2016;Ho et al. 2019). Herein, we report a new record of the genus Stephostethus from Taiwan, add three species of Stephostethus from Taiwan, including one new record and two new species, and provide an identifi cation key for all species in the region. We have also investigated the abdominal segments of the genus and attempt to determine the appropriate terminology for the genital segments.

Material and methods
Specimens were collected and preserved dry for morphological observation. Dissections of male genitalia were performed. The abdomen was removed, soaked in a high concentration KOH solution for at least ten minutes (depending on the specimen condition), and was then cleaned in distilled water. The abdomen sternite, tergite and aedeagus were removed for further examination under a stereo microscope. Photographs of adults were taken with a Canon EOS 650D camera equipped with a Canon MP-E65 f/2.8 1-5 × macro lens, and photographs of genital segments were taken with a Canon EOS 650D camera attached to a Zeiss Axioskop 2 microscope. All photographs were subsequently focus stacked with Helicon Focus software. Figures of male tibiae and the structure of genital segments were drawn using Adobe Illustrator CS6. The terminology used herein follows Ho et al. (2019) and Rücker (2018Rücker ( , 2020.

Diagnosis
Species of Stephostethus LeConte can be distinguished from related genera in Taiwan by the following characters: mandible with single apical tooth and inner margin smooth. Eyes well developed. Pronotum square, sides more or less parallel, with two carinae on disc; prosternal process short, narrow and not extending to apex, epimera not separated by prosternal process and meeting each other on median line. The genital segments are defi ned as the abdominal 8 th -10 th segments herein .

Diagnosis
This species is closely related to Stephostethus chinensis (Reitter, 1877), but can be distinguished by the 7 th interstriae, which are less protruding at the front, the structure of the genital segments of the male, and the characters of the teeth on the male tibiae. Stephostethus taiwanus sp. nov. has four indistinct teeth on the hind tibia, whereas S. chinensis has three distinct teeth on the hind tibia.

Etymology
The specifi c epithet, taiwanus, is named after its country of discovery, Taiwan.  (2021) COLOUR. General body yellowish brown to dark brown, with tibiae, tarsi and antennae light brown.

Material
HEAD. Slightly longer than wide, width to length ratio 1.00 : 1.11; strongly punctate, clypeus narrower than head, with short setae. Eyes well developed, with more than 20 facets; temple narrower than eye, about half length of eye, hind angle of temple with or without a sharp tooth. Antennae with 11 segments, 3 rd segment slightly shorter than 4 th segment, 4 th to 8 th segment same in length; apical three segments clubbed.
PRONOTUM. Almost as long as wide, width to length ratio 1.00 : 0.94; sides almost parallel, widest at anterior margin, narrowest at posterior one-third. Front angle barely protruding and bluntly rounded, posterior one-third with a pair of depressions. Surface irregularly and densely punctate, with a pair of carinae on disc. Sometimes covered with wax on lateral and ventral sides.
METASTERNUM. Strongly convex, each side with fovea situated under mid coxa, and surrounded by radial striae, sometimes covered with wax on meso-and metasternum.
LEGS. Long and slender, covered with short setae on femora and tibiae. Male with one distinct tooth on anterior end of protibia and four indistinct teeth on anterior end of hind tibia, sometimes barely visible, mid tibia without any teeth; anterior end of protibia straight, apex expanded, mid and hind tibia straight. MALE GENITALIA. Aedeagus weakly chitinized, long and slender, sides parallel, with apex sharp, curve at middle in lateral view. Genital segments weakly chitinized, with apical end truncate, broadest at base (Fig. 2).

Distribution
Taiwan (Fig. 12). Widely found in various altitude levels ranging from 100 to 2300 m a.s.l.

Remarks
This species is widely distributed in Taiwan, and partly overlaps with the range of S. yuanfengensis sp. nov. in central and southern Taiwan. So far, of the three species of Stephostethus LeConte in Taiwan, only S. taiwanus sp. nov. is found in northern Taiwan. Some of the specimens were collected by beating the dead dry branches in a broadleaf forest (~100 m a.s.l.).
HEAD. Slightly longer than wide, width to length ratio 1.00 : 1.20, strongly punctate, clypeus narrower than head, with some short setae. Eyes strongly developed, with more than 20 facets; temple narrower than eye, about half length of eye, hind angle with or without a sharp tooth. Antennae 11-segmented, 3 rd segment slightly longer than 4 th segment, 5 th to 8 th segment same in length, apical three segments clubbed.
PRONOTUM. Slightly longer than wide, width to length ratio 1.00 : 1.05, widest at anterior margin, narrowest at anterior third. Sides carinate; front angle strongly protruded and bluntly rounded, posterior one-third with a pair of round depressions. Surface irregularly and densely punctate, with a pair of carinae on disc. Sometimes covered with wax on lateral and ventral sides.
METASTERNUM. Strongly convex, with fovea situated under mid coxa on each side and surrounded by radial striae. Sometimes covered with wax on meso-and metasternum.
LEGS. Long and slender, covered with short setae on femora and tibiae. Male with one distinct tooth on each anterior end of protibia, mid tibia and hind tibia; anterior end of protibia expanded and curved, mid tibia and hind tibia straight. Female without any teeth on tibia. MALE GENITALIA. Aedeagus weakly chitinized, long and slender, sides parallel, weakly curved at middle, and straight at apex in lateral view. Genital segments long and slender, broadest at base, middle area less chitinized, apical end spear-shaped (Fig. 5).

Distribution
Central to southern Taiwan (Fig. 12). This species can be found in areas from low to high elevation (300-3518 m a.s.l.).

Remarks
From our records, S. yuanfengensis sp. nov. can be caught in Malaise traps in large numbers (ca 100 individuals at a time) at the type locality. Some of the specimens were collected by beating dry dead branches and damp leaves in an artifi cial red oak forest (~2300 m a.s.l.) (Fig. 10).

Diagnosis
Stephostethus chinensis (Reitter 1877) is similar to S. carinatus Sen Gupta, 1976 from India. However, the former species can be distinguished from the latter by the structure of the genital segments of the European Journal of Taxonomy 735: 1-14 (2021) male, and the characters of the teeth on male tibiae, as S. carinatus has one tooth on the mid tibia, and S. chinensis has no teeth on the mid tibia. COLOUR. General body colour brown to dark brown, with legs and antennae yellowish brown.

Material examined
HEAD. Slightly longer than wide, width to length ratio 1.00 : 1.20, surface strongly punctate, base of head depressed, clypeus narrower than head, covered with some short setae; temple narrower than eye, about half length of eye, with sharp hind angle. Antennae 11-segmented, second segment slightly shorter than third segment, apical three segments clubbed. Eyes strongly developed, with more than 20 facets. Sometimes covered with wax in ventral view.
PRONOTUM. Slightly wider than long, width to length ratio 1.00 : 0.95; sides almost parallel, widest at anterior margin, narrowest at posterior one-third. Front angle slightly protruded and bluntly rounded, anterior third with a pair of triangular depressions. Surface irregularly and densely punctate, with a pair of carinae on disc. Prosternum short, procoxa separated. Sometimes covered with wax in ventral and lateral views.
METASTERNUM. Strongly convex, with fovea situated under mid coxa on each side and surrounded by radial striae. Sometimes covered with wax on meso-and metasternum.
LEGS. Long and slender, covered with short setae on femora and tibiae. Tarsi 3-3-3, tarsomere 3 longer than 1 and 2 combined; arolium indistinct. Male protibia expanded and curved at apex, with one distinct tooth on anterior end; mid tibia straight, without any teeth; hind tibia straight, with three distinct teeth on anterior end. Female without any teeth on legs.
MALE GENITALIA. Aedeagus weakly chitinized. Long and slender, sides parallel, sharp at apex; bent at anterior two fi fths, and weakly curved at anterior fi fth. Genital segments broad and short, broadest at base, apical end deeply concave with two rounded lobes (Fig. 8).

Distribution
This species is only known from Asia, including Eastern Siberia, China, Japan and Mongolia (Johnson 2007;Rücker 2018Rücker , 2020, and is new to Taiwan (Fig. 12). It is distributed in mid to southern Taiwan, and is widely recorded in various areas, ranging in altitude from 300 to 2300 m a.s.l.

Remarks
Stephostethus chinensis was recorded as a household pest in Japan (Tanaka & Tahira 1995). However, we have never found this species in indoor environments in Taiwan. Some specimens of this species were collected by beating damp leaves in an artifi cial red oak forest (~1700 m a.s.l.), and some were collected with fl ight interception traps in the forest (2113 m a.s.l.) (Fig. 11).

Discussion
The Palaearctic realm is the most species-rich area for Stephostethus, with 28 species, mostly distributed in the temperate regions (Johnson 2007 Gupta 1976Gupta , 1983. Sen Gupta (1983) also mentioned that the genus seemed to be associated with decaying plants. This observation is consistent with the fi rst author's fi eld experiences in Taiwan; the species of Stephostethus can be collected by beating dead branches, especially dead, dry branches. However, most of our specimens were collected by Malaise and fl ight interception traps, which also collect other latridiid species. No specimens of Stephostethus were collected with a light trap during our fi eld investigations, and none were found during specimen examination in various institutes, which suggests that species of this genus are not attracted to light.
Our detailed examination during this study revealed that Stephostethus has ten abdominal segments, a fi nding missed by previous investigators. The term "7 th tergite" used in Muona (1983) and the "fusion of last tergite and sternite" in Rücker (2018Rücker ( , 2020 are actually the 8 th -10 th abdominal segments, in terms of genital segments. These errors may result from overlooking the segmentation of the genital segments or the 1 st tergite. The genital segments are usually retracted inside the 7 th tergite and sternite, but in dead specimens they are sometimes exposed. The structure of genital segments of Stephostethus, especially the shape of 10 th tergite, varies between species but is stable within species, suggesting that genital segment structure can serve as a reliable character for species identifi cation.
Although we have described the current distribution of Stephostethus in Taiwan, it is clear that much remains to be learned. Further research is warranted to better understand the morphology, phylogeny, distribution and ecology of these beetles.
and Dr Chi-Feng Lee (Division of Applied Zoology, Taiwan Agricultural Research Institute) are thanked for kindly loaning important specimens to us. Special thanks also to Dr Ling-Hsiu Liao (Department of Entomology, University of Illinois at Urbana-Champaign) and Dr David L. Evans for the manuscript editing and improvement of the English. Permission to collect specimens in the national park was authorized by Shei-Pa National Park (Permission Number 1001000534). This study was supported by the Ministry of Science and Technology (Most-107-2515-S-178 -002 -MY3).