Review of the Korean Species of the Genus Edaphus Motschulsky (Coleoptera, Staphylinidae) with Description of Four New Species

Simple Summary Four new species, Edaphus haenamensis sp.n., E. odaesanensis sp.n., E. suyuensis sp.n., and E. ulsanensis sp.n., are described in the Korean Peninsula. Additional two species, E. koreanus and E. lederi, are redescribed, and the latter species is recorded for the first time from Korea. Abstract The cosmopolitan euaesthetine genus, Edaphus Motschulsky, 1857, with about 90 Palaearctic species, was formerly known by a single species, E. koreanus Puthz, 2011, of which 2 specimens were collected in the southern part of the Korean Peninsula. In this paper, the knowledge of the Korean Edaphus fauna is expanded to include six species, including four described here based on a rich material collected in recent years. A key to all six species of Korean Edaphus, illustration of the habitus and diagnostic characters, and a distribution map are provided.


Introduction
The genus Edaphus Motschulsky, 1857 [1], is the largest genus of Euaesthetinae Thomson, 1859 [2], including about 600 species in the world [3,4]. More than half of the species are distributed in the Palaearctic and Oriental regions, and about 100 species are distributed in the Neotropical region, as well as the Afrotropical region [3]. Approximately 55 species have been recorded in Japan, but a single species, E. koreanus Puthz, 2011 [5], was recorded in the southern part of the Korean Peninsula [5,6]. During a revisionary study of the Korean Edaphus species based on 110 specimens, 4 new species and 1 additional, so far unrecorded species, were recognized. This is the first revisionary study of the Korean Edaphus, increasing the number of species identified in the Korean Peninsula to six.

Materials and Methods
All specimens were collected using sifting, mushroom window trap, flight intercept trap and lindgren funnel methods. At least a one specimen of each species was fully dissected to observe the male genitalia and other detailed features. These permanent microscopic slides were prepared using the method described by Hanley and Ashe [7]. The terminology and nomenclature were presented using the description by Chandler [8] and Puthz [3]. Numbering of abdominal sclerites indicated the morphological segment. The specimens were observed using a Leica M80 and MD 1000 LED optical microscope, and the images were generated using Las version 4.12 and Zerene stacker. The map of Korea was based on an image from SimpleMappr [9], which was subsequently modified to add locality marks. Specimen label data for holotypes were transcribed verbatim. Data for other specimens were standardized for consistency.
Holotypes of all species described herein are deposited in the National Institute of Biological Resources (NIBR, Incheon, Republic of Korea). Paratypes and voucher specimens are deposited in CBNUIC (Chungbuk National University Insect Collection, Cheongju, Republic of Korea) and NIBR (National Institute of Biological Resources, Incheon, Republic of Korea), indicated parenthetically. The following abbreviations were used ( Figure 1): Figure 1. Abbreviation of morphological character: DE-distance between eyes; dlbc-distance of the latero-basal carinae of the pronotum; EL-greatest length of elytra; EW-greatest width of elytra; G-gena; HW-width of head; LE-length of eyes; LG-length of genae; LT-length of temples; mbc-medio-basal carina of the pronotum; mbct3-medio-basal carina of tergite III; PL-length of pronotum; PW-width of pronotum; T-temple.
Aedeagus as in Figure 9A and internal sacs of median lobe movable. Distribution. South Korea ( Figure 10: circle).
Etymology. This species is named after the type locality, Haenam-gun, Jeonnam Province.
Aedeagus as in Figure 9C and internal sacs of median lobe movable. Distribution. South Korea (Figure 10: square).
Etymology. This species is named after the type locality, Suyu-dong, Seoul.
Aedeagus as in Figure 9D and internal sacs of median lobe movable. Distribution. South Korea (Figure 10: reverse triangle).
Etymology. This species is named after the type locality, Ulsan Metropolitan City.
Aedeagus as in Figure 9E and internal sacs of median lobe movable. Distribution. South Korea (Figure 10: Diamond).

Discussion
Species of the genus Edaphus are difficult to distinguish from each other. The main external diagnostic characters in this genus are the head shape, antennomeres X-XI shape, medio-basal fovea, mbc (medio-basal carina of the pronotum), and mbct3 (medio-basal carina of tergite III). The shape of abdominal sternites VIII and IX in males are used as the the main identification characters, as well as the aedeagus. The bionomics in this genus are poorly known, but most specimens were found in wet leaf litter and the upper layer of soil, sampled by sifting, and occasionally collected by soil-washing, flight intercept traps, etc. As regards the Korean fauna, because of their cryptic habits, more Edaphus species are expected to be found in the future.

Conclusions
This genus has approximately 600 species worldwide. Most species are distributed in the Oriental region. Previously, a single species was recorded in South Korea. In this study, four new species (Edaphus haenamensis sp.n., E. odaesanensis sp.n., E. suyuensis sp.n., and E. ulsanensis sp.n.) and one unrecorded species (E. lederi) were recorded in Korea fauna.