Trechus Clairville, 1806

Deuve, Thierry, Kavanaugh, David H. & Liang, Hongbin, 2016, Inventory of the Carabid Beetle Fauna of the Gaoligong Mountains, Western Yunnan Province, China: Species of the Tribe Trechini (Coleoptera: Caraboidea), with Descriptions of Four New Genera, One New Subgenus and 19 New Species., Proceedings of the California Academy of Sciences 63 (12), pp. 341-455 : 379-381

Genus Trechus Clairville, 1806

Trechus Clairville, 1806:22 .

TYPE SPECIES.— Carabus rubens, Clairville, 1806 [nec Fabricius, 1801] (= Carabus quadristriatus Schrank, 1781 ), designated by Blanchard (in Audouin et al. 1841, plate 25). See also comments on type species by Bousquet (2012: 505).

DIAGNOSIS.— Adults of this genus ( Fig. 17 -25) can be recognized by the following combination of character states: size very small to small for family (BL = 2.5 to 7.0 mm), fully-winged or apterous, eyes large and projected or reduced, with some members eyeless; body color varied, from pale yellowish-tan to black; body form varied, compact and convex in most members, more slen- der and depressed in some members; labrum with anterior margin concave; right mandible bidentate or tridentate, but with the premolar fused with the retinaculum; submentum free, not fused with mentum, with six setae anteriorly in most members; pronotum with disc glabrous, two pairs of setae lateral present, one each side near middle and near basal angle; elytra with discal striae distinctly impressed and complete or more or less effaced, recurrent stria distinct, discal setae only on interval 3, near or in stria 3 in most members, two setae present in most members, but with more, one or none present in a few members; preapical seta present near discal stria 2 or absent, in a few members present and inserted more anteriorly in a discal position on interval 3 near stria 2 or 3; umbilicate setae of the humeral group equally spaced; protibiae longitudinally furrowed or not.

COMMENTS.— As can be inferred from the above diagnosis, the large genus Trechus is markedly heterogeneous and probably polyphyletic. This hypothesis of polyphyletism has been corroborated by early results of analyzes of nucleic acid sequences data ( Faille et al. 2010, 2013a).

Among morphological features commonly used in comparative systematic studies of genus Trechus , two deserve special attention because they have allowed us to distinguish three new genera, described below, among species occuring in the Gaoligong Shan Mountains. These features include (1) the presence and position or the absence of a preapical elytral seta, and (2) the dentition of the mandibles.

1) Presence and position of preapical seta: The primary elytral discal setae of carabid beetles are located on the odd intervals: 3, 5, 7 and 9 ( Jeannel 1941). Jeannel named the setae of interval 9 the “ série ombiliquée ”, the umbilicate series.

In members of subtribe Trechina , the umbilicate series includes a group of four consecutive humeral setae, a middle group of two consecutive setae, and two more isolated posterior setae; discal setae are absent from interval 7; they occur on interval 5 in some members (eg., in Trechiama Jeannel (1927) and Epaphiopsis Uéno (1953)) . In most members, there are three setae on interval 3, inserted subbasally, near the middle and preapically, respectively. Although this can be considered the basic number for members of the subtribe, but this number is varied, more or less.

In members of genus Trechus , there are typically three discal setae in interval 3, the first two inserted in or against stria 3, the third in prepical position inserted against stria 2. In some species (eg., Trechus perissus Andrewes (1936) , described from Sikkim (see Uéno 1972a), or Trechus setitemporalis Deuve (2005) , described from southern Xizang Autonomous Region), an additional discal seta is present, inserted next to stria 3, between the middle and preapical setae. In a few species, it is the preapical seta itself, typically inserted preapically against stria 2 that is advanced anteriorly to a discal position on the 3rd interval and inserted either in the center of the interval or even against stria 3. In the latter case, it is difficult to know if it is actually the preapical seta shift- ed forward or a supernumerary discal seta with the preapical seta absent. Forward displacement of the preapical seta has been observed in other Trechina as well, such as in members of Epaphiopsis subgenus Pseudepaphius Uéno (1962) , occuring in subtropical China.

Among the representatives of the genus Trechus occuring in the Gaoligong Shan, we have identified a particular group of species that we call the “ Trechus qiqiensis Group”, members of which share this forward displacement of the preapical seta. We suggest that this is a synapomorphy for this group. Moreover, with the exception of T. shiyueliang sp. nov., members of this group share another synapomorphy: the recurrent stria is continuous anteriorly with stria 7, which is unusual in genus Trechus , although previously observed in Trechus yasudai Ueno (1973) from eastern Nepal. Based on these two unusual features, this group of species appears to represent a natural, monophyletic group.

Members of the Trechus qiqiensis group may be related to some Himalayan species, such as Trechus himalayanus Ueno (1972b) , in which the preapical seta is displaced forward ( Deuve 1988) but the recurrent stria is not in line anteriorly with stria 7. Forward displacement of the preapical seta has long been known to occur also in members of genus Epaphius Samouelle (1819) .

2) Dentition of the mandibles: Jeannel (1926, 1941) separated the Trechini into two groups: (1) the “Tridentati”, with a premolar tooth on the mandibles, which grouped what he called the “more primitive” lineages; and (2) the “Bidentati’, “without a premolar tooth”, which corresponded to the Trechina , including genus Trechus . This fundamental dichotomy was accepted by most authors, who, as seemed appropriate, described the mandibles as either “tridentate” or “bidentate”. Howev- er, this was actually a source of confusion because assigned to the Bidentati were some members with a cleft retinaculum that appeared trifid. The mandibles of those Bidentati with a trifid retinaculum were thus often called “tridentate” in species descriptions. However, Jeannel defined the distinction between the Bidentati of Tridentati precisely, with the criterion being the presence or absence of the premolar tooth.

The mandibles are naturally asymmetrical in order to allow meshing of the teeth when closed. It is the right mandible which serves as the benchmark because it best shows the components: molar, premolar and retinacular blade [For a good understanding of this classic nomenclature, see Acorn and Ball (1991)].

Study of cave Trechina of China recently has revealed that, within the genus Guizhaphaenops Vigna Taglianti (1997) , members of some species had the right mandible tridentate while in those of other species it was bidentate. The explanation given was that the premolar tooth was merged with the retinaculum to form a trifid (“tridentate”) process, and that in the species with the “bidentate” mandible, the median point of this process had been lost subsequently, resulting in a bidentate process, formed in reality of the merged premolar tooth and the retinaculum retaining only its anterior tooth (Deuve and Queinnec 2014). It appears that what was described by Jeannel as disappearance of the premolar tooth was actually the result of a merger of the latter with the retinaculum.

The combination of the unifid premolar with the bifid retinaculum to form a trifid process is evident in genus Queinnectrechus , for which the right mandible has been described and illustrated by Deuve (1992a, 1992b), then by Belousov and Kabak (2003), and in which the two teeth, premolar and retinacular, are not yet fully merged.

Among Trechus members, the right mandible has been considered as of the “bidentate” type, but with both bidentate and tridentate retinacula represented ( Jeannel 1941). In fact, in both cases the premolar tooth is present but fused with the retinaculum. This is the case among all the true Trechus we have examined from the Gaoligong Shan, which all show a trifid state ( Fig. 16 b-d). However, in members of a very specific and homogeneous group of species in the study area, the right mandible has dentition of another type: the premolar tooth is incompletely fused with rétinacle (a relatively symplesiomorphic condition) and the anterior tooth of the retinaculum is located forward (a synapomorphy), a greater distance from the posterior tooth ( Fig. 16f ). Members of this group of species also present two additional remarkable features. First, there is only one or no discal setae on elytral interval 3; and second, the tempora are sparsely pubescent, whereas they are glabrous in all other “ Trechus ” of the Gaoligong Shan region. Members of some species in Tibet, such as Trechus setitemporalis Deuve (2005) , or those of the “ Trechus dacatraianus Group” ( Schmidt 2009), also have pubescent tempora. However, it is the combination of the three states mentioned above, especially the mandibular structure, which leads us to exclude these species from Trechus and consider them as representing a distinct genus within the Epaphiopsis Complex of genera. Descriptions of this genus and the included species are provided below. A related species, but one in which members have the tempora glabrous and the premolar and retinaculum of the right mandible ( Fig. 16h ) more fully fused, is also excluded from Trechus and described as a separate genus. Finally, we also exclude two additional species from the southern part of the Gaoligong Shan from Trechus . In members of these species, the right mandible ( Fig. 16g ) is very similar to a bidentate type, but the premolar tooth is not fused with the retinaculum. We consider these also as representing a new and distinct genus described below.

GEOGRAPHICAL DISTRIBUTION.— Genus Trechus is a megadiverse taxon with more than 900 described species and subspecies arrayed in eight subgenera ( Lorenz 2005); and about 95% of these species-group taxa are currently classified in the nominate subgenus. The genus is predominately Holarctic in distribution and widespread in that Region ( Jeannel 1927, Casale & Laneyrie 1982), with a few species also recorded from the Afrotropical and Oriental Regions. Several species from subtropical or tropical parts of Southeast Asia have been described in genus Trechus . Examples of such species include Trechus thai Deuve (1995) from Thailand, Trechus myanmarensis Deuve (2005) and Trechus natmataungensis Donabauer (2010) from Myanmar and Trechus vietnamicus Uéno (1995) from Vietnam. However, the genus is not known from tropical or subtropical parts of China, where it appears to be replaced by species representing the Epaphiopsis Complex of genera.

Figures

FIGURE 17. Trechus indicus Putzeys; a. Dorsal habitus (CASENT1016115). b. Median lobe of aedeagus of male (CASENT1015874), left lateral aspect. c. Map of locality records (red circles) for T. indicus in the Gaoligong Shan region. Scale lines a, b = 0.5 mm, c = 100 km.

FIGURE 16. Trechine right mandibles, ventral aspect. a. Agonotrechus xiaoheishan sp. nov. b. Trechus indicus Putzeys with dentition enlarged. c. Trechus gongshanensis sp. nov. d. Trechus shibalicus sp. nov. e. Pseudepaphius gonggaicus Deuve with dentition enlarged (China, Sichuan Province, Moxi Township, NE slope of Gongga Shan). f. Trechepaphiopsis uniporosa sp. nov. with dentition enlarged. g. Epaphiotrechus fortipesoides sp. nov. with dentition enlarged. h. Trechepaphiama gaoligong sp. nov. Scale lines = 0.5 mm.