Leiodes Latreille 1797

Genus Leiodes Latreille, 1797

Leiodes Latreille, 1797: 22. Type species: Sphaeridium ferrugineum Fabricius, 1787, designated by LATREIILE (1802).

Leiodes: HATCH (1929): 13 (synonymy and references); DAFFNER (1983): 38 (key to Palaearctic species); PEEZ (1971): 247 (key to Central European species); LAFER (1989a): 321:(key to species in the Russian Far East); BARANOWSKI (1993): 16 (key to North and Central American species); COOTER (1996): 233 (key to British species); DOWNIE & ARNETT (1996): 330 (key to the Northeast American species); ŠVEC (2008): 242 (key to Chinese and Nepalese species).

See HATCH (1929) and BARANOWSKI (1993) for detailed synonyms and diagnosis of the genus.

Diagnostic characters of Leiodes

Almost all species of Leiodes show sexual dimorphism in the hind legs, especially in the shape of the metatibiae. DAFFNER (1983) considered the median carina of the mesoventrite, male metatibiae and the aedeagus (in dorsal view) to be important characters for species-level taxonomy of the genus. Later, BARANOWSKI (1993) added another taxonomic characters: shape of protibiae, length of metatarsi, presence/absence of elytral subhumeral row (= a part of row 9) and presence/absence of metathoracic wings. In this study, I generally follow BARANOWSKI (1993) in use of diagnostic characters, but also tried to find additional ones by examining mainly Japanese specimens of Leiodes. In this chapter, I discuss some of these morphological characters important for species-level taxonomy.

Head. Characters of the head are of rather minor importance for distinguishing species in principle (Figs. 6 A–6I) (BARANOWSKI 1993). For example, the mandibles of all species examined in this study look like those on Figs. 6J, 6K and are not useful for identification. As an exception, Leiodes yukihikoi sp. nov. has a characteristic head with a distinctly concave frons and vertex (Fig. 6E). Antennae sometimes show diagnostic features on antennomeres 7 and 9–11. The relative width of antennomere 11 compared with antennomere 10 is important. Moreover, antennomere 11 of L. ohtai sp. nov. is unique in shape (Fig. 85D). Furthermore, coloration of antennomeres 7 and 9–11 is usually clearly darker than that of the remaining antennomeres, and is therefore not useful for identification. However, L. araii sp. nov. has almost unicolor antennae and hence may be easily separated from related species by antennal coloration.

Pronotum. Most Japanese species of Leiodes have the pronotum with dense and distinct minute discal punctures and some large punctures near the basal margins (see figure of body of any species). The only exception is L. ohtai sp. nov., whose pronotum is almost impunctate (Fig. 85A). BARANOWSKI (1993) used the presence of very minute punctures on the posterior margin of pronotum as a taxonomic character. In fact, some Japanese species have those punctures (see, e.g., Fig. 33D for L. toyoshimai sp. nov.), but the punctures are extremely small and a very careful examination is needed to determine their presence or absence. In this study, I do not attach a high diagnostic value to this character.

Elytra. In previous studies of Leiodes, the shape of elytra and the size and densitiy of elytral punctures are treated as useful taxonomic characters at the species level. In this study, I follow these traditionally used characters as well.

Metathoracic wings. Some species inhabiting North and Central America have reduced metathoracic wings (BARANOWSKI 1993), and the wing reduction may be used as diagnostic feature for identification of species. However, all species of Leiodes in Japan and North Chishima Islands have fully developed wings. Therefore, wings do not provide useful taxonomic characters for this study.

Ventral body parts. The configuration of the median and transverse carinae on the mesoventrite is frequently considered of great taxonomic value, both to separate related species and to distinguish species groups. In this study, characters are used from previous studies and illustrations of these characters are provided for all species. Moreover, it is clear that the pubescence on the middle portion of the metaventrite sometimes show distinct (e.g., Figs. 21F, G) or indistinct (e.g., Figs. 64F, G) sexual dimorphism which was not recognized in previous studies, although it often becomes an effective character to distinguish the species. Similar dimorphism is for example known in the Scaphidiini (Staphylinidae) which possesses a patch of closely packed setae on the middle portion of the male metaventrite (LESCHEN & LÖBL 1995). In contrast to the Scaphidiini, in which nearly all species exhibit this dimorphism, in Japanese Leiodes the metaventral pubescence is present only in males of some species. Moreover, the sexual dimorphism in the pubescence of the metaventrite of Leiodes seems not to represent a synapomorphy of species groups, but rather are parallelisms among various species. For example, in the L. circinipes species group, L. yoshitakei sp. nov. has the sexual dimorphism on the metaventrite (Figs. 24G, H) but L. circinipes does not have this dimorphism. In Leiodidae, Colon itoi species group (Coloninae) is known to exhibit sexual dimorphism on the metaventrites (HOSHINA 2009b). In this case, the dimorphism does not concern the pubescence, but concavities on the middle portion of the metaventrite.

Legs. Most species of Leiodes exhibit sexual dimorphism in the shape of legs (some or all of them). Male morphological features of legs, especially of metatibiae, are very important taxonomic characters at species level. In Leiodes of Japan and the North Chishima Islands, profemora do not show distinct morphological differences among species (see figures of fore leg of all species) in both sexes. In contrast, male protarsi are useful for specific identification. For example, the male of L. toyoshimai sp. nov. has extremely expanded protarsi and mesotarsi (Figs. 34A, C), whereas those of L. irregularis Portevin, 1927 are only slightly expanded