Lathrobium yufuense, Sato & Maruyama, 2023

Sato, Yuya & Maruyama, Munetoshi, 2023, Taxonomy of the Lathrobium nomurai group (Coleoptera: Staphylinidae) from Northern Kyushu, Japan, with descriptions of two new species, Acta Entomologica Musei Nationalis Pragae (Acta. Ent. Mus. Natl. Pragae) 63 (1), pp. 111-124 : 117-119

Lathrobium yufuense sp. nov.

[Japanese name: Yufu-ô-kobane-naga-hanekakushi]

( Figs 5 , 6 , 9 )

Type material. HOLOTYPE: 3, Japan:Kyushu,“JPN:Oita-ken / Beppu-shi / Higashiyama / 19. IX. 2021. / Hashizume T. & Nishiya K” ( KUM) . PARATYPES: 1 3, same data as holotype ( KUM); 1 3 (smaller-sized specimen), 1 ♀, “ JAPAN: Oita-ken / Beppu-shi / Mt.Yufudake / 2. X. 2022 / Y. Sato & T. Hashizume” ( KUM).

Description. BL = 11.2–13.3 mm, FBL = 4.9–5.5 mm (n = 3). Coloration: Body ( Fig. 5A ) reddish brown, moderately shining; maxillary palpi light red; legs reddish brown but basal part of tibia black or darken; mandible, scutellum, bases of antennomeres 1–10 black or darken; elytra reddish brown but elytral suture black; abdomen reddish brown, posterior margin of tergite VII and VIII brownish light red; tergite IX and X light red.

Head suborbicular, HL = 1.61–1.68 mm, HW = 1.56– 1.78 mm, HW/HL = 1.01, widest at the basal 1/3 of head; frontal area flattened; surface coarsely punctate; punctures sparser on frons and vertex, becoming denser toward posterior and lateral margins, with light brown setae. Eyes very small, slightly protruding; longitudinal diameter of eye about 1/5 as long as temple in dorsal view. Antennae elongate, AL= 3.55–4.20 mm, AL/HL = 2.37, with whitish yellow setae; antennomere I robust, widest at apical 1/4; antennomere II slightly elongated and shorter than III; antennomeres III–X slightly narrow at base and widening towards apex; antennomeres V–IX almost same size; antennomere XI fusiform and narrowest; relative length of antennomeres as follows: 1.98: 1.02: 1.35: 1.19: 1.08: 1.08: 1.08: 1.08: 1.08: 1.00: 1.23; relative maximum width of antennomeres as follows: 1.63:1.25: 1.25: 1.38: 1.25: 1.25: 1.25: 1.25: 1.13: 1.13: 1.00.

Pronotum oblong-oval, with anterior margin wider than posterior one, PL = 1.85–2.10 mm, PW = 1.44–1.60 mm, PL/PW = 1.31, PL/HL = 1.21, PW/HW = 0.92, widest at apical 1/4; lateral sides of pronotum gently dilated to widest point, thence gradually convergent toward posterior margin, almost straight; all corners obtusely rounded; disc sparsely covered with coarse and weak punctations except medial longitudinal line; punctures slightly sparser and less than on head, with brownish yellow setae.

Scutellum with sparse punctures. Elytra subtrapezoidal, widened posteriorly, EL = 1.10–1.22 mm, EW = 1.55–1.75 mm, EW/EL = 1.39, EL/PL = 0.58, EW/PW = 1.09; lateral margins almost straight; posterior corners rounded; disc covered with sparse and coarse punctations, gently shining; punctations denser than on pronotum, with brownish yellow setae. Hind wing completely reduced. Legs with shortened tibiae and tarsi which are covered with golden setae; tarsomeres I–IV of protarsus dilated.

Abdomen elongate, gradually widened from segment III to V, thence contracted to the posterior end; each tergite covered with micropunctations and brownish yellow setae, distinctly long setae on each side near anterior margin; tergite X as long as posterolateral processes of tergite IX.

Male. Sternite VII ( Fig. 5C ) transverse, with weak posteromedian impression; posterior area of sternite VII with longer setae than in anterior area; sternite VIII ( Fig. 5D ) with weak right-sided posteromedian impression in ventral view; several thick setae on posterior area; sternite IX elongate.

Aedeagus ( Figs 6A–C ) 2.21 mm long, oblong; basal part of aedeagus with V-shaped impression; ventral process well sclerotized, asymmetrical in ventral view, gradually narrowed toward apical 1/4, thus strongly narrowed toward apex, curved ventrally from 1/3 to apex; apical part of ventral process slightly curved toward right side in ventral view; apex of ventral process with small projection; basal and middle parts of ventral process slightly thicker than apex in lateral view; part above basal foramen triangular, with two projections at lateral side; dorsal plate sclerotized, widest at apical 1/4, with acute apex, curved dorsally from basal to its apical 1/2; lateral side from basal part to 1/2 straight, widened at apical 1/4, thus contracted toward apex; two tubes attached with apex of ventral process in between ventral process and dorsal plate; internal sac large, with sclerotized and ringed part; middle area of internal sac folded complexly, with sclerotized bilobate projections; apical area of internal sac flattened.

Female. Sternite VIII elongate and triangular, densely fringed with numerous setae.

Variation. A smaller-sized male specimen has been discovered in this species ( Fig. 5B ) This specimen has elongated head which has almost straight lateral side rather than suborbicular. Each measurement of this specimen as follows: BL = 12.0 mm, FBL = 4.7 mm, AL = 3.48 mm, HL = 1.46 mm, HW = 1.25 mm, PL = 1.85 mm, PW = 1.35, EL = 1.08, EW = 1.50. Compared to other specimens, the body of this specimen is smaller sized, but does not differ from the aedeagus of the larger specimen in the structure. Therefore, we consider it conspecific with the holotype and include it to the type series of L. yufuense sp. nov.

Differential diagnosis. The new species is similar to Lathrobium fujimotoi from Mt. Kurodake near Mt. Yufu- -dake, Oita Pref., in general appearance and aedeagal shape. However, the new species can be easily distinguished from L. fujimotoi by the combination of the following characteristics: 1) small aedeagus; 2) oblong aedeagus; 3) small and asymmetric male sternite VIII with impression; (in contrast, L. fujimotoi has large-sized aedeagus, about 1.5 times longer than that of L. yufuense sp. nov., the shape of its aedeagus is elongate; and male sternite VIII is large and symmetric with weak impression).

Etymology. The specific name of new species is derived from the type locality, Mt. Yufu-dake.

Biology. All specimens were collected from only Mt. Yufu-dake and found under stones in a deciduous broadleaf forest, at an altitude of about 1000 m.

Distribution. Japan (Oita Pref., north of Kyushu).

Figures

Fig. 5. Lathrobium yufuense sp. nov. A – habitus in dorsal view; B – habitus of small-sized specimen in dorsal view; C – male sternite VII; D – male sternite VIII. Scale bars = 2.0 mm for A, B, 0.5 mm for C, D.

Fig. 6. Male aedeagus of Lathrobium yufuense sp. nov.A – ventral view; B – lateral view; C – dorsal view. Scale bar = 0.5 mm.

Fig. 9. Map showing the distribution of the Lathrobium nomurai group in Kyushu, Japan. Black rhombus – L. nomurai Nakane, 1955; black triangle – L. fujimotoi Y. Watanabe, 2001; black circle – L. hikosanense Y. Watanabe, 1998; black square – L. yufuense sp. nov.; black pentagon – L. denchu sp. nov.; A–G – localities of L. hikosanense: A – Mt. Daisen; B – Mt. Hiko-san (type locality for L. hikosanense); C – Hiraodai; D – Mt. Buccho-zan; E – Mt. Tachibana-yama; F – Mt. Iwara-yama; G – Kinsenji Temple.