Homoeusa laevigata Sharp, 1888

Figs 2 A, D, 3 B, 7 A – I, 8 A – H (Japanese name: Tsuya-hirata-ariyadori)

Homoeusa laevigata Sharp, 1888: 283 (original description); Schülke and Smetana 2015; 682 (catalogue); Maruyama et al. 2013: 24 (distribution and bionomics mentioned).

Type material.

Holotype (Fig. 2 A, D) • ♂; “ Homoeusa ” / “ laevigata ” / “ Type ” / “ D. S. ” (written on the card which the specimen mounted) // “ Seba ” / “ 30. y. ’ 81. ” // “ Type ” (red round curator label) // “ HOLOTYPE ” / “ Homoeusa ” / “ laevigata ” / “ SHARP, 1888 ” / “ det. MARUYAMA, 2003 ” // “ NHMUK 014379778 ” (dissected by MM) (NHM).

Additional material examined.

Japan: Honshu: Miyagi-ken • 2 exs.; Aoba-yama, Sendai-shi; 10. VII. 2004; K. Mizota leg. LFN (KUM) • 3 ♂♂, 1 ♀, 7 exs.; same locality; 17. VII. 2004 K. Mizota leg. LFN (KUM) • 2 ♂♂; Aoba Forest Greenery [38.2577, 140.8255], Sendai-shi; 12. VIII. 2024; TS. Nozaki leg. LFN (KUM) . Fukushima-ken • 2 ♀♀; Kuraizaka-toge, Nishiaizu-machi; 18. VI. 2022; K. Haga leg. LFN (KUM) • 1 ♂; Ueda dam, Kaneyama-machi; 25. VI. 2023; K. Haga leg. LFN (KUM) . Ibaraki-ken • 1 ♂, 1 ex.; Mt. Yamizo, Daigo-machi; 4. V. 2022; Y. Komatsuzaki leg. (KUM) . Saitama-ken • 1 ex.; Hashidate riv. (alt. 500 m), Chichibu-shi; 17. VII. 1999; K. Toyoda leg. LFN (KUM) • 2 ♂♂, 1 ♀, 3 exs.; Hashidate, Chichibu-shi; 17. VII. 1999; K. Toyoda leg. LFN (KUM) • 2 ♂♂, 1 ♀, 12 exs.; same locality; 30. VII. 1999; K. Toyoda leg. LFN (KUM) • 1 ♂, 1 ex.; same locality; 30. VII. 2000; (NHM) . Yamanashi-ken • 2 exs.; Kissawa [35.7219, 138.5376], Kai-shi; 31. V. 2025; M. Maruyama leg. LFN (KUM) • 1 ex.; Gozaishi-kôsen (alt. 900 m); Nirasaki-shi; 25. VII. 2002; S. Nomura leg. LFN (KUM) . Nagano-ken • 1 ♂, 3 ♀♀, 3 exs.; Mt. Iwatakeyama, Hakuba-mura; 16. VI. 2001; T. Watanabe leg. LFN (KUM) • 1 ♂, 1 ♀, 6 exs.; Midarebashi, Chikuhoku-mura; 21. VII. 1999; T. Watanabe leg. (KUM) • 1 ex.; Shiozawa [36.3268, 138.5983], Karuizawa-machi; 5. VI. 2024; K. Goino leg. LFN (KUM) • 1 ex.; Nagakura, Karuizawa-machi; 12. V. 2024; S. Sakurai leg. LFN (KUM) • 1 ♂, 1 ♀, 5 exs.; Jôyama, Matsumoto-shi; 12–13. VII. 1998; M. Maruyama leg. LFN (KUM) • 1 ♂, 5 exs.; Satoyamabe [36.2457, 138.0096], Matsumoto-shi; 12. V. 2021; TS. Nozaki leg. LFN (KUM) • 1 ex.; same locality; 30. VII. 2021 TS. Nozaki leg. LFN (KUM) • 1 ex.; Kamimaki [35.85, 137.98], Ina-shi; 1–4. VII. 2021; T. Hashizume leg. LFN (KUM) • 1 ex.; same locality 26. VI. 2022; I. Hashizume leg. (KUM) .

Diagnosis.

This species is distinguished from other species of the genus by the following combination of characteristics: body blackish, polished; pronotal postero-lateral angle acute (Fig. 7 B, C); elytra distinctly widened posteriad entirely (Fig. 7 B); pronotum and elytra covered with shortened setae (Fig. 7 B, C); metaventral process hardly produced; male 8 th sternite (Fig. 7 E) slightly emarginated at the middle of the posterior margin; median lobe of aedeagus bulbous; basal part of copulatory piece large. This species is similar to H. gigantea sp. nov. in body size and shape but can be distinguished by its blackish color and shortened setae on the pronotum and elytra.

Redescription.

Body (Figs 3 B, 8 G, H) medium-sized, broad, somewhat limuloid; dorsal surface mostly polished.

Head small; color blackish brown; eyes small. Antennae (Fig. 7 A) short, gently clubbed; relative length of each antennal segment from first to 11 th, 3.2: 1.95: 1.48: 1.18: 1.14: 1.00: 1.00: 1.11: 1.43: 1.64: 4.5.

Thorax. Pronotum (Fig. 7 B) subrectangular, transverse (PW / PL, 1.53–1.57), widest at posterior 1 / 3, postero-lateral angle distinctly acute, posterior margin distinctly sinuate, blackish brown, surface finely covered with shortened setae and punctures, polished and hardly reticulated. Elytra (Fig. 7 B, C) distinctly widened posteriad entirely, posterior margins shallowly notched near lateral corners, blackish brown, surface finely covered with shortened setae and punctures, polished and hardly reticulated. Hind wings developed. Mesoventral process (Fig. 7 D) very narrow, with indistinct medial carina, apex sharply pointed, reaching middle of mesocoxal cavities. Metaventral process hardly produced.

Abdomen elongate, narrowed posteriad; surface covered with very short setae and each posterior margin with long stout setae; slightly reticulated.

Male: 8 th sternite (Fig. 7 E) slightly emarginated at postero-median margin; median lobe of aedeagus (Fig. 7 G) bulbous, length about 0.60 mm, apical lobe thick and almost straight, apex gently pointed in lateral view, apical valves broad and mitten-shaped, dorsal arms very short, basal part of copulatory piece large. Paramere (Fig. 7 H) length about 0.68 mm; apical lobe of paramere long and narrow, length about 1 / 3 of whole paramere, slightly curved ventrally; four setae, normally arranged, velum normal.

Female: 8 th sternite (Fig. 7 F) slightly rounded at posterior margin; spermatheca (Fig. 7 I, J) S-shaped, apex of basal part weakly swollen.

Variations.

In some individuals, the parameral apical lobe is irregularly sharpened apicad. The arrangement of the four setae varies slightly.

Measurements (in mm) and ratios.

Body parts (N = 10): BL ≈ 2.44–3.96; AL, 0.91–1.01; HW, 0.52–0.64; PL, 0.6–0.75; PW, 0.94–1.15; EL, 0.48–0.56; EW, 0.96–1.16; HTL, 0.6–0.72; PW / PL, 1.53–1.57; AL / PL, 1.34–1.51; HTL / PL, 0.96–1.03.

Differences between sexes: AL / PL (male, N = 5), 1.43–1.51; AL / PL (female, N = 5), 1.34–1.42.

Distribution.

Japan (Honshu) (Fig. 8 A).

Symbiotic hosts.

Lasius fuliginosus species group: L. nipponensis .

Bionomics.

Homoeusa laevigata can be observed in Lasius nipponensis foraging trails on forest floors or at the base of trunks (Fig. 8 B) from May to August. No individuals were collected using FIT.

This species appears to be more integrated into its host colony than other Homoeusa species. Trophallactic behavior with the host ant worker has been observed around nests and foraging trails (Maruyama et al. 2013). In addition, near a colony, TN observed them licking the workers’ legs and bodies as the worker ants groomed each other. In the indoor observations, they frequently raised the tip of their abdomen toward host ant workers (Fig. 8 C), grooming (Fig. 8 E), and displaying trophallaxis (Fig. 8 D, F). Unexpectedly, they were also observed eating food by themselves indoors.

Remarks.

The presently known distribution of H. laevigata (Fig. 8 A) is restricted to the east of Hida Mountains in central Honshu. TN examined the collection by Mr. K. Kinomura from some colonies of L. nipponensis in Takayama-shi, Gifu-ken, and surveyed a single colony of the ant in June in Motosu-shi, Gifu-ken. These surveys did not identify H. laevigata west of the Hida Mountains. Considering the absence of this species with Lasius species other than L. nipponensis, and their behavior toward host ant workers, this species could be a specialist for this ant species.