Dineutus australis (Fabricius, 1775)

(Figs. 1C–D, 4A, 5A–E, 7C, 8A)

Material examined. THAILAND: Chiang Mai Province: Doi Inthanon Natl. Park, Mae Klang Waterfall, 18°29'N 98°40'E, 415 m a.s.l., 3.IV.2002, leg. CMU Team, 1 female (GTGC). Khon Kaen Province: Chum Pae District, 16°34.585'N 102°01.668'E, 415 m a.s.l., 3.V.2004, leg. A. Vitheepradit, L-660, 1 female (GTGC). Nakhon Ratchasima Province: Sakaerat Environmental Research Station, Bon weir, U-dom Sap Subdistrict, Wang Nam Khiao District, 14°29'49.2"N 101°54'55.5"E, 472 m a.s.l., 22.II.2014, leg. B. Suksai, 1 male (KKU); same locality except for, 29.III.2018, leg. P. Chanteenok, 1 female (KKU); same locality except for, 8.IV.2018, leg. B. Suksai, O. Pornsophon, T. Jantaranakee & S. Phengsalung, 2 males, 2 females (THNHM). Phang Nga Province: Ban Bang Klag Klang, Koag Kien Subdistrict, Takua Pa District, 8°52.469'N 98°22.679'E, 17 m a.s.l., 4.I.2006, leg. A. Vitheepradit, R.W. Sites & T. Prommi, L-881, 1 male (UMC). Prachuap Khiri Khan Province: Ban Fah Pa Tarn, Hua Hin District, 12°31.810'N 99°32.062'E, 149 m a.s.l., 28.V.2004, leg. A. Vitheepradit & T. Prommi, L-723, 1 male (UMC); same locality except for, Bue Sawan Stream, Huay Yang Subdistrict, Thap Sakae District, 11°40'29.4"N 99°36'02.4"E, 208 m a.s.l., 23.V.2017, leg. B. Suksai & C. Yatfung, 1 female (THNHM).

Diagnosis. Male (Fig. 1C): Size: 7.6–8.2 mm. Body form oval; apex of flagellomere VI darkly colored; elytral apices obliquely truncate with epipleural spines and serrations present (Figs. 1C, 5A); lateral marginal of pronotum and elytron black to brown; protrochanter apically with patch of thick setae on ventral surface (Fig. 4A); profemur without sub-apicoventral tooth; protibia wedge-shaped; venter black, epipleura brownish; aedeagus (Figs. 5C–D) with median lobe slightly shorter than parameres, swollen in basal 1/9, strongly narrowed after basal 1/9, apex with tip strongly pointed, weakly curved ventrally in lateral view.

Female (Fig. 1D): Similar to male except for size: 8.1–8.2 mm; elytral apices truncate without epipleural spines (Figs. 1D, 5B), protrochanter apically without patch of thick setae on ventral surface; gonocoxae (Fig. 5E) elongate, lateral margin expanded and weakly rounded, apex nearly straight.

Differential diagnosis. Dineutus australis is closest to D. unidentatus, which also is found in Thailand, and can be distinguished from all other species of Dineutus in this country by the protrochanter of the male having a distinct patch of setae. Both sexes of D. australis can be distinguished from those of D. unidentatus by the oval body form and larger size, whereas in D. unidentatus the body is narrowly oval (Fig. 1G) and smaller (6.0– 6.9 mm). The elytral apices of males of D. australis have weak epipleural spines, whereas in the males of D. unidentatus these are longer and more developed (Fig. 6A). In dorsal view, the aedeagus of D. australis is distinct from that of D. unidentatus, as the median lobe is very narrow and without a constricted apex (Fig. 5C), in comparison to the broader, more parallel-sided median lobe of D. unidentatus, which is abruptly constricted at its apex (Fig. 6B).

The females of D. australis can be distinguished from those of D. unidentatus by the elytral apices lacking epipleural spines, which are presented in D. unidentatus. The reproductive tract of D. australis has broader gonocoxae with the apex nearly straight, whereas in D. unidentatus the gonocoxae are more elongate, with the apex obliquely truncate and the lateral angle acuminate.

Distribution. This species is widely distributed in the Oriental and Australian Regions. It has been recorded from China, Taiwan (Mazzoldi 1995); the Philippines (Ochs 1924; Freitag et al. 2016); Japan (Takizawa 1931); Indonesia (Ochs 1949, 1953): Java, Bali, Lombok, Sumba, Sulawesi, Buru; New Guinea (Ochs 1955), Australia (Ochs 1949; Watts & Hamon 2010); New Caledonia (Satô 1966; Mazzoldi 2010); and the Pacific Islands: Vanuatu (Watts & Hamon 2010) and Fiji (Ochs 1949). This is the first time it has been recorded in Thailand.

Habitat. In Australia, D. australis has been found in reservoirs, swamps, and pools in rivers and streams (Watts & Hamon 2010). In the present study, BS collected D. australis on the water surface of ponds in the forest (Fig. 7C) where it occurred among aquatic plants in shallow water. Additionally, it was found in shallow, stagnant streams.

Discussion. Within Thailand, it was found in the northern, northeastern, western, and southern regions (Fig. 8A) and was collected at low elevations ranging from 17–472 m a.s.l. It co-occurred with D. unidentatus and D. spinosus in ponds.