Dineutus spinosus ( Fabricius, 1781 )

Suksai, Benjamart, Gustafson, Grey T., Sites, Robert W. & Sangpradub, Narumon, 2021, The Gyrinidae (Coleoptera) fauna of Thailand: Key to tribes and genera, with new records and keys to species of Dineutini and Gyrinini, Zootaxa 5071 (1), pp. 97-117 : 106-108

Dineutus spinosus ( Fabricius, 1781)

( Figs. 1F, 1J , 4C , 5J–M , 7C, 7E , 8A )

Material examined. THAILAND: Amnat Charoen Province: Kork Stream, Kham Khuean Kaeo Subdistrict, Chanuman District , 16°12'29.9"N 104°52'11.6"E, 188 m a.s.l., 23.XII.2017, leg. B. Suksai, 2 males, 4 females ( THNHM) . Kalasin Province: Phu Pan Natl. Park, water supply pond at Park HQ, 16°47'38.8"N 103°50'37.8"E, 7.VI.1998, leg. K.B. Simpson & A. Vitheepradit, L-165, 1 male ( UMC) . Mukdahan Province: Huai Lao Waterfall, Ban Kho Subdistrict, Khamcha-I District , 16°44'36.9"N 104°21'04.7"E, 226 m a.s.l., 22.XII.2017, leg. B. Suksai, 1 female ( THNHM) ; Tadton Waterfall, Non Yang Subdistrict, Nong Sung District , 16°29'40.2"N 104°18'47.6"E, 208 m a.s.l., 22.XII.2017, leg. B. Suksai, 1 female ( THNHM) . 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., 27.III.2018, leg. P. Chanteenok, 1 male ( THNHM) ; same locality except for, 29.III.2018, leg. P. Chanteenok, 1 male, 1 female ( THNHM) ; Thap Lan Natl. Park, Khok Krachai Subdistrict, Khon Buri District , 14°20'13.6''N 102°14'48.0''E, 224 m a.s.l., 27.IV.2014, leg. K. Piraonapicha, 7 males, 8 females ( KKU, THNHM) ; same locality except for, Wang Tao Waterfall, Khok Krachai Subdistrict, Khon Buri District , 14°19'52.0''N 102°14'05.0''E, 224 m a.s.l., 23.III.2013, leg. K. Piraonapicha, 2 males, 4 females ( KKU) . Nakhon Si Thammarat Province: Chulabhorn District , 56 km N of Phatthalung, 8°03'N 99°53'E, 21 m a.s.l., 31.V.2003, leg. A. Vitheepradit & M.L. Ferro, L-583, 7 males, 6 females ( UMC) . Sisaket Province: Huay Sala Wildlife Sanctuary, Sum Sai Waterfall , 14°31.894'N 104°20.419'E, 202 m a.s.l., 12.IV.2004, leg. R.W. Sites & A. Vitheepradit, L-622, 5 males, 3 females ( UMC) . Songkhla Province: Prince of Songkla University , 2.V.1993, leg. Apinya, 1 female ( UMC) . Surat Thani Province: Ban Tha Rau Tai, Ban Na Doem District , 8°56.567'N 99°15.130'E, 4 m a.s.l., 20.VI.2004, leg. A. Vitheepradit & T. Prommi, L-782, 1 female ( UMC) . Ubon Ratchathani Province: Huay Sae Stream, Na Pho Klang Subdistrict, Khong Chiam District , 15°32'05.2"N 105°31'06.7"E, 131 m a.s.l., 23.XII.2017, leg. B. Suksai, 3 males, 2 females ( THNHM) .

Diagnosis. Male ( Fig. 1F ): Size: 6.4–8.0 mm. Body form oval; apex of flagellomere VI lightly colored; elytral apices weakly serrate, with parasutural and epipleural spines ( Fig. 5J ); lateral margin of pronotum and elytron orange or yellow ( Fig. 1F ); protrochanter apically with single series of few setae on ventral surface ( Fig. 4C ); profemur without sub-apicoventral tooth; protibia wedge-shaped; venter yellow to brown ( Fig. 1J ), epipleura yellow ( Fig. 1J ); aedeagus ( Figs. 5K–L ) with median lobe shorter than parameres, parallel-sided for 2/3 length, slightly narrowed in apical half, acuminate in apical fifth, with tip narrowly rounded, weakly straight in lateral view.

Female: Similar to male except for size: 6.9–8.1 mm; gonocoxae elongate, lateral margin rounded, apex weakly rounded ( Fig. 5M ).

Differential diagnosis. Dineutus spinosus can be distinguished from congeners in Thailand by the lightly colored margin of the pronotum and elytron and by the spinose elytral apex having both parasutural and epipleural spines developed ( Table 1 ). No other species of Dineutus in Thailand has this combination of characters. Porrorhynchus marginatus has these features as well, but is much larger in size and can be distinguished by the elongate, triangular labrum in addition to other features of the forelegs.

Distribution. This is a widespread species found in the eastern portion of the Indian subcontinent and throughout Southeast Asia from Sri Lanka and eastern India through Assam, Bangladesh, Myanmar, Thailand, Laos, as far east as Vietnam ( Ochs 1929, 1930; Mouchamps 1949; Brinck 1981; Vazirani 1984), and as far south as Singapore ( Hendrich et al. 2004), Sumatra ( Ochs 1929), and Borneo ( Ochs 1928).

Habitat. It occurs on exposed rivers, streams, ponds, and water tanks ( Figs. 7C, E ). ( Brinck 1981).

Discussion. Dineutus spinosus is currently known from only the northeastern and southern regions of Thailand ( Fig. 8A ) where it occurs at low to medium elevations (4–472 m a.s.l.). It has not been found at high elevation. We suspect that it might occur in other localities in Thailand with the same habitats at similar elevations. Both D. spinosus and the similar congener D. orientalis , which has a primarily more eastern and northern distribution, are known to co-occur in Laos and Vietnam ( Mouchamps 1949; Brinck 1981). The latter species has yet to be encountered in Thailand and was not found during our surveys, despite extensive sampling in northeastern Thailand near the Laotian border ( Fig. 8A ).

Figures

FIGURE 1. Habitus of Gyrinini and Dineutini species: (A) Gyrinus sericeolimbatus, dorsal view, female; (B) G. smaragdinus, dorsal view, male; (C–D) Dineutus australis, dorsal view: (C) male; (D) female; (E) D. sitesi, dorsal view, male; (F) D. spinosus, dorsal view, male; (G) D. unidentatus, dorsal view, male; (H) Porrorhynchus marginatus, dorsal view, male; (I) D. sitesi, ventral view, male; (J) D. spinosus, ventral view, male. Scale bars = 3 mm.

FIGURE 4. SEM photographs of protochanters in species of Dineutus and Porrorhynchus (males): (A) D. australis, patch of thick setae (arrow), scale bar = 100 μm; (B) D. sitesi, protrochanter without setae (arrow), scale bar = 1 mm; (C) D. spinosus, setae (arrow), scale bar = 100 μm; (D) D. unidentatus, setae (arrow), scale bar = 100 μm; (E–F) P. marginatus, cluster setae (square and arrow): (E) scale bar = 500 μm; (F) scale bar = 100 μm.

FIGURE 5. Elytral apex, aedeagus and gonocoxae of species of Dineutus: (A–E) D. australis: (A–B) elytral apex, scale bar = 2 mm: (A) male; (B) female; (C–D) aedeagus, scale bar = 0.5 mm: (C) dorsal view; (D) lateral view; (E) gonocoxae, ventral view, scale bar = 0.5 mm; (F–I) D. sitesi: (F) male elytral apex, scale bar = 2 mm; (G–H) aedeagus, scale bar = 1 mm: (G) dorsal view; (H) lateral view; (I) gonocoxae, ventral view, scale bar = 1 mm; (J–M) D. spinosus: (J) male elytral apex, scale bar = 2 mm, (K–L) aedeagus, scale bar = 0.5 mm: (K) dorsal view; (L) lateral view; (M) gonocoxae, ventral view, scale bar = 0.5 mm.

FIGURE 7. Habitats of species of Gyrinini and Dineutini: (A–B) G. smaragdinus: (A) stream at Siriphum Waterfall, Doi Inthanon Natl. Park, Chiang Mai Province; (B) pond at Ban Buak Thoei, Chiang Mai Province; (C) D. australis, D. spinosus and D. unidentatus, pond at Sakaerat Environmental Research Station, Nakhon Ratchasima Province; (D) D. sitesi, Tum Din Stream, Thung Salaeng Luang Natl. Park, Phitsanulok Province; (E) D. spinosus, Huay Sae Stream, Ubon Ratchathani Province; (F–G) D. unidentatus, ponds at Ban Kho, Khon Kaen Province; (H) P. marginatus, Lam Takong Stream, Nakhon Ratchasima Province.

FIGURE 8. (A–B) Distributions of species of Dineutini and Gyrinini in Thailand.