Eotrechus vietnamensis, Tran & Yang, 2006

Tran, A. D. & Yang, Chang Man, 2006, New Species Of The Water Strider Genera Eotrechus Kirkaldy And Rhyacobates Esaki (Heteroptera: Gerridae) From Vietnam, Raffles Bulletin of Zoology 54 (1), pp. 11-20 : 12-14

Eotrechus vietnamensis , new species

( Figs. 1-6, 26)

Material examined. – Holotype (apterous male) and allotype (apterous female), Vietnam, Vinh Phuc province, Tam Dao National Park, suoi Thac Bac (near Doi Che), 21°27.005'N 105°38.771'E, 749 m, coll. A. D. Tran & Q. K. Hoang, 17 Jun.2003, TAD0351, ( ZMHU).

Paratypes: Vietnam: apterous 4 males, 3 females, same locality data as holotype; apterous 4 males, 1 female, Vinh Phuc province, Tam Dao National Park, Suoi Mo, 21°27.103'N 105°38.872'E, 924m, coll. A. D. Tran & Q. K. Hoang, 16 Jun.2003, TAD0350; apterous 3 males, 2 females, Vinh Phuc province, Tam Dao National Park , 21°27.747'N 105°38.754'E, 1000m, coll. A. D. Tran & Q. K. Hoang, 18 Jun.2003, TAD0354; apterous 1 male, macropterous 3 females, Vinh Phuc province, Tam Dao National Park , 21°27.439'N 105°39.193'E, 1000m, coll. A. D. Tran & Q. K. Hoang, 18 Jun.2003, TAD0355; apterous 5 males, 5 females, Vinh Phuc province, Tam Dao National Park , Suoi Bua Lon , 600m, coll. A. D. Tran & Q. K. Hoang, 19 Jun.2003, TAD0356; apterous 5 males, 3 females, Dien Bien province, Muong Phang , upstream and water fall of Muong Phang stream, 21°27.000'N 103°10.548'E, 1070m, coll. A. D. Tran, 28 Jul.2004, DY0419 ( NHMW, ZMHU, and ZRC); apterous 1 male, Ha Tay province , Ba Vi National Park , small stream, 575 m, coll. J. T. Polhemus, D. A. Polhemus & P. Nguyen, 4 Apr.2000, CL4391; apterous 1 male, 1 female, Ha Tay province , Ba Vi National Park , seeping rock face on upper road, 895 m, coll. J. T. Polhemus, D. A. Polhemus & P. Nguyen, 4 Apr.2000, CL4391; apterous 6 males, 5 females, Lao Cai province, roadside seeps, 11 km NE Sa Pa, 22°23.42'N 103°52.92'E, 1220 m, coll. J. T. Polhemus, D. A. Polhemus & P. Nguyen, 7 Apr.2000, CL4396; apterous 2 females, Lai Chau province, Nam Ceung stream, 15 km N Lai Chau, 22°08.67'N 103°11.55'E, 207 m, coll. J. T. Polhemus, D. A. Polhemus & P. Nguyen, 11 Apr.2000, CL4409; apterous 5 males, 5 females, Lai Chau province, cascading tributary to Nam Na River , 12 km N Lai Chau, 22°07.325'N 103°11.50'E, 290 m, coll. J. T. Polhemus, D. A. Polhemus & P. Nguyen, 11 Apr.2000, CL4410 ( JTPC) .

Description. – Apterous male, length 5.5-5.9 (holotype 5.9), width 1.85-2.07 (holotype 1.97) (n=20); apterous female length 6.3-7.0 (allotype 6.9), width 2.22-2.39 (allotype 2.32) (n=14); macropterous female length 7.2-7.8, width 2.20-2.44 (n=3).

Colour. Apterous form, body mainly brown on dorsal side and pale yellow on ventral side (females with two brown markings on mesosterno-pleura and median brown patches on metasterno-pleura); dorsal surface covered with silvery or greenish pubescence. Head with one median yellow stripe; antennae yellow to brown. Pronotum with five longitudinal yellow stripes on dorsal and lateral sides. Mesonotum mainly yellow with six longitudinal markings: two slender dark brown lateral stripes, two slender dark brown sub-lateral stripes and two light brown markings in the centre. Metanotum and abdominal tergum mainly dark brown. Pro-, meso- and meta-sternopleura with dense silvery and reflective pubescence. Legs: all coxae, trochanters and femora yellow (slightly darker in females), all tibiae and tarsi brown. In macropterous form, anterior part of pronotum with five yellow stripes as in apterous form, posterior part totally brown, wings brown.

Structural characteristics

Apterous male (holotype): Head width across eyes 1.29; interocular width 0.60; eye kidney-shaped on dorsal view, length of eye 0.63. Antennae about 1.2x body length (6.99: 5.90), lengths of segments 1-4: 1.94: 1.55: 1.46: 2.04; first segment with 2-3 black spine-like hairs in apical part. Pronotum, broader than long, slightly shorter than head length (0.84: 1.16). Lengths of mesosternum and metasternum: 1.97 and 0.37. Posterior margin of metasternum with a median fringe of short black hairs ( Fig. 3). Lengths of leg segments (femur: tibia: tarsal segment 1: tarsal segment 2) as follows: fore leg: 2.43: 1.89: 0.22: 0.32; middle leg: 6.90: 5.10: 0.61: 0.49; hind leg: 7.20: 5.00: 0.73: 0.49. Fore femur ( Fig. 2) simple, length about 6.57x maximum width (2.43: 0.37), ventral surface with 2 black stout hairs (2-6 hairs in other paratypes); fore tibia almost straight, with some long black spine-like hairs on apical margin. Middle and hind femur slender and slightly longer than the body, with scattered small brown spines. Claws stout, length 0.20. Abdomen relatively short, pregenital length 1.22, with patch of long yellow hairs on median sterna 1-5. Sternum 7 about 2.25x length of two preceding sterna combined (0.61: 0.27), posterior margin with very deep rectangular median notch (about half the length of sternum 7) ( Fig. 3). Genital segments large, length 0.54, pygophore broadly suboval, with a pair of disto-lateral processes, each directed obliquely upwards, plate like, and with slightly pointed apex in lateral view ( Figs. 3-4). Parameres small and blunt.

Apterous female (allotype): slightly bigger than the male. Head width across eyes 1.37; interocular width 0.65; eye kidney-shaped, length of eye 0.61. Antennae about 0.9x of body length (6.20: 6.90), lengths of segments 1-4: 1.79: 1.41: 1.16: 1.84; first segment with 2-3 black spines sub-apically. Pronotum slightly shorter than head length (0.83: 1.16). Lengths of mesosternum and metasternum: 2.24 and 0.51. Lengths of leg segments (femur: tibia: tarsal segment 1: tarsal segment 2): fore leg: 2.38: 1.79: 0.24: 0.39; middle leg: 6.80: 4.80: 0.76: 0.61; hind leg: 6.90: 4.90: 0.83: 0.54. Fore femur simple, length about 7.0x maximum width (2.38: 0.34), ventral surface with five black stout hairs; fore tibia almost straight with some long black spines on apical margin. Middle and hind femur slender and subequal to body length, scattered with small brown spines. Claws stout, length 0.20. Pregenital abdominal venter 0.32x body length (2.24: 6.90). Venter of sterna 1-6 without patch of long hairs. Sternum 7 about 1.18x length of two preceding sterna together (0.60: 0.51), posterior margin straight. Genital segments not concealed, proctiger round and slightly deflected ( Fig. 6).

Macropterous female: similar to apterous female but slightly bigger in size. Fore wings distinctly surpassing abdominal apex. Wing veins as shown in Fig. 5.

Macropterous male unknown.

Etymology. – This species is named after its country of origin.

Distribution & habitat. – Northern Vietnam (Vinh Phuc, Ba Vi, Lai Chau, Dien Bien, and Lao Cai provinces). Eotrechus

vietnamensis was collected on wet surfaces of rocks, cliffs

covered with mosses at waterfalls or along forest streams at different elevations (from 200-1200 m) of mountainous areas in northern Vietnam. Adults and nymphs were seen resting on almost vertical rock surfaces. When disturbed, they jumped away or hid in shaded spaces beneath the rocks. They were found in the same habitat as Onychotrechus species.

Remarks. – In the key given by Andersen (1982), the male of E. vietnamensis could be keyed to E. brevipes by having plate-shaped processes in the pygophore, and the relatively short middle and hind femura which are only slightly longer than body. However, males of this species can be distinguished form E. brevipes by the following characters: lateral processes of pygophore flattened, expanded distally and without finger-like process; median emargination of sternum 7 much deeper than in all known Eotrechus species; fore trochanter without patch of spinules, fore femur of males more slender, fore tibia without apical process. The female of E. vietnamensis , could not be keyed to any described species because the genital segments are not concealed and the proctiger is not elongated but deflected. In lateral view, sternum 7 of the female is rather similar to that of E. sinensis but it has fewer stout hairs on fore femur and a lesser ratio of sternum 7: sternum 5+6.

Male specimens from Dien Bien province and Lai Chau province differed from those collected in locality of holotype in the following characters: fringe of short black hairs on posterior margin of metasternum less dense, hair patch on sterna 1-5 less dense, median notch of sternum 7 gradually widened towards posterior margin, disto-lateral processes of pygophore slightly thicker and less pointed, posterior margin of pygophore slightly produced on median. However, the presence of a hair fringe on metasternum, hair patches on sterna 1-5, and a very deep median notch of sternum 7 are unique among Eotrechus species. Therefore, we treated these differences as intraspecific variations.

As the manuscript was being prepared, Dr. J. T. Polhemus (Colorado, U.S. A) informed us that he had collected specimens which he believed could be the same species as E. vietnamensis . He kindly sent us part of his material (lot number CL4391, CL 4396, and CL4410) to confirm its identity. His specimens are conspecific with E. vietnamensis as he had suspected, and as such, we have included all his material as paratypes.