Rhyacobates gongvo, 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 : 16-18

Rhyacobates gongvo , new species

( Figs. 17-25, 28 )

Material examined. – Holotype (apterous female) and allotype (apterous male), Vietnam, Lao Cai province, Sa Pa, Hoang Lien National Park, Sin Chai , 22°20.421'N 103°48.844'E, 1366 m, coll. A. D. Tran, 1 Jun.2003, TAD0337 ( ZMHU).

Paratypes: Vietnam: de-alated macropterous 2 males, 3 females, same locality data as holotype ( ZRC); apterous 3 males, 6 females, same locality as holotype, coll. A. D. Tran, 3 Jul.2004, TAD0415 ( NHMW, ZRC) .

Description. – Apterous male: length 6.3-6.5 (allotype 6.5), width 2.2 (n=2). Apterous female: length 8.3, width 2.52. Dealated macropterous male: length 6.4, width 1.97 (n=2). Dealated macropterous female: length 7.5, width 2.44 (n=3).

Colour. Body mainly black, covered with silvery pubescence. Head yellow with black markings dorsally. Antennae mainly black, fourth antennal segment with whitish area in distal two fifths. Pronotum with large sub-triangular yellow spot in apterous female and smaller and ovate in apterous male ( Fig. 28 ). Pronotum in macropterous form with ovate (in males) or diamond-shaped (in females) yellow marking in anterior part and yellow posterior margin. Mesonotum in apterous form black with longitudinal yellow stripe posteriorly, stripe length about three fourths of mesonotum length. Metanotum and dorsal abdomen black. Venter of female light yellow except anterior 2/3 of mesosternum. Venter of male mainly black or dark brown, except acetabula and genital segments. All coxae and trochanters yellow. Fore femur yellow with one brown dorsal stripe. Middle and hind femora yellow at base, brown or black at distal part. All tibiae and tarsi dark brown or black.

Structural characteristics

Apterous female (holotype): Head width across eyes 1.37, interocular 0.52, eye length 0.56. Lengths of antennal segments 1-4: 3.54: 0.80: 1.10: 0.80. Pronotum broader than long, length 0.68, width 1.46. Mesonotum length 2.19. Metanotum without spine on median. Lengths of leg segments (femur: tibia: tarsal segment 1: tarsal segment 2): fore leg: 3.50: 2.91: 1.63: 0.81; middle leg: 10.10: 5.60: 2.52: 0.37; hind leg: 10.20: 3.10: 0.16: 0.20. All coxae with a ring of long dark hairs at apical margin. Fore trochanter with some long yellow hairs ventrally ( Fig. 21). Middle and hind trochanters without hairs. Fore femur slender, with a row of 6-8 long dark bristle-like hairs and some scattered long soft yellow hairs on venter. Middle femur without small spinules. Abdomen elongate and straight, posterior part of sternum 7 slightly depressed ventrally ( Fig. 17). Abdomen relatively long, pregenital segments length 3.15. Length of sterna 5 and 6: 0.45 and 0.57. Sternum 7 length 0.95, not totally enclosing genital segments, posterior ventral margin straight without process. Dorsal processes of sternum 7 long, straight and flatten ( Figs. 18-20).

Apterous male (allotype): Head width across eyes 1.29, interocular width 0.51, eye length 0.49. Lengths of antennal segments 1-4: 3.25: 0.78: 1.22: 0.78. Pronotum short, length: width 0.66: 1.39. Mesonotum length 1.93. Metanotum without median spine or process on posterior margin. Lengths of leg segments (femur: tibia: tarsal segment 1: tarsal segment 2): fore leg: 3.40: 2.91: 1.10: 0.61; middle leg: 9.80: 5.10: 2.24: 0.34; hind leg: 10.00: 2.39: 0.15: 0.17. Other characters similar to apterous female except venter of fore femur with a row of 4 long, dark, bristle-like hairs at basal half. Middle femur with small spinules not placed in a row. Abdomen short and slightly curved downwards posteriorly. Pregenital abdomen length 1.68, about 0.27x body length. Sternum 7 length 0.51. Venter of abdominal segment 8 length 0.40. Genital segments length 0.88. Proctiger with small angular projections on each side ( Fig. 22). Parameres relative long and slender ( Figs. 24-25). Vesical sclerites as illustrated in Fig. 23.

De-alated macropterous female: similar to apterous female except slightly smaller in size. Head width across eyes 1.32, eye length 0.49, interocular width 0.48. Pronotum length: width 2.63: 2.00. Lengths of antennal segments 1-4: 3.25: 0.73: 1.11: 0.78. Lengths of leg segments (femur: tibia: tarsal segment 1: tarsal segment 2): fore leg: 3.40: 2.86: 1.54: 0.79; middle leg: 9.80: 5.60: 2.44: 0.38; hind leg: 10.00: 2.91: 0.16: 0.20.

De-alated macropterous male: similar to apterous male. Head width across eyes 1.25, interocular width 0.48, eye length 0.48. Pronotum with longitudinal ridge along mid-line, pronotum length: width 2.44: 1.78. Lengths of antennal segments 1-4: 3.30: 0.78: 1.19: 0.78. Lengths of leg segments (femur: tibia: tarsal segment 1: tarsal segment 2): fore leg: 3.35: 2.96: 1.11: 0.63; middle leg: 10.00: 5.40: 2.37: 0.36; hind leg: 10.40: 2.52: 0.15: 0.17.

Etymology. – The word “gong vo” in Vietnamese means water skaters, it is used here specifically as a noun in apposition.

Distribution & habitat. – Northern Vietnam, only known from the type locality. Specimens were collected from a fast flowing rocky mountainous stream in open area. They were seen skating swiftly on the water surface and well camouflaged in the torrential environment by their silvery pubescence. They were also found resting on shaded sides of exposed surfaces of rocks in the stream. Both Rhyacobates gongvo and R. abdominalis were found in the same habitat.

Remarks. – Rhyacobates gongvo matches diagnostic characters of the genus Rhyacobates except for characters (j) and (k) (see remarks for R. anderseni above): posterior segments of female straight, not curved dorsad; seventh segment of female abdomen not completely enclosing the genital segments. This species is relatively similar to R. malaisei in the following characters: abdomen of female elongate, almost straight in lateral view, tube-like seventh sternum shorter than two preceding sterna combined, seventh abdominal segment with long projections; male elongate with relatively short abdomen, eighth abdominal segment ventrolaterally depressed; similar lengths of antennal segments. However, it could be separated from R. malaisei by the following characters: proctiger of male without hook-shaped projection on each side; paramere long and slender; projections on abdominal segment 8 of female straight, not curved.

Figures

Fig. 28. Habitus of Rhyacobates gongvo, holotype.