Rhyacobates anderseni, 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 : 14-16

Rhyacobates anderseni , new species

( Figs. 7-16 , 27 )

Material examined. – Holotype (apterous female) and allotype (apterous male), Vietnam, Ha Tinh province, Vu Quang National Park, Khe Lim , 18°16.416'N 105°26.467'E, 291 m, coll. A. D. Tran, 24 Apr.2003, TAD0304 ( ZMHU).

Paratypes: Vietnam: apterous 3 males, 6 females, same locality data as holotype; apterous 1 male, 1 female, macropterous 2 males, Ha Tinh province, Vu Quang National Park, Song Con, Sao La station , 18°15.386'N 105°27.442'E, 293 m, coll. A. D. Tran, 25 Apr.2003, TAD0307a ( NHMW, ZMHU, and ZRC) .

Additional material. – 1 apterous female, China, Yunnan,

Xishuangbanna, Hill stream, 90km from Jinghong to Simao, 1070 m, coll. H. H. Tan, 20 May.2000, THH0068 ( ZRC).

Description. – Apterous male: length 6.0-6.1 (allotype 6.0), width 1.83-1.85 (allotype 1.83) (n=5); apterous female: length 6.8-7.0 (holotype 6.8), width 2.52-2.57 (holotype 2.52) (n=8); macropterous male: length 6.1-6.2, width 1.85-1.88 (n=2).

Colour. Body almost black dorsally, covered with silvery pubescence. Head and pronotum black with semi-circular yellow markings. Antennae mainly dark brown to black, first antennal segment with yellow basal half, last segment with whitish area in distal two fifths. Male with longitudinal thin yellow stripe on posterior half of mesonotum. Yellow stripe on mesonotum of female broader than that of male. Venter bright yellow except anterior part of mesosterno-pleura black. All coxae, trochanters and femora yellow. Fore femur of both sexes with two brown longitudinal stripes on dorsal and external side, more slender and lighter brown in the female. Middle and hind femora yellow at base but brown or black at distal end. All tibiae and tarsi dark brown to black.

Structural characteristics

Apterous female (holotype): Head width across eyes 1.22, eye length 0.54, interocular width 0.48. Lengths of antennal segments 1-4: 2.86: 0.68: 1.02: 0.73. Pronotum broader than long, length and width: 0.63 and 1.36. Mesonotum length 2.02. Posterior margin of metanotum with a median pointed process ( Fig. 7 ). Lengths of leg segments (femur: tibia: tarsal segment 1: tarsal segment 2): fore leg: 2.86: 2.37: 1.33: 0.71; middle leg: 8.50: 5.20: 2.24: 0.32; hind leg: 8.60: 3.10: 0.15: 0.20. All coxae with rings of dark bristle-like hairs at apical margin. Fore trochanter with long hairs ventrally, hind trochanter with dense long hairs dorsally. Fore femur with nine long dark bristle-like hairs posteriorly and scattered with soft long yellow hairs on venter ( Fig. 11 ). Middle tibia lined with brownish hair-fringe ventrally. Hind femur with long yellow hairs on basal part. Abdomen relatively short, pregenital abdomen length 1.27. Length of sterna 5 and 6: 0.30 and 0.40. Abdominal segment 7 long, length 0.80, raised slightly upwards dorsally, bearing a pair of long projections pointing outwards and downwards ( Figs. 8-10 ); posterior margin more or less straight with two short lateral processes ( Figs. 9 & 10 ). Abdominal segment 7 almost enclosing the genital segments.

Apterous male (allotype): Head width across eyes 1.16, interocular width 0.43, eye length 0.46. Lengths of antennal segments: 2.67: 0.68: 1.05: 0.71. Pronotum broader than long, length and width: 0.59 and 1.22. Mesonotum length 1.76. Posterior margin of metanotum without a median process. Lengths of leg segments (femur: tibia: tarsal segment 1: tarsal segment 2): fore leg: 2.73: 2.18: 0.83: 0.51; middle leg: 8.10: 4.50: 2.02: 0.34; hind leg: 8.00: 2.52: 0.12: 0.17. Structure of legs similar to female except middle femur with small spinules but not in a row, spinules more scattered on distal part. Abdomen short, pregenital abdomen length 1.37, about 0.23x of body length. Sternum 7 length 0.43, posterior margin straight with long hairs. Genital segments slightly curve downwards. On lateral view, abdominal segment 8 with concave venter, dorsal margin straight. Venter of abdominal segment 8 length 0.35. Pygophore large, ovate; proctiger with round angular projections on each side ( Fig. 12 ). Parameres falciform, slightly broad, long, not conspicuously setose ( Figs. 13-14 ). Vesical sclerites as illustrated in Fig. 15 .

Macropterous male: Head width across eyes 1.15, eye length 0.46, interocular width of head 0.48. Head with long bristlelike hair around eyes. Lengths of antennal segments 1-4: 2.70: 0.67: 1.00: 0.71. Posterior margin of metanotum with a median pointed process. Lengths of leg segments (femur: tibia: tarsal segment 1: tarsal segment 2): fore leg: 2.73: 2.21: 0.78: 0.51; middle leg: 8.20: 4.61: 2.05: 0.32; hind leg: 8.30: 2.47: 0.13: 0.16. Fore wings surpassing abdominal apex, wing vein shown in Fig. 16 . Other characteristics similar to apterous male.

Macropterous female unknown.

Etymology. – This species is dedicated to the late Prof. N. M. Andersen (Copenhagen) for his great contributions to the research on semi-aquatic Heteroptera.

Distribution & habitat. – Northern Vietnam and Yunnan, China. The type material was collected from moderate flowing streams of a forest at an elevation of 300 m. The specimen from Yunnan was collected from a stream above 1000m in elevation.

Remarks. – Andersen & Chen (1995) listed the generic characteristics of the genus Rhyacobates as: (a) mesonotum black with pale median stripe; (b) first antennal segment longer than other three segment together, last antennal segment with whitish area in distal two fifths; (e) middle and hind tarsi without claws; (f) male parameres moderate in size, falciform and not conspicuously setose; (h) middle femur without distinct row of black spines; (i) eighth abdominal segment of male reduced ventrally, shorter than seventh segment; (j) posterior segments of female abdomen usually curved dorsad (apterous form); (k) seventh abdominal segment of female tube-like, long and completely enclosing the genital segments. Rhyacobates anderseni possesses all the above characters except that the female abdomen is relatively short, not curved dorsad, and abdominal segments 1-6 combined are only slightly longer than abdominal segment 7. This new species is also distinctly different from other known Rhyacobates species by having a very conspicuous median process on the posterior margin of metanotum in the female. This process is also found in Andersenius and Pleciobates . However, elongated hind coxae which are diagnostic for the genus Andersenius were not present in this new species. It is also distinct from Pleciobates by the colouration of mesonotum, general structure of male paramere and endosoma (for Pleciobates spp., see Zettel & Chen, 1996), and the absence of a row of black spines on the male middle femur. The dorsal projections of seventh abdominal segment in the new species are rather similar to those of R. malaisei but differ in the curvature of the internal margin.

We examined a single female from Yunnan, China which is almost identical to the Vietnamese specimens except for slight colour differences: head mainly yellow, larger yellow marking on pronotum, first and second antennal segments yellow, third and fourth antennal segments light brown.

Figures

Figs. 7-16. Rhyacobates anderseni, new species. 7-11, female holotype: 7, lateral view. 8-10, subgenital segments: 8, lateral view. 9, dorsal view. 10, ventral view. 11, right fore leg. 12-16, male: 12, proctiger. 13-14, left paramere, two different views. 15, vesical sclerites. 16, right fore wing. Scales bars 7-12, 16: 1 mm, 13-15: 0.1 mm.

Fig. 27. Habitus of Rhyacobates anderseni, holotype.