Bioacoustics of Rhyacobates zetteli

Remarks. Rhyacobates zetteli sp.n. differs from all of its congeners in the combination of following characters: the unique dorsal colour pattern of the body ( Figs. 12, 13 ); the abdomen of the female is straight; each connexival corner of segment 6 has a small, blunt process ( Fig. 21 ); abdominal segment 7 of the female is prolonged and in lateral view, tapers apically ( Figs. 21–23 ), the connexival margin of sternum 7 is much shorter than the ventral length ( Figs. 21, 23 ); the connexival corner of sternum 7 of the female is produced into a small blunt process ( Fig. 21 ), the posterior margin of sternum 7 is bilobate, but without a median process ( Fig. 22 ). The shape of the paramere of this new species is similar to that of R. gongvo , but males of the latter can be separated from this new species by other characteristics, i.e., colouration, shape of the proctiger and endosomal structures. Both new species, Rhyacobates angustus sp.n. and R. zetteli sp.n. , are closely related to each other, as both taxa possess the prolonged and rather straight abdomen of the female, the posteromedian process on tergum 7 of the female, and the sub-apical tooth-like elevation on the fore femur of the female. In the subfamily Ptilomerinae , similar modification on the posterior margin of female tergum 7 is previously known only in the genus Stridulobates Zettel & Thirumalai, 2001a (see Zettel & Thirumalai 2001a : Figs. 15, 16 ). However, in species of Stridulobates , tergum 7 of the female is prolonged and covers most of tergum 8, whereas in R. angustus sp.n. and R. zetteli sp.n. , tergum 7 is shorter and covers only a small anterior portion of tergum 8. Other characteristics, e.g., the absence of a metanotal process in females, the lack of a "stridulatory device" on the middle trochanter and sterna 2–6 in males, also suggests that R. angustus sp.n. and R. zetteli sp.n. do not belong to Stridulobates . Additionally, males of R. angustus sp.n. and R. zetteli sp.n. clearly differ from males of Stridulobates in the shape of the parameres and structure of endosoma (see Matsuda 1960: Figs. 677, 679; Zettel & Thirumalai 2001a : Figs. 9, 10 ). Rhyacobates angustus sp.n. and R. zetteli sp.n. can be easily separated from each other by the yellow median markings on the nota, the shape of the male proctiger and paramere, and the structures of female sternum 7. In R. angustus sp.n. , yellow markings on the pro- and mesonota are slender (the metanotum of the male is totally black and without yellow marking, the metanotum of the female is with very slender with a yellow median marking; the male proctiger has a rounded lobe on each side) ( Fig. 3 ); the apex of the male paramere is more abruptly narrowed ( Figs. 4, 5 ), sternum 7 of the female has large, sub-triangular connexival processes and a broadly-arched posterior margin ( Figs. 8–10 ). In R. zetteli sp.n. , yellow markings on the nota of both sexes are broad; the male proctiger has a broadly angular lobe on each side; the male paramere gradually tapers apically ( Figs. 17, 18 ); sternum 7 of the female has small blunt connexival processes ( Fig. 21 ), the posterior margin of sternum 7 is bilobate ( Fig. 22 ). Habitats. Most specimens of Rhyacobates zetteli sp.n. were collected in a shaded and fast flowing mountain stream at an elevation of over 1800 m ( Fig. 11 ). They were found skating in schools of numerous individuals: adults and nymphs in a mixture of which the nymphs were predominant. Seasonal fluctuation in population size and ratios of nymphs to adults are still unknown. The individuals of this species were also found often resting on partially submerged rocks in the middle the stream, as do other species of Rhyacobates ( Esaki 1923 ; Tran & Yang 2006 ). One macropterous specimen (with a de-alated wing) was found in an unshaded, tiny water flow (locality TAD0418), which continues underground and was ca. 500 m from the main stream (locality TAD0417). None of the specimens found in the main stream were the macropterous form. This observation suggests that this species has good flying ability (probably for dispersal), but upon migrating, the macropterous individuals were likely to have their wings broken off.