Tenuibaetis frequentus ( Müller-Liebenau & Hubbard 1985 ) Muller-Liebenau & Hubbard, 1985

Kubendran, T., Balasubramanian, C., Selvakumar, C., Gattolliat, J. L. & Sivaramakrishnan, K. G., 2015, Contribution to the knowledge of Tenuibaetis Kang & Yang 1994, Nigrobaetis Novikova & Kluge 1987 and Labiobaetis Novikova & Kluge 1987 (Ephemeroptera: Baetidae) from the Western Ghats (India), Zootaxa 3957 (2), pp. 188-200 : 189-192

Tenuibaetis frequentus ( Müller-Liebenau & Hubbard 1985) n. comb.

Figs. 1–21

Baetis frequentus Müller-Liebenau & Hubbard, 1985

Material examined. 7 male larvae and 9 female larvae and 5 male imagos, INDIA, Tamil Nadu, Theni, Kurangani stream, tributary of Vaigai River, 10º05’01.97”N, 77º14’55.35”E, 1744 m, 30.vii.2012, Colls. Balasubramanian, Kubendran and Selvakumar. 1 male larva (on slide) and 1 female larva, INDIA, Tamil Nadu, Bas. Vaigai, Riv. Valipparai, 9o43’35.67”N, 77o31’00.24” E, 1300 m, 29.vii.2012, Colls. Balasubramanian, Kubendran and Selvakumar. 1 male larva and 4 female larvae, INDIA, Tamil Nadu, Kodaikanal, Bas. Manjalaru, Riv. Mulaiyaru, 10o14’19.99”N, 77o29’19.90”E, 1216 m, 29.vii.2012, Colls. Balasubramanian, Kubendran and Selvakumar.

Mature larva. Maximal length: Body 9.0– 9.5 mm; cerci 4.5 mm; terminal filament 3.5 mm. Size variable between different populations. Colouration: Head uniformly brown ( Fig. 1 ). Thorax brown with a pale yellow transverse band on the posterior half of mesonotum, legs light yellow with dark pattern ( Fig. 2 ). Abdominal tergites dark brown with paired pale yellow maculae on abdominal tergum IV and abdominal terga IX–X pale yellow ( Fig. 1 ); sternites pale brown except sternites VIII and IX pale yellow ( Fig. 2 ).

Head: Antennae: scape and pedicel bare ( Fig. 3 ), light yellow. Labrum ( Fig. 4 ): rounded with an anteromedial emargination, dorsal surface with one central seta and a distolateral row of 5 short to long simple setae, abundant short fine setae scattered on the surface, subapical row of feathered setae on anterior margin. Hypopharynx ( Fig. 5 ): lingua covered with short thin setae, much longer apically; superlingua with thin setae apically and laterally. Left mandible ( Fig. 6 ): with incisors composed of 7 denticles; outer denticle longer than others; prostheca with elongated, thin and comb-shaped structure; margin between prostheca and mola not crenate, almost straight without hump and without setae. Right mandible ( Fig. 7 ): with incisors composed of 7 denticles; stout prostheca with small denticles; margin between prostheca and mola not crenate, without setae. Maxillae ( Fig. 8 ): with 4 caninae, lacinia with 2 rows of setae, one row with abundant thin setae ending with stout and long setae, second row with 2 long stout dentisetae; palp 2- segmented longer than galea-lacinia, segment 1 equal in length to segment 2, apex of segment 2 rounded with few fine setae. Labium ( Fig. 9 ): glossae shorter than paraglossae; inner and apical margins of glossae with long setae; paraglossae apically rounded with 3 rows of long setae; labial palp threesegmented, segment 1 longer than segment 2 and 3 combined; segment 2 slightly produced inward to form a moderately expanded lobe at distal corner, dorsally with a row of 6 medium setae; segment 3 conical, slightly asymmetrical and covered with small and stout setae.

Thorax: Legs ( Fig. 10 ): dorsal margin of femora with one row of robust setae; lateral surface with spatulate setae; villopore on anteromedial corner. Dorsal margin of tibiae with short spatulate setae; ventral margin with short pointed setae. Dorsal margin of tarsi with few short and pointed setae, ventral margin with stout setae increasing in length towards apex. Tarsal claws with a single row of about 12 acute teeth increasing in length towards apex ( Fig. 11 ). Hindwing pads present ( Fig. 12 ).

Abdomen: Single lamellate gills present on segments 1–7 with poorly developed tracheation and serrated margin ( Fig. 14 ); gill 1 ( Fig. 13 ) and 7 smaller than others. Paraproct ( Fig. 15 ): with patch of notched scales medially; margin with numerous short spines; margin of lateral extension with about 9 short to medium triangular spines. Tergites with scale bases; distal margin with triangular spines ( Fig. 16 ); sternites with abundant thin setae; without scales and scale bases; posterior margin smooth. Cerci light brown without dark stripe; median terminal filament shorter ¾ of cerci and with lateral hairs.

Male imago: Length: male body 8.7 mm; fore wing 7.6 mm; cerci 14–16 mm ( Fig. 17 ). Colouration: head ( Fig. 18 ): antennal scape, pedicel and flagellum medium reddish brown; upper surface of compound eye medium reddish brown; lateral face lighter. Thorax: medium to reddish brown. Legs pale yellow without marking or stripe. Forewings ( Fig. 19 ) hyaline with light brown venation; pterostigma with about 4 cross veins generally reaching subcostal vein; double intercalary veins shorter or slightly longer than half distance between corresponding main veins. Hindwings ( Fig. 20 ) with an erect costal spur at ¼ length of wing; two longitudinal veins reaching margin, none of them bifurcated. Abdomen: tergites I–VI whitish without marking or pattern; tergites VII–X medium brown without marking or pattern; sternite colouration similar to corresponding tergites. Genitalia ( Fig. 21 ): segment 1 and 2 completely fused; segment 3 elongated, apically slightly expanded; well-developed sclerotized plate between forceps, as broad as distance between forceps, apically convex without setae.

Diagnosis. Tenuibaetis frequentus ( Müller-Liebenau & Hubbard 1985) can be differentiated from other species of the genus described so far by the following combination of characters in the larval stage: (i) dark brown tergal color pattern typical of the genus but with a pale yellow transverse band on the posterior half of mesonotum, paired pale yellow maculae on abdominal tergum IV and abdominal terga IX–X pale yellow ( Fig. 1 ); (ii) segment 2 of labial palp with a row of 6 long setae ( Fig. 9 ); (iii) abdominal gills 1–7 with poorly developed tracheae and with serrated margin ( Figs 13, 14 ) and (iv) number and size of the spines of the distal margin of paraproct ( Fig. 15 ).

Discussion. Tenuibaetis was originally established as a subgenus by Kang and Yang (1994) within the genus Baetis designating B. pseudofrequentus Müller-Liebenau 1985 from Taiwan as type species and describing two more species viz., B. (Tenuibaetis) inornatus Kang & Yang 1994 and B. (Tenuibaetis) arduus Kang & Yang 1994 . The subgenus Tenuibaetis was established based on the following combination of characters: (i) mandible with smooth medial margin; (ii) Conical segment 3 of labial palpus; (iii) presence of villopore on femur and (iv) paraproct with a patch of notched scales ( Kang et al. 1994). Subsequently, Fujitani et al. (2003) elevated Tenuibaetis to the generic level based on the presence of robust setae with median ridge on the dorsomedian surface of the nymphal femur as the exclusive diagnostic features of this genus. Fujitani et al. (2011) associated nymphs of three Tenuibaetis species with their respective imagos by rearing. They redescribed T. flexifemora Gose 1980 and T. pseudofrequentus Müller-Liebenau 1985 and also provided description of a new species, T. parvipterus Fujitani 2011 .

According to Fujitani et al. (2011), Tenuibaetis presently encompasses five species: T. flexifemora (Gose 1980) , T. pseudofrequentus (Müller-Liebenau 1985) , T. arduus Kang & Yang 1994 , T. inornatus Kang & Yang 1994 , and T. parvipterus Fujitani 2011 . Baetis frequentus was attributed to Tenuibaetis in the website “ Ephemeroptera of the World” (http://www.insecta.bio.spbu.ru/z/Eph-spp/%29 frequentus %28 Baetis %29.htm, last visited 26 February 2015), but the combination was never formally made. Considering that Baetis frequentus perfectly fits the diagnosis and characters of Tenuibaetis as defined by Kang et al. (1994) and Fujitani et al. (2003, 2011) and regarding the close affinity between B. frequentus and T. pseudofrequentus , we formally proposed the new combination Tenuibaetis frequentus ( Müller-Liebenau & Hubbard 1985) . The species was already reported from India ( Balaji et al. 1990; Sivaramakrishnan & Venkataraman 1990). The genus is known therefore from Japan, Taiwan, Hong Kong, Sri Lanka and India.

Ecology. The larvae were collected in a perennial stream of the Vaigai River basin with 2–3.5 m wide and 60 cm depth and medium water current (0.6 m /sec.) on the eastern part of southern Western Ghats. The water temperature ranged between 22˚C–25˚C (seasonal variations) and the pH between 6.5 and 7.4.

Figures

FIGURES 1 – 9. Larva of Tenuibaetis frequentus (Müller-Liebenau & Hubbard 1985) n. comb. 1, Dorsal view of male; 2, Ventral view of male; 3, Antenna; 4, Labrum (left: dorsal; right: ventral); 5, Hypopharynx; 6, Left mandible; 7, Right mandible; 8, Maxilla; 9, Labium.

FIGURES 10 – 16. Larva of Tenuibaetis frequentus (Müller-Liebenau & Hubbard 1985) n. comb. 10, Foreleg; 11, Claw; 12, Hindwing pad; 13, Gill 1; 14, Gill 4; 15, Paraproct; 16, Posterior marginal spines of terga.

FIGURES 17 – 21. Imago of Tenuibaetis frequentus (Müller-Liebenau & Hubbard 1985) n. comb. 17, Male; 18, Lateral view of male head; 19, Forewing; 20, Hindwing; 21, Male genitalia.