Nymphs of the genus Isoperla Banks (Plecoptera, Perlodidae) from the Eastern Palaearctic Region Author Teslenko, Valentina A. Author Zhiltzova, Lidiya A. text Zootaxa 2006 1130 1 33 journal article 10.5281/zenodo.171865 411e4ba3-3168-4039-b168-5dca22472936 1175­5326 171865 Isoperla flavescens Zhiltzova & Potikha 1986 ( Figs. 22–28 ) Description. Nymphs were correlated with adults by rearing from Lasovka River. Length of mature male nymph 9.0– 9.6 mm , female 10.0– 13.5 mm ; cerci of male nymph 4.0– 4.5 mm ; female 5.0–6.0 mm. General body color brownish­yellow; labrum, frontoclypeus and anterior part of the head dark brown; body yellowish ventrally, top of the abdomen slightly brownish. Clothing hairs on body surface dark and numerous. Head with occipital spinule row irregular and interrupted medially; color dark­brown in anterior half ( Fig. 22 ), with sharp yellowish M­line; thin transverse, light stripe on the frontoclypeus not always distinct; two light, oval spots posterior to anterior edge of frontoclypeus; interocellar area with an indistinct pale triangle; area along epicranial suture pale; occiput pale, with 2 indistinct spots forward of occipital suture. Lacinia bidentate ( Fig. 23 ), 6–7 stout, dark setae below subapical tooth, followed by thin setae to base. Tip of galea reaches the base of subapical tooth ( Fig.23 ). Mandible ( Fig. 24 ) similar to other species. FIGURE 22. Isoperla flavescens Zhiltzova and Potikha , nymph. FIGURES 23–28. Isoperla flavescens : 23. Right maxilla, ventral. 24. Right mandible, ventral. 25. Right leg, dorsal. 26–28. Basal, medial, and apical sections of right cercus, lateral. Scale (mm): 25 = 0.51; 23, 24, 26–28=0.4. Thorax. Pronotum ( Fig. 22 ) transverse­oval, fringed with short setae, occasional long hairs interspersed at anterior angles, lateral and posterior pronotal margins; light median spot close to anterior pronotal margin indistinct; lateral pronotal margins light; anterior and posterior margins and sublateral fields brownish. Meso­ and metanotum wing pad bases slightly darker than lateral margins and median area. Legs light­brownish ( Fig. 25 ), with dense fringe of silky hairs along outer margin of tarsi, femora, and tibiae. Abdominal terga ( Fig. 22 ) with thin brown stripe medially surrounded by pale stripe, lateral tergal margins brownish; posterior tergal margins with fringe of long setae, intercalary bristles numerous. Cerci yellowish ( Figs. 26–28 ), apical half with dorsal fringe of long silky hairs; length of these hairs exceeds the length of corresponding cercal segment in the apical third; one dorsal and one ventral seta in apical whorl longer than others, their length exceeds one half length of corresponding cercal segment. Material examined: Russia . Primorsky Region, Lazovka R., below the pass, rearing 13.VI 1998 , V. Teslenko, 4 nymphs; Komissarovka R., 11.VI 1988 , V. Teslenko 1 nymph; Ussuri R., 29.V 1992 , T. Tiunova, 1 nymph; Yedinka R., 9.VII 1985 , E. Postnikova, 11 nymphs; Khabarovsky Region: Sukpai R., 22.VI 1998 , V. Teslenko, 2 nymphs; Tumnin R., 17.06.1997 , T. Tiunova, 1 nymph. Distribution. Russia : Primorsky and Khabarovsky Regions; South Korea .