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.

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.