Isoperla obscura ( Zetterstedt, 1840 )

Zwick, P & Surenkhorloo, P, 2005, The Mongolian Species Of Isoperlinae (Plecoptera: Perlodidae), Acta Zoologica Academiae Scientiarum Hungaricae 51 (3), pp. 253-276 : 269-270

Isoperla obscura ( Zetterstedt, 1840) ( Fig. 9 )

Perla obscura Zetterstedt , Insecta Lapponica: 1058.

Material. MONGOLIA; Chövsgöl aimak, Alag Mort, 42 km NO vom Pass Chaldzan Sogotyn davaa, 1900m, Tesijn gol, 14.VII.1968 [KASZAB 1110], 1 f; Bajan-Ölgij aimak; ca 20 km NNW Ölgij , 2100m, 2.VII.1968 [KASZAB 1053], 1 f; Bajan-Ölgij aimak, Ölgij , 1750m, Chovd gol, re[chtes] Ufer; 30. VI.1968 [KASZAB 1046] numerous adults. Selenge aimak, Mandal sum (leg. P. SURENKHORLOO): Khonin Nuga, Eroo sum, Minj River (49°00’N, 108°02’E), 1 m (?), 02.VII.2001 .

Isoperla obscura is widespread in the northern part of the Palaearctic Region ( LEVANIDOVA & ZHILTZOVA 1979) and was previously recorded from Mongolia ( ZHILTZOVA & ZAPEKINA-DULKEIT 1986).

Size. Fore wing length, mm 7.7–9.6 mm, ff 9.0– 12.8 mm ( LILLEHAMMER 1988).

Detailed descriptions of all life stages are available ( BRINCK 1949, 1952, ILLIES 1952, LILLEHAMMER 1988), the species can be recognized by the combination of the following characters: – a narrow lanceolate pale mark between the ocelli is separate from a pale mark at the rear of the occiput ( Fig. 9a ); – the appendage to male sternite 8 is slender, narrower than long ( Fig. 9b ); – the penis membrane carries a V-shaped row of sharp broadly triangular teeth and surface is rough on its other side ( Figs 9c, d ); – female subgenital plate long, approximately triangular, pointed, similar to Kaszabia nigricauda which, however, has a distinctly horseshoe-shaped mark on the head.

The egg ( Figs 9e, f ) is regularly oval; when dissected from females, eggs are concave on one side, like most European Isoperla species. Collar with straight, slightly irregular rim, base of anchor shallowly arched, chorion about 4 µm thick, at maginification 400 almost imperceptibly punctate. Size of eggs ranges 252–268×169–177 µm in a Mongolian specimen, but 276–289×194–202 µm in a specimen from Norway (Varanger Peninsula, Kongsfjordelv, 9.8.1973, leg. TOBIAS, from Senckenberg Museum, Frankfurt).

Figures

Fig. 9. Isoperla obscura (ZETTERSTEDT): a = head (after AUBERT, 1959); b = male abdominal tip, ventral view (after DESPAX 1936), c = penis membrane with blunt warts and V-shaped row of pointed teeth, d = detail of pointed teeth, e = egg of specimen from Varanger Peninsula in full view, f = the same in oblique view to show concavity.Figures c andd after ILLIES, 1952. Figs a-d and f not to scale