Perlodes microcephalus ( Pictet 1833 )

Zwick, Peter, 2011, Polymorphism And Taxonomic Problems In The Perlodes Microcephalus Group (Plecoptera: Perlodidae); Perlodes Mortoni Removed From Synonymy, Illiesia 7 (26), pp. 291-296 : 292

Perlodes microcephalus ( Pictet 1833)

Material examined. Numerous specimens from Germany, Switzerland, Austria, North and South Italy, Greece and Anatolia were examined for egg structure. Biometry was additionally performed on the following: Germany: Hesse, upper course of river Fulda between Obernhausen and Ried, 11♂, 11♀; Hesse, Spessart, tributary to river Schmale Sinn , 7♀ ; Lower Saxony, Harz Mts, Hohegeiss , 1♀ ; Northrhine Westphalia, Albaum, 2♂, 1♀ (det. J. Aubert); Baden-Württemberg, river Kocher at Gaildorf , 2♂, 1♀ ; Bavaria, Bavarian Forest, Rotbach at Böbrachmühle , 3♂ . Austria, Pongau, Eben , 2♂ . Switzerland, Hochrhein at Sargans , 3♂, 2♀ . Turkey, Armenia, Pülümür Pass , 3♂, 1♀ ; North Anatolia, Pass between Terfenni and Korkuteli, 1500m, 8♂, 13♀ .

Assigned to P. microcephalus with doubt: Germany, Lower Saxony, Medingen , 8♂, 5♀ .

Brachypterism. Males range from strongly to barely brachypterous, several have a RWL similar to females. Wing length variation does not seem to be random but to occur stepwise. Should this be confirmed in larger samples the phenomenon might be related to number of larval instars through which specimens grew before metamorphosis.

Egg structure. Sclerites on the anchor disc margin are well delimited and large. They are 2-3 times longer in radial direction than they are wide in peripheral direction. Sclerite orientation is oblique, sclerite tips point in a clockwise direction.

Variation between specimens from central Germany, Italy (Sila Grande), or Anatolia is normally not greater than between individual platelets of the illustrated specimen ( Fig. 5 ). However, a female from N. Italy and one from Greece, Olympus, had shorter platelets.

Aberrant population. A sample from N. Germany, Medingen near Uelzen, is assigned to P. microcephalus with some doubt. Variation of male wing length ( Fig. 2 ) seems to resemble P. microcephalus but sclerites on the egg anchor are different between specimens and resemble some of the P. mortoni eggs shown in Fig. 5.

A single female of P. dispar was taken at the same site.

Notes. Types of Perla microcephala are no longer available ( Zwick 1972). I regard Berthélemy (1964) as first revisor in the sense of the INTERNATIONAL CODE OF ZOOLOGICAL NOMENCLATURE and follow his interpretation of the name.

Figures

Fig 5. Perlodes spp., sclerite platelets on periphery of anchor disc of German P. microcephalus (River Fulda at Ried), P. dispar (River Fulda nr Schlitz), and Scottish P. mortoni. mo-1 to mo-7 show individual ♀♀, most from River Tweed, mo-2 from River Dee. There are 5 ♀♀ similar to mo-3 (including one from River Tay), 4 ♀♀ are similar to mo-6, 5 ♀♀ (rivers Tweed and Dee) are similar to mo-7. Orientation (centre of anchor disc is towards right hand side) and scale same for all.

Figs. 1-4. Perlodes spp., frequency (% of sample) of particular relative wing-lengths (RWL = WL/HCW) in males and females. 1. P. microcephalus. 2. P. microcephalus (?) from Medingen, N. Germany. 3. P. dispar. 4. P. mortoni. Figures in legends are the numbers of specimens measured; compare text for origin of samples.