Isoperla popijaci: A new species of Yellew Sally from Croatia.

Stoneflies, Plecoptera, are an ancient (at least Permian) family of Insects with a global distribution. They are considered useful environmental indicators, as the adults tend to be large and conspicuously coloured, and the larvae live exclusively in well oxygenated fresh water. The genus Isoperla, commonly known as Yellow Sallys, comprises about 188 species found throughout Eurasia and North America, with the Balkan Peninsula being somewhat of a biodiversity hotspot for them; 21 of the 60 species recorded in Europe are found there, with 12 being endemic to the peninsula. Ten of these species have been recorded in Croatia, but it is thought likely that the country is home to more, undiscovered, species, due to its extensive karstic waterways, which make an excellent habitat for Stoneflies.

In a paper published in the journal ZooKeys on 16 December 2021, Dora Hlebec of the Department of Biology at the University of Zagreb, Ignac Sivec of the Slovenian Museum of Natural History, Martina Podnar of the Croatian Natural History Museum, and Josip Skejo and Mladen Kučinić, also of the Department of Biology at the University of Zagreb, describe a new species of Yellow Sally from Croatia.

The new species is described from specimens collected from karstic waters around the Ševerova Cave system. It is named Isoperla popijaci in honour of Aleksandar Popijač, for his work on the Plecoptera of Croatia. These Stoneflies are generally a light brown in colour, lighter on the belly and sides, and with yellowish markings. Adult males measure 17-19 mm in length, while females are 16.5-18 mm long.

 

Morphology of Isoperla popijaci. (A) Head and pronotum in dorsal view (adult male). (B) Habitus (larval). (C) Habitus (adult male). (D) Female terminalia in ventral view. (E) Everted male copulatory organ. Scale bars 0.5 mm. Hlebec et al. (2021).

No truly trogloditic species of Stoneflies are known, but many species, like Isoperla popijaci, are known only from waters close to caves and cave systems, with the same waterways often lacking Stoneflies further downstream. This strongly suggests that when surveying areas such as the Dinaric Alps of Croatia, particular attention must be paid to caves and pits, and underground and temporary rivers and streams associated with them, which are likely to be the homes to highly endemic Stonefly species.

 

Type locality of the Popijač’s Yellow Sally, Isoperla popijaci: Ševerova Cave in Croatia; (A) and (B) photographs in wet phase, (C), (D) photographs in dry phase, (E) map (blue circle indicates type locality). Hlebec et al. (2021).

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