Fieldwork and laboratory analysis. Adults of the new species were collected using ultraviolet light traps, adhering to the methodology outlined by Malicky (2004) for nocturnal light trapping. Subsequently, these specimens were preserved in 90% ethanol and are presently deposited at the Department of Biology, Faculty of Mathematics and Natural Sciences, University of Prishtina “Hasan Prishtina” in Prishtinë, Kosovo.

To assess the morphological features of Potamophylax kosovaensis sp. nov., we used specimens of Potamophylax juliani Kumanski, 1999, Potamophylax winneguthi Klapalek, 1902, Potamophylax idliri Ibrahimi, Bilalli & Kučinić, 2022, Potamophylax coronavirus Ibrahimi, Bilalli & Vitecek, 2021 and Potamophylax humoinsapiens Ibrahimi & Bilalli, 2023. These specimens were obtained from Osogovo Mountain in Bulgaria, Zlatibor Mountain in Serbia, Jastrebac Mountains in Serbia, Bjeshkët e Nemuna in the Republic of Kosovo and Sharr Mountains in the Republic of Kosovo, respectively. For species that were unavailable (Potamophylax haidukorum Malicky, 1999), comparative assessments was conducted, based on existing literature (Kumanski and Malicky 1999, Malicky 2004).

Morphological analysis of the male terminalia of the new species involved specimens treated with 10% potassium hydroxide (KOH). The nomenclature for male terminalia adheres to Nielsen (1957) for Limnephilus flavicornis (Fabricius, 1787) and Kumanski and Malicky (1999). Additionally, systematic nomenclature follows Morse (2023).

For the analysis of the genitalia features of Potamophylax kosovaensis sp. nov., we utilised 15 male specimens, employing an Olympus SZX16 stereomicroscope. The resulting illustrations were prepared in Adobe Illustrator (version Creative Cloud 2018) by digitising pencil templates derived from pictures taken with the Olympus SC50 camera.

Sampling area. The Ibër River, spanning eastern Montenegro, northern Kosovo and central Serbia, boasts a total length of 272 km. Originating in the Hajla Mountain of Rozhajë in eastern Montenegro, the River winds its way through south-western Serbia and northern Kosovo before re-entering Serbia, ultimately merging with the West Morava River near Kraljevo in central Serbia. The Ibër River Basin holds the distinction of being the second-largest in Kosovo, encompassing a network of several significant rivers that contribute to its hydrological complexity. Amongst these rivers are the Llap River, Sitnica River, Bistrica River and Kaçandoll River which are the most significant ones (Ibrahimi et al. 2018, Bulliqi 2000).

The specimens of the new species were collected at two distinct locations within the Kopaonik Mountains, falling under the jurisdictions of the Podujevë and Mitrovicë Municipalities in the Republic of Kosovo.

The first sampling site is situated in a spring area of a small tributary of the Kaçandoll River in the Bajgorë area. Until recently, the site was surrounded by dense vegetation, but over the past few years, it has gradually transformed into an open stream due to deforestation in the surrounding area.

The second sampling station (Fig. 1) is located at a spring area of a tributary of the Llap River in Marincë Village. The spring itself is nestled within a beech forested area and, as it progresses, it traverses through a semi-forested region comprised of deciduous and coniferous trees. It represents one of the main contributers to the Llap River.

a

b

Figure 1.

Kroi i Konakut spring, Marincë, Podujevë, Kosovo

a: the spring;  
b: the stream.  

Kopaonik is a mountain range stretching along the border line between the Republic of Kosovo and Serbia. Currently, only few data are available regarding the diversity of caddisflies in this mountain range, with most of them coming from the Kosovan part. Potamophylax kosovaensis sp. nov. represents the second known endemic caddisfly species exclusive to the Kopaonik Mountains, with the first being Drusus dardanicus Ibrahimi, Kucinic & Vitecek, 2015, both of them known currently only from the Republic of Kosovo. Both species were found together in sampling station 2. It is worth noting that the distribution of species within the Potamophylax winneguthi species group often aligns with the distribution of endemic species belonging to the genus Drusus in the Balkan Peninsula. A similar case was noted with P. humoinsapiens and Drusus sharrensis Ibrahimi, Vitecek & Previšić, 2016 in the Sharr Mountains, then P. coronavirus with D. krusniki Malicky, 1981 in Bjeshkët e Nemuna, as well as P. juliani with D. osogovicus Kumanski, 1982 in Osogovo Mountain (Kumanski 1988, Kumanski and Malicky 1999, Ibrahimi et al. 2015, Ibrahimi et al. 2016, Ibrahimi et al. 2021b). Both groups inhabit isolated habitats in mountainous spring and upstream areas at high altitudes. However, in contrast to the above-mentioned endemic species of the genus Drusus, which are primarily confined to spring areas, some species of the Potamophylax winneguthi species cluster, for example, P. idliri and P. humoinsapiens, are also found in lower stream segments, occasionally overlapping with endemic species of the genus Drusus (Previšić et al. 2014, Ibrahimi et al. 2014, Gashi et al. 2015, Ibrahimi et al. 2016, Hinić et al. 2020). On the other hand, although we sampled lower sections of streams, we only found P. kosovaensis sp. nov. within a few metres around the spring area.

Morphological analysis of male genitalia, based on a high number of specimens, confirms the stability of distinguishing characters of Potamophylax kosovaensis sp. nov. Additionally, genetic differentiation, determined through analysis of the cytochrome c oxidase subunit I gene (COI) barcode region sequencing, aligns with the observed morphological distinctions amongst species within the Potamophylax winneguthi species group. The molecular analyses conducted by Ibrahimi et al. (2021b) and Ibrahimi et al. 2022 indicate that the most closely-related species to P. kosovaensis sp. nov., referred to as Potamophylax sp. Bajgorë in their analysis, is a population from the Rila Mountains in Bulgaria, with a p-distance of 4.7%. However, the status of this Rila species remains unresolved due to limited sampling. Initial analysis shows notable differences between P. kosovaensis sp. nov. and the Rila species, particularly in shorter and thicker parameres and shorter and thinner apical spines in the latter. Furthermore, the p-distance between P. kosovaensis sp. nov. and two other morphologically closely-related species within this cluster is significantly higher, measuring 5.3% with P. idliri and 6.6% with P. humoinsapiens.

Microendemic freshwater aquatic insect species, often confined to small and isolated habitats within specific geographic regions, face heightened vulnerability in the face of environmental changes in the Balkan Peninsula. These specialised insects, adapted to distinct ecological niches, are particularly sensitive to alterations in water quality, habitat degradation and shifts in hydrological patterns. Their limited distribution makes them more susceptible to localised threats, including pollution, habitat destruction and climate change impacts. The interplay of these factors can lead to a rapid decline in population size and, in some cases, the outright extinction of these microendemic species. Conservation efforts for such species must prioritise the preservation and restoration of their unique habitats, coupled with proactive measures to mitigate the broader environmental pressures that contribute to their vulnerability. In assessing Potamophylax kosovaensis sp. nov., we noted the severe degradation of forested areas around its designated type locality, which now largely lies in ruin, with the stream itself serving as a dumping ground for garbage. Despite the challenges posed by this deteriorated environment, we deliberately chose this locality as type locality, even though the recent sampling efforts in the past years have failed to yield any specimens. The only recorded specimens from this area date back to 2013, involving the collection of just two males. This intentional decision aims to underscore the urgent need for heightened awareness regarding the destructive impacts of human activities on these rare habitats. Conversely, a nearby second locality harbouring the population of Potamophylax kosovaensis sp. nov. appears to remain stable and unaffected by anthropogenic pressures, likely attributed to the site's inaccessibility in the absence of proper roads. Addressing the challenges faced by these microendemic species involves not only understanding their ecological requirements, but also advocating for the preservation of their habitats in the face of human-induced threats.

The new species exhibits characteristics of a habitat specialist, predominantly confined to specific environments, such as spring areas and the upstream segments of pristine streams. This specialisation renders it a distinctive and indicative species, particularly within the context of the Ibër Basin. The exclusive association with these particular habitats positions the species as a valuable indicator, offering insights into the ecological health and conditions of such environments in the region. The composition of aquatic bioindicator fauna at such spring habitats is still largely unknown in Kosovo, making impossible usage of these areas as reference sites in the water quality assessment studies. We found Potamophylax kosovaensis sp. nov. in sympatry with dozens of species. While most of these species were not found to be strict eucrenal species (Potamophylax pallidus Klapalek, 1899, Rhyacophila tristis Pictet, 1834, Micropterna caesareica Schmid, 1959, Wormaldia subterranea Radovanovic, 1932 and Wormaldia sp.), a few of them were only found at eucrenal sites, such as: Chaetopteryx bosniaca Marinkovic-Gospodnetic, 1959, Chaetopteryx sp. and Drusus dardanicus Ibrahimi, Kučinić & Vitecek, 2015. We have also collected larvae simultanously in order to contribute to the water quality assessment purposes. However, considering that there are many species with undescribed larval stages in the Balkans, linking larvae with adults will require additional studies, including molecular ones. In this context, this study contributes to the knowledge of possible reference sites for Ibër River Basin in Kosovo. Such findings emphasise the vulnerability of this species' group to environmental changes, underscoring the importance of rigorous conservation efforts to preserve these ecologically unique and sensitive caddisflies in the Western Balkans. In this regared, the increase of knowledge on aquatic insect taxonomy in Kosovo and Western Balkans will improve the usage of these bioindicator animals for freshwater quality assessment purposes.