Evidence of new chironomid taxa (Diptera, Chironomidae) for Croatia from a mountain stream in the Pannonian Plain

According to the first Croatian check-list (Čerba et al. 2020), a total of 239 Chironomidae species has so far been recorded from the country. In the present paper we report the finding of two new taxa from the mountain stream Šumetlica, eastern Croatia, namely Boreoheptagyia legeri (Goetghebuer, 1933) and Diamesa cf. insignipes Kieffer, 1908. Šumetlica in the Psunj Mountain is about a 27 km long stream that rises near the highest mountain peak in this area, Brezovo Polje. Macroinvertebrate samples were collected at 415 m a.s.l. in June 2020 and May 2021 according to the AQEM standard multi-habitat protocol. Physico-chemical water parameters were measured in situ. Isolation and identification of macroinvertebrates were carried out in the laboratory. A total of 79 macroinvertebrate taxa were recorded, of which 26 were Chironomidae. The most abundant Chironomidae taxa were, Tvetenia calvescens, Conchapelopia agg. and Brillia bifida in the first sampling period, and Polypedilum convictum in the second. The species Boreoheptagyia legeri was collected with the abundance of 24 individuals per m2 in 2020, while 30 individuals per m2 Diamesa cf. insignipes larvae was recorded in 2021. Representatives of Diamesinae subfamily are usually found in cool, oxygen rich mountain or glacial streams. Diamesa larvae inhabit springs and streams in the mountain region, mainly on stones and gravel, especially those covered with moss cushions, while species of the genus Boreoheptagyia prefer a constant trickle of water. Both inhabit higher elevation mountainous regions, but occasionally Diamesa species are found in the foothills. Boreoheptagyia legeri is the only species of the genus that has been recorded outside the highest mountainous regions, in temperate elevations, under 500 m a.s.l. Our findings contribute to the knowledge of ecology and distribution of Diamesinae representatives.