After 5 blank years since the last symposium and 3 years of COVID-19 pandemics, the 21st International Symposium on Chironomidae (ISC2022) was held for the first time online from the 4th to the 7th of July, 2022. The symposium gathered a total of 45 presentations organized around the major topics of ecology, taxonomy, genomics, phylogeny, and physiology. We introduce here a general overview of the studies presented during the symposium, together with the few papers published in the present proceedings special issue.

The mature and immature stages of Clunio ponticus Michailova, 1980 are diagnosed and described based on associated material recently collected in the marine littoral zone of Varna, St-Konstantin and Helena Resorts, Black Sea (eastern Bulgaria). Male and female adults, pupae and larvae of C. ponticus can be easily distinguished from other known European Clunio species on the basis of some atypical features found in the male and female adults, pupal exuviae and fourth instar larvae. In addition, the biological cycle (reproduction and emergence) of C. ponticus is not synchronized with lunar periodicity (new and full moon) as for some other known Clunio species from Europe, but closely related to the typology of the intertidal zone along the coastline of the Black Sea. This indicates that this species is a local biogeographic representative of the ‘Pontus Region’, which includes the eastern coastline of the Black Sea. Remarks on related known Clunio species from Europe with comments on the ecology and geographical distribution of C. ponticus are given.

Four new species of the genus Chaetocladius s. str. (C. berythensis sp. n., C. callauensis sp. n., C. guardiolei sp. n. and C. parerai sp. n.) are diagnosed and described based on material collected in some glacial springs and small streams located at high altitude (1800-2300 m). While C. berythensis sp. n. is described only as male adult from the upper basin of the Beirut River (Lebanon Mount, Western range, Mount Sannine), C. callauensis sp. n. C. guardiolei sp. n. and C. parerai sp. n. are described as male adult accompanied by descriptions of tentatively associated male pupal exuviae from the upper basin of the Mantet River and Soques stream (eastern Pyrenees, West France). Additional taxonomic notes including illustrations and brief descriptions of 10 taxa/species based on male adults, male pharate adults and pupal exuviae collected in glacial springs, peat bogs and streams located at high altitude are provided. On the basis of characters in the male adult, only C. berythensis sp. n. keys to the laminatus-group, which is reported for the first time from the Levantine sub-region. Based on the unusual shape of both inferior volsella and gonostylus, the four new Chaetocladius species each belong to local biogeographic elements: C. berythensis sp. n. to a ‘Levantine element’, while C. callauensis sp. n., C. guardiolei sp. n. and C. parerai sp. n. belong to a ‘Pyrenean element’. All of the four new species are considered to be relict representatives of glacial helocrenes and cold stenothermic streams. Such species may be biological indicators and biogeographic representatives of global warming and local climate change.

Associated Procladius Skuse (Holotanypus Roback) material from the Sublette collection was found to have specimens with undescribed immature stages. Pupal exuviae of two species are described for the first time: P. barbatulus Sublette and P. clavus Roback. Adult and larval features are included for P. barbatulus. In addition, specimens of Nearctic P. denticulatus Sublette are compared to Palearctic P. signatus (Zetterstedt) to determine if exuviae can separate these species or suggest that P. signatus is a senior synonym. Finally, associated pupal and larval traits of P. prolongatus Roback are compared to the original description, corroborating the theory that features are unique enough to warrant subgeneric status.

This paper presents the karyotype and external morphology of larva, pupa and adult male of Stictochironomus sticticus (Fabricius, 1781) from Poland. The species of the genus Stictochironomus are generally identified on the basis of pupal and adult morphology. However, the species described in this paper has species-specific markers in the salivary gland chromosomes which allow identification at the larval stage. Karyological markers are evaluated for the Polish population in comparison with other European populations and Stictochironomus species.

Online early -only onlineThis issue (Number 28) of the CHIRONOMUS Journal of Chironomidae Research includes three research papers and six short communications.The number of contributions is lower than what we have had in a while, and we have therefore considered which actions to take to make the journal a more attractive publication channel for the Chironomidae research community.In a world in which the number of online, open access journals is rapidly increasing and the turn-around time between manuscript submission and publication is rapidly decreasing, the competition between small journals is tough.A periodical like CHIRONO-MUS, in which a submission in January cannot be expected to be published before December, is of course less appealing than one with frequent publication dates.

A pupal exuviae of a non-biting midge (Chironomidae) is recorded in Eocene Rovno amber from Ukraine. The exuviae belongs to an Orthocladiinae species. It possesses several traits characteristic for terrestrial species including non-fringed anal lobes without macrosetae, tergites with only minute shagreen, bare conjunctives, and absence of thoracic horns and frontal warts. Up to now, this is the earliest record of a preimaginal stage of Orthocladiinae, and the only record of a chironomidae pupal exuviae from amber.

The species composition of the Chironomidae fauna in the Czech Republic is still poorly known despite a long tradition in Chironomidae research, already established by Prof. Jan Zavřel in the beginning of the 20th century. The major reasons are a low number of researchers dealing with Chironomidae in the Czech Republic and their traditional focus on larvae, which usually cannot be identified to species. As a result, only a small portion of the chironomid fauna living in the Czech Republic has been discovered so far and many chironomid species are first to be recorded in the future. This concerns both (common) species that are already known from Slovakia and other neighbouring countries, and species living in poorly studied habitats, such as montane springs or bogs.

The spatial distribution of chironomid communities in the littoral zone (0-20 m) of the western coast of the southern Baikal basin is investigated. The fauna is composed of 16 species and forms of chironomid larvae, comprising 10 communities. It has been found that the communities are characterized by rather poor species diversity; Shannon’s index varies from 0.7 to 2.1 bit. Their distribution is affected by hydro-lithodynamic conditions, type of bottom sediments and macrophyte development. The peak of maximal biomass of chironomid larvae on the facies of non-rounded rock debris near Berezovy Cape is recorded in spring.

Three new pupal types from Norway are described, one with an associated male: Pseudosmittia parspinispinata n.sp.

The paper describes larval, pupal and adult morphology as well as the karyotype of Chironomus polonicus sp. n. from southern Poland. The material has been obtained from reared egg masses collected in Bolesław pool, near Kraków. The species belongs to the pseudothummi cytocomplex with 2n = 8 and chromosome arm combinations AE, BF, CD, G. Several homozygous inversions distinguish arm A of the new species from that of C. pseudothummi Strenzke. Arm F is similar to that of C. aprilinus Meigen and differs from it by few steps of homozygous inversions. Few morphological differences in the pupa and adult are also presented.

Diagnoses and descriptions of the adults and pupal exuviae of Stygocladius multisetosus gen. nov., sp. nov., are provided based primarily on male and female pharates collected in temporary basaltic and karstic helocrenes in southern France and Algeria. Features on the adult male, female and pupa indicates that it belongs to the Heterotrissocladius group of genera and is probably most closely related to Paratrissocladius Zavřel. The immature stages of the new species are stygobiontic. doi: 10.5324/fn.v31i0.1363. Published online: 17 October 2012.

The pupa and imago of Chironomus acerbiphilus (a senior synonym of C. crassimanus) show wide variation of external morphology characters. This paper describes the external morphology of larva, pupa and adult of C. acerbiphilus from Poland. Variability of morphological characters is evaluated for the Polish population hi comparison with other European, Asian and North American populations. Pupal subgeneric characters are discussed.

The description of Rheotanytarsus dactylophoreus sp. nov. is based on adult males, pharate males and pupal exuviae collected in low and middle mountain streams located in the Eastern Pyrenees and Corsica is presented. The most distinctive character in the adult male is the unusually long, finger-like, digitus and in the pupal exuviae is the thoracic horn which is spinulate laterally (extending from swollen base into tapered apical half). The distribution of R. dactylophoreus sp. nov. indicates that this pyreneocorsican species is a Tyrrhenian faunal element which spread westwards to mountain streams of the Eastern Pyrenees perhaps during the repeated waves of migration from the Paleocene (Montian) till the late Miocene.doi: 10.5324/fn.v31i0.1375.Published online: 17 October 2012.

Three new species of Paratanytarsus are described, from Corsica, southern France and Lebanon, based on the adult males and associated pupal exuviae. These descriptions increase the number of western Palaearctic species in the genus to 23. The pupal exuviae of the new species resemble those of P. bituberculatus (Edwards). Main diagnostic characters as well as additional illustrations of P. bituberculatus are also presented. Characters are given for distinguishing the adult males and the pupal exuviae from other related species. A key to the adult males and pupal exuviae of the described species is provided.doi: 10.5324/fn.v31i0.1372.Published online: 17 October 2012.

Une récapitulation de la bibliographie à l''échelle de l''ensemble du territoire marocain des données faunistiques relatives aux espèces de Chironomidés (Diptera) depuis 1977 est présentée dans ce travail. Un total de 388 taxa est répertorié actuellement à l''échelle du Maroc. Ce total regroupe sept sous-familles, à distribution très hétérogène entre les différentes régions. Une répartition des différents taxa recensés grâce à un découpage géographique du Maroc est fournie également.

Psectrocladius (P.) sensilipes sp. n., P. (P.) subsensilis sp. n. and P. (P.) dubius keoweensis subsp. n. are described in all stages and both sexes; P. (P.) dubius dubius sp. n. described as male, pupa and larva; and the male of Nearctic P. (P.) limbatellus (Holmgren) described. Preliminary keys to males, females, pupae and larvae of the Psectrocladius limbatellus group are given.

New data on the Chironomidae (Diptera) of the Rif (Northern Morocco) New collections of pupal exuviae of chironomids in various fresh water ecosystems in the Rif in the north of Morocco revealed an interesting inventory. The chironomid community collected is diverse enough and interesting, and rare species are present. Of a total of 141 identified taxa, 46 species have proved to be new for the Rif and 31 for Morocco. The chorological tendency is mainly Palaearctic and Mediterranean. The majority of the sites investigated belong to protected areas in the north of Morocco, such as SIBE Jbel Moussa, SIBE Jbel Tidirrhine, SIBE Jbel Bouhachem and Talassemtane National Park, which belong to the Intercontinental Reserve of the Mediterranean Biosphere.