The genus Cricotopus v.d.Wulp (Dipt., Chironomidae) in the running waters of the Sompio area, northern Finland

<p>Emerging aquatic insects were collected using floating cage or submerged funnel traps in May - September 1959 through 1961 in the running waters of Sodankyl&auml;, northern Finland. The biotopes represented areas of rather weak current in the upper Kemijoki system. They ranged from crenal to hyporhithral. Ever since 1970 the Lokka Reservoir has inundated them. The number of individuals emerged per site ranged from 870 up to 19938 ind./m&sup2;. The variation is mainly attributable to trophic level, which ranged from oligotrophy to eutrophy. Peak emergence was observed in the vicinity of ancient abodes of the Lapps as well as more recent camps of the reindeer husbandry (Tables 8, 12).There were no evident sewage outfl ows in the area.A majority of species started to emerge when the air temperature rose to about &gt;8&ordm;C. Nevertheless, spring or other cold stenothermous species were able to pupate in temperatures lower than the ones mentioned above.In the fashion of other species they used warm air at the water surface for emergence. The peak of the emergence of insects in the Sompio area was as far as it was possible to discover during the light and warm hours of the day. The following species of Cricotopus were found in the running waters of the area: C. (Cricotopus) tibialis (Meigen) is a rather constant member of crenon and hypocrenon communities. C. (C.) cylindraceus (Kieffer), C. (C.) festivellus (Kieffer). C. (Isocladius) intersectus Fabricius, C. (I.) pilitarsis Edwards, C. (C.) polaris Kieffer, C. (I.) reversus Hirvenoja and C. (I.) sylvestris Fabricius, all of which inhabit the nearby lakes, were accidentally found in very low numbers as xenocoen species from hypocrenal to hyporhithral sites. C.(C.) claripes Hirvenoja (cf. the text) and C. (C.) septentrionalis Hirvenoja were found only under metarhithral conditions. The following species, some of which are rheophilous, emerged from variable meta- or hyporhithral sites: C. (C.) albiforceps (Kieffer), C. (C.) annulator Goetghebuer, C. (C.) bicinctus (Meigen), C. (I.) suspiciosus Hirvenoja, C. (C.) triannulatus (Fabricius) and C. (C.) tristis Hirvenoja. Species found only in the lakes of the study area were C. (C.) pilidorsum Hirvenoja, C. (C.) magus Hirvenoja, C. (C.) coronatus Hirvenoja, C. (C.) patens Hirvenoja, C. (I.) tricinctus (Meigen), C. (I.) arcuatus Hirvenoja, C. (I.) obnixus (Walker). The production, saprobity and phenology are discussed. A majority of the species of the genus Cricotopus belong to the fauna of &ldquo;sound&rdquo; aquatic habitats.</p>