Systematics and Ecology of Chironomidae (Diptera) Associated with Tobin Lake Reservoir and the Saskatchewan River

Abstract

One hundred and thirty-one species belonging to 56 genera of the family Chironomidae are recorded from the Saskatchewan River and Tobin Lake , a hydroeIectric impoundment on the lower reaches of the river. The larva and pupa for each species are described and keys for identification are presented. Seventy-three species were assigned existing names. Paratanytarsus confusus Palmen, P. laccoph i Ius (Edwards), Cricotopus curtis Hirvenoja and Orthocladius rivicola Kieffer are recorded from North America for the first time. The following information is presented for each species: original literature reference, description of pupa and larva, remarks, biological notes and distribution. Illustrations of important taxonomic characters are presented. Examination of available information suggests that the post-glacial origin of the Saskatchewan River Chironomidae was primarily from refugia south of the Wisconsin ice sheets. A few species such as Synorthocladius semivirens may have originated from Beringia. Analysis of the Saskatchewan River chironomid fauna in the vicinity of the Squaw Rapids Hydroelectric Development showed that this family represented more than 2/3 of the aquatic insect species. Comparison of the upstream and downstream fauna showed distinct differences in the chironomid community. Downstream, some upstream species were eliminated and replaced by others, some species became less abundant, others became more abundant and still others remained unchanged. A number of environmental parameters appear to influence the chironomid community. An altered thermal pattern caused delay in the onset of spring emergence of most species examined.