Life Cycles of Benthic Insects in Lapland Streams (Ephemeroptera, Plecoptera, Trichoptera, Diptera Simuliidae)

A large material of larvae and nymphs of Ephemeroptera, Plecoptera, Trichoptera and Diptera Simuliidae from lotic biotopes in Lapland streams was used for an analysis of life cycle patterns. Flight-periods were determined from collection of winged insects. Although each species had its own distinctive life cycle, certain patterns prevailed and could be classified in several phenological types. The study area was situated on the border between the high boreal and subalpine zones and had an accordingly severe climate with a long period of ice-cover. However, life cycle patterns were not consistently different from those of the same or related species in regions with a milder climate. The life cycles of some species varied from place to place. Some such differences are probably explicable in terms of local temperature differences. The life cycles of some species varied from year to year. Within the same species, some individuals took one year, others two years before reaching emergence.