PLECOPTERAN COMMUNITIES AND ANNUAL EMERGENCE IN 5 FOREST STREAMS AND 2 LAKE OUTLET STREAMS OF CENTRAL FINLAND

The plecopteran fauna was studied by means of slit traps and hand net during the summers of 1982-1987. A total of 19 plecopteran species com prising c. 4 500 adults and c. 2 900 larvae were sampled in streams. O f these, Capnia atra, Capnopsis schilleri, Nemurella pictetii and Isop erla difformis were recorded for the first time in the streams of the province Pohjois-Hame (Tb). The plecopteran fauna was richest in the s mall forest streams and relatively poor in the largest outlet. Both, t he character of the stream bed and the quantity and quality of food av ailable seemed to be the most important factors affecting the occurren ce of the plecopteran species. In the brooks the emergence of stonefli es had two clear maxima: one in spring and another in late autumn. Ver nal species were Taeniopteryx nebulosa, Isoperla difformis, Nemoura av icularis, N. flexuosa and Leuctra hippopus. Dominant species in the au tumnal cathes were Leuctra fusca and Leuctra digitata. In the outlet s treams the succession of emergence was somewhat different owing to the weak emergency and due to the cold summer with strong floods in 1987. The slit trap method worked well in the catching of stoneflies except during the snow melting seasons and the flood periods.