Emergence of Stoneflies (Plecoptera) from South Duck River and Cowan Creek in the Duck Mountain Region, Manitoba

Abstract

Eight species of Plecoptera were collected in emergence traps located along two streams in the Duck Mountain region of W-central Manitoba. Imagines were collected throughout the mid-May to mid-September 1980 sampling period with most emergence occurring in spring and autumn. Over 95% of the emergence consisted of Hastaperla brevis and Malenka californica. Peak emergence of H. brevis occurred in late spring. Malenka californica had two different emergence patterns; at two stations, one in each stream, emergence began in midto late June and continued, intermittently, to the end of the sampling period with lowest emergence occurring during July and August. At all other stations, emergence was mainly restricted to late August and September. Sex ratios in each species were either approximately equal or there were generally more or only females collected. In species where large numbers of animals emerged, emergence of sexes overlapped. These are the first records of M. californica and Suwallia pallidula for the Province of Manitoba. INTRODUCTION Studies of insect emergence are valuable in providing information on diversity and seasonal occurrence of aquatic insects. Systematic studies of seasonal emergence of Plecoptera in Canada have been conducted in Quebec (Harper and Magnin, 1969; Harper and Pilon, 1970), Ontario (Sprules, 1947; Harper, 1973a, b; Harper and Hynes, 1972), Saskatchewan (Dosdall and Lehmkuhl, 1979) and Alberta (Radford and Hartland-Rowe, 1971; Donald and Anderson, 1977). No emergence studies of Plecoptera in Manitoba have been published. This paper describes an investigation of species composition, emergence periods, spatial distribution and abundance of adult Plecoptera, based on emergence data obtained over most of the open-water season, from two small, permanent streams in the Duck Mountain Region of W-central Manitoba. METHODS South Duck River (SD) and Cowan Creek (C), originate on the Manitoba Escarpment and flow into Lake Winnipegosis. The streams are spring-fed and are ice-covered in winter. Emergence trap stations were located on the Manitoba Escarpment (52048'N, 100040'W). Stations SD1, C1, C2 and C3 were located in areas with mixed forest (spruce, aspen, birch); the remaining stations were surrounded by forested and agricultural lands. Stream habitats ranged from fast-flowing riffle areas to siltbottomed pools. General features, including substrate types, of areas where emergence trap stations were located are listed in Table 1. Two 1 m2 emergence traps (Flannagan, 1978) were set at each station except at C4 where there was only one. One trap at each station was located over a riffle and the other over a pool, except at SD3 which had no pool areas and where both traps were located over riffle areas. Each trap was cleared every 2nd day and specimens were preserved in 70% alcohol. Sampling began 11 May 1980 and continued until 19 September 1980, except for Cl and C2 where sampling began on 21 May 1980. The