Life cycle of Isoperla lata (Plecoptera: Perlodidae) in a Central Wisconsin trout stream

Abstract

Monthly qualitative samples of Isoperla lata Frison were made from January 1992 to June 1993 in Ripley Creek, a small second order trout stream in Lincoln County Wisconsin. Additional collecting and an in-stream hatching experiment were conducted in 1994. This species exhibited an S1 (slow) univoltine life cycle. Emergence was synchronous and occurred in late April through early May when stream temperatures in the field were approximately 9-14°C and laboratory stream temperatures were 7-17°C. Laboratory longevity was 2-25 (χ = 18.2 ± 4.51) days for males and 739 (χ = 21.7 5.35) days for females. Mean fecundity of dissected females was 322 ± 122 eggs/female. Females did not deposit egg masses in the laboratory until Field-collected females did not have eggs. The egg shape was ovoid and circular in cross section. Mature eggs were light brown and measured 371.7 ± 12.6 Trim and 260.7 ± 10.2 mm in length and width respectively. Eggs required a 40-46 day in-stream incubation period and first instar nymphs hatched synchronously over a two day period when stream temperature reached 20°C. Nymphal growth was nearly exponential from June to January and then declined until emergence. The greatest growth increment occurred between June and October and the average maximum size attained occur in February. Males and females had approximately 18 and 19 instars respectively. Nymphs were primarily carnivorous throughout development and fed on larval Chironomidae, Ephemeroptera, and Plecoptera.