Hatching time and growth of Nemurellapictetii (Plecoptera: Nemouridae) in the laboratory and a Lake District stream

SUMMARY. 1. Nemurella pictetii Klapæplek took 2 years to complete its life cycle in both the laboratory and a small stream in the English Lake District. 2. Hatching time (days after oviposition for 10%. 50% and 90% of the eggs to hatch) and hatching period (days between dates for 10% and 90% hatched) decreased with increasing water temperature in the laboratory, and the relationships were well described by a power‐law. Estimates of the mean time for 50% hatching in the stream varied between 16 and 31 days after oviposition. depending on temperature. 3. Larval instars numbered fifteen for males and seventeen for females with a constant ratio of 1.18 between successive instars (conformed with Dyar's rule). Larval growth was exponential at four constant temperatures in the laboratory; mean instantaneous growth rates were 0.40±0.01% day−1 at 5.9°C, 0.43±0.01% day−1 at 8.2°C, 0.46±0.01% day−1 at 12. 1°C. 0.56±0.02%day−1 at 19.8°C. No larvae survived after instar XI at 19.8°C. 4. Larval growth was exponential in the stream and was scarcely affected by variations in water temperature (range 4.2 ‐14.0°C); mean growth rates for three year‐classes were 0.41±0.02, 0.43±0.08, 0.54±0.05% day−1. Their similarity to laboratory growth rates under optimum conditions suggests that the availability of resources, such as food and space, was not restricting growth in the stream.