Effect of temperature on larval growth of Ecdyonurus dispar (Ephemeroptera: Heptageniidae) from two English lakes

Mature larvae of Ecdyonurus dispar were collected from Ennerdale Water and Windermere (English Lake District) and reared to adult males and females in the laboratory. The females were then fertilized artificially and their progeny were kept at constant temperatures (range 4.2–20.2°C). Larvae collected directly from the two lakes were also reared under the same conditions. The maximum number of instars from egg to subimago was 25, the average body length increment (mm) per moult was proportionately constant at c. 15% and Dyar's rule was applicable. The interval between moults decreased with increasing temperature and the relationship between the two variables within the temperature range 4.2–19.8°C was described by a power law. Larval growth was exponential and variations in mean specific growth rate (range 0.23–5.23% length day−1) were related to mean temperature which was the major factor affecting growth in the laboratory. A few experiments were also performed in the lake to test the adequacy of the estimated values for larval growth at different temperatures in the laboratory. There was agreement between the estimates and the actual growth rates in the lake. Therefore, the regression equations obtained from the laboratory experiments are probably applicable to larval growth in the field. Values for daily production in the laboratory ranged from 0.53 to 9.33 mg dry wt day−1 m−2. The lowest value was obtained at 8.9°C and the highest at 20°C. Information on different life cycles of E. dispar is briefly reviewed and it is concluded that E. dispar from the lakes can only achieve one generation per year.