EMBRYOGENESIS OF DINOCRAS-CEPHALOTES, PERLA-GRANDIS AND PERLA-MARGINATA (PLECOPTERA, PERLIDAE) IN DIFFERENT TEMPERATURE REGIMES

1. Temperature dependence of embryogenesis of the three perlid stonefl ies Dinocras cephalots, Perla grandis and P. marginata was investigate d by means of incubation experiments. Special emphasis was laid on the effect of fluctuating temperatures and on intraspecific differences b etween populations from two different field sites in the Swiss prealps (i.e. River Necker and River Thur). 2. Dinocras cephalotes embryos de velop between 6.3 and 26.6 degrees C. The lower threshold temperature is lower than has been reported for more northern populations (i.e. fr om England and Norway), indicating the existence of a latitudinal grad ient. Perla grandis eggs only developed between 9.9 and 18.4 degrees C . In P. marginata, successful embryogenesis was observed between 9.9 a nd 18.4 degrees C, but not enough eggs were available to explore the t hreshold temperatures. 3. Embryogenesis of D. cephalotes and P. grandi s was significantly faster at a 12/16 degrees C daily fluctuating temp erature regime than at a constant 14 degrees C. However, no significan t difference was found between the development under simulated field t emperature regimes (with less distinct daily amplitudes) and constant temperatures. 4. D. cephalotes, hatching of eggs from the Necker popul ation was much less synchronous than that in the Thur population. Sinc e the Necker discharge regime is harsher than the Thur regime, it is p ossible that this asynchrony spreads the risk of destruction during be d-moving floods.