Adaptations and Resistance to Anoxia in Cloeon dipterum (Ephemeroptera) and Nemoura cinerea (Plecoptera)

The survival of larvae of Cleon dipterum L. (Ephemeroptera) and Nemoura cinerea (Retzius) (Plecoptera) was studied after exposure to anoxia for 40 h at temperatures between 0?C and 11.5?C. If the larvae were acclimated to 2?C for 6 wk C. dipterum survived temperatures close to 0?C better than N. cinerea. If they were acclimated to 10?C, most C. dipterum died at all experimental temperatures. N. cinerea died to 60 % at 5?C; at higher or lower temperatures the mortality increased. A 6-d stay in 2?C of C. dipterum previously acclimated to 10?C was not long enough to induce resistance to anoxia. When exposed to anoxia N. cinerea became unconscious within 10 min, whereas larvae of C. dipterum did so first within 60 min. It is concluded that a long term acclimation to low temperatures induces in C. dipterum but not in N. cinerea a high degree of resistance to anoxia at temperatures close to 09C. This resistance is of great importance for C. dipterum since in cold temperated regions this species usually overwinters in anoxic conditions. The different rate at which the species lose consciousness in anoxia may be important for their survival in natural habitats.