Fig. 5. Relationship between the duration of the exposure to –15°C and the concentrations of sodium and potassium ions in haemolymph in the adults of Pyrrhocoris apterus belonging to the acclimation group SDA (see Fig. 1). Each data point represents mean ± S.E.M. of 10 samples of haemolymph taken from individual insects. The probabilities that slopes of linear regressions deviate from zero were: K⁺, P<0.001; Na⁺, P=0.013. The solid arrow shows time necessary to kill 50% individuals of the population sample (Lt50). For comparison, the Lt50 (broken arrow) and linear regressions (broken lines) of the haemolymph concentrations of the two ions in the acclimation group LD exposed to –5°C are shown (redrawn from Fig. 4A,C).