830 “Bordeaux” temperature conditions (log rank: χ²= 140; Gehan–Wilcoxon: χ²= 304; both: P <0.001; Fig. 3a). Hatch- ings of 25%, 50%, and 75% of were reached, respectively, at 8, 17, and 25 days in cold winter conditions, whereas in mild winter, it took 17, 22, and 27 days. The hatching percentage peak was reached 6 days after hatching commenced for the eggs exposed to cold winter, while this peak was reached 20 days later for eggs exposed to mild winter. Despite the differences between the two Kaplan– Meier curves, the daily hatching variations over time were significantly correlated (N =50; rS= 0.44; P=0.001; Fig. 3a). The proportion of increase or decrease in number of hatchings evolved in the same way for the two conditions. The difference between the two hatching dynamics was mainly due to the difference in peak timing and affected 70% of the egg population. After the hatching peak of mild winter at 26 days, the dynamics were similar. Fig. 3 a Cumulative percentage of hatching (Kaplan–Meier; non marked lines) and dynamics of hatchings in percentage of the overall (marked lines) of egg populations subjected to a Burgundy (cold) or a Bordeaux (mild) winter. b Cumulative percentage of hatching (Kaplan–Meier) from egg populations subjected to different 5 °C durations: 0, 20, 28, 36, 49, and 65 days. The no statistical different curves (28, 36, and 49 days) were pooled into a single curve Naturwissenschaften (2009) 96:827–834 The 5 °C duration exposure clearly affected hatching dynamics (N = 6; χ² = 834.98; P < 0.001; Fig. 3b). Four statistical different classes of dynamics were obtained from the six treatments tested: class 0 day, class 20 days, class 28–36–49 days, and the class 63 days (Table 1). First day and hatching length The onset of hatching was negatively correlated to the cold time exposure (N = 8; rS= −0.97; P< 0.001), as the time for 50% of hatching (N = 8; rS =−0.87; P< 0.001). The number of days elapsed before the first hatching decreased with the exposure duration at 5 °C, with a minimum for 80 days at 5 °C. Furthermore, the earlier hatching started, the faster the 50% of hatching was reached (N = 8; rS =0.82; P< 0.001). There was no significant difference between hatching lengths whatever the cold time exposure (N = 8; rS= 0.12; P=0.286). Thus, for all the conditions, the longer the eggs were exposed to 5°C, the quicker the first 50% hatchings occurred (Fig. 3b). The last half of hatching was (1) later than the control (no exposure at 5°C) for 20 days at 5°C, (2) the same for 28–36–49 days, and (3) earlier for 63 days. So, a short exposure to 5°C was necessary to obtain differences in the beginning of hatching dynamics when a long time was necessary to affect the end of hatchings. Discussion This work demonstrates that winter temperatures modify egg hatching in S. titanus. In countries where summer conditions are adequate for the complete achievement of the life cycle, warm winters (e.g., in Greece or southern Spain) may prevent the extension of the Flavescence dorée disease possibly by an asynchrony between diapause break and grape bud bursting. The time spent by the eggs at cold temperature (i.e., ≤5°C) was negatively correlated to the time needed by an egg population to initiate hatching and to reach 50% of hatchings. Although chilling enhanced precocity and synchrony of hatchings, cold temperature did not induce a significant reduction of hatchings duration. Diapause is a dynamic state during which the physio- logical conditions (diapause depth and intensity) change and for which photoperiod and temperature constitute the major diapause-maintaining environmental factors (Tauber and Tauber 1976). Low temperature, especially during the end of diapause, may help to prevent the exhaustion of metabolic reserves before diapause ends. Except for some species, chilling hastens insect diapause termination. This is the case for the burnet moth Zygaena trifolii (Lepidoptera: Zygaenidae) in which the shorter time to hatch results from longer chilling periods (Wipking 1995). Equally, the percentage of early-emerging Delia radicum (Diptera: