832 breaking buds per vine stock, and synchrony between first and last bud to break increase with the duration of chilling in grapevines (Kliewer and Soleimani 1972). Increasing temperature causes earlier budburst in V. vinifera (Duchêne and Schneider 2005), and we show here that it may delay egg hatching. Therefore, asynchrony between egg hatching and bud burst may be associated with higher temperatures in winter and has severe consequences in larval survival (Watt and McFarlane 1991). As a comparison, the modeling of climatic warming on synchrony of Operophtera brumata (Lepidoptera: Geometridae) and Picea sitchensis (Pinales: Pinaceae) in Scotland show a time-lag of 20 ± 2.5 days when subjected to a 2°C increase in ambient temperature (Dewar and Watt 1992). With future warmer winters (Parry et al. 2007), one should expect an increase in the time required for a batch of eggs to hatch with a peak delayed, while grapevine bud burst will be advanced. This could result in a desynchronization between the host and parasite. The majority of larvae will be expected to appear on older leaves that have poorer nutritional value (Mooney and Gulmon 1982). This may lead to a general fitness decline in S. titanus populations. These differences between cold winter vineyard conditions (i.e., good synchrony between hatching and plant phenology) and mild winter vineyard conditions (i.e., bad synchrony) were observed for 7 years in Burgundy and 5 years in Côte d’Azur vineyards (Sentenac unpublished data). After an insect inoculation in a leaf, phytoplasmas move down to the roots and multiply (Boudon-Padieu 2000a). The next spring, phytoplasmas move up to developing shoots with an irregular distribution (Boudon-Padieu 2000a). It has been demonstrated that phytoplasma distri- bution gets more uniform over time (Wei et al. 2004). Therefore, the more the hatching peak is close to the bud break, the smaller the probability to meet a phytoplasma for a leafhopper is. Because of the period of latency (4 to 5 weeks) after phytoplasma acquisition before the insect becomes infective, the younger they acquire phytoplasmas, the longer they will be vectors. Males hatch before females, are more efficient at phytoplasma acquisition (Lefol et al. 1994; Beanland et al. 1999), and also move more than females (Hunt et al. 1993; Lucchi et al. 2004). Therefore, males are better vectors than females. So, even though the effect of temperature on phytoplasma multiplication in the plant has been poorly documented, the consequences of winter on hatching dynamic may greatly impact the Flavescence dorée spread. After a cold winter, grapevine bud break is delayed (Duchêne and Schneider 2005) and S. titanus hatchings are earlier. So, fewer young leafhoppers (especially males which hatch the first) will be in contact with a high occurrence of phytoplasma in the plant, conversely after a mild winter when bud break occurs sooner and hatchings later. Naturwissenschaften (2009) 96:827–834 The Flavescence dorée vector was introduced from North America to Europe in the 1950s, and the cold temperatures request for diapause control is consistent with its origin. Sufficient cooling thus regulates the diapause termination and the egg hatching. This may result in peaked egg hatching dynamics, while warm winters provoke the spreading of the hatchings over time as it may be observed in several French south east vineyards (Doncarli 1990). This requirement for cold is a likely explanation for the insect’s limited spread into Southern Europe in comparison to its spread to the East and North. If short summers are a barrier to northern progression of this leafhopper because insects have difficul- ties to achieve their complete life cycle (Boudon-Padieu 2000a), climate change with longer and hotter summers should favor the spreading of S. titanus to northern vineyard as in Germany by extending the favorable developing season (Boudon-Padieu and Maixner 2007). However, winter warming, in the Southern limit of their current distribution, may eventually lead to a decrease in insect density or extinction in certain areas such as Basilicate (South of Italy) where populations are small (Viggiani 2002). This work is a first step toward understanding the population dynamics of S. titanus and how it synchronizes with its host-plants, V. vinifera. Here, we limited our focus on the responses of the eggs to cold temperature exposure and particularly on the effects of this upon spring hatching. Our results may lead to a better understanding of the distribution spread of this invasive species and its popula- tion dynamics under different vineyard areas. Acknowledgments Mrs. E. Dion (UMR BIO3P, Univ. Rennes) is acknowledged for her experimental contribution, G. Sentenac (Institut Français du Vin, Beaune) for providing us personal unpublished observations, Dr. J. Moreau (UMR Biogéosciences, Univ. Dijon) for his contribution in statistics, P. Cartolaro (our lab) for his help in carefully surveying the microclimatic chambers functioning, and Dr. S. Ahmed (Univ. Reading) for help with the English check of our manuscript. This project and first author were supported by a Ph.D. grant from the Conseil Interprofessionnel des Vins de Bordeaux, the region Aquitaine, and the scientific Dept. INRA SPE. Conflict of interest The authors declare that they have no conflict of interest and certified that the experiments comply with the French current laws. Open Access This article is distributed under the terms of the Crea- tive Commons Attribution Noncommercial License which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited. References Beanland L, Hoy CW, Miller SA, Nault LR (1999) Leafhopper transmission of the aster yellows phytoplasma: Does sex matter? Environ Entomol 28:1101–1106