Naturwissenschaften (2009) 96:827–834 DOI 10.1007/s00114-009-0541-x ORIGINAL PAPER Cold winter temperatures condition the egg-hatching dynamics of a grape disease vector Julien Chuche & Denis Thiéry Received: 20 October 2008 / Revised: 10 April 2009 / Accepted: 10 April 2009 / Published online: 29 April 2009 # The Author(s) 2009. This article is published with open access at Springerlink.com Abstract The leafhopper Scaphoideus titanus is the vector of a major phytoplasma grapevine disease, Flavescence dorée. The vector’s distribution is in Eastern and Northern Europe, and its population dynamics varies as a function of vineyard latitude. We tested the hypothesis that hatching dynamics are cued by cold temperatures observed in winter. We exposed eggs from a natural population to simulated “cold” and “mild” winters and varied the exposure time at 5 °C from 0 to 63 days. We show that temperature cooling mainly affected the onset of hatching and is negatively correlated to the cold time exposure. The majority of hatchings occurred more quickly in cold rather than in mild winter simulated conditions, but there was no significant difference between the duration of hatching of eggs whatever the cold time exposure. In agreement with the Northern American origin of the vector, the diapause termination and thus the timing regulation of egg hatching require cold winters. Keywords Diapause . Flavescence dorée . Leafhoppers . Risk-spreading strategies . Invasive species . Scaphoideus titanus Introduction Growing international trade may increase the incidence of alien species and could lead to crop injuries and important environmental and/or economic problems (Pimentel et al. J. Chuche : D. Thiéry (*) UMR INRA 1065 en Santé Végétale, INRA, BP 81, Institut Supérieur de la Vigne et du Vin, IFR 103, 33883 Villenave d’Ornon Cedex, France e-mail: thiery@bordeaux.inra.fr 2005; Meyerson and Mooney 2007). A major factor for geographical extension or shift of nonindigenous species is the occurrence and availability of suitable food resources. When food is not available throughout the year, the synchrony of larval stages with food availability is often the critical step for phytophagous insects (Van Asch and Visser 2007). For many species living in temperate environments, one way to escape an adverse season like winter is entering diapause (Tauber and Tauber 1976). Fitness is thus often conditioned to this survival strategy (Kroon and Veenendaal 1998; Ellers and van Alphen 2002; Wang et al. 2006), which is a key factor for synchrony with food resources. Larvae that emerge when food availability is not optimal for their development must disperse to more suitable habitats and will thus often pay fitness costs (Van Asch and Visser 2007). On the contrary, those emerging from diapause when the host plant is suitable for their development should increase their fitness (Dixon 1976; Watt and McFarlane 1991; Yukawa 2000). Diapause is genetically controlled and regulated by environmental factors such as photoperiod and temperature (Tauber and Tauber 1976; Denlinger 2002). However, diapause entry or termination is subjected to polymorphism, which is supposed to allow risk-spreading strategies (Menu and Desouhant 2002). The effect of chilling on the end of diapause and its consequences on insect emergence is well known in orders as diverse as Orthoptera (Higaki and Ando 2002), Diptera (Collier and Finch 1983), or Lepidoptera (Wipking 1995). Better understanding of this species’ life history traits and behavior will aid our understanding of its geographical range, and this in turn will improve one’s ability to forecast the occurrence of this disease. However, if environmental conditions are major factors in the establishment and the spread of an exotic species and act to determine its invasive potential, biotic (e.g., food, predation, parasitism) and abiotic