The Mediterranean fruit fly, Ceratitis capitata (Wiedemann), northernmost distribution is 41⁰ north. Under cold winter conditions flies disappear as winter commence and reappear in the following summer. The tropical C. capitata is not known to possess cold tolerance. Thus, its presence in areas with subfreezing winter temperatures remains unexplained. Two questions were addressed in this study: Is there evidence for C. capitata overwintering in the mountains of Israel, and if flies do not overwinter in the mountains, then where do they come from. The study was conducted from 1996 to 2003 covering large portion of the central and southern parts of Israel. Using direct and indirect experiments and observations. No support was found for C. capitata overwintering in the central mountains. A net of trimedlure traps was deployed throughout the entire region from Tel-Aviv to Mitspe-Ramon (2000), and Tel-Aviv to Be'er-Sheva (2001). Traps were monitored on a weekly basis and data was analyzed using GIS techniques. The patterns of change in population sizes through time were consistent in both years, suggesting that C. capitata overwinters along the coastal plain and the Jordan Valley. In early summer flies invades the highlands, reproducing throughout the summer and completely disappearing as winter commence. The large distances between settlements in the south, and the lack of hosts between settlements, suggests that flies are able to migrate at least 50 km, probably over a single generation.