Ten F1Aedes albopictus samples collected from Réunion Island in the Indian Ocean were tested for oral susceptibility to dengue 2 virus and 20 were analysed for genetic polymorphism by starch gel electrophoresis. Data from infection rates defined two distinct geographical areas: east coast vs. west coast. Genetic differentiation was found to be dependent on ecological factors and the biological characteristics of Ae. albopictus. These results have implications for the vector ecology and pattern of migration, and have importance in the understanding of dengue transmission.