Emergence of Blue Tongue in the Mediterranean Basin and Entomological Surveillance in France

Bluetongue (BT) is an arboviral disease transmitted by biting midges (Diptera: Ceratopogonidae), which emerged in the Mediterranean in 1998 as a result of the northern spread of its main vector Culicoides imicola Kieffer 1913. In France, C. imicola was detected in the south of Corsica Island in October 2000, a few days before BT serotype 2 outbreaks. An entomological surveillance network was established in 2002 (i) in Corsica, to study the population dynamics of C. imicola and other Culicoides species associated with livestock, and (ii) on the mainland, to detect the introduction of C. imicola. Night catches were performed every three weeks on 12 sites in Corsica and monthly on 19 sites on the mainland. In 2002 in Corsica, a total of 180 night catches were performed. On average C. imicola accounted for 18% of the specimens collected and prevailed in the south of the island. Adult densities reached a peak in September. C. imicola was present on all the sites during eight months, confirming that BT main vector overwinters and is now well established on the island. Moreover, in 2003, C. imicola populations increased in the North, particularly in Balagne region. The risk of invasion in the mainland was then more significant. On the mainland, out of 233 night catches (2002-2003), two specimens of C. imicola were found in 2003 at two different sites. After extensive investigations the hypothesis of the installation of C. imicola was ruled out. The geographical and seasonal distribution of C. imicola and other species are discussed in relation with their bioecology and environmental factors. Entomological surveillance appears essential to better understand BT epidemiology, and to develop and validate predictive models of risk areas