Eight years of entomological surveillance in Italy show no evidence of Culicoides imicola geographical range expansion.
Abstract
Assessing changes in species range is based on identifying new occurrences in areas where absence has been inferred due to lack of previous records. This technique depends on creating a consistent observational dataset, based on comparable detection methods. In Mediterranean countries, the midge Culicoides imicola is the principal vector of bluetongue virus (BTV) that causes an infectious disease of domestic and wild ruminants. Over the last 10 years, BTV has invaded Mediterranean countries (1998) and much of Northern Europe (2006); this unprecedented spread is reported to be a possible consequence of climate change. In southern Europe, based on recent observations found in northern latitudes, BTV spread has been attributed in part to changes in C. imicola distribution. However, current sampling of Culicoides spp. is far more intensive and targeted than that undertaken before the first BTV epidemics; this obviously results in new information from areas in which collections would have had little chance of positive identification in the past. Since 2001, a national surveillance programme based on permanent traps was established in Italy to follow C. imicola population dynamics in space and time. Based on data from 2000 to 2001 cross-sectional studies, Italy was divided into three zones (I: endemicity; II: transition; III: absence) in which longitudinal data on C. imicola presence and abundance were analysed as a function of time between 2002 and 2007 through linear and quantile regressions. The results from the surveillance programme demonstrate no detectable range expansion of the C. imicola population in Italy between 2002 and 2007. Synthesis and applications. This study provides strong evidence that there has been no measurable range expansion between 2002 and 2007 in a species previously described as moving northwards as a result of climate change. For any reliable conclusions to be drawn on the range distribution of C. imicola or other similar vector species in Southern Europe, the Culicoides surveillance system across all European countries should be designed to provide comparable data based on a constant detection probability over time.