The use of path analysis to determine effects of environmental factors on the adult seasonality ofCulicoides(Diptera: Ceratopogonidae) vector species in Spain

Abstract

AbstractCulicoidesbiting midges (Diptera: Ceratopogonidae) are the main vectors of livestock diseases such as bluetongue (BT) which mainly affect sheep and cattle. In Spain, bluetongue virus (BTV) is transmitted by severalCulicoidestaxa, includingCulicoides imicola, Obsoletus complex,Culicoides newsteadiandCulicoides pulicaristhat vary in seasonality and distribution, affecting the distribution and dynamics of BT outbreaks. Path analysis is useful for separating direct and indirect, biotic and abiotic determinants of species' population performance and is ideal for understanding the sensitivity of adultCulicoidesdynamics to multiple environmental drivers. Start, end of season and length of overwintering of adultCulicoideswere analysed across 329 sites in Spain sampled from 2005 to 2010 during the National Entomosurveillance Program for BTV with path analysis, to determine the direct and indirect effects of land use, climate and host factor variables.Culicoidestaxa had species-specific responses to environmental variables. While the seasonality of adultC. imicolawas strongly affected by topography, temperature, cover of agro-forestry and sclerophyllous vegetation, rainfall, livestock density, photoperiod in autumn and the abundance ofCulicoidesfemales, Obsoletus complex species seasonality was affected by land-use variables such as cover of natural grassland and broad-leaved forest.Culicoidesfemale abundance was the most explanatory variable for the seasonality ofC. newsteadi, whileC. pulicarisshowed that temperature during winter and the photoperiod in November had a strong effect on the start of the season and the length of overwinter period of this species. These results indicate that the seasonal vector-free period (SVFP) in Spain will vary between competent vector taxa and geographic locations, dependent on the different responses of each taxa to environmental conditions.