Entry of bluetongue vector Culicoides imicola into livestock premises in Spain

Culicoides imicola Kieffer is considered to be the main vector of bluetongue disease (BT) and African horse sickness (AHS) in the Mediterranean basin. It has been assumed that this midge species is exophilic and, consequently, that stabling of livestock should provide effective protection against these diseases. This study presents the results of sampling surveys for C. imicola carried out both inside and outside stables on three farms in mainland Spain. The number of C. imicola captured varied as a function of the populations sampled and trap location (inside vs. outside). The daily mean number captured inside during the sampling of each farm population was directly correlated with the daily mean number captured outside, but daily correlation of captures was not observed. By contrast with previous studies, the mean catch of C. imicola inside was consistently higher than that outside. No clear effect of stable characteristics on the degree of entry was detected. In addition, proportions of males and age-graded female groups varied among populations and with trap location. Proportionately more males and fewer engorged females were captured outside than inside, although the proportions varied among stables. These results contrast with those of previous studies, and with the assumed pronounced exophilic behaviour of C. imicola, and raise important questions about the vector activity of this species in the study area and its implications for the epidemiology of BT and/or AHS.