First detection of Wolbachia -infected Culicoides (Diptera : Ceratopogonidae) in Europe: Wolbachia and Cardinium infection across Culicoides communities revealed in Spain

Biting midges of the genus Culicoides (Diptera: Ceratopogonidae) transmit pathogens that cause important diseases. No effective technique has been found to properly control either Culicoides spp. abundance or their likelihood to transmit pathogens. Endosymbionts, particularly Wolbachia, represent powerful alternatives to control arthropods of health interest. In arthropods, Wolbachia can reduce vector fitness and vector's pathogen transmission capacity, thus being a potential target for population reduction and replacement strategies. The presence of Wolbachia and Cardinium endosymbionts was screened in Spanish Culicoides spp. populations at livestock premises and natural habitats. The first detection of Wolbachia -infected Culicoides spp. in Europe is reported. The putative Palaearctic vectors for bluetongue and Schmallenberg diseases, C. imicola, C. obsoletus (s. s.) and C. pulicaris (s. l.), were infected with Wolbachia. Four genetic clusters of closely-related Wolbachia strains from A and B supergroups were detected infecting Culicoides. Cardinium strain of the C-group was detected in C. obsoletus (s. l.). Both endosymbionts, Wolbachia and Cardinium, were detected in Culicoides species of minor epidemiological relevance as well. Higher prevalence of Wolbachia infection was detected in natural habitats, while livestock premises lead to higher prevalence of Cardinium. Significant differences in the prevalence of Wolbachia, but not Cardinium, were also detected between some Culicoides species and between locations. The presence of Wolbachia and Cardinium endosymbionts in Culicoides is expected to trigger new research towards the control of Culicoides -transmitted diseases. The results of the present study could have an impact beyond the Culicoides arena because successful Wolbachia transfection is possible even across genus and species barriers.