Oral susceptibility to bluetongue virus of Culicoides (Diptera: Ceratopogonidae) from the United Kingdom.

Oral susceptibility to infection with bluetongue virus (family Resviridae, genus Orbivirus, BTV) serotype 9 was characterized in three Palaearctic species of Culicoides (Diptera: Ceratopogonidae). Variation in susceptibility to infection by using a recently described feeding technique was shown to occur between populations of Culicoides obsoletus Meigen complex midges from different geographic regions of the United Kingdom with virus infection rates varying from 0.4 to 7.4% of those tested. Susceptibility to infection was consistent on an annual basis at selected sites. Prevalence of infection in the most susceptible populations of both the C. obsoletus and Culicoides pulicaris L. complexes was comparable with that of Culicoides imicola Kieffer, the major vector of BTV in southern Europe and throughout Africa, when using the same feeding method and virus. These results are discussed with reference to the potential threat of the virus to susceptible livestock in northern Europe.