Occurrence of biting midges (Culicoides spp.) at three different altitudes in an alpine region of Switzerland

The aim of this field study was to investigate the occurrence of biting midges (Culicoides spp.), the potential vectors of the bluetongue virus (BTV), in an alpine region of Switzerland (Vals/GR) at altitudes between 1300 and 2000 meters above sea level (m a.s.l.). For this purpose, insects were caught with UV-light traps once weekly from the end of June to the end of October 2008. Midges were found on all altitudes investigated, but distinct differences in the abundance at different stations were noticed. Most midges were caught at the intermediate station (about 1500 m a.s.l.) whereas the catches on the two alps (approximately 2000 m a.s.l.) varied considerably. The predominance of midges belonging to the Pulicaris complex, whose vector competence regarding bluetongue virus (BTV) is largely unknown, rose with increasing altitude. To identify potential breeding habitats, 17 soil samples of three farms were incubated in the laboratory. Different insects emerged but none of them was a Culicoides spp. and, therefore, the habitats of juvenile stages remain unknown. From our results we can conclude that most likely there are no midges-free zones in all of the agriculturally utilized areas (including the alpine summer pastures) of Switzerland. This strongly indicates that cattle, sheep, goats and camelids which are permanently or temporarily kept in regions of higher altitude in Switzerland should be vaccinated against bluetongue.