Emergence of Culicoides obsoletus group species from farm-associated habitats in Germany.

Biting midges of the genus Culicoides (Diptera: Ceratopogonidae) may transmit several arboviruses to ruminant livestock. The species of the Obsoletus group are considered to be among the most important vectors of bluetongue virus (BTV) in northern Europe. As agricultural environments offer suitable habitats for the development of their immature stages, the emergence of adult Culicoides from potential breeding sites was investigated at 20 cattle farms throughout Germany in 2012 and 2013. In analyses of species-specific habitat preferences and relationships between Culicoides abundance in breeding substrates and their physicochemical characteristics, dungheaps emerged as the most important substrate for the development of Culicoides obsoletus sensu stricto (s.s.) (Meigen), whereas Culicoides chiopterus (Meigen) and Culicoides dewulfi Goetghebuer were generally restricted to cowpats. A decreasing pH value was associated with a higher abundance or a higher probability of observing these three species. Furthermore, the abundance of C. obsoletus s.s. was positively related to increasing moisture. Dungheaps were very productive breeding sites for this species and are therefore suggested as a target for potential control measures.