Deep litter as a production substrate of Culicoides biting midges (Diptera: Ceratopogonidae)

Culicoides biting midges are the putative vectors of several arboviruses. Livestock farms are considered to provide suitable breeding sites for Culicoides spp. development, but detailed knowledge is missing. Therefore, Culicoides specimens were trapped with emergence traps placed on deep litter substrate in a stable and outdoors over several weeks, starting in late May and July, respectively, immediately after the cattle were moved to other enclosures. Culicoides specimens captured in the stable exclusively belonged to the Obsoletus Group and were caught sporadically in all traps from the beginning of the investigation until the ninth study week when the substrate began to dry out. In most outdoor traps, only a few Culicoides specimens, mainly from the Obsoletus Group, were caught, while some traps produced a considerable number of specimens from this group. In a further study, emergence traps were set up outdoors in summer on either sun-exposed or shaded deep litter. Culicoides, again mainly from the Obsoletus Group, were caught in all traps, with significantly lower numbers in the sun than in the shade, where a higher substrate moisture was measured. A female:male ratio of 1.8:1 was determined in the sun, while this was 1:2 in the shadow. Apparently, deep litter is a suitable breeding substrate for Obsoletus Group Culicoides, but significant differences were found due to the different moisture contents in the shadow and sun. Mucking out the deep litter and removing it from the vicinity of the livestock are expected to reduce the emergence and abundance of potential Culicoides vectors.