BackgroundHost preference studies in haematophagous insects e.g. Culicoides biting midges are pivotal to assess transmission routes of vector-borne diseases and critical for the development of veterinary contingency plans to identify which species should be included due to their risk potential. Species of Culicoides have been found in almost all parts of the world and known to live in a variety of habitats. Several parasites and viruses are transmitted by Culicoides biting midges including Bluetongue virus and Schmallenberg virus. The aim of the present study was to determine the identity and diversity of blood meals taken from vertebrate hosts in wild-caught Culicoides biting midges near livestock farms.MethodsBiting midges were collected at weekly intervals for 20 weeks from May to October 2009 using light traps at four collection sites on the island Sealand, Denmark. Blood-fed female biting midges were sorted and head and wings were removed for morphological species identification. The thoraxes and abdomens including the blood meals of the individual females were subsequently subjected to DNA isolation. The molecular marker cytochrome oxidase I (COI barcode) was applied to identify the species of the collected biting midges (GenBank accessions JQ683259-JQ683374). The blood meals were first screened with a species-specific cytochrome b primer pair for cow and if negative with a universal cytochrome b primer pair followed by sequencing to identify mammal or avian blood meal hosts.ResultsTwenty-four species of biting midges were identified from the four study sites. A total of 111,356 Culicoides biting midges were collected, of which 2,164 were blood-fed. Specimens of twenty species were identified with blood in their abdomens. Blood meal sources were successfully identified by DNA sequencing from 242 (76%) out of 320 Culicoides specimens. Eight species of mammals and seven species of birds were identified as blood meal hosts. The most common host species was the cow, which constituted 77% of the identified blood meals. The second most numerous host species was the common wood pigeon, which constituted 6% of the identified blood meals.ConclusionsOur results suggest that some Culicoides species are opportunistic and readily feed on a variety of mammals and birds, while others seems to be strictly mammalophilic or ornithophilic. Based on their number, dispersal potential and blood feeding behaviour, we conclude that Culicoides biting midges are potential vectors for many pathogens not yet introduced to Denmark.

Culicoides vectors are critical to the survival and transmission of bluetongue virus as infection only occurs in areas or regions where competent vectors are present. The success of Culicoides biting midges as vectors is mainly related to their vast population sizes and to their means of dispersal. Their choice of host for blood feeding is sparsely described. The aim of the present study was to establish methods for the identification of bloodmeal hosts and determine the identity and diversity of bloodmeals of vertebrate hosts from wild-caught biting midges near livestock farms. The study includes some of the most common and abundant species of biting midges in Denmark: Culicoides obsoletus, Culicoides scoticus, Culicoides pulicaris and Culicoides punctatus. We collected 8,378 biting midges including nine species of Culicoides of which blood-fed specimens were found from six species. We identified 251 blood engorged biting midges, and hosts were identified in 115 of 125 analysed specimens (90%). Cow, roe deer, horse, mallard and wood pigeon were identified as hosts. The most abundant host species was cow, which constituted 73.9% of the total identified bloodmeals, but the common wood pigeon was found with a frequency as high as 18.3%. In conclusion, the molecular methods applied were proven useful in identifying bloodmeal hosts from different Culicoides species. The results indicate that Culicoides species are opportunistic in their choice of bloodmeal host with a preference for cattle when present, which is important to have in mind for epidemiologist when making predictive models. Accordingly, the results of this study will add useful parameters for modelling bluetongue virus transmission and in the development of veterinary contingency plans.

Identification of Culicoides biting midges to species has attracted attention due to the recent outbreak of bluetongue disease in Northern Europe. Identification of Culicoides to species level has been based on morphological characters and is difficult as several species belonging to species complexes are hard to distinguish. We evaluated the use of the mitochondrial DNA cytochrome oxidase I gene (COI) barcode region in the identification of species within the subgenus Culicoides. COI barcode sequence divergence within species was <1%, whereas it ranged from 12.5% to 19.8% between subgenus Culicoides species. The divergence of subgenus Culicoides species to C. nubeculosus from the subgenus Monoculicoides ranged from 24.4% to 26.1%. Specimens were differentiated into eight unique clusters, including the four common Palaearctic species Culicoides punctatus, Culicoides pulicaris, Culicoides impunctatus, and Culicoides grisescens. Additionally, this study confirms the existence of Culicoides halophilus as a valid taxon and presents the first Culicoides deltus barcode sequences. Three additional groups of specimens were identified: Culicoides dk1 with a COI barcode diverging by 14.3% to 17.2% from other subgenus Culicoides species and Culicoides Kalix and Culicoides dk3, which diverged by 5.9% from each other and showed 12.5% to 17.6% divergence in COI barcode to subgenus Culicoides specimens.