Abstract
BackgroundCulicoides obsoletus (s.l.) is the most abundant Culicoides species in northern Europe and an important vector of bluetongue virus and Schmallenberg virus. Nevertheless, information on its subadult life stages remains scarce and no laboratory-reared colony exists.MethodsC. obsoletus (s.l.) adults were collected in Belgium and transferred to the laboratory in an attempt to establish a laboratory-reared colony. C. obsoletus (s.l.) were reared from eggs to adults at different temperatures (28 °C, 24 °C, 20/16 °C) and under different food regimes.ResultsThe most suitable temperature for rearing seemed to be 24 °C for most developmental parameters, but resulted in a biased 3:1 male/female sex ratio. The latter could be optimized to a 1:1 sex ratio when a 20/16 °C day/night temperature gradient was applied, but rearing at these low temperature conditions resulted in significantly lower egg hatching and pupation rates and a longer subadult development time. Independent of the rearing temperature, adding dung as an additional food source during larval development resulted in a significantly higher adult emergence rate and a decrease in subadult development time. Furthermore, blood-feeding rates of field-collected C. obsoletus (s.l.) were compared for different blood sources and feeding systems. The overall blood-feeding success was low and only successful with cotton pledgets (2.7% blood-fed midges) and through a membrane system with chicken skin (3.5% blood-fed midges). Higher feeding rates were obtained on cattle blood compared to sheep blood.ConclusionsThese results will help us to determine the necessary conditions to rear a viable laboratory colony of this important vector species, although further optimization is still required.Graphical abstract
Highlights
Culicoides obsoletus (s.l.) is the most abundant Culicoides species in northern Europe and an important vector of bluetongue virus and Schmallenberg virus
The obstacles to establishing a colony of C. obsoletus (s.l.) and related species include their reluctance to mate under laboratory conditions [12, 13], high mortality of fieldcaught midges [14], limited knowledge on their larval nutrition and larval substrates [12] and a reluctance of field-collected females to blood feed under laboratory conditions through artificial blood-feeding systems [12, 15]
The aim of our study was to improve our understanding of subadult development and the requirements to establish a viable laboratory colony of C. obsoletus (s.l.) by (i) evaluating the effect of different combinations of temperature and larval substrates on subadult development and emergence patterns of eggs laid by field-collected midges; and (ii) comparing different methods for artificial blood-feeding of Belgian C. obsoletus (s.l.) Methods Collection of Culicoides Culicoides were collected at cattle and sheep farms in Belgium where abundant C. obsoletus (s.l.) populations have been found during previous surveillance studies [4, 21]
Summary
Culicoides obsoletus (s.l.) is the most abundant Culicoides species in northern Europe and an important vector of bluetongue virus and Schmallenberg virus. Culicoides obsoletus Meigen and Culicoides scoticus Downes and Kettle are the most abundant and widespread Culicoides species (Diptera: Ceratopogonidae) in northern Europe [1,2,3] and the most important vectors. Despite the importance of C. obsoletus (s.l.) as vectors of important veterinary disease agents, no laboratory colonies of C. obsoletus (s.l.) exist, resulting in very limited information on the life cycle traits of this species, of subadult life stages. The obstacles to establishing a colony of C. obsoletus (s.l.) and related species include their reluctance to mate under laboratory conditions [12, 13], high mortality of fieldcaught midges [14], limited knowledge on their larval nutrition and larval substrates [12] and a reluctance of field-collected females to blood feed under laboratory conditions through artificial blood-feeding systems [12, 15]
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