Culicoides (Diptera: Ceratopogonidae) Abundance Is Influenced by Livestock Host Species and Distance to Hosts at the Micro Landscape Scale

Simple Summary Culicoides abundance is a critical component for transmission modelling of vector-borne diseases. It can be anticipated that Culicoides abundance is not homogeneously distributed in the landscape. Modelling parameter estimates are mostly extrapolated from indirect measurements using the most commonly used method worldwide: the light-trap (LT). However, it would be difficult to extrapolate Culicoides LT catches for modelling purposes due to the inherent biases of LT catches. The use of a sweep-net and performing collections during the hours before nightfall, when the LT is ineffective, can circumvent this bias. The aim of our study was to investigate the influence of baits (dairy cow, sheep, and LT) and the distance of measurement to hosts on Culicoides abundance using sweep-net catches. Our results indicate that cows are a far stronger attractor of Culicoides midges than sheep, and that both livestock hosts are far stronger attractors of Culicoides midges than LTs. Culicoides abundance declined significantly with increasing distance from hosts; this phenomenon was much stronger for dairy cows than for ewes. In contrast, Culicoides abundance increased with increasing distance from the LT, pin-pointing the apparent shortcomings of the LT as a surrogate host to lure midges. The vector/host ratio and host preference are important parameters for the modelling of vector-borne livestock diseases. It can be anticipated that Culicoides abundance is not homogeneously distributed in the landscape. We investigated the influence of host species (dairy cow, sheep, and a light-trap (LT) as a surrogate host) and distance of measurement to hosts on Culicoides abundance using a randomized block-design with 12 measuring days and seven 3-min aerial sweep-netting sessions per whole hour at three distances to the host (0, 10, and 25 m), from five hours before to and including one hour after sunset. Dairy cows were found to be a far stronger attractor of Culicoides midges than sheep, while both hosts were far stronger attractors of midges than the LT. Culicoides abundance declined significantly with increasing distance from the livestock hosts; this phenomenon was much stronger for dairy cows than for ewes. In contrast, Culicoides abundance increased with increasing distance from the LT, pin-pointing the apparent shortcomings of the LT as a surrogate host to lure midges. Our data indicate that livestock host species and the distance from these hosts have a profound effect on Culicoides abundance in the landscape.