Selection of sheep skin bacteria to reduce blood-feeding by biting midges under laboratory conditions

Biting midges of the genus Culicoides (Diptera: Ceratopogonidae) are of huge veterinary importance, mainly as vectors of pathogens, such as Bluetongue virus. Currently, there are no effective methods to protect animals against biting midges since insecticides have limited or short-lived efficacy. Biting midges are attracted to hosts by carbon dioxide and by their body odours, which are mainly produced by skin bacteria. In humans, it has been shown that differences in attractiveness between individuals to mosquitoes is mediated by these skin bacterial volatiles. This opens the possibility to protect individuals from biting insects by supplementing their skin microbiome with probiotics. In this study, we investigated this approach by culturing sheep skin bacteria on different media and assessed their effects against field-caught Culicoides (overwhelmingly Obsoletus group species) as well as laboratory-reared Culicoides nubeculosus (Meigen). Aerococcus urinaeeequi, Bacillus safensis, Bacillus subtilis, Jeotgalicoccus psychrophilus, Micrococcus sp. and Staphylococcus equorum were selected to be tested in a dual-choice Y-tube olfactometer, assessing their behavioural effects towards biting midges. We revealed an avoidance effect towards laboratory-reared C. nubeculosus when testing B. safensis (P [≤] 0.001) and B. subtilis (P [≤] 0.001). Bacillus safensis (P = 0.006) and Micrococcus sp. (P [≤] 0.001) yielded significant repellent potential towards field-caught Culicoides. These two candidates were subsequently tested in a membrane blood feeding assay. When the bacterial species B. safensis was applied to the membrane, a feeding reduction of 83 % was observed with field-caught Culicoides.