Molecular basis of olfactory-driven behaviours of Culicoides imicola

Culicoides imicola (Diptera: Ceratopogonidae) is a successful biting midge, infamous for its role as a biological vector for numerous pathogens of veterinary significance. Like in most insects, olfaction is likely to play a central role in the long-range attraction of Culicoides towards hosts and oviposition sites. However, studies of their sensory apparatus are scarce, and the vast majority of semiochemicals used by Culicoides are unknown. Our tanscriptome analysis shows that C. imicola exhibits many members of receptor gene families and provided for the first time evidence for molecular mechanisms mediating the detection of CO2, 1-octen-3-ol, Indoles, and lactic acid. Using behavioural experiments, we also establish the basic attractiveness to 1-octen-3-ol and lactic acid, two substances for which we identified corresponding olfactory receptors.

Moreover, we investigated C. imicola's preference for oviposition sites. Our molecular analysis and comparison of bacterial populations residing in three different faecal sources indicated a unique bacterial population in equine faeces that may emit specific odorant cues. Our behavioural tests indicated that C. imicola prefers ovine and equine excrement over bovine. We created a bacterial library to examine the effect of different bacteria isolates on the oviposition preference of C. imicola. We have identified candidate bacterial species that emit mVOCs that may signal "suitable oviposition sites".

This novel, basic information of the mechanisms governing C. imicola attraction to nutritional sources and oviposition sites may may find its way in several applications such as new monitoring and or biocontrol strategies aiming at the destabilization of these notorious veterinary pests.