Identification of host volatiles and their role in the behavioural modulation of host-seeking Culicoides biting midges
Sammanfattning: Culicoides biting midges are important vectors of Bluetongue and Schmallenberg viruses in Europe. The introduction of these viruses highlighted the need to develop novel surveillance and control tools to monitor and manage biting midges. Biting midges, as most insects, primarily use olfactory cues to recognize and discriminate resources for their survival and reproduction. Blood feeding insects rely on host-derived volatiles to locate their vertebrate hosts, and these odours can be exploited to manipulate insect-host interaction. The primary goal of this thesis was to identify host volatiles that modulate the host-seeking behaviour of biting midges. Through coupled gas chromatography and electroantennographic detection (GC-EAD) analysis of odour collections from cattle hair and urine, I identified several compounds that, in combination with carbon dioxide, elicited behavioural attraction or inhibition in Culicoides nubeculosus, in a dose dependent manner. Some of these host odours were evaluated in the field showing similar behavioural responses of C. impunctatus. Both laboratory and field assays emphasized the importance of release rate to obtain optimal behavioural responses. The impact of using host volatiles to monitor host-seeking biting midges was shown in another study. Here, I showed that incandescent light traps baited with two cattle kairomones, 1-octen-3-ol and carbon dioxide, caught significantly more insects than UV light traps. UV light traps are to date the most commonly used method for monitoring biting midges. That said, differences were observed between trap types, both concerning species composition and the physiological state of the female biting midges caught. Incorporating the novel bioactive compounds, formulated in blends and released in proper ratio and rate, could further increase the efficacy of this trapping method. By incorporating these attractants together with repellent compounds identified in this project, a "push-pull"- system for biting midges could also be envisioned. The host volatiles identified are detected by the peripheral olfactory system of biting midges. A comparative analysis across biting species with different host preferences revealed a correlation between host preference and the number and types of antennal and maxillary palp sensilla. Functional characterisation of these sensillum types will be the next step to increase our understanding of how host odours are detected by biting midges With this thesis I have increased our understanding of the chemical ecology of host-seeking female biting midges and their peripheral olfactory system. Future research projects will need to develop viable commercial products that could be incorporated into management strategies for Culicoides biting midges.
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