Odour-mediated host seeking and discrimination in mosquitoes : chemistry, neurobiology and behaviour

The majority of the world’s population is at risk of one or more mosquito-borne diseases that are transmitted by blood-feeding female mosquitoes, affecting both human health and economic development. Especially Anopheles gambiae, the principal malaria vector, and Aedes aegypti, the vector of dengue and yellow fever, are of primary concern due to their strong specialisation on human hosts, and the high number of casualties caused by the pathogens they transmit. Host seeking and discrimination are crucial for disease transmission, and are predominantly mediated by olfaction. Using a wind tunnel system and a custom analysis pipeline, this thesis confirms that the two mosquito species use volatile host cues, derived from breath and body, differentially, as carbon dioxide on its own drives host seeking in Ae. aegypti, but not in An. gambiae (paper I). To discriminate between host and nonhost species (paper V), Ae. aegypti encode human identity by the relative activation of two glomeruli within the antennal lobe, the primary olfactory centre, of which one is tuned to long-chain aldehydes enriched in human odour. A synthetic blend mimicking the glomerular activation elicited host seeking in Ae. aegypti (paper II). Next to preferring human over non-human hosts, Ae. aegypti also prefer some human individuals to others, which was demonstrated to be affected by the ABO blood type and pregnancy or menstrual cycle phase. Analysis of the volatiles associated with individual volunteers, identified 1-octen-3-ol to be significantly associated with very high attractiveness (paper III). The molecular regulation of host seeking acquisition during An. gambiae female adult maturation was independent of odorant receptor gene AgamOR39 expression (paper IV). The results presented in this thesis contribute to the understanding of mosquito host seeking and discrimination from multiple perspectives, which is a prerequisite to ultimately develop novel tools for mosquito monitoring and control