Oviposition site selection in mosquitoes : the role of conspecific larvae, heterospecific larvae and microbes

Abstract

In mosquitoes, the evaluation and selection of oviposition sites is critical for the growth, development and survival of the offspring. Gravid mosquitoes rely primarily on olfactory cues emanating from breeding water containing, e.g., intra- and interspecific aquatic stages, as well as bacteria for this purpose. In this thesis, I investigated the odour-mediated mechanisms regulating the oviposition preferences of Aedes aegypti and Culex quinquefasciatus to intra- and interspecific aquatic stages and the commensal Klebsiella sp., bacterium. Using multi- and dual-choice oviposition assays, in combination with chemical and electrophysiological assays, volatile organic compounds (VOCs) associated with intraspecific aquatic stages of Ae. aegypti were identified and shown to regulate oviposition site choice and egg laying in a stage- and dose-dependent manner (Paper II). Using a similar approach, oviposition site selection by Ae. aegypti and Cx. quinquefasciatus were shown to be regulated by hydrocarbons emitted by interspecific 4th instar larvae, emphasising that these VOCs are able to regulate niche separation and competitive exclusion between these species (Paper III). The bacteria, Klebsiella sp., constitutes a major food resource for Ae. aegypti larvae, and gravid mosquitoes are attracted to this resource and the VOCs emitted by the bacteria (Paper IV), which strengthens their commensal interaction. This thesis identified the odour-mediated mechanisms by which mosquitoes detect intra- and interspecific aquatic stages, as well as mosquitoassociated bacteria. Furthermore, results of this study provide functional evidence that hydrocarbons, which previously have not been shown to regulate odourmediated behaviours in mosquitoes, play an important role in regulating oviposition. Besides, adding to our understanding of factors regulating oviposition preference in mosquitoes, this thesis has identified VOCs that may be evaluated under field conditions for their assessment as complementary vector control tools.