Multimodal integration between optic flow and olfactory cues in Drosophila melanogaster: a comparative take on insects' navigation

During my Master thesis internship, I was working on a paradigm revolving around the selection-for-action mechanism in a context requiring action-centred attention during a navigational task1, which got me hooked to the top-ics of animal navigation and cognition, and more in particular to the role of odours and multisensory integration in animals navigating through the envi-ronment. Recently in the EU, there has been renewed interest and impulse for studying the interaction of repellents on insect, as several older compounds used against pests have been prohibited in favour of natural compounds and newly synthetized ones. These factors contributed to the conceiving of my PhD project, where I analysed the effect of repellent and masking compounds on insects exposed to them while undergoing optokinetic and optomotor tasks. These tasks were chosen as they are related to the visual stimulation the ani-mals may experience when navigating in the environment. Therefore, by cou-pling contrasting visual and odorous cues (coming from opposing directions), I looked at how insects could behave when experiencing conflictual infor-mation in the environment. I conducted these studies in Drosophila melano-gaster, as it shares a common organization of its central nervous system with other hazardous insect species (like D. suzukii and Aedes aegypti), while being relatively easy to nurture and rear, and in the last part of the work presented in Appendix I, I also adapted the same paradigm in the mosquito A. aegypti. If I were to sum up in a couple of questions the rationale behind this work, it would be like this: “How can odorous compounds impact elementary process-es at the basis of insect navigation behaviour? Should we be worried by a pos-sible wide-spread effect of commonly implemented repellents on non-target species?” I will start this dissertation by introducing the theoretical frameworks I had in mind while designing my experimental paradigm: the first point is about a comparative approach in research, while the second is about animal naviga-tional strategies. Both were of inspiration in designing the protocols for my experiments. Then I will follow with sections related to the optokinetic reflex and the optomotor response, also presenting the involved circuits both in gen-eral in Vertebrates and in Drosophila, describing the general organization of its brain, and the vision and olfactory pathways. One last introductory chapter re-lates to the fundamental role of odorous compounds for the insect species life-history in their relationship with plants. Lastly, I will present the methods of this research, and the results obtained in flying and walking D. melanogaster, which show that repellents can affect and cause changes in the modulation of basal mechanisms like the optokinetic re-flex and the optomotor response. I will discuss the results and try providing an answer to the above questions. In Appendix I, I illustrate the methods and the preliminary results I achieved translating the very same behavioural investigation in A. aegypti. In Appendix II, there is the list of published articles. I briefly comment two of them, as they were not directly cited in the dissertation but share the same comparative philosophy.