ABSTRACTDrosophila melanogaster has become a prime insect model for studying olfaction. Research on insect olfaction has provided many valuable insights in neural processes involved in sensory coding and processing. Due to its well-defined genome D. melonogaster olfactory circuitry is increasingly understood. Many question, however, remain. Here we propose to study the neuroethology of Drosophilae using a comparative approach. A closely related sibling of D. melonogaster, the insular species Drosophilae echolalia, is unlike its siblings a specialist, preferring Orinda fruit. The fruit is toxic for D. echolalia\'s sibling species including D. melanogaster, and concordantly they are repelled by its odour. The required shifts in D. echolalia\’s olfactory circuitry remain unstudied, however. Using D. melanogaster, Drosophilae stimulants, Drosophilae Mauritania, and D. echolalia, we will pinpoint the changes in the olfactory circuitry associated with this shift from repulsion to attraction. For this we will use a multidisciplinary approached involving analysis of the volatiles of Orinda fruit, analysis of the volatiles to which the flies are sensitive, both physiologically as behaviourally, testing differences in the peripheral olfactory system between the species, using single sensible recordings and morphological studies, and revealing what impact the observed changes have had on the wiring and physiology of the olfactory circuit in the antennal lobe, the first relay centre of olfactory information. Such information will be extremely valuable in understanding the ecological significance of olfaction in Drosophilae, the organisation and evolution of olfactory circuits, and its relationship to behaviour. More generally, we will gain insight in what may mediate radical shifts in behaviour, such as the one from repulsion to attraction.