Project Summary The long-term goal of this project is to elucidate at the molecular and cellular levels how chemosensory systems function and evolve so as to generate new behaviors that are adaptive to new environments. It focuses on one of the most ancient and fundamental problems in biology: how sensory systems adapt to allow an organism to exploit a new environment. Drosophila suzukii provides an excellent opportunity to decipher chemosensory mechanisms that have contributed to its unique oviposition behavior. Whereas other species of Drosophila lay eggs in fermenting fruit of no value, D. suzukii lays eggs in ripe fruit, ruining crops. The oviposition preferences of flies are based largely on taste. This proposal takes advantage of the wealth of knowledge about the mechanisms of taste in D. melanogaster. We aim to elucidate how these mechanisms have changed in D. suzukii to produce a preference for ripe, as opposed to overripe, fruits. The first aim will provide a rigorous analysis of the expression and functional requirements of candidate genes in the oviposition shift of D. suzukii. The experimental plan is designed to test hypotheses as to molecular mechanisms underlying the oviposition shift of D. suzukii. The second aim will provide a rigorous analysis of the role of candidate genes in oviposition preference for individual candidate oviposition cues. The proposed experiments are designed to identify key oviposition cues, to test them behaviorally, and to examine the role of candidate genes in the oviposition preference to them. The third aim takes advantage of a recent advance in electrophysiology that allows an unprecedented view of how a taste system has evolved at the cellular level. It will elucidate the cellular basis of a major shift in oviposition behavior that has immense economic implications. It may decipher the molecular logic of taste coding of a complex natural stimulus. Advances in understanding how the chemosensory systems function and evolve may lead to new means of controlling agricultural pests and insect vectors of human diseases, which afflict hundreds of millions of people each year.