Olfaction is the single most studied means of insect chemoreception. Many insects are sensitive to olfactory signals that advertise relevant ecological information concerning nutrient resources, competitors, predators, potential mates, and host suitability (Price et al., 2011). The olfactory system of the vinegar fly, Drosophila melanogaster, serves as a genetically and anatomically simple model for studying how sensory input is translated into behavioral output, because only two synapses isolate the input peripheral detection of ecologically relevant olfactory signals from the output behavioral navigation. This genetic and anatomical simplicity of the Drosophila olfactory system allowed us to further our understanding of the Drosophila olfactory neuroecology. Here, we have shown that the vinegar fly, Drosophila melanogaster, has two olfactory pathways, one that underlies the hardwired innate avoidance of harmful microbes and a second pathway for oviposition in Citrus substrates. We also showed that the peripheral odor detection machinery of D. erecta and D. mojavensis have been modified to match the olfactory needs of their respective ecological systems and associated host plants. Thus the findings of this thesis, while most directly pertinent to the advancement of our understanding of the basic science behind olfactory mechanisms, may also be useful in integrated pest management strategies for these and other potential pest insects