In humans, finding a partner is quite a difficult task because there are many criteria that one needs to consider. However, in comparison to many animals, when choosing a partner, we easily discriminate between ourselves and members of other species through various communication systems. On the contrary, many fly species (Diptera) are morphologically similar and overlap in their geographical distributions and ecological habitats. Sexual interactions of most drosophilid flies occur on their hosts. Therefore, flies rely on olfactory sex pheromones, as well as on non-pheromonal chemicals such as host volatiles – which guide and restrict the search for conspecifics within limited locations – as honest signals for pre-mating reproductive isolation. A subtle divergence in the perception of these signals can lead to accumulated changes among populations of the same species, and ultimately to a reduction in gene flow and reproductive isolation. In recent years, we have seen an increased interest in how olfactory systems diverge to drive host adaptation and speciation. In this review, we discuss the evolutionary changes of the neural circuits that underlie mate recognition. We shed light onto sex pheromone communication systems, the construction of olfactory nervous systems, and the role of host specialization in reproductive isolation. Finally, leveraging the incipient speciation of Drosophila mojavensis Patterson populations, we highlight the underlying sensory mechanisms of the reproductive isolation barriers. In the end, we propose future research topics of the evolutionary neuroecology field of sexual communication.