Symbiosis can favor rapid shifts in host phenotypic traits, particularly through the contribution of symbionts to the host's physiology. In addition, variations in the microbiota composition between individuals can be associated with pre-zygotic and post-zygotic barriers. All together, these phenomena may contribute to insect diversification and speciation. Recent advances have also shown that the host–microbiota molecular dialog, mediated notably by host immune and developmental pathways, is critical for the acquisition and control of the microbiota, and could also contribute to reproductive isolation. While still a controversial hypothesis, adaptation through symbiosis could thus trigger host–symbiont coevolution and accelerate differentiation.