Insects harbor a diversity of microbes that are known to affect their host’s response to biotic and abiotic stressors. This is important in the context of climate change and human-caused habitat alterations, during which drastic changes are so rapid that organisms have little time to adapt. Symbionts often accompany invading species, and might play a role in the success or failure of insect invasions. Yet, few studies have examined the evolutionary dynamics and role of gut-associated symbionts at different stages of an insect invasion. We focus on the family Tephritidae (Diptera), which comprises many invasive pest species, and examine how gut-associated bacteria might influence their invasion process based on literature review. Based on our review, we first summarize the prevalence and diversity of gut-associated bacteria harbored by tephritid species. Next, we highlight how those gut communities may influence the fitness of invasive species during the colonization process. We conclude that gut-associated symbionts are highly flexible, and can respond rapidly to changes in biotic and abiotic factors and compensate for limited adaptive capacities of their hosts to counteract these stressors, through changes in the taxonomic composition or prevalence of the community. However, bacteria of Enterobacteriaceae are dominant as well as constitute constant and stable populations in fruit fly gut under different environmental stressors. Our review reveals that this family represents a key bacteria group in all studied tephritid species. This review indicates that knowledge on symbiont–insect interactions is crucial for understanding the success of insect invasion and it should be considered in risk analyses, impact modeling and optimizing invasive pest management.