We investigated the fate of ingested Enterobacter (Pantoea) agglomerans and Klebsiella pneumoniae within adult Mediterranean fruit fly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae), in a mass rearing facility. This examination revealed the establishment of both bacterial strains as biofilms within the adult intestines, on the apical end of developing and developed eggs, and throughout all subsequent life stages. The bacteria were detected in adults through two generations. Irradiation treatment for the sterile insect technique did not disrupt the vertical transmission of E. (P.) agglomerans or K. pneumoniae. This is the first demonstration of maternal spread of Enterobacter/ Pantoea spp. and Klebsiella spp. through populations of C. capitata. A mixed pattern of vertical and horizontal transmission of symbionts associated with tephritids may be one explanation for the difficulty in defining the symbiotic associations of tephritids.