Gut microbionts play a fundamental ecological and evolutionary role in phytophagous insects by making the plant tissue edible and by promoting adaptation between insects and host plants. SYMDIV is a collaborative project between the Royal Museum for Central Africa (Tervuren, BE) and the Laboratory of Microbiology of the University of Ghent funded by the Belgian Science Policy (BELSPO). This project, consisting of four work packages (WPs), aims at describing and comparing the gut microbiomes of phytophagous tephritid flies (Diptera, Tephritidae) with different feeding strategies (from strictly monophagous to highly polyphagous). In particular we aim at (a) comparing the 16S microbiome profiles of species such as Bactrocera dorsalis, Ceratitis capitate, etc., across multiple African and Mediterranean locations and across different host plants (WP1 and 2) (b) cultivating and isolating selected microbial strains (WP3) and (c) compiling and publishing a database of endosymbionts host associations (WP4). A pilot methodological test is currently ongoing in collaboration with IAEA, with the objective of optimising the experimental and analytical protocols. The SYMDIV project will provide baseline data to better understand relationship between gut microbionts, host range spectrum and metabolic processes in tephritid fruit flies. We will also isolate and characterise bacterial strains that could be tested as probiotics for SIT mass rearing.