The fruit fly ceratitis capitata, also called the medfly, is a very destructive pest all around the world against a wide range of hosts, including stone fruits and citrus. Several operational control programs have been launched against the medfly in California, Central America, in Southern-Europe (Spain, Croatia) and in South Africa, using the sterile insect technique (SIT). SIT is an environmentally-friendly insect pest control method involving the mass-rearing and sterilization, using radiation, of males that are repeatedly released to mate with wild females resulting in no viable o¿spring. A new SIT project against medfly is now ongoing in Corsica (a French island in the Mediterranean Sea), CeraTIS-Corse. A new and very destructive pest, the oriental fruit fly, bactrocera dorsalis, has appeared in R´eunion island (a French overseas department in the Indian Ocean) in 2017. Since then, it has invaded the whole island, infesting most of the crops from the sea level till 500 m. The damages are important, in particular in Mango orchards where crop yields have been reduced by 50% to 80%. A feasibility SIT project, GEMDOTIS, is ongoing in La R´eunion. While conceptually very simple, in practice, SIT is very complex. In particular, it requires a very good knowledge of the targeted pest ecology and biology. It is also crucial to ensure that the released sterile males are of very good quality to disperse and compete against wild males. However, release strategies often seek for a balance between the quality of the males and the minimum level of sterility acceptable. In, using a generic model we studied the impact of residual fertility (RF), i.e. irradiated males are not fully sterilized, that is, a proportion, say? of sperms is always fertile. At the population level, this means that a proportion, ?, of sterile males is able to have progeny. In, we show that RF is strongly linked to the basic O¿spring/Reproduction Number of the pest, N, i.e. the average number of female o¿