Technical Abstract: The Sterile Insect Technique (SIT) is a highly successful biologically-based strategy to control plant and animal insect pest populations, that relies on the large-scale release of sterilized males that renders females in the field non-reproductive. Despite its success, the more widespread use of SIT is limited by the lack of methods, in most species, to eliminate females early in development, resulting in higher costs and lower efficacy. For medfly, a mutant-based sexing system is available as well as a transgenic system where a tetracycline-suppressible (Tet-off) toxic molecule is female-specifically produced. However, the former classical genetic system took many years to refine, and the latter system results in female death primarily in the pupal stage after rearing costs have been incurred. Here we describe a new transgenic Tet-off sexing strategy that is not only highly efficient, but eliminates female insects early in embryogenesis by a well-characterized apoptotic mechanism.