Genetic improvement through heterosis has been little exploited in beneficial insects. Heterosis could contribute to increased competitiveness of lab strains in the field with a consequent savings in rearing costs. Heterosis has been quantified for many insects, such as the flour moth where significant F1 and F2 values were observed and applied at a reduced scale to make silkworms more productive. Heterosis values were estimated as the difference between hybrid performance and the mean of the parental lines. Genetic sexing (GS) based on pupal colour dimorphism could be an excellent mechanism to “exploit” heterosis if the two GS lines have a good combining ability. GS based on pupal colour separation is an easy mechanism for exploiting heterosis in the Mediterannean fruit fly and some other insects employed for Sterile Insect Technique. The chapter provides some heterosis data for the Mediterranean fruit fly, Ceratitis capitata.