Improving sterile male performance in support of programmes integrating the sterile insect technique against fruit flies

The sterile insect technique (SIT) is being applied against fruit fly pests in many areas of the world. Currently, factories have a capacity to produce several billion sterile insects per week, to irradiate them and to make them available for shipment to their destinations. There the emerging flies are fed and maintained for various periods of time in fly emergence and release facilities, and then collected for release. While much research effort has been invested in improving mass rearing and quality control procedures at the fly factory level, the post-factory handling of sterile flies has received much less attention. A 6-year FAO/IAEA Coordinated Research Project (CRP) was initiated with the participation of 31 research institutes from 17 countries to assess and validate ways to improve sterile male performance through better management during the critical period that starts with the arrival of pupae at the fly emergence and release facility and ends with the release of the sterile flies in the field. This review summarizes the research that was conducted under the CRP focusing on fruit fly species from the genera Anastrepha, Bactrocera and Ceratitis against which the SIT is being applied. To increase the effectiveness of SIT programmes, exposure of sterile males to nutritional, hormonal and semiochemical supplements was assessed and improved handling and release methods tested. Incorporation of protein and juvenile hormone into pre-release diets significantly accelerated sterile male maturation and improved sexual performance among several species, while semiochemical treatments using ginger root oil or citrus oils in Ceratitis capitata and methyl eugenol in Bactrocera dorsalis complex species significantly increased sterile male mating competitiveness. Improved fly emergence, holding and release procedures were also assessed, together with the compilation of all this knowledge into a manual. Several of these findings have been transferred to and are being applied in operational programmes.