CRP Success Story: Comparing Rearing Efficiency and Competitiveness of Sterile Male Strains Produced by Genetic, Transgenic or Symbiont-based Technologies (CRP D42016)

SIT is a species-specific and environment-friendly control technique, which is based on the mass-production and release of radiation-induced sterilised male insects over a target area, that breed with wild female mosquitoes that then fail to produce offspring. Although both sterile males and females can be released in SIT programmes, many studies have shown that by releasing only sterile males, the efficiency and the cost-effectiveness of SIT can be significantly enhanced. Additionally, when working with mosquitoes, the importance of achieving male only release is magnified as female mosquitoes feed on blood and can transmit numerous dangerous pathogens to humans.

The development of sexing systems, including genetic sexing strains (GSS), can ensure the release of sterile males only. Strains which can produce sterile males can be developed using different approaches, including classical genetic technologies to select desirable mutations and using them to separate males and sterilize them with radiation; transgenic technology, in which genes, not already present in the animal are added and manipulated; or symbiont-based technologies, in which another species, such as a bacterium is introduced to the host. It is important to assess the rearing efficiency, genetic stability and male mating competitiveness of any new strain developed prior to its use in large scale SIT operational programmes in open field conditions.

In this respect, the IAEA, in cooperation with the Food and Agriculture Organization of the United Nations has now completed the coordinated research project (CRP), D42016, on Comparing rearing efficiency and competitiveness of sterile male strains produced by genetic, transgenic or symbiont-based technologies. This initiative involved 18 scientists from 13 countries and resulted in the following key achievements and findings:

1. Anastrepha fraterculus sp. 1 GSS was developed using irradiation and classical genetics-based approaches using pupal coloration as a selectable marker. This is the first GSS developed for SIT applications against this fruit fly pest species.
2. Aedes aegypti GSS with an eye-colour selectable marker, and an irradiation-induced inversion for enhanced genetic stability, was developed and introgressed into different genomic backgrounds. This GSS can be a valuable tool for the elimination of females and the release of sterile males for SIT applications against this major mosquito vector species.
3. Novel or refined strains of Ceratitis capitata, Anastrepha ludens, Cochliomyia hominivorax, Aedes aegypti and Aedes albopictus were developed with different technologies, which can enhance mass-rearing and SIT applications against these species.
4. More than thirty strains of different SIT target species were evaluated in respect to their rearing efficiency and mating competitiveness under laboratory rearing conditions, and some of them also under open field conditions (Anastrepha ludens, Cochliomyia hominivorax and Aedes albopictus). Open field validation is a prerequisite prior to the development and implementation of a large-scale operational SIT programmes against insect pests..
5. No evidence of genetic instability or horizontal gene transfer was observed in the strains tested, which indicates the robustness of the stains developed for SIT application.
6. The gene responsible for male sex determination in tephritid fruit flies (Ceratitis capitata, Bactrocera dorsalis, Bactrocera oleae, and their related species), maleness-on-the-Y (MoY), was discovered paving the way for the development of novel and more stable GSS for SIT target species.

Several lines of evidence have clearly shown that the use of GSS can significantly reduce the cost and improve SIT application against insect pests and disease vectors. However, the development of such strains is challenging, and future research should investigate whether generic approaches can be developed which can facilitate and reduce the time needed for the development of GSS for SIT applications. The research carried out through this CRP generated more than 120 scientific publications in peer-reviewed journals and numerous presentations in international and national scientific meetings. The final CRP results will be published in a Special Issue of a peer-reviewed scientific journal.