Exploring Genetic, Molecular, Mechanical and Behavioural Methods of Sex Separation in Mosquitoes

With the absence of efficient drugs and vaccines, the combat against the pathogens causing these diseases has been largely based on methods including larval source reduction and use of insecticides. Novel approaches for the suppression of mosquito vector populations, such as the sterile insect technique (SIT), are urgently needed because the traditional methods used alone are neither efficient nor environmentally sustainable. Male-only releases is a prerequisite for mosquito SIT because female mosquitoes can bite, blood-feed and potentially transmit major human pathogens that cause malaria, dengue, chikungunya, Zika and yellow fever. Mosquito SIT faces a major challenge: efficient sex separation tools. Current sex separation methods are not efficient and robust enough in eliminating females to ensure safe and bio-secure releases of sterile males only. The Insect Pest Control Subprogramme of the Joint FAO/IAEA Programme of Nuclear Techniques in Food and Agriculture completed a five-year long coordinated research project (CRP) entitled “Exploring genetic molecular, mechanical and behavioural methods of sex separation in mosquitoes”, which aims at developing methods for sex separation as well as actual strains that can be used for genetic sexing.

Through the joint effort of medical entomologists, mosquito geneticists, molecular geneticists and engineers both genetic sexing strains and mechanical methods were developed and tested in the laboratory under small scale rearing conditions. The novel strains and new sex separation methods developed in the framework of this CRP need to be further tested and validated under large scale rearing conditions. They may also need to be further refined, beyond the laboratory scale in terms of their efficacy and stability prior to their deployment in large-scale operational programs.

The scientific results of this 5 years CRP include the following achievements:
-Aedes albopictus and Anopheles arabiensis genetic sexing strains were developed using irradiation and classical genetics-based approaches with an insecticide resistance gene as selectable marker.
-Aedes genetic sexing strains were developed using irradiation and classical genetics-based approaches, and a visible marker for selection.
-Sexing strains (female-specific lethality, sex ratio distortion and sex-conversion) using Molecular biology-based approaches were utilized in Aedes and Anopheles species to develop strains for female-specific lethality, sex ratio distortion and sex-conversion.
-A laser sex sorting machine prototype based on Aedes mosquito pupal size dimorphism was developed.

The results of the CRP are presented in a series of 17 review and original research articles in a special issue of the peer-reviewed scientific journal Parasites and Vectors