A new paper published on 8 January in Nature Communications describes a ‘precision-guided sterile insect technique’ that can effectively alter insect genes to control female viability and male fertility. The method could potentially be used to suppress increasing pest populations that threaten agricultural crops and to prevent the transmission of deadly diseases. The controllable, noninvasive CRISPR-based genetic technology could be transferred across species and adopted around the world.
The sterile insect technique has been used to control insect populations since the mid-1930, typically by using DNA-damaging agents to sterilise males in order to reduce their overall fitness and mating competitiveness. This has gradually transformed into the new field called ‘Active Genetics,’ aimed at global solutions to improve agriculture, combat vector-borne diseases, and control invasive species.
Current sterilization methods are environmentally safe but rely on the propagation of genetic alterations from generation to generation, referred to as “gene drive” systems. Therefore, the approach is limited by the rapid evolution of resistance. For example, sterile male mosquitoes have been released into areas where they mate and pass on a gene that results in the death of progeny, thereby leading to a decline of the target population. The ‘self-limiting’ feature of this method makes it controllable, reliable, and reversible but seriously limits the amount of population suppression that can be achieved.
The newly developed precision-guided sterile insect technique (pgSIT) uses the precision and accuracy of CRISPR to simultaneously disrupt genes essential for female viability and male fertility. The technique ensures that only sterile adult males emerge from the genetically modified eggs. Researchers from UC San Diego and UC Berkeley were able to demonstrate 100 per cent efficiency in Drosophila, commonly known as the fruit fly. Moreover, they found that pgSIT-generated sterile males were fit and competitive. This means that in the wild, sterile males will be able to mate with females but are incapable of producing offspring, thereby reducing the overall population.
Another recent study predicted that pest activity in crop-growing regions will continue to increase as average temperatures rise due to climate change. The increasing insect pest numbers could result in significant losses in global crop yields, affecting many areas crucial to global food security, such as the “corn belt” in the US, wheat fields in France, and the rice paddies of China (2).
According to the authors, “pgSIT could potentially be used in the future to mass produce and release eggs into the environment to suppress target populations.” The modified genes are common to many insects, therefore, the technology could be applied to a range of insects, including not only crop-munching insects, but disease-spreading mosquitoes, such as Aedes aegypti, which is responsible for transmitting dengue fever, Zika, yellow fever, and other diseases to millions of people.
While new technologies offer interesting solutions to some of humankind’s biggest and most pressing issues, it is equally important to ensure they developed and implemented in both an ethical and safe way.
(1) Kandul, N.P. et al. Transforming insect population control with precision guided sterile males with demonstration in flies. Nature Communications (2019). 10 (1) DOI: 10.1038/s41467-018-07964-7
(2) Deutsch, C. A. et al. Insect metabolic and population growth rates predict increasing crop losses in a warming climate. Science (2018). DOI: 10.1126/science.aat3466