Daniel Becerril | Reuters

Ways to use genetically modified mosquitoes

A worker sprays anti-mosquito fog in an attempt to control dengue fever at a neighborhood in Jakarta, Indonesia. Highly populated areas in the country are often hit with severe outbreaks of the mosquito-borne disease especially during the annual rainy season due to poor health services and unsanitary living conditions. Achmad Ibrahim / AP Photo There are two alternative methods currently used to control mosquito-borne diseases using GM mosquitoes. The first is "population replacement" in which a mosquito population biologically able to transmit pathogens is "replaced" by one that is unable to transmit pathogens. This approach generally relies on a concept known as "gene drive" to spread the anti-pathogen genes. In gene drive, a genetic trait – a gene or group of genes – relies on a quirk on inheritance to spread to more than half of a mosquito's offspring, boosting the frequency of the trait in the population. The second approach is called "population suppression." This strategy reduces mosquito populations so that there are fewer mosquitoes to pass on the pathogen. While the concept of gene drive in mosquitoes is many decades old, the gene-editing technique CRISPR has finally made it possible to easily engineer it in the laboratory. However, CRISPR-based gene drives have not yet been deployed in nature, mostly because they are still a new technology that lacks a firm international regulatory framework, but also due to problems related to the evolution of resistance in mosquito populations that will stop the gene from spreading. It may not be immediately obvious, but the gene in "gene drive" need not be a gene at all – it can be a microbe. All organisms exist not just with their own genomes, but also with the genomes of all their associated microbes – the "hologenome." Spread of a microbial genome through a population by inheritance can also be thought of as gene drive. By this definition, the first gene drive that has been deployed in mosquito populations for disease control is a bacterial symbiont known as Wolbachia. Wolbachia is a bacterium that infects up to 70 percent of all known insect species, where it hijacks the insect reproduction to spread itself through the population. Thus, the Wolbachia itself (with its genome of approximately 1,500 genes) acts as the genetic trait that is driven into the population. When Wolbachia is transferred into a previously uninfected mosquito, it often makes the mosquito more resistant to infection with pathogen that can cause disease in humans, such as multiple viruses (including dengue and Zikaviruses) and malaria parasites.

A bacterium that fights disease

GM mosquitoes that eliminate mosquitoes