A Switch That Turns Deadly Female Mosquitoes Into Harmless Males

An international team of scientists have isolated a gene within the Aedes aegypti mosquito that partially transforms females into males. Since only females spread diseases by feasting on human blood, the discovery could lead to powerful population control strategies.

Female mosquitoes bite because they require blood for their developing eggs. Thus, it’s the female half of Aedes aegypti that’s responsible for spreading diseases such as malaria, yellow fever, and dengue. This is why researchers have long sought to find a way to control the sex ratio of this problematic species. As a new study published in Science Express now shows, it may be possible to reduce the number of females within a population by essentially turning them into males — a transformation made possible by flipping a single sex-determining genetic switch.


Prior to the new study, geneticists struggled to find a single male-determining gene, or M Factor, in A. aegypti. Virginia Tech’s Andrew Hall, along with his colleagues at the Fralin Life Science Institute, finally isolated the gene, called Nix, by analyzing male-specific genome sequences that were exclusively expressed during the mosquitoes’ embryonic development.

Image: Nix located within the M locus (Credit: A. Hall et al./Science Express)

When Nix was injected into the genomes of developing mosquito embryos, more than 65% of females began to develop male genitals and testes. And when the researchers used the CRISPR-Cas9 gene editing tool to extract Nix from male embryos, they developed female sex organs.


“Here we demonstrate that an M-locus gene, Nix, is an M factor in A. aegypti because it is both required and sufficient to initiate male development,” conclude the authors in their study, adding that “complete sex conversion has not been achieved in our transient assays.”


It may be a partial sex change, but it’s enough to render the female mosquitoes harmless. The researchers are now hopeful that genetic control methods can be used to “introduce a male bias” for the purpose of reducing dangerous mosquito populations.

“We’re not there yet, but the ultimate goal is to be able to establish transgenic lines that express Nix in genetic females to convert them to harmless males,” noted Virginia Tech entomologist Zach Adelman in a statement.


Scientists could introduce their transgenic Nix-carrying mosquitoes to native populations by engaging in “gene drives.” Once these lab-grown mosquitoes have blended in, nature would take care of the rest. A similar plan is currently being considered by the U.S. Food and Drug Administration in the Florida Keys.

Read the entire study at Science Express: “A male-determining factor in the mosquito Aedes aegypti”.


Top image: Andrew Wild

Contact the author at george@io9.com and follow him on Twitter

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