Researchers at Virginia Tech have found that they can turn female Aedes aegypti mosquitoes into males by tweaking a single gene in their DNA.
The findings could help us reduce the spread of mosquito-borne diseases. Female mosquitoes need to bite mammals in order to absorb their blood — which is converted into nutrients for their eggs. Males, on the other hand, don’t. They spend their days sipping on nectar.
Mosquito bites create an ideal opportunity for diseases such as malaria, Zika, or Dengue to spread, as they involve a small amount of the insect’s saliva entering the victim’s tissues. Shifting the ratio towards males can thus nip such diseases in the bud.
“The presence of a male-determining locus (M locus) establishes the male sex in Aedes aegypti and the M locus is only inherited by the male offspring, much like the human Y chromosome,” said Zhijian Tu, a professor in the Department of Biochemistry in the College of Agriculture and Life Sciences, lead author of the study describing the process.
“By inserting Nix, a previously discovered male-determining gene in the M locus of Aedes aegypti, into a chromosomal region that can be inherited by females, we showed that Nix alone was sufficient to convert females to fertile males. This may have implications for developing future mosquito control techniques.”
The team produced several such gene-modified mosquitoes that express an extra copy of the Nix gene that is activated by its own promoter.
This sex conversion was found to be highly effective and “stable over many generations in the laboratory”, the team explains, suggesting that it would be useful in wild populations without constant reintroduction of modified mosquitoes.
However, these converted males can’t fly naturally. In order to remedy this, the team found that a second gene (myo-sex) needs to be added to the M locus as well. The team inactivated the myo-sex gene in wild-type males to confirm its function — and these insects lost their ability to fly.
Flight is important for these sex-changed insects as mosquitoes rely exclusively on flight for feeding, mating, and escaping predators. In other words a flightless mosquito, no matter how well-engineered, won’t do us much good. This being said, however, the authors report that sex-changed males were still able to father sex-converted offspring if they were presented with an anesthetized wild female.
All in all, the Nix gene has great potential as a tool to reduce the population of biting mosquitoes, and thus, the spread of disease. However, there’s still a lot of work to be done in the lab before such insects can be released into the wild.
The paper “Nix alone is sufficient to convert female Aedes aegypti into fertile males and myo-sex is needed for male flight” has been published in the journal Proceedings of the National Academy of Sciences.