A female mosquito will mate just once in her entire lifetime. After doing the deed, her drive to mate is turned off, and her drive to lay fertilized eggs is turned on. Now, scientists from Imperial College London have tricked female mosquitoes into wasting their one go at fertility by swapping out normal males with spermless ones.
Their findings, which are reported in the Proceedings of the National Academy of Sciences, represent a milestone in the fight against the spread of malaria, the deadly mosquito-borne infectious disease responsible for nearly a million deaths worldwide every year.
The mosquito Anopheles gambiae is the world's most efficient transmitter of malaria. With insecticide resistance on the rise, scientists are now experimenting with sterilization techniques to keep the insect population in check. The problem? A popular method of sterilizing male mosquitoes, dosing them with radiation, left these males weak and unable to compete with fertile males for female attention.
What scientists needed was a more precise targeting system – one that would allow them to sap the sperm-producing capabilities of male mosquitoes while leaving them fit enough to compete for a female partner.
Entomologist Flamina Catteruccia, along with her graduate student Janis Thailayil, found such a targeting system in the form of small RNA molecules that are capable of turning off specific parts of the A. gambiae genome. By targeting a gene called zpg, which is responsible for germ cell development (germ cells are the cellular precursors to sperm in males), Catteruccia and Thailayil were able to generate mosquitoes equipped with the ultimate form of birth control: male mosquitoes with no sperm. What's more, these mosquitoes were not only spermless, they were physically capable of competing with genetically-normal males for female mosquitoes. The researchers describe their findings:
These spermless males appeared competent for mating, were fully capable of inducing oviposition, and switched off female receptivity to further insemination. Matings with sperm-deficient males achieved complete sterility, as the 34 females mated to them produced no progeny.
In other words, the spermless males tricked 34 females into not reproducing.
The researchers' findings, while exciting, are just the first steps on the path to making spermless male mosquitoes a feasible option in the fight against the spread of malaria. The method used by Catteruccia and Thailayil to induce sterility in the males, for example, is far too inefficient to deploy on a large scale. Nevertheless, the fact that a mating between an infertile male and an otherwise normal female could eliminate the female mosquito's reproductive potential for the rest of her life makes the approach of insect sterilization too attractive to pass up. It won't be long before we see a perfected version of this technique — or one that scales better — used to stop malaria by decimating the population of its hosts.