China: Scientists Released Millions of Infected, Sterilized Mosquitoes into Wild to Wipe out Disease-carrying Bugs

Scientists have almost eliminated a mosquito that carries diseases such as Zika in an experiment in China.

The approach involved two techniques: sterilizing female mosquitoes and spreading an infection among males. The findings were published in the journal Nature.

The Aedes albopictus mosquito targeted in the study carries viruses including dengue, Chikungunya and Zika.
Other insects have been controlled by what are known as the sterile insect technique (SIT) and the incompatible insect technique, but these techniques haven't been successfully used against mosquitoes.

The SIT involves releasing sterilized males into the wild to prevent them from making viable offspring with females. But this doesn't work in mosquitoes because it makes it harder for mosquitoes to find a mate versus the wild population.

The incompatible insect technique infects insects with the Wolbachia bacteria, which is inherited from the mother and causes sterilization. But infecting males with the Wolbachia bacteria alone hasn't worked in mosquitoes because if fertile females with the same strain are accidentally set free they might take over the wild population. This would render the technique useless. Also, Aedes albopictus mosquitoes are superinfected with two strains of Wolbachia, adding another layer of complication.

So the authors launched a two-pronged attack against the pests. They reared millions of mosquitoes infected with an artificial three-strain Wolbachia infection, which isn't found in the wild. Next, the bugs were irradiated to make sure the females were sterile but the males were still able to mate.

The insects were released in residential areas in two isolated islands near the river in Guangzhou, China, which has the country's highest transmission rates. In the first year, the average number of wild mosquitoes dropped by 83 percent, and 94 percent the second year. None were found for up to six weeks after they were released. In other words, after two years, the wild mosquitoes were almost totally wiped out.

Study co-author Professor Zhiyong Xi, a researcher at Michigan State University, told Newsweek the approach was environmentally friendly and had the potential to be used widely to manage disease-carrying mosquitoes.

He explained the SIT technique had already been used to successfully suppress and predicate a number of agricultural insect pests, such as screen worm, medfly and tsetse flies. But despite a huge effort, it had never before been successfully used in tackling mosquitoes.

The findings are promising, but Xi acknowledged: "In terms of disease control, this approach may not be suitable in emergency situations during disease outbreak."

That's because the females, even after mating with the males and becoming sterilized, may take one month to die. Thus, they can still transmit the disease.

"A quick knockdown of the population through other tools should be used together with our approach to reach fast and sustainable disease control," he said.

"This research can be extended to control malaria and other mosquito-borne diseases, and for agricultural pest control as well," he said. The technique could be used to create areas protected for humans, as well as food and plants.

"It can also be used to prevent the global expansion and invasion by highly invasive insect species to restore the ecosystem. This green technology is especially useful and cost-effective for those island countries in tropical regions to generate 'mosquito vector-free' environment," Xi concluded.

Moritz Kraemer, a research fellow in epidemiology and zoology at the University of Oxford who didn't work on the study, told Newsweek the results were "remarkable."
However, he pointed out: "The big limitation of these studies are the settings in which they work and do not work. At this stage, the results are encouraging but are not yet generalizable to other geographic settings (such as areas where there is high abundance of Aedes albopictus all year round or highly connected areas where frequent importations of the species are occurring)."

This article has been updated with comment from Moritz Kraemer.