21-Jul-2017: Scientists to release 20 million mosquitoes to shrink mosquito population.

Scientists in California are releasing 20 million mosquitoes in an effort to shrink the population of mosquitoes that can carry diseases. It sounds counterintuitive. But the plan is to release millions of sterile male mosquitoes, which will then mate with wild female mosquitoes. The eggs the females lay won't hatch.

The project is called Debug Fresno and it's being undertaken by Verily, a subsidiary of Alphabet, Google's holding company. It's the company's first field study involving sterile mosquitoes in the U.S.

Scientists say the goal is to cut the population of Aedes aegypti mosquitoes — the species responsible for spreading Zika, dengue and chikungunya. A. aegypti have been present in California's Central Valley since 2013 and have been a problem in Fresno County.

Each week for 20 weeks, the company plans to release 1 million of the sterile, non-biting male mosquitoes in two neighborhoods in Fresno County. The male mosquitoes are bred and infected with Wolbachia, a bacterium that is "naturally found in at least 40 percent of all insect species,"  though it's normally not found in A. aegypti.

Wolbachia also helps mosquitoes to avoid carrying diseases like Zika in the first place. A. aegypti "carrying Wolbachia bacteria were highly resistant to Zika virus infection, and were unable to transmit the virus via their saliva,". The bacterium "is not known" to infect humans.

Verily has developed "automated mass rearing and sex-sorting processes," which enable it to breed and release so many of the mosquitoes in such a short time.

The method Verily is using to cut the mosquito population differs from the experiment the British company Oxitec proposed last year in the Florida Keys. In contrast to the mosquitoes being infected by bacteria, Oxitec has released males that are genetically modified with "a gene that causes the mosquito's offspring to die in the first two to three days of life".