“It's a terrible nuisance, a terrible biting nuisance. It's changed the way people can enjoy their back yard and it's a threat for disease transmission,” said Steve Mulligan, district manager for the region's Consolidated Mosquito Abatement District. “So we're looking for new ways to eliminate it.”
To do so, district officials have partnered with tech companies to use an approach that has gained traction in recent years. Inside a lab, millions of the mosquitoes will be infected with Wolbachia bacteria, which changes the reproductive ability of males. Afterward, only those male mosquitoes — which don't bite — will be released to mate with unsuspecting female Aedes aegypti.
Even if the females lay eggs, those eggs will never hatch. Eventually, officials hope to reduce the population of Aedes aegypti, generation by generation, until they are eliminated from the area.
“It's kind of contrary to what a person would think. 'What, you're doing what? You're releasing mosquitoes to control mosquitoes?' " Mulligan said. “We are releasing male mosquitoes because male mosquitoes do not bite and cannot transmit disease.”
If all this sounds like the opening of a sci-fi movie, that's because the endeavor represents a cross-section of the health-care and technology industries. The “Debug Fresno” project is a continuation of a similar strategy that started last summer, when county officials partnered with Kentucky-based MosquitoMate to release 40,000 Wolbachia-infected male mosquitoes each week in Fresno County.
This year's mosquitoes are being bred and distributed by Verily, a subsidiary of Alphabet that was formerly known as Google Life Sciences. Verily officials estimate that this year, they will release 1 million mosquitoes per week in Fresno County, more than 25 times last summer's numbers. That is possible because they've developed ways to breed and separate male and female mosquitoes on a larger scale.
“Automated sex-sorting is a key advancement for this research,” Verily spokeswoman Kathleen Parkes said in an email. “Traditionally, mosquito sex-sorting is a very labor-intensive process. Verily has developed a system that uses computer vision algorithms to identify the sex of the mosquitoes and only let the males through.”
Unlike last year, when officials simply opened up cardboard tubes of mosquitoes at fixed points in the county, this year long white vans — emblazoned with the “Debug Fresno” logo — will drive through two neighborhoods in the cities of Fresno and Clovis to make sure the mosquitoes are evenly distributed. Verily officials anticipate that up to 20 million male mosquitoes could be released between now and the fall.
Mulligan said they don't anticipate eliminating Aedes aegypti would have any negative effects on flora and fauna there because the invasive species is not an essential part of the natural ecosystem in Fresno County.
“Invasive species disrupt and impact the environments into which they invade,” Mulligan said. “We do not expect that reducing or eliminating the populations of Aedes aegypti would have any negative effect on the environment, nor would it harm any insect-eating animals. In fact, the eradication of Aedes aegypti from California would actually have a positive effect on the human environment and on human health.”
Scientists have studied ways to use Wolbachia bacteria to control mosquito populations since the 1980s, but a number of successful field tests have shown its effectiveness in recent years. In 2011, Australian researchers released batches of Wolbachia-infected female mosquitoes around two neighborhoods near Cairns, Queensland, and then monitored the mosquito populations there.
Their goal then had been to stop the spread of the dengue virus — “Wolbachia completely blocks the ability of dengue virus to grow in the mosquito,” Monash University researcher Scott O’Neill explained to The Washington Post's Brian Vastag — and they found that that strain of Wolbachia had been successful in spreading through 100 percent of the population in one Cairns neighborhood and 90 percent in the other.
As Vastag reported at the time:
That’s because the bacterium is a cunning manipulator of insect reproduction. Somehow — scientists are unsure exactly how — females carrying Wolbachia reproduce more successfully than females that don’t carry it. This evolutionary strategy has been so successful that various strains of Wolbachia infect an estimated 70 percent of all insect species.Strikingly, though, this evolutionary marvel does not naturally infect the species of mosquito that carries dengue virus, [Aedes aegypti].So O’Neill and his colleagues set about finding a strain of Wolbachia that could infect Aedes aegypti while simultaneously protecting against dengue virus. They found that strain in their own back yard, inside Australian fruit flies.
An approach closer to the one being tried in Fresno this year was carried out last summer in southern China, where scientists released millions of Wolbachia-infected male Aedes aegypti mosquitoes on Shazai Island in an effort to stem the spread of the Zika virus. As The Post's May-Ying Lam reported, results were “stunning,” with 99 percent of the population suppressed after a year of tests.
Wolbachia mosquitoes have been released near Key West since earlier in the spring. And though there have been no local infections of Zika or dengue reported in California, Mulligan said they want to be prepared in case someone travels back from a country where they were infected. An Aedes aegypti mosquito could easily spread the virus from one person to another, as happened in Florida and parts of Texas last year, he said.
In a video produced to educate Fresno County residents about the project, Jodi Holeman, a director with the region's mosquito abatement district, agreed.
“Even though they're not actively and currently transmitting disease in California, it's our job to try to stay ahead of these diseases,” she said.