More mosquitoes? In Fresno, a truck sprays millions of bacteria-infected mosquitoes to halt advance of Aedes aegytpi.

By now, Bonnie Smith and her three children are used to seeing it. Every couple of days, a white van rumbles slowly down their street in suburban Fresno, Calif. It’s the shape and size of a mail truck‚ but it delivers only annoyance. Specifically: mosquitoes.

As it drives, it sprays out millions of them. It’s been a couple of months since the sprayings started and already Smith has seen a difference in the air.

“We’ve noticed ’em buzzing around and in the house more than usual,” Smith says. “For sure!”

To explain why a program called “Debug Fresno” is spreading more bugs, you have to go almost 400 kilometres south, to Long Beach.

“We have two,” says Lamar Rush, examining a mosquito trap with a magnifying glass. “So far.”

Rush, operations director for the City of Long Beach’s vector control program, has set dozens of traps for his tiny, potentially dangerous prey: Aedes aegypti, the main mosquito behind the spread of the Zika virus, a disease associated with microcephaly in infants. It prefers to live in and around houses, side-by-side with its preferred food source: humans.

The mosquito, which can also transmit dengue, yellow fever and other diseases, has been working its way north. And this summer, for the first time ever, it was spotted in this city only 40 kilometres from Los Angeles.

One was found in Luz Rosales’s Long Beach backyard. The yard is littered with toys, tarps covering furniture, and odds-and-ends, all of which can hold enough water to allow the mosquito to breed. The news that her house might be sheltering this dangerous insect, Rosales says, was a shock.

“I have a friend who’s pregnant,” Rosales says. “I’m worried about her.”

She needn’t worry too much about Zika, not yet. Cases in the U.S. are way down, according to Dr. Henry Walke, chief of the Bacterial Special Pathogens Branch at the U.S. Centers for Disease Control.

“There is only one case,” Walke says. “And … at this time last year, we were seeing a significant number of local transmission cases.”

For reasons scientists still can’t explain, the spread of the disease has seemingly slowed worldwide. But experts warn that ignoring the mosquitoes that can transmit Zika would be a big mistake, because Aedes aegypti is slowly spreading across the country. This year, according to the CDC, the number of U.S. counties reporting the mosquito has increased by 21 per cent.

Which brings us back to that mosquito truck. The technology used by the Debug Fresno program was designed by Verily, a Silicon Valley company owned by Alphabet Inc, Google’s parent company.

Steve Mulligan, who oversees mosquito control in Fresno County, says the mosquitoes being spread were infected by bacteria called Wolbachia. It’s naturally occurring in many mosquitoes, but if transmitted to Aedes aegypti, it interrupts the females’ reproductive cycle. All the infected mosquitoes being released are non-biting males.

“They have a job to do,” Mulligan says, “and that job is to seek out and find all of these local females so that the eggs are infertile and no offspring are produced. And so as we continue this program we’ll see fewer and fewer of these local mosquitoes.”

To determine whether it’s effective at reducing the Aedes aegypti population, they’ve set up traps across the area where the males have been released.

Mulligan checks one trap the size of a small flower pot.

“Any small container that holds water can be attractive and serve as a source for this mosquito to lay her eggs and for her young to develop,” Mulligan says.

Then they transport their catch to the lab and count the mosquitoes to see if the species they’re targeting is actually declining.

Brittany Deegan dumps a bunch of mosquitoes onto a petri dish, teases and separates each mosquito with her forceps, then peers at them through a microscope.

“We’re looking for the Aedes aegypti,” she says, “we separate the male and female, and we count them.”

Other mosquito-release programs exist, but most involve genetically altering the mosquitoes with a gene that causes the offspring to die. Verily’s program involves automated mass rearing and sex-sorting to allow them to release so many males into the targeted neighbourhoods.

Already those with Debug Fresno say they’re fielding calls from around the world, including Canada.

Fiona Hunter, an entomologist at Brock University in St. Catharines, Ont., has found that for the past two years, mosquitoes that can carry Zika have been found in Ontario.

“If you had asked me whether these (Aedes) albopictus and aegypti would establish in Canada even five years ago, I would have laughed at you,” Hunter says.

“We are hoping that they don’t become established populations and therefore we don’t have to have this discussion of whether we would use the Debug Fresno model.”

Hunter doubts this is the most effective way to control them, because while releasing millions of infected males every year could work, it’s expensive.

“It’s a great business model to have to continuously release infected males to bring down the populations,” Hunter says. “But whether or not society wants to absorb those costs, that’s another issue.”

Debug Fresno is still in its pilot stage, and researchers say it’s still too early to tell if the program is paying off. Anecdotally, there certainly seem to be more mosquitoes in the air. Mulligan says even though the males don’t bite, they’re attracted to humans, because that’s where they expect to find females.

Bonnie Smith says she doesn’t mind being a tasty guinea pig.

“It’s kind of interesting to find out how it’s going to work and ultimately reduce the mosquito population,” Smith says.

So when that van comes around, she’s actually happy to see it. More mosquitoes, she says: just what they need.
By Kim Brunhuber, CBC News
Photo credit: Kim Brunhuber/CBC