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Do They Bite, Or Don’t They? Common Myths And Misconceptions About “Debug Fresno”

James Gathany, via Wikimedia Commons
The goal of the Debug Fresno project is to develop a tool that can reduce populations of Aedes aegypti, an invasive mosquito species that can transmit dangerous diseases.

Debug Fresno is a pilot project aimed at developing a technique to control a nasty species of invasive mosquito known as Aedes aegypti. It involves releasing millions of mosquitoes infected with wolbachia, a naturally occurring bacteria, in three test areas in Fresno and Clovis. It may seem like a paradox, but the ultimate goal is to reduce the overall A. aegypti population, and techniques like this have succeeded in other parts of the world.

That’s what Debug Fresno is—but it’s also important to talk about what Debug Fresno isn’t. Many Fresno residents feel squeamish, uncertain and even mistrustful about lab-grown mosquitoes in their neighborhoods, and they’ve raised a lot of questions about the project with local authorities and in online communities. Here, we’ve collected some of the most common concerns and addressed them with the help of scientists involved in the project.

1) Debug Fresno is releasing biting mosquitoes into Fresno County.

Mostly false. Steve Mulligan of the Fresno Consolidated Mosquito Abatement District says this is the most common misconception that he has to clear up. Only female mosquitoes bite, and the intent is that all mosquitoes released by Debug Fresno are males. Is it possible some females could hitchhike into these releases? Yes, though it’s very unlikely.

Jacob Crawford, a senior scientist with Verily, the company that’s growing the mosquitoes, says he and his colleagues meticulously sort the mosquitoes by gender in the lab—first by hand and then using a computer algorithm, to keep females out. “We have extremely stringent [quality control] processes before any of the male mosquitoes leave the factory or our headquarters here in San Francisco,” he says, “so the probability of anything like that happening is extremely low.”

2) These mosquitoes are genetically modified.

Myth. This technology involves no genetic changes, and no insertion of genetic material from one organism into the genetic material of another. These mosquitoes are infected with wolbachia, a naturally occurring bacteria that’s found in about two-thirds of insect species—including other mosquitoes. Scientists infect the mosquitoes by micro-injecting wolbachia into their eggs, without making changes to their genes.

That being said, at least one company out there that has created genetically modified mosquitoes. It’s a British company called Oxitec, and it is in no way related to Debug Fresno. The EPA did approve Oxitec’s mosquitoes for a field trial in the Florida Keys, but residents there wouldn’t allow it—and instead approved of a test of the same mosquitoes used by Debug Fresno.

3) They could mutate in the wild.

Almost entirely false. All species mutate over time, extremely slowly, regardless of what humans do to them—it’s one way organisms evolve and adapt. But since no genetic changes were introduced in these mosquitoes, there’s no reason to believe this project alone could cause any mutations.

"Debug Fresno" Is Back - And It Seems To Be Working

4) They could develop a resistance to wolbachia.

Mostly false—but with caveats. The only way this could happen is if a critical mass of females with wolbachia make it into the mosquito releases that are supposed to be males-only. This technique only works if a male with wolbachia mates with a female without it. But if they both carry it, they create offspring who also carry it, and they go on reproducing. That’s why Debug Fresno partners are going to great lengths to release only males with wolbachia.

However, should females make it into the releases, and should wolbachia become common within the local A. aegypti population, this tool wouldn’t be as effective in controlling the population—but it would still reduce disease transmission, which is the ultimate goal of the project. Female A. aegypti mosquitoes with wolbachia don’t transmit disease as well as females without the bacteria.

This technique of establishing wolbachia in the entire population is already being used in Africa to reduce dengue fever. However, Debug Fresno partners say they are going to great lengths to make sure this doesn’t happen.

5) They could disrupt pollination.

Myth. While it’s true that mosquitoes are pollinators, this concern is unfounded for three main reasons:  1) A. aegypti mosquitoes are invasive—they only arrived around five years ago, and so the ecosystem does not need them in order to survive. 2) Close to 30 other mosquito species exist in this region, and would continue to pollinate even if A. aegypti were knocked out of the ecosystem altogether. 3) It’s estimated that almost two-thirds of all insect species contain wolbachia naturally, without human intervention, so this species is not introducing anything that’s not already out there in the wild.

6) They’ll infect the animals that eat them and disrupt the food chain.

Myth. “Wolbachia is a naturally occurring bacterium that is found in numerous insect species, including some butterflies, some dragonflies, and several mosquito species including mosquitoes that we have in this area,” says Steve Mulligan, manager of the Fresno Consolidated Mosquito Abatement District. “So any predators are already exposed to eating insects with wolbachia.”

When frogs, birds, bats, lizards, and other predators eat these mosquitoes, they’re not ingesting anything they can’t handle, and they’re not in turn passing anything harmful up to their predators.

7) They can infect humans with wolbachia—and possibly sterilize them.

Myth. First, wolbachia doesn’t affect humans. It will not sterilize us. Plus, only female mosquitoes bite, and female mosquitoes with wolbachia should not be released as a part of this project. Plus, many other mosquito species do carry wolbachia—including many species that bite humans—so we’re already exposed to it from other mosquito species.

Joe Moore is the President and General Manager of Valley Public Radio. During his tenure, he's helped lead the station through major programming changes and the COVID-19 pandemic, while maintaining the station's financial health. From 2010-2018 he served as the station's Director of Program Content. In that role, he also served as the host of Valley Edition, and helped launch and grow the station's award-winning local news department. He is a Fresno native and a graduate of California State University, Fresno.
Kerry Klein is an award-winning reporter whose coverage of public health, air pollution, drinking water access and wildfires in the San Joaquin Valley has been featured on NPR, KQED, Science Friday and Kaiser Health News. Her work has earned numerous regional Edward R. Murrow and Golden Mike Awards and has been recognized by the Association of Health Care Journalists and Society of Environmental Journalists. Her podcast Escape From Mammoth Pool was named a podcast “listeners couldn’t get enough of in 2021” by the radio aggregator NPR One.
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