Controlling Mosquito Populations by Releasing Mosquitoes

The original pilot program targeted Asian tiger mosquitoes, which can carry Zika, yellow fever and dengue, among other diseases.

The original pilot program targeted Asian tiger mosquitoes, which can carry Zika, yellow fever and dengue, among other diseases. Shutterstock

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Los Angeles County officials are hoping to replicate a successful pilot program that mated sterile male mosquitoes with biting females, leading to a reduction in the overall population.

Four years ago, officials in California’s Los Angeles County were approached by scientists with a strange-sounding proposal: release Asian tiger mosquitoes into residential neighborhoods to help control the population of Asian tiger mosquitoes.

The science behind the premise was relatively simple, according to MosquitoMate, the Kentucky-based company behind the concept. The mosquitoes, all non-biting males, had been sterilized. Once released into the wild, they’d seek out and mate with females, who would then lay sterile eggs that wouldn’t hatch. The males would die shortly after mating, hopefully leading to a population decline without having to rely on chemicals or pesticides. 

Officials with the Greater Los Angeles County Vector Control District were intrigued. Asian tiger mosquitoes were first detected in the county in 2011 and had spread through 15 communities in four years despite traditional remediation efforts throughout the district, a 1,340-square-mile area designated for targeted insect prevention and treatment. The mosquitoes can carry disease, including West Niledengue, chikungunya and Zika, among others. Grant funding was available to pay for a pilot release, and in 2015, the Greater Los Angeles County Vector Control District launched sterile mosquitoes across a 5.7-acre test neighborhood called south El Monte.

“We actually took boxes of mosquitoes and went into different yards and released them into the area,” said Susanne Kluh, scientific-technical services director for the vector control district. 

Following the release, scientists kept tabs on the mosquito population by doing regular trapping and by collecting eggs from release areas and monitoring the hatch rates. The results were impressive.

“We saw egg hatch rates reduced by 74 percent, meaning only 25 percent of the eggs hatched compared to before the releases,” Kluh said. “That would have to result in a significant reduction of adult activity, and anecdotally, our residents reported fewer bites.”

But the trapping results were less definitive, Kluh said, possibly due to lower-than-expected populations of adult mosquitoes in the test area. The county’s pilot program concluded after that first year, but MosquitoMate continued to test its technology in California, launching a large-scale release effort in Fresno with the help of Verily, a subsidiary of Google’s holding company. 

The Debug Fresno project, which began in 2017, targeted the Aedes aegypti mosquito, a different species of day-biting insect that had proliferated across the city. That first year, the project reported a 65 percent reduction of biting females; last year, that percentage went up to 95.

Kluh is hoping to establish a similar large-scale release targeting that mosquito in Los Angeles County, beginning next year. The Aedes aegypti has spread there as well, she said, and while the mosquito can carry disease, the main problem so far is one of comfort: the bugs are bugging the residents.

“California is such an outdoorsy environment, and our residents are really not pleased with the situation,” she said. “They cannot use their backyards because in a matter of minutes, you get a lot of mosquito bites if you don’t wear repellent. We’re not used to that.”

Traditional control methods, such as spraying, have thus far not been effective. There are too many yards, Kluh said, with too many wet hotspots that serve as breeding grounds for the insects. Informational campaigns urging residents to empty vessels with standing water haven’t helped.

“We are on this uphill battle trying to get the residents to help, trying to educate, and even so we’re not seeing the reduction we would need to bring the nuisance level down, let alone eliminate the disease risk,” she said. “We are really looking to this as maybe our potential savior.”

The vector control district is in the early stages of negotiations with MosquitoMate, trying to determine how much the program would cost to implement long-term. Early estimates are around $2 million per year, which would cost each resident around $4.70 annually. Kluh is hopeful that the county’s past success with the program will generate enthusiasm among both area residents and the vector control district’s board of directors, who would have to approve the measure.

“I’m really glad that we were part of this on the very ground level,” she said. “And I’m really hoping that this is going to be at a price point where we can afford to provide this to our residents as one of our mosquito-control options.”

Kate Elizabeth Queram is a Staff Correspondent for Route Fifty and is based in Washington, D.C.

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