EPA approves release of billions of ‘friendly’ mosquitoes in Visalia

Pilot project will use genetically engineered, non-biting mosquitoes carrying a gene to kill invasive mosquitoes that have been plaguing Visalia neighborhoods

VISALIA – Neighborhoods in Visalia will soon be swarming with more mosquitoes than ever before, but in a good way, according to local and federal agencies. 

The Delta Mosquito and Vector Control District, which handles mosquito abatement in northwestern Tulare County, has approved a pilot project to release billions of lab grown mosquitoes designed to reduce the population of Aedes aegypti, an invasive mosquito that has been plaguing Visalia for the last few years. Unlike mosquitoes native to California, this smaller breed prefers to feed on human blood rather than animals and has adapted to its food. Native mosquitoes are much larger and prefer to feed on cattle, which have trouble swatting away the mosquitoes, while they take long drinks of blood. The aedes aegypti is smaller, so it is harder to see, and takes many tiny sips quickly and usually around the mid back or ankles. This makes them harder to swat and gives the appearance there is a swarm of mosquitoes, when in reality it might be one mosquito biting your ankles a dozen times. They also bite day and night, and not just at dawn and dusk, because humans are active at all hours.

Since first being detected in 2013, this invasive mosquito has rapidly spread to more than 20 counties throughout the state, increasing the risk of transmission of dengue, chikungunya, Zika, yellow fever and other diseases. While chikunga, yellow fever and Zika are typically not associated with severe illnesses, dengue can lead to shock, internal bleeding, and even death, according to the Centers for Disease Control and Prevention.

“Given the growing health threat this mosquito poses across the U.S., we’re working to make this technology available and accessible,” said Grey Frandsen, CEO of Oxitec, a British developer of biological solutions to control pests that transmit diseases. “These pilot programs, wherein we can demonstrate the technology’s effectiveness in different climate settings, will play an important role in doing so. We look forward to getting to work this year.”

Under the pilot project, Oxitec will release “friendly” male mosquitoes genetically engineered with a self-limiting gene that infects female mosquitoes and prevents them from creating female offspring, leaving only male mosquitoes in the gene pool. Only female mosquitoes bite and are capable of transmitting diseases, which is why they are targeted and the engineered males will only mate with Aedes aegypti females. The altered mosquitoes also have a fluorescent marker gene which enables them to be distinguished from invasive mosquitoes for effective monitoring.  The self-limiting gene cannot establish in the ecosystem and does not impact non-target species, such as bees, butterflies, and other wildlife. 

Dr. Mustapha Debboun, general manager of the Delta Mosquito and Vector Control District, said the pilot project is just part of the district’s integrated approach and will not replace insecticides and other control measures but will be an additional tool as Aedes aegypti has become resistant to pesticides. 

“We look forward to working in partnership with Oxitec and have been impressed with results from their previous projects in Brazil and the Florida Keys,” Dubboun said. “They have proven the effectiveness that their biological solution can deliver in suppressing this non-native invasive and disease-spreading mosquito.”

The pilot project for the genetically altered mosquitoes was approved March 7 by the U.S. EPA specifically for Tulare County, Calif. and Monroe County, Fla. This approval is an extension of the Experimental Use Permit (EUP) granted in 2020 by the EPA for a pilot project in the Florida Keys, which was successfully carried out in 2021. 

The release of mosquitoes is expected to happen this spring but not until after it is approved by the California Department of Pesticide Regulation. The DPR has not made any announcement on the issue and did not return calls as of press time. The DPR’s review will include a scientific evaluation of Oxitec’s Aedes aegypti technology and will include opportunities for the public to engage and review the results of the state’s evaluations. If approved, billions of genetically engineered (GE) mosquitoes will be released over a 2-year period in Tulare County, beginning in 2022, and the current GE mosquito release in Monroe County, Fla., will be extended for another 2 years.

In anticipation of this research approval, the Delta Mosquito and Vector Control District’s seven-member Board of Trustees unanimously approved the pilot project in October 2021. Oxitec is also developing a research and development facility in Visalia, which will provide support to Oxitec programs in the US and globally.


Environmental Concern
While Visalians might want to rid their backyards of the mosquitoes at all costs, environmental groups are asking the government to do more studies and provide more information to the public before moving forward with the live experiment.

Friends of the Earth, an outspoken environmental policy advocacy group, and the Center for Food Safety, an environmental group promoting organic, ecological, and sustainable alternatives to industrial agriculture, issued a joint statement following the EPA’s approval of the world’s largest release of GE mosquitoes into the nation’s most populous and agriculturally significant states. 

Based in Washington, D.C. with offices in Berkeley and Sacramento, the groups stated there is no publicly available data supporting Oxitec’s claims that GE mosquitoes will reduce incidence of mosquito borne diseases. They cited an independent peer-reviewed study from Yale University revealing that over two years of continual releases in Brazil the GE mosquitoes failed to reduce populations of Aedes aegypti. The Yale study also found that the GE mosquitoes bred with local Aedes aegypti, resulting in hybrid mosquitoes in the wild that may be more aggressive, more difficult to eradicate and may increase the spread of mosquito-borne disease.

“GE mosquitoes could result in far more health and environmental problems than they would solve,” said Dana Perls, Food and Technology Program Manager at Friends of the Earth, and a California resident. 

Oxitec’s mosquitoes are regulated under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) and the EPA stated the mosquitoes would not have any “unreasonable adverse effects to humans or the environment.” Additionally, animals are not expected to be harmed from the potential reduction in the local Aedes aegypti population because predators that eat mosquitoes generally have a diverse diet and none are known to use the invasive pest as a sole or critical food source. No mosquitoes will be released within 500 meters from wastewater treatment facilities, commercial fruit orchards or livestock facilities. 

The experimental release will purportedly investigate whether the GE mosquito can reduce the population of Aedes aegypti mosquitoes and the diseases it carries yet California does not have any known human cases of yellow fever, dengue, chikungunya and Zika. 

“Releasing billions of GE mosquitoes makes it likely that female GE mosquitoes will get out and create hybrid mosquitoes that are more virulent and aggressive,” said Jaydee Hanson, Policy Director for the International Center for Technology Assessment and Center for Food Safety. “Other public health strategies, including the use of Wolbachia infected mosquitoes, could better control the Aedes aegypti in California and Florida.”

The EPA said no hybrid female mosquitoes have been detected during Oxitec’s field testing so far, and no detections are expected based on its risk assessment. The EPA said it is requiring Oxitec to monitor and sample the mosquito population every week to ensure no female mosquito offspring survive. If an unforeseen detection occurs, Oxitec will be ordered to stop the releases and apply adulticide and larvicide pesticides to the treated area where the surviving females were detected. The EPA continues to maintain the right to cancel the EUP at any point during the 24-month period.

The groups argue the EPA did not publicly release any data from Oxitec field trials in Florida or Brazil and key information about health effects, including allergenicity and toxicity, was redacted from the company’s application for a permit citing proprietary concerns about the technology. The EPA did not require key scientific assessments, including an endangered species assessment, public health impact analysis, or caged trials ahead of any environmental release. The EPA declined to convene a Scientific Advisory Panel as it does for other new pesticides.

The EPA stated it did an in-depth scientific evaluation process prior to its Experimental Use Permit in May 2020, the pilot project in the Florida Keys in 2021 and now the extension of the permit to expand the pilot project to Tulare County and three other California counties (Stanislaus, Fresno, and San Bernardino). The EPA’s process also included a 30-day public comment period after which the agency reviewed and responded to each public comment before issuing its approval.

The environmental groups claim there was strong opposition to the release of the GE mosquitoes in Monroe County, Fla. in April 2021. They said neither the Florida Keys Mosquito Control Board nor Oxitec  informed community residents about the locations of release until three days beforehand, and there was no informed consent by affected community members prior to release.

Delta Mosquito and Vector Control District said it will identify neighborhoods that have an abundance of invasive Aedes aegypti mosquitoes and then carry out a “robust community education and outreach process” to identify homeowners that are interested in hosting a mosquito release box or trap.

Oxitec said it will work hand-in-hand with its government partners in Florida and California as well as with residents, communities, civic groups, non-profits, businesses, and many other stakeholders who will guide, shape, or contribute to the projects. Oxitec said outreach efforts include extensive public engagement efforts, ensuring that each project benefits from local participation, local leadership, inclusive outreach and education, and opportunities for learning and sharing feedback. 

“After a successful start to our project in 2021, we look forward to continuing our partnership with Oxitec,” said Andrea Leal, executive director of the Florida Keys Mosquito Control Board. “We made significant progress during the pilot project last year, we look forward to continuing this important work during this year’s mosquito season.”

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