The world’s first attempt at landscape-scale mosquito control for conservation holds promising health benefits for people too.

There are no environmental stumbling blocks in conservationists’ ambitious plan to save Hawaii’s imperiled honeycreepers by attempting to crash the mosquito population in native forest bird habitat, state regulators decided last month.


The National Park Service and Hawaii Department of Land and Natural Resources are planning to deploy a new conservation tool dubbed “mosquito birth control” to suppress mosquitoes on 65,000 acres of mountainous terrain in East Maui that aims to inhibit the invasive insect’s ability to produce fertile offspring.

The Board of Land and Natural Resources has endorsed a 250-page environmental assessment of the project’s impacts, setting Hawaii on course to pioneer the world’s first conservation use of landscape-scale mosquito control. The approval also builds momentum for a parallel project by state health officials that would tamp down on mosquitoes that spread deadly human disease, such as dengue fever and Zika virus.

Scientists predict warmer temperatures associated with climate change will amplify the risk of mosquito-borne illness affecting both animals and humans in the coming decades. Tandem mosquito control proposals in Hawaii stand to alter this trajectory by debuting the most powerful tool yet to reduce the spread of disease.

apapane, mosquito, forest birds, avian malaria
A mosquito bites the face of an apapane, a species of Hawaiian honeycreeper that is endemic to the islands. With its bright crimson feathers, the bird was prized by Hawaiian royalty. (Courtesy: Jack Jefferey Photography)

The measures would not eliminate mosquitoes in Hawaii, but in some targeted wilderness areas where forest birds dwell their presence could crash by more than 90%, researchers predict.

“Mosquitoes, like cockroaches, are probably going to survive a nuclear war,” said Grace Simmons, manager of the state Health Department’s Environmental Management Program. “(Eliminating them) is our ultimate goal, but at this time I don’t think that’s realistic.”

Mosquitoes infected with avian malaria can kill a bird with a single bite. First arrived in Hawaii in 1826, the insect has contributed to steep declines in populations of native honeycreepers, which evolved without mosquitoes for thousands of years.

Forest birds’ mountaintop habitat has historically been too cool for mosquitoes to exist, but climbing temperatures, a consequence of climate change, have allowed the blood-sucking bugs to invade new terrain toward the islands’ summits, setting off increasingly dire honeycreeper population declines.

These birds face many threats, including habitat loss and a host of invasive plants and predators, but mosquitoes carrying avian malaria are their worst enemy

Only 17 forest bird species are left in the islands, down from more than 50 that evolved here over thousands of years, according to the Audubon Society. Nearly all of those that persist appear poised for extinction in this century.

The project targets Maui as a starting gate because it hosts two of the birds at highest risk of being lost forever. Without interference, scientists predict the endangered kiwikiu and akohekohe could become extinct within two to 15 years. Four more threatened Hawaiian honeycreepers also reside on Maui.

This male kiwikiu was one of 13 endangered Maui parrotbills moved from one side of Haleakala to the other in 2019 in an effort to establish an “insurance population.” All but one of them died from disease-carrying mosquitoes. (Courtesy: Bret Nainoa Mossman/MFBRP)

Kauai is next in line for intervention. An environmental assessment of a plan to intervene in malaria’s death march to save the endangered akikiki, akekee and puaiohi, as well as five other at-risk forest bird species, is still being drafted.

Meanwhile, state health regulators are forging ahead to employ the same tactics as conservationists to reduce the public health risk of human mosquito-borne illnesses, including West Nile virus, Zika virus, chikungunya virus, yellow fever and dengue fever. The Hawaii Department of Health has hired a consultant to draft an environmental assessment of the project, a process set to begin on July 1 that’s expected to take about a year.

Mosquito control is a more powerful, innovative and environmentally friendly method of reducing human mosquito-borne disease, Simmons said. But it’s also more expensive.

“This is a costly venture for the state,” said Simmons, adding that California, Louisiana and Florida have similar mosquito-control programs. “We’re talking about millions of dollars. And we still have a long way to go. But I think that’s one of the biggest fears when it comes to climate change, that there will be more vector-borne diseases.”

Human mosquito-borne diseases are not currently present in Hawaii, although the state has a recent history of dengue fever outbreaks. Avian malaria and avian pox, which affect birds but cannot be spread to humans, are the only active mosquito-borne diseases in the state.

Bill Cullum aims his Stihl backpack sprayer during demonstration in Honaunau.  Cullum was infected with the Dengue virus in November and experienced terrible fevers, loss of apetite, joint pain and skin peeling with rash.
Big Island resident Bill Cullum sprays mosquito larvicide on his employer’s property during a 2015-2016 dengue outbreak. Cullum, who contracted dengue fever from a mosquito bite in 2015, experienced high fevers, loss of appetite, joint pain and skin rashes and peeling. (Courtesy: Cory Lum/Civil Beat/2016)

In 2016 more than 10,000 scientists, public health experts and government leaders from around the world convened at the International Union for the Conservation of Nature’s World Conservation Congress in Hawaii with the goal of advancing solutions to some of the most pressing problems facing the planet.

At a workshop aimed at identifying strategies to address the spread of dengue fever in the islands, landscape-scale mosquito control was identified as the most promising means to reduce the threat of a wide spectrum of mosquito-borne diseases for both public health and conservation.  

Scientists have since collected wild southern house mosquitoes from high-elevation forests on Maui, Kauai and Oahu where native honeycreepers live and, in a California lab, those bugs have been inoculated with a bacterium called Wolbachia.  

The southern house mosquito, and most insects in the world, already carry one of five strains of Wolbachia in their reproductive tract. But scientists are finding that if they drain the southern house mosquito of its natural bacterium strain and infect it with a different strain sourced from another species of Hawaii mosquito, they’ll achieve a new form of mosquito birth control.

“There is literally almost no risk to the environment, to public safety,” said Cynthia King, an entomologist for DLNR. “The only risk is that this doesn’t work. We need to move this forward to see if this is what can save our honeycreepers because the alternative is that they will go extinct.”

None of the inoculated insects have been imported to Hawaii yet. Researchers are studying shipping routes to figure out the most efficient way of transporting the mosquitoes to the islands.

Scientists are still awaiting a decision from the Environmental Protection Agency that could come this month and would allow the project to move forward with releasing into the wild a large batch of male mosquitoes, which are infected with the different Wolbachia strain, to mate with wild females. The distinction in bacteria strains between the males and females would render their offspring sterile.

Since female mosquitoes mate only once, this incompatibility would send the wild mosquito population plummeting, achieving some relief for the birds.

And since male mosquitoes don’t bite, there would be no risk to the birds (and no added nuisance for humans) by releasing the batch of male mosquitoes into the birds’ mountaintop habitat.

The EPA decision would set guidelines for mosquito releases as well as monitoring, and it would set the project up to achieve another required regulatory approval from the Hawaii Department of Agriculture. This would clear the project to begin feasibility studies where researchers would study how far the Wolbachia-infected mosquitoes travel and how they behave upon release across small sites of about 3,000 acres.

It’s not a one-and-done method. Like pulling weeds or trapping rats, mosquito releases would need to be performed again and again to prevent a population rebound. 

Welsh artist Ralph Steadman depicted this mosquito as part of an effort to raise awareness for endangered species. (Courtesy: Ralph Steadman)

Conservationists anticipate small-scale mosquito releases could begin on Maui as soon as 2024, with larger landscape-scale releases to follow in 2025. Mosquito releases would be primarily conducted by high-flying drones.

Tens of millions of dollars would be required to support the endeavor in the long term. Funding has already been secured from numerous federal and state agencies and nonprofit organizations, including the U.S. Fish and Wildlife Service, the U.S. Geological Survey, NPS, DLNR, the Hawaii Legislature, the American Bird Conservancy and The Nature Conservancy.

The use of this tool in Hawaii would be the world’s first for conservation purposes. But it’s been employed for a half-century as a public health tool to tamp down on diseases that are spread to humans by mosquitoes in several U.S. states and 15 different countries. 

In parallel with conservationists, public health officials in Hawaii want to utilize the mosquito birth control method to build a reserve of Wolbachia-infected male mosquitoes to be deployed in targeted areas in the event of a human mosquito-borne disease outbreak. 

Hawaii’s most recent and largest mosquito-borne disease outbreak infected 264 people on the Big Island with dengue fever in 2015 and 2016. Four people contracted dengue on Oahu in 2011. And 122 people on Maui, Oahu and Kauai were sickened with dengue in 2001 and 2002.

Dengue, sometimes called breakbone fever for the severe joint pain it can bring, is a mosquito-borne disease that can be deadly in humans, with symptoms ranging from nausea and headache to high fever and internal bleeding. 

Instead of targeting only the southern house mosquito, which can carry avian malaria as well as West Nile virus, health officials would also incorporate two additional human disease-carrying species: the aedes aegypti and the aedes albopictus.

Of the roughly 3,000 mosquito species roaming the earth, six of them reside in Hawaii.

There are several ways to control mosquitoes. While there are efforts outside of Hawaii to sterilize mosquitoes with genetic modification, the Wolbachia method is not one of them. 

Testimony in opposition to the mosquito project is peppered with misconceptions about what’s actually being proposed.

All of the organisms involved in the project are already found in Hawaii. The southern house mosquito is abundant in the islands. So is Wolbachia, a naturally occurring bacteria found in more than half of all insect species worldwide, including honeybees and fruit flies.  

For scientists working on the project, this is an important distinction. There are no foreign imports. Nothing in the insect’s genome will be manipulated. In short, it’s not GMO.

Mosquitoes naturally infected with Wolbachia already regularly bite people in Hawaii. None of the mosquitos associated with the proposed projects would bite people, however, because the project is limited to male mosquito releases. Only female mosquitoes bite.

“This is a method that’s been successful and that’s been studied for many, many years but because of misinformation the message tends to get mixed,” Simmons said. “We really want to focus on that this is a natural form of (mosquito) suppression that we’re taking advantage of.”

Civil Beat’s coverage of Maui County is supported in part by a grant from the Nuestro Futuro Foundation.

Civil Beat’s coverage of climate change is supported by the Environmental Funders Group of the Hawaii Community Foundation, Marisla Fund of the Hawaii Community Foundation and the Frost Family Foundation. 

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