Mosquitoes have eliminated the last safe place for endangered forest birds on Maui, and the only solution may require releasing millions more mosquitoes.
Climate change has made once-uninhabitable higher altitudes now amenable to mosquitoes that infect the kiwikiu, or Maui parrotbill, with avian malaria at greater rates. Transmission of the disease has driven the bird population down to around 150, a number that places them at the edge of extinction, scientists said.
After a failed effort in 2019 to translocate kiwikiu from one side of Haleakala to the other — avian malaria still killed the birds — conservationists and officials are now pursuing two plans: Capture and ship a small group of kiwikiu to mainland zoos to breed the next generation, and cut down the mosquito population with what’s come to be called “mosquito birth control.”
Controlling the mosquito population will increase the chances of survival for not just the kiwikiu but “many, many Hawaiian forest bird species,” Lainie Berry, forest bird recovery coordinator at the Hawaii Department of Land and Natural Resources, told the Board of Land and Natural Resources last month.
“We don’t have anywhere on Maui that we feel we can move the birds into a safe location that is free of avian malaria,” she said.
Using this method to protect an endangered species “would be a first,” Berry told the board. But landscape-scale mosquito control is “not going to happen soon enough to prevent extinction of kiwikiu in the wild, which is why we want to have this insurance population in captivity,” she said.
Avian malaria rises and falls like a tide. All year, mosquitoes can transmit the fatal disease at lower elevations — the “low tide.” Generally from June to December, mosquitoes can travel to higher elevations, spreading the disease as they go — the “high tide,” according to Berry. Then there’s what she calls the “king tide.”
“If the conditions are right, we can have much higher influxes of mosquitoes and avian malaria into the forest bird zone, and this is devastating for the remaining populations up there,” Berry told the land board.
Climate change is exacerbating the issue with changing temperatures and precipitation patterns that create a climate more amenable to mosquitoes and disease transmission in what scientists thought of as safe refuges for Hawaiian forest birds, she said. Gradual warming now leads mosquitoes to higher elevations, while warm and wet weather that may have been historically uncharacteristic for an area now helps mosquitoes “swamp a previously ‘safe’ bird area,” Hanna Mounce, coordinator of the non-profit Maui Forest Bird Recovery Project, said in an email.
“So this a hot problem that is getting steadily worse every year, and we are running out of time.”
There are still small patches of forest where these birds are surviving, but “those are not protected from the continued encroachment of mosquitoes and disease,” Mounce said. And a single bite can infect and kill a kiwikiu, she wrote.
As the kiwikiu population has declined, the geographic range the birds can inhabit has shrunk. “We’re only finding them up at the very highest elevations now in a distribution of about 3,000 hectares, or 7,400 acres, which is very, very small,” Berry told the board. “And the highest densities that you see on that map are really only in about a thousand feet of vertical elevation.
So when a “king tide” comes, she said, “it doesn’t take very much for the mosquitoes to completely inundate the remaining kiwikiu habitat.”
To move the birds to the mainland, Berry and her team still need to plan, find funding, hop through some regulatory hoops, and consult experts and the public alike. Once the team plans with mainland zoos to build the infrastructure necessary to take in the birds, they’ll need to schedule a time that would impact the birds least.
Berry said they are aiming for January 2022, right before the breeding season.
The project will require about $300,000 in funding, she estimated. The three institutions that have committed to hosting the birds — the National Aviary in Pennsylvania, the Smithsonian Conservation Biology Institute in Virginia, and the Tracy Aviary in Utah — altogether can only hold 20 individuals, shy of the 30 birds Berry wants to keep safe, according to the newsletter Environment Hawaii.
“We are still looking at options for further capacity at zoos,” she said, adding that Hawaii island is also being investigated as a site to translocate birds.
But to prevent extinction and make Maui safe in the long run for kiwikiu and other endangered forest birds, the mosquito population will have to be controlled, Berry said.
“We have other species on Maui, too, that we’re incredibly concerned about, like ‘akohekohe which is also listed as endangered,” she said.
Many others throughout the state are in trouble too, such as the ‘i‘iwi, ‘akikiki, ‘akeke‘e, puaiohi, Oahu ‘elepaio, ‘alawi, palila, ‘akiapola‘au, Hawai‘i ‘akepa and ‘alala. Berry said there are other species that are not listed as threatened or endangered but are still at risk from avian malaria, such as Kaua‘i ‘amakihi, ‘anianiau and ‘alauahio.
“Avian malaria is present and impacting forest birds on all the Hawaiian Islands,” she said.
The mosquito control program is now underway, but “taking a little longer than we would hope,” she said. “We sent mosquitoes from Hawaii to the mainland for them to breed this line of Wolbachia into the mosquitoes. And those are the ones that when we release male mosquitoes, those are incompatible with the wild ones.”
In a 1967 experiment in Burma (now Myanmar), scientists nearly eradicated the local mosquito population in 12 weeks without understanding exactly how.
“At that time, people didn’t know the reason that causes this sterility, but they find this phenotype so they want to test it, and they find it is very successful,” said Dr. Zhiyong Xi, a medical entomologist at Michigan State University.
The experimental results showed that the population was eradicated in about three months — five or six generations — suggesting “the incompatibility principle can operate in nature.” That evidence helped Xi convince the State of Hawaii at a workshop in 2016 that he had the best technology to eradicate mosquitoes, he said, because he had already figured out the “Incompatible Insect Technique.” There is no genetic modification involved.
Without knowing it, the researchers in 1967 used the Wolbachia method that Xi now uses in his Michigan laboratory where, for two to three years, he’s been breeding Hawaii mosquitoes that won’t produce offspring. By injecting a strain of Wolbachia bacteria from a different mosquito species into the embryo of the invasive species that transmits avian malaria, the southern house mosquito (Culex quinquefasciatus), Xi renders the males unable to fertilize viable eggs.
“If males and females carry different Wolbachia strains, eggs don’t hatch,” Mounce said in her email.
In 2016 and 2017, Xi and his team released 197 million specially bred male mosquitoes in two locations in China, and pretty soon, the local populations of Aedes albopictus were almost entirely eliminated, according to the results published in the journal Nature in 2019.
“(In) six to eight weeks, we had almost zero mosquitoes,” Xi said. “Still, mosquitoes will be brought in from outside, so we’ll have some mosquitoes still.”
But the problem of neighboring mosquitoes flying in to fill the void wouldn’t be as severe on Maui. “This technology is especially good for an isolated island,” Xi said.
Xi already has the technology to breed about 60 million mosquitoes per week, about a third of which turn out to be males ready to leave eggs inert. To separate the 20 million male mosquitoes from the rest, Xi uses a machine that separates the slightly smaller male pupae from the female.
Should he receive the go-ahead to release the males in Hawaii, Xi estimated that the population would “go down largely in about three weeks.”
But when it comes to fully eradicating the mosquito population, he said, “How quickly that can happen depends on how much resources the government will put, and also the density of the Culex in that region. It is difficult to predict how much time it will take for the whole island.”
To move forward with the mosquito control program, Berry’s team is working on the environmental assessment. A public consultation process, which is months away, will give citizens a chance to comment on the prospect. The team will also need to develop methods for monitoring the effects on both the mosquitoes and the birds.
The next step, Berry said, is to get an import permit approved by the state Department of Agriculture to import the mosquitoes back into Hawaii. The University of Hawaii has applied for this permit, and the application is under review. Her team will need to build massive facilities for rearing and holding mosquitoes, the technology to distribute them, and “a lot of mosquitoes.”
Civil Beat’s coverage of Maui County is supported in part by a grant from the Nuestro Futuro Foundation.
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