July 22, 2024

Millions of mosquitoes are released from helicopters Hawaii in a last ditch effort to save rare birds that are sliding into extinction.

The archipelago’s endemic, brightly colored honeycreepers are dying of malaria carried by mosquitoes first introduced by European and American ships in the 1800s. Because the birds have developed no immunity to the disease, they can die after just a single bite.

Thirty-three species of honeycreeper have become extinct and many of the 17 that remain are highly threatened, with concerns that some could become extinct within a year if action is not taken. Now conservationists are urgently trying to save them with an unusual strategy: to release more mosquitoes.

Every week a helicopter goes down 250,000 male mosquitoes with a naturally occurring bacterium that acts as birth control on the islands of the remote archipelago. Already 10 million have been released.

“The only thing more tragic is ashes [the birds] died out and we didn’t try. You can’t try,” said Chris Warrenthe forest bird program coordinator for Haleakalā National Park on the island of Maui.

The population of one honeycreeper, the Kauaʻi creeper, or ʻakikikidropped from 450 in 2018 to five in 2023, with only a single bird left in the wild on Kauai Island, according to the national park service.

Honeycreepers have a canary-like song and incredible diversity: each species has evolved special beak shapes, adapted to eat different foods, from snails to fruit to nectar. They are an important part of the ecosystem, helping to pollinate plants and eat insects.

Southern house mosquitoes (Culex quinquefasciatus) is responsible for the transmission of avian malaria to honey planters across the Hawaiian Islands. Photo: Courtesy of NPS

Since Hawaiian birds did not co-evolve with avian malaria, they have very little immune response to it – the scarlet honeycreeper (‘i’iwi), for example, has a 90% chance of dying if bitten by an infected mosquito.

The remaining birds generally live at high altitudes above 1,200-1,500 meters (4,000-5,000 feet), where mosquitoes with the avian malaria parasite do not live because it is too cold. However, as the climate warms, mosquitoes move to higher altitudes.

Researchers use the incompatible insect technique (IIT), which involves releasing male mosquitoes with a naturally occurring bacterium that prevents the eggs of wild females they mate with from hatching.

Female mosquitoes only mate once, and the idea is that over time this reduces the overall population. The bacteria, Wolbachia, live naturally in most insects, which can only produce viable offspring with partners that have the same strain of Wolbachia.

The technique was used successfully to reduce mosquito populations in China and Mexico, with programs continuing in California and Florida. The effectiveness of this program should become apparent in the summer when mosquito populations typically boom.

The project is led by a coalition of groups including the US National Park Service, the State of Hawaii and the Maui Forest Bird Recovery Project, working under the auspices. Birds, not mosquitoes.

Dr Nigel Beebe, from the University of Queensland, researched how the IIT technique works on other mosquito species. “It’s much better than using pesticides that have huge off-target effects. Especially for things like the conservation of critical species,” he said.

However, he added that long-term eradication of mosquitoes is challenging, especially for mainland countries. “Eradication can be difficult unless one can prevent migration back into the landscape,” he said. “Islands are ideal for this.”

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