Drones and helicopters dropped dozens of biodegradable pods filled with around a thousand mosquitoes in the forests of Hawaii in June.
These mosquitoes are special because they are lab-reared and do not bite. These are male mosquitoes that carry a common bacterium. This bacterium results in eggs that do not hatch when the males mate with female mosquitoes. Scientists are hopeful about this approach in reducing the population of the island’s invasive mosquitoes, which are decimating native bird populations, such as the scarce Hawaiian honeycreepers.
These birds are key pollinators and seed dispersers. They also play a central role in Hawaiian culture. At one point in time, there were more than 50 known species of honeycreepers in Hawaii; however, there are only 17 left today, most of which are endangered.
Development and deforestation are to blame, but according to Dr. Chris Farmer, Hawaii program director for the American Bird Conservancy (ABC), the threat lies in avian malaria, which is spread by mosquitoes. The insects are not indigenous to Hawaii. They were first reported in 1826, likely carried over by whaling vessels without any intention. These mosquitoes led to waves of extinction as many local birds, like honeycreepers, had no resistance to avian malaria.
Since mosquitoes thrive better in the tropical habitats, which are warmer, in the low elevations of Hawaii’s islands, the remainder of the honeycreepers found a refuge higher up in the mountains of islands such as Maui and Kauai. However, with climate change, even higher elevations are receiving warmer temperatures, and mosquitoes are moving upwards. Populations of birds have been dwindling even at higher altitudes. Ultimately, as the mosquitoes move upwards, habitable spaces for the birds are reducing.
The search is on for a solution to control mosquito populations and provide a chance at survival to the honeycreepers. However, it is difficult to deal with mosquitoes on a landscape scale. Pesticides cannot be used either, as they might kill fruit flies and damselflies, which are essential for the ecosystem. Mosquitoes are also a considerable risk to human health, spreading human malaria, dengue fever, and the Zika virus, among others. To thwart this problem, scientists have come up with various solutions, including the incompatible insect technique (IIT).
IIT involves releasing male mosquitoes that contain a strain of naturally occurring bacteria called Wolbachia, which results in eggs that do not hatch when they mate with wild females. With repeated releases over time, the wild population should decline as a result.
In 2016, ABC, together with Birds, Not Mosquitoes, a multi-agency partnership that aims to protect Hawaiian honeycreepers, concluded that IIT had the best chance of succeeding in Hawaii.
Different strains of Wolbachia were tested within southern house mosquitoes found in Hawaii. This is because mosquitoes that cause avian malaria are different from the ones that transmit human malaria. The process took several years due to community engagement and regulatory processes.
The project gained speed in 2022, rearing millions of mosquitoes with the suitable Wolbachia strain. In the following year, they started releasing the lab-grown mosquitoes in areas where the honeycreepers live in Maui, dropping them in biodegradable pods from helicopters.
Right now, scientists are releasing 500,000 mosquitoes in Maui and 500,000 in Kauai. Scientists have made a rough estimate of the number of mosquitoes present in the wild, and are planning to release 10 times as many of these lab-grown mosquitoes, so that they find these females and mate with them. This leads to the production of eggs that don’t hatch.
This is the first instance of using IIT for conservation purposes. However, the process isn’t applicable in every scenario. In Hawaii, the process worked out because the invasive mosquitoes have only been around for 200 years, and are not ecologically that crucial. In the case of dealing with native populations, the process might be detrimental to the ecological balance.
One of the major hurdles in releasing these insects is due to mountainous terrain, which is prone to strong winds and unpredictable weather. The program has mainly relied on helicopters, which are expensive. Drones, on the other hand, have been more successful in deploying the mosquito-laden pods.
It is the “first known instance of specialized mosquito pods being dropped by drones,” says Adam Knox, project manager for ABC’s aerial deployment of mosquitoes. “We have more flexibility with deployment timing in areas that generally have very unpredictable weather, and it’s safer because no humans need to ride in the aircraft to deploy the mosquitoes.”
Drones reduce costs, team flight times, noise, and emissions, leading to cheaper and sustainable flights. Scientists expect to see results of the deployments in about a year. However, the developments will buy time for the birds to recover.
If mosquito populations were brought under control, the honeycreepers would have time to replenish their dwindling populations with greater genetic diversity. They may even develop their resistance to avian malaria. One such honeycreeper species, the ‘amakihi, is already showing signs of such resistance.
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