Will Mosquitoes Rescue The Honeycreepers?

KAHULUI, HAWAII – “Three, two, one, drop! Three, two, one, drop!” Sophie Shelbourne voices the countdown she uses when she’s riding shotgun in the yellow helicopter that is parked a few feet away outside a hangar at Kahului Airport.

The MD500 chopper is waiting to lift off on a sunny Maui morning and swoop over to Haleakalā mountain, the volcanic peak towering above the eastern side of the island. Commercial pilot Mike Piatt will ferry Shelbourne and her colleague from the Maui Forest Birds Recovery Project, Eden MacKinnon, about halfway up the mountainside, then fly close above the forest canopy in remote, rugged landscape.

There, Shelbourne will repeat her countdown mantra at roughly 8-second intervals. “I have an iPad that shows me the grid. Every time we drop, I can see where we are,” she said. At each “drop!” MacKinnon slides a biodegradable, cylindrical pod into an open-ended, plastic tube attached diagonally outside the chopper.        

That’s when the mosquitoes fly free. One thousand buzz their way out of each successive capsule, 250 pods in all, as they plummet into the forest. This is the crux of a multiagency strategy to curb mosquito-borne avian malaria that is wiping out native forest birds in and around Haleakalā National Park.

Under the Incompatible Insect Technique (IIT) that is being used, the 250,000 non-biting male mosquitoes dropped from each flight have been laboratory-reared in San Francisco with a naturally occurring Wolbachia bacteria strain. They are transported in special pressurized containers to Maui and released over forest-bird habitat to thwart mosquito reproduction: They mate with the island’s malaria-infected females which carry an incompatible Wolbachia strain, so the resulting eggs won’t hatch.

Forty-five minutes after takeoff, the chopper clatters back onto the tarmac. The release went smoothly, the team reports.  

The IIT project began in late 2023. It now releases a total of 1 million IIT mosquitoes each week onto Maui and Kauai, with two weekly flights on each island. Birds Not Mosquitoes (BNM), the federal-state-private collaboration that sponsors the effort, says it is a vital strategy in the race to thwart extinction of native honeycreepers. The birds' main threat to survival is avian malaria.

BNM partner American Bird Conservancy developed the drone option for dropping IIT pods when  dangerous weather or availability interferes with helicopter runs, said Adam Knox, the drone pilot and ABC mosquito project manager. The nonprofit’s drone, measuring about 8 feet in diameter between rotor tips, avoids the $1,500-per-hour cost of a commercial helicopter, is quieter, and operates on two 44-volt batteries rather than pricey fuel, he said.

But it takes longer for a drop mission because it carries just 23 pods in its rotating carousel and needs a new battery or a charge after about 15 minutes of flight. It thus takes many flights to release the 250,000 mosquitoes a chopper can drop in less than an hour. On the other hand, said Knox,  “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 as pilot and crew.”

Knox swaps out and charges batteries in the deep-forest location where he launches the drone. “It’s pretty efficient,” he said. “The drone will be on autopilot, so it's going to fly and all I need to do is watch.” He pointed to the plot points on a tablet screen that he uses to monitor it remotely. “As soon as it gets over that point, I just hit the button.”

The Wolbachia IIT strategy has been used around the world to fight mosquito spread of human diseases, and the insects cannot transmit Wolbachia to humans, officials say. The Hawai’i project is believed to be its first use for conservation goals.