Saving Maui's Honeycreepers: The Plan to Suppress Malaria-Carrying Mosquitoes

Written by Haleakalā National Park for the public review of the project's environmental assessment, with comments due January 23, 2023.

Within the next ten years, avian malaria spreading unchecked will push many native Hawaiian honeycreepers to extinction — but it is not too late to save them. The Department of the Interior, with other federal agencies, organisations and partners, and with public input, plans to suppress southern house mosquitoes across Hawaiʻi to slow the spread of malaria and give the honeycreepers a chance to recover.

The plan starts on Maui, to save two endangered species: the kiwikiu, of which fewer than 200 remain, and the ʻākohekohe, of which fewer than 2,000 remain. Haleakalā National Park, the Hawaiʻi Department of Land and Natural Resources, the U.S. Fish and Wildlife Service, The Nature Conservancy and partners are coordinating the work.

Why an environmental assessment

The birds live on state and federal land, so the project must follow the National Environmental Policy Act and the Hawaiʻi Environmental Policy Act, which require agencies to assess environmental effects before deciding to act. That is done in an environmental assessment, published for public review — and, because such documents are full of scientific and legal jargon, the park summarised its main points.

Southern house mosquitoes carry avian malaria to honeycreepers across the Hawaiian Islands. Credit: Centers for Disease Control and Prevention.

What is happening

Honeycreepers live in cool, high-elevation forest that was safe from mosquitoes through their evolutionary history. Climate change is warming those areas, letting the invasive southern house mosquito move in, feed on the birds and spread avian malaria — a blood parasite passed on by mosquito bites. Long separated from mosquitoes, the honeycreepers lost whatever resistance their mainland ancestors had, so a single infected bite can kill. Unchecked, the mosquito could drive Maui's native honeycreepers extinct in as little as two years.

The incompatible insect technique

After years of research and planning, the project team found the incompatible insect technique (IIT), already used in the United States and elsewhere, one of the most reliable ways to suppress the mosquitoes.

• How. Incompatible male mosquitoes are released to mate with wild females; their eggs never hatch. A female mates only once, storing the sperm until she lays, so a female that mates with an incompatible male has lost her one chance. Releases must outnumber the wild males, and scientists calculate how many are needed.
• Wolbachia. What makes the males incompatible is a naturally occurring bacterium in the sperm and egg cells of southern house mosquitoes — and of most insects worldwide. Its many strains have diverged so far that some cannot combine; mosquitoes carrying mismatched strains lay eggs that never hatch.
• Safe. Wolbachia spreads only from mother to offspring; it cannot pass by contact or bite, so birds, people and other insects are not at risk — nor can it pass between adult mosquitoes. The approach is safer and more effective than common options such as pesticides.
• Males only. Releasing females with the same strain would let them breed with the released males and increase mosquitoes, so females are carefully sorted out in laboratories — most likely on the mainland, breeding mosquitoes originally caught in Hawaiʻi — before the males are packaged and shipped for release.
• For how long. IIT would continue, with monitoring, until malaria is reduced enough to stabilise threatened and endangered honeycreeper populations, or until new techniques are developed.

Releasing the mosquitoes

• Where and when. Males would go to existing breeding grounds across East Maui, where mosquitoes most threaten the birds. In the coldest months, mosquitoes are thought to breed mostly at warmer, lower elevations — which coincides with most honeycreepers' breeding season, so fewer releases would be needed up high while the birds nest. Releases at lower breeding grounds would likely continue year-round, from twice a week to once a month, with monitoring to show how well it works.
• How. Mainly by drone — safe, efficient, cheaper and quieter than helicopters, and already used successfully for similar mosquito control, though the exact drones and release method were still to be chosen. Field teams may sometimes release mosquitoes by hand, and helicopters may be used briefly for releases and to carry monitoring teams.

Effects

The assessment analysed 64,666 acres of East Maui.

• Wilderness. About 14 percent of the area is congressionally designated wilderness, which the Wilderness Act of 1964 and the Park Service protect through measurable qualities including untrammeled, natural, undeveloped, and solitude or primitive recreation. The project would harm the untrammeled quality but benefit the natural quality, by preventing the extinction of species essential to the wilderness.
• The public. Residents would see neither fewer nor more mosquitoes. The southern house mosquito bites only at night; the project targets remote breeding grounds far from homes; and the species does not usually travel far — males probably even less than females.

How to help

The park asked the public to read the assessment and comment through its planning website, and to share information about the project from Haleakalā National Park, the Maui Forest Bird Recovery Project and Birds, Not Mosquitoes.

Sources

• Haleakalā National Park, National Park Service, "The Time Is Now: Saving Maui's Honeycreepers Before It Is Too Late." https://www.nps.gov/articles/the-time-is-now-saving-maui-s-honeycreepers-before-it-is-too-late.htm
• The source says wilderness has "five" qualities but lists four, so no count is given here. The photograph pairing an ʻākohekohe (NPS) and a kiwikiu (by C. Robby Kohley) is not reproduced.
• Rewritten in hubnx's own words.