avian malaria — Maui Invasive Species Committee (MISC)

The Aedes aegypti mosquito is the primary vector of dengue worldwide. This species is not widespread in Hawaii. Photo by James Gathany,CDC.

The news is abuzz with mosquitoes these days; outbreaks of dengue fever on Hawaiʻi Island have us all a little more nervous when the high-pitched whine of a tiny pest reaches our ear. Mosquito-vectored viruses like Zika and chikungunya are on the horizon. Health officials in both South America and Hawaiʻi Island are scrambling to find ways to reduce mosquito populations and protect human health. Scientists are busy making nearly daily advances in the lab as well. All of the energy focused on removing these pests raises the question: how would the total removal of mosquitoes alter ecosystems?

There are over 3,500 species of mosquitoes in the world, of which only a few hundred bite. Mosquitoes and their larvae are food for fish, bats, birds, and dragonflies. Male mosquitoes don’t suck blood, they daintily sip nectar. In return, they help to pollinate some aquatic plants. But despite their service as prey and pollinator, many scientists think ecosystems would recover just fine if mosquitoes were gone–other insects could fill that niche, and we’d have one less vector for disease. Good news globally, but it only gets better for Hawaiʻi.

The Culex mosquito, larvae shown here, is the mosquito responsible for spreading avian malaria between introduced and native birds. Photo by James Gathany, CDC.

In Hawaiʻi, mosquitoes are food for native bats (ʻōpeʻapeʻa) and dragonflies (pinao). Would these species go hungry without this imported food source? Not in the least, explains Dennis Lapointe, an ecologist with the US Geological Survey who researches the ecological role of mosquitoes and birds in Hawaiʻi. “[Mosquitoes] are all non-native and everything that is native and endemic got along fine without them.” Some species of native damselfly larvae eat mosquito larvae, but they have other food sources.

The greatest ecological benefit would be to our native birds. Disease-spreading mosquitoes are a significant factor keeping iʻiwi,ʻ apapane, and other Hawaiian honeycreepers from flitting through the trees in your yard.

Aedes albopictus is widespread in Hawai’i and is a vector of Zika among other human diseases. Photo by James Gathany, CDC.

Mosquitoes first arrived in Hawaiʻi when sailors dumped a barrel of water containing larvae of the Culex mosquito into the wetlands that once surrounded Lahaina. The Culex mosquito became the vector that spread avian pox and malaria from non-native birds to Hawaiian forest birds, precipitating their decline. The native passerines lacked any resistance against these foreign diseases.

Today, our few remaining native forest birds are relegated to high-elevation refuges, protected by temperatures cool enough to keep mosquitos at bay. But protection could be short lived; current estimates of climate change indicate these refugia could disappear within 80-100 years.

If mosquitoes disappeared, so would the threat of avian malaria.

Currently, the fate of native birds is not foremost in our minds as human-health threats loom: the Aedes mosquitoes, which are also found in Hawaiʻi, are in the news now. A. albopictus, widespread throughout the Islands, is the primary carrier the Zika virus. A. aegypti, a mosquito found only in a few areas on Hawaiʻi Island, is the optimum carrier of dengue. Both Aedes species carry chikungunya. Both of these mosquitoes cause harm, with negligible environmental benefit.

Meanwhile, scientists are working on a tool to reduce mosquito populations without pesticides. Using genetic technology, a self-limiting gene is inserted into the DNA of male mosquitos. Reared in labs, the mosquitos are released to seek out and mate with females, but the self –limiting genes is passed along and their offspring die as

Mosquitoes breed in standing water, and removing breeding sites is one way to help reduce the density of mosquitoes. Photo by Mary Hollinger, NOAA.

larvae. The existing adults die off and are not replaced. Though years from being ready for release into the wild, scientists predict that these altered mosquitoes could be up to 99 percent effective in reducing mosquito populations, with no risk of developing resistance to pesticides. Each species of mosquito has to be targeted specifically, but Hawaiʻi has only a handful of invasive mosquitoes, all of which are non-native.

It’s something to think about: Hawaiʻi without mosquitoes, without the threat of dengue, Zika, or chikungunya. And, as an added benefit, Hawaiian forests with a few more native birds.

Until then, continue with mosquito-control efforts: dump standing water, treat bromeliads and other plants that hold water and mosquito larvae, and regularly apply repellent. These actions can help keep these blood-suckers at bay in your backyard.

Eliminate mosquito breeding sites: https://health.hawaii.gov/docd/files/2017/01/Eliminate-Mosquito-Breeding-Sites.pdf
Ecological role of mosquitoes: www.nature.com/news/2010/100721/full/466432a.html
Avian diseases in Hawaiʻi: https://mauiforestbirds.org/avian-disease/

Kia’i Moku, “Guarding the Island,” is prepared by the Maui Invasive Species Committee to provide information on protecting the island from invasive plants and animals that can threaten the island’s environment, economy and quality of life.

Written by Lissa Strohecker. Originally published in the Maui News on February 14th, 2016 as part of the Kia‘i Moku Column from the Maui Invasive Species Committee.

An adult ‘i’iwi sips nectar form the flowers of a native lobelia in the Waikamoi preserve. The habitat for the i”iiwi and other Hawaiian honeycreepers is threatened by climate change. As climate warms mosquitoes that transmit disease to the native birds will increase in range. Photo by Forest and Kim Starr

On just about any given day you can find ‘i‘iwi, among the more charismatic species of Hawaiian honeycreepers, flitting around Hosmer’s grove, just past the entrance to Haleakalā National Park. These energetic little bursts of red flit from tree to tree feeding on the nectar of ‘ōh‘ia flowers and the occasional spider or insect. Once abundant on all islands from sea level up into the mountains, these brilliant birds are now rarely seen lower than 5000 feet. Below that elevation, avian malaria, a bird disease transmitted by mosquitoes, has decimated Hawaiian honeycreepers. Today, even the birds subsisting in the high-mountain pockets of habitat are threatened—not only by invasive plants and animals, but also by climate change.

Avian malaria is not new in Hawai’i. Migratory birds carrying malaria regularly visited Hawaiian shores—but before mosquitoes were introduced, the disease had no way to infect resident bird populations. In 1826, sailors on the whaling ship Wellington dumped barrels of mosquito-infested water into a Lahaina canal. That marked the beginning of the end for low- and mid-elevation native honeycreepers.

Since then, mosquito-born diseases have caused two major waves of extinction in Hawaiian honeycreepers. Native forest birds have shown scant resistance to foreign diseases. Those that survive inhabit forests above the “mosquito line,” where neither mosquitoes nor the diseases they carry can thrive. In cooler temperatures, avian malaria can’t reproduce fast enough to infect birds. Thus the largest populations of ‘i‘iwi dwell in the cloud forests of East Maui and Hawai’i; the birds are increasingly rare or nonexistent on islands without tall mountains. ‘I‘iwi have vanished from Lāna‘i and only a few remain on Moloka‘i and West Maui. With a warming climate, the remnants of disease-free habitat may shrink or disappear.

Introduced mosquitoes transmit avian malaria and pox from non-native birds to native birds.

Introduced mosquitoes, such as the tiger mosquito above, transmit avian malaria and pox from non-native birds to native birds. Having evolved in isolation, native birds lack resistance to these diseases. Photo by James Gathany, CDC

And Hawai‘i is heating up. Each decade since 1975, minimum nighttime temperature has increased an average of almost 1°F. Nighttime temperature is the determining factor in estimated elevational range of avian malaria. Over the last 50 years, the mosquito line has steadily marched up the mountain, from 2000 feet in the late 1960s to nearly 5000 feet today.

Climate change may affect our native birds in other ways. Summer storms are predicted to become more frequent, creating more habitat for mosquitoes during their optimum breeding season, increasing their density and the likelihood of transmission of avian malaria. Meanwhile, overall rainfall may decrease, compromising the health of the native Hawaiian rainforest and the inhabitants that rely on it.

The ‘i‘iwi is not the only bird likely to be chased out of remaining habitat by avian malaria and climate change. In Hawaii all of our non-migratory birds, such as the Maui crested honeycreeper or ‘ākohekohe, Maui parrotbill or kiwikiu, and the ‘apapane, face the same danger. These species are unique among the world’s creatures; they exist nowhere else on earth. Many of them are highly significant to the native Hawaiian culture and all play critical roles in their natural environments. Their loss would be devastating.

In response to concerns raised about the ‘i‘iwi’s perilous situation, the United States Fish and Wildlife Service is proposing to list the ‘i‘iwi as federally threatened or endangered, with climate change noted as a factor in its decline. How can you help? Support efforts to address the causes of climate change. Work to protect the remaining natural areas that shelter ‘i‘iwi. And take a trip to Hosmer’s Grove to witness just how spectacular these winged treasures are.

By Lissa Fox Strohecker. Originally published in the Maui News, July 8th, 2012 as part of the Kia‘i Moku Column from the Maui Invasive Species Committee.
You can find all the articles in the Kia‘i Moku series http://www.hear.org/misc/mauinews/

What if there were no mosquitoes in Hawaiʻi?

A changing climate and the plight of the ‘i‘iwi

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