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What if there were no mosquitoes in Hawaiʻi?

Posted on March 18, 2016 by Lissa Strohecker

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

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.

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.

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.

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.

Read more:

  • 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.

Filed Under: Featured Pest, In the field, Invasive Animals, Kia'i Moku Column, Solutions Tagged With: 2016, Aedes, avian malaria, chikungunya, Culex, dengue, dengue in Hawaii, GMO mosquitoes, mosquitoes in Hawaii, Zika

The public health threat of invasive species-mosquitoes and dengue

Posted on August 23, 2013 by Lissa Strohecker Leave a Comment

Aedes aegypti is famous the world over for spreading dengue.

Aedes aegypti is famous the world over for spreading dengue. This species is not established statewide, but it has shown up at the Honolulu International Airport five times since January of 2012. Photo by Muhammad Mahdi Karim

Back in 2001, several East Maui residents started reporting fever, body aches, and rashes. One of the people sickened had just traveled in French Polynesia during a dengue fever outbreak. The Department of Health eventually confirmed 20 cases of dengue fever in East Maui and a crew hired with funds allocated for environmental emergencies went to work removing mosquito habitat. What made this outbreak interesting was that it was spread by the tiger mosquito, Aedes albopictus, common in Hawai‘i.

“We may be the only place in the world to confirm [that] dengue could be spread by the albopictus mosquito. It’s not an efficient carrier of the disease,” explains Gary Gill, Deputy Director of the Environmental Health Administration with the Hawai‘i Department of Health. “In places where dengue is endemic [regularly occurring], it is the aegypti mosquito that is the carrier.”

The invasive mosquito, Aedes aegypti, is famous for spreading dengue. Neither the mosquito nor dengue is widespread in Hawai‘i. Both periodically appear, but luckily not at the same time. Though conditions are prime as Hawai‘i is a global hub for tourism and commerce..

Dengue outbreaks in Hawai‘i are rare and typically occur when someone travels to an infested area, returns to Hawai‘i and is bitten by a mosquito, as happened in 2001. According to Gill, immediate family members and neighbors are at risk, but the common tiger mosquitoes rarely eat from more than one source. The female mosquito finds a person (or animal), and, given the chance, feeds until her belly is about to burst.

In contrast, Aedes aegypti flit from person to person, taking a blood meal from multiple people and spreading any disease carried by the bloodsuckers. Aedes aegypti is not normally found on O‘ahu. “We have not, up until last year, identified any aegypti since the 1940s,” says Gill.

In January of 2012, a Department of Health entomologist collected a trap containing what was later identified as Aedes aegypti at the Honolulu International Airport. “We’ve found aegypti five times in the last year.  Every indication is that this mosquito is either living and breeding at the airport, or it is regularly being reintroduced,” Gill says.   Mosquitoes can survive in the cabin, cargo hold, or underbelly of an airplane coming from an infested area. Aedes aegypti are originally from Africa but have spread to tropical and sub-tropical regions of the world including Mexico, Asia, and Australia.

Dengue fever is a widespread subtropical disease that is continuously present in areas with established population of Aedes aegypti.  This map shows the distribution of Aedes aegypti (blue) and Aedes aegypti and dengue fever (red). Image from Centers for Disease Control

Dengue fever is a widespread subtropical disease that is continuously present in areas with established population of Aedes aegypti. This map shows the distribution of Aedes aegypti (blue) and Aedes aegypti and dengue fever (red). Image from Centers for Disease Control

From a public health standpoint having a thriving population of dengue-spreading mosquitoes at the airport is a worst case scenario according to Gill. “A person carrying the virus walks through the airport, and then it spreads to any number of people at the airport who will then take it to wherever they are going. A single population of aegypti could easily spread dengue throughout the state. A dengue-carrier mosquito would be a concern for people who come here as much as for people who live here.”  If Aedes aegypti became established throughout Hawai‘i, it would set the stage for a consistent presence of dengue, like does in parts of Central and South America, India, Southeast Asia, and Africa.

Ongoing surveys for mosquitoes are the best way to ensure early detection of this species. The Department of Health continues to monitor mosquitoes at Honolulu International Airport, but surveys are limited to that airport and don’t include surrounding areas. Funding cuts in 2009 gutted the Department of Health. At one point 40 people worked on O‘ahu on environmental health but now only seven positions remain. Staff cuts throughout the state have left no capacity for mosquito monitoring elsewhere. “What’s at Kahului? We have no idea,” worries Gill.

The Department of Health is working with Hawai‘i’s Departments of Agriculture Transportation to explore options for mosquito surveys at airports and harbors statewide. They are working to reduce mosquito habitat at the airport, removing bromeliads and dark undergrowth and replacing it with less mosquito-friendly landscaping. Gill encourages homeowners to do the same, along with removing or changing water in outside open containers every week. For now it’s our best hope. Unless and until capacity is restored at the Department of Health, early detection of this devastating mosquito is up to the public.

By Lissa Fox Strohecker. Originally published in the Maui News, August 11, 2013 as part of the Kia‘i Moku Column from the Maui Invasive Species Committee.

Filed Under: In the field, Invasive Animals, Kia'i Moku Column, Solutions Tagged With: 2013, Aedes aegypti, Aedes albopictus, dengue in Hawaii, mosquitos in Hawaii

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