A new research initiative could be the beginning of the end for mosquito-borne diseases that are killing off Hawaii’s native birds.
A new research initiative could be the beginning of the end for mosquito-borne diseases that are killing off Hawaii’s native birds.
Scientists at the Manoa and Hilo campuses of the University of Hawaii are using a genus of bacteria called Wolbachia to create what’s been described as a form of birth control for the Culex quinquefasciatus mosquito.
Culex is a vector for avian pox and avian malaria, which have wreaked havoc on Hawaiian bird populations. A study published last year in Science Advances found that honeycreeper populations on Kauai were dropping to the point where multiple extinctions could be expected in the coming decades.
Study authors attributed the rising extinction rate in part to climate change, which allowed disease-carrying mosquitoes to push into high-elevation areas of the island that were previously inaccessible to the insects because those areas were too cold.
“Avian malaria is not the only problem for the native Hawaiian birds, the Hawaiian honeycreepers, but it’s a big one,” said UH-Manoa project lead Floyd Reed in a release.
There are six types of mosquito found in Hawaii. All were introduced.
Culex quinquefasciatus “can bite humans, but it does seem to prefer birds,” said UH-Hilo project lead Jolene Sutton.
The Culex mosquito is a vector for some diseases that affect humans, such as lymphatic filariasis (elephantiasis), but not those that have been found in Hawaii, such as dengue fever.
Using Wolbachia bacteria to control mosquito populations is not a new idea — it has been around since the 1960s. It is more expensive and time consuming than using pesticides, and fell out of favor for a while, said U.S. Geological Survey research ecologist Dennis Lapointe.
Different strains of Wolbachia bacteria are symbiotes with many insect species, from butterflies to fruit flies. They are not found in humans or other animals.
Each strain is symbiotic with an individual insect species and is passed down to that insect’s offspring.
But not all strains of Wolbachia are compatible with one another. When these come in contact, the insect hosting the bacteria can’t produce offspring.
It’s not yet known why some strains are incompatible with others.
“It’s still kind of a mystery,” said USGS research ecologist Carter Atkinson. Atkinson and Lapointe conducted a survey last year to determine what strains of Wolbachia were found in Hawaii.
The UH teams are working to give lab-raised male Culex mosquitoes a strain of Wolbachia found in a different type of mosquito living in the islands. That way, if the males try to mate, they won’t be able to have young. If those males are released into the wild, populations of Culex mosquitoes should, with time, begin to fall.
A similar technique employing Wolbachia strains has been used to reduce fruit fly populations in Hawaii.
The idea of using Wolbachia for mosquitoes came from a meeting held shortly after the IUCN World Conservation Congress, which took place last September in Hawaii. The technique, after being relatively dormant for so long, has “exploded” in the past five years, Atkinson said.
“It became clear from this meeting that people were very excited about trying Wolbachia here,” Sutton said. She and Reed set to work writing a project proposal.
What was particularly exciting for the researchers was that they wouldn’t have to import a new strain of incompatible Wolbachia — which would mean importing a new mosquito — to carry out the work. They could use the Wolbachia already here.
A group in Kentucky conducted similar research, extracting tissue from a male Culex quinquefasciatus that was infected with its own Wolbachia bacteria and micro-injecting that bacteria into an Aedes albopictus mosquitoto to create incompatibility.
“You’re using what was locally available, and you’re not doing any kind of genetic manipulation,” Lapointe said.
“That was kind of the big, bright moment for everybody in the room,” he said. “We have Aedes … and we have Culex, so we can do it locally … . ‘Wow, we don’t have to import a naturally occuring type from across the world.’ We just have to get over this technical hurdle.”
“It’s safe, it’s been used elsewhere, and we’re just employing this at a local scale,” Sutton said.
The Hilo and Manoa UH labs already were raising mosquito colonies for research, so “we’re making very good headway,” she said. She said she wasn’t sure of an exact timetable for completing the project.
“We’re at a point where we have a consensus among the agencies involved, and we’re going in the right direction,” Lapointe said. “It’s pretty much a clear-cut series of steps from here on out to see if this will work.”
The research is funded by the state Department of Land and Natural Resources and the U.S. Fish and Wildlife Service, with each agency contributing $50,000. The DLNR’s funds come from the Division of Forestry and Wildlife budget.
DLNR spokesman Dan Dennison said the $100,000 total would allow the mosquito project to be more comprehensive in scope.
The standard way of preventing avian malaria and avian pox from spreading has been to improve bird habitat. For example, in Hakalau Forest Reserve on the Big Island, fencing was put up to keep pigs out, since holes the pigs dig up can fill with water and become prime mosquito breeding habitat. Prevalence of disease in Hakalau has declined during the past two decades.
Habitat improvement works, “but it doesn’t work super well,” Atkinson said.
“This is the first time in the 20-something years I’ve been here that we’ve gotten excited about the possibility of controlling these diseases,” he said. “It’s gotten people interested — it’s gotten people interested to the point of funding (projects).”
“I would call it a game changer,” he said.
Email Ivy Ashe at iashe@hawaiitribune-herald.com.