Current Control Methods
'alauahio © Zach Pezzillo
Humans have been trying to eliminate mosquitoes from their living areas for millennia. Although some larger-scale approaches have limited mosquito-borne diseases in urban areas, most control methods target small, localized infestations.
Options for mosquito control include:
mosquito habitat reduction; and
biological insecticides that target mosquito larvae.
These techniques are unlikely to be effective against avian disease-carrying mosquitoes in rural, roadless forests - the places our native birds live.
Broadscale application of chemical insecticides in forested areas could harm native species, watersheds and human health. Deployment of ovitraps that entice females to lay their eggs in water with an insecticide would also be impractical due to the need for ongoing monitoring and replacement across a broad landscape; if left in place more than a few weeks, the traps can become breeding grounds. Mosquito habitat reduction and use of biological insecticides are not practical in Hawaii’s multi-layered forests, which contain micro-pools for breeding mosquitoes.
Incompatible Insect Technique
'alauahio © Zach Pezzillo
The Sterile Insect Technique
The approach contemplated for use in Hawaiʻi is a method that uses a form of “mosquito birth control” similar to the Sterile Insect Technique (SIT). SIT has been in use since the 1950s as a tool to control agricultural pests. SIT is credited with eradicating the Mediterranean fruit fly in California, the New World screwworm in the U.S. and Mexico, and controlling the tsetse fly in Africa.
Male mosquitoes are sterilized and released into the wild; matings with females either produce no offspring or none that survive and reproduce. With repeat releases, insect population suppression is achieved. Irradiation of males is one option for sterilization, but studies have shown that irradiated male mosquitoes may be less “competitive” or attractive to females, thus reducing the effectiveness of the technique.
The Incompatible Insect Technique
The Incompatible Insect Technique (IIT) approach currently under consideration uses Wolbachia, a naturally-occurring bacteria that commonly infects many insect species.
This approach takes advantage of the fact that mosquitoes with different, incompatible strains of Wolbachia can’t produce offspring. When infected males mate with uninfected females or females with an incompatible strain of Wolbachia, no offspring results.
Male mosquitoes can be intentionally infected with a specific strain of Wolbachia in a controlled laboratory setting. Only males are used for mosquito control. Because crossing female and male mosquitoes carrying the same type of Wolbachia would cancel out the benefit, it’s important to ensure that no infected females are released simultaneously.
Using a small amount of irradiation can sterilize undetected females while not reducing the “fitness” of the males. Because Wolbachia are passed only from mother to offspring, released males cannot spread the novel Wolbachia.
See this video for more information about how the technique works.
Wolbachia: World Wide Use
The IIT method has been successfully used around the globe to reduce populations of mosquitoes that carry diseases such as dengue and Zika. Homeowners in Kentucky can now purchase regular releases of Wolbachia-incompatible mosquitoes to reduce the presence of Asian tiger mosquitoes (Aedes albopictus) around their homes.
These successes came only after rigorous testing, in compliance with established regulatory requirements. Hawaiʻi has the opportunity to learn from these efforts and build off what is already known, including simultaneous work to explore potential human-health benefits in Hawaiʻi.
Potential Genetic Tools
'alauahio © Zach Pezzillo
Are Wolbachia mosquitoes genetically modified?
No changes have been made to the Wolbachia or mosquito's genetic sequence or to the mosquitoes in which the bacteria reside. The Wolbachia bacteria occurs commonly in many insects, and an incompatible strain of the bacteria is inserted into male mosquitoes hatched in a rearing facility.
Adding the different Wolbachia bacteria into a male mosquito makes it incompatible with the Wolbachia in wild female mosquitoes. As a result, the eggs produced from these pairings do not hatch, causing the population size of wild mosquitoes to drop.
Are there potential genetic tools to control mosquitoes?
Researchers around the world, including scientists at the University of Hawai‘i, are studying the potential of genetic techniques to protect human health and native species from the impacts of mosquitoes. While mosquito genetic control tools have not yet be used in the U.S., they have been used elsewhere in the world.
There are a variety of promising lines of research that could someday result in the ability to control mosquitoes across landscapes or even potentially remove them from our islands entirely. Just like with Wolbachia IIT, genetic control strategies must carefully consider ways to ensure project safety and need to be registered with federal agencies and within Hawai‘i before use.
Any future projects in Hawai‘i that utilize genetic technology would, like any other large project, require public engagement and input.
Is Birds, Not Mosquitoes considering the use of genetically modified mosquitoes?
Not at present. The current focus of Birds, Not Mosquitoes is on the use of Wolbachia bacteria. This is because the technique of using Wolbachia mosquitoes has already been approved in other states and is considered the most feasible to use in the near-term future. Time is running out for the native forest birds of Hawaiʻi. Wolbachia-infected mosquitoes are already being used around the world to reduce mosquito populations.
Birds, Not Mosquitoes supports research into additional mosquito control tools, including genetic tools, to save the native birds of Hawaiʻi from extinction. Birds, Not Mosquitoes will continue to monitor research developments in this area to evaluate the full suite of mosquito control tools.
The community engagement process is expected to provide an opportunity for public discussions about different approaches.