A groundbreaking technique that utilizes two methods to target disease-carrying mosquitoes can effectively eradicate biting buzzing in two testing sites in China, according to research recently published.
The targeted mosquito is a very difficult type of control called Aedes albopictus – better known as the Asian tiger mosquito – which is the main vector for diseases including Zika and dengue fever.
The study "shows the potential for a powerful new tool," wrote Peter Armbruster, a professor in the Georgetown University biology department, in a review of the work.
The researchers used two population control methods: the use of radiation – which effectively sterilizes mosquitoes – and a strain of bacteria called Wolbachia that makes mosquito eggs die on arrival.
They conducted a two-year trial at two locations on river islands in Guangzhou, where Asian tiger mosquitoes were to blame for the highest transmission rates of dengue in China.
The results are "extraordinary", writes Armbruster: the number of eggs that hatch mosquitoes falls 94%, with no eggs that can last up to 13 weeks in some cases.
And the average number of female mosquitoes – which transmit disease to humans when bitten – is captured by traps down between 83% and 94%.
In some cases, nothing is detected for up to six weeks.
The results were also supported by a decline of almost 97% in the bites suffered by local residents – which in turn changed attitudes among residents, who were initially skeptical of the project plan to release more mosquitoes to the local area.
This research is based on two methods: radiation-based sterile insect technique (SIT) and incompatible insect technique (IIT).
SIT works by releasing radiation-sterilized male mosquitoes into the environment to mate with wild female mosquitoes, reducing population size over time because females fail to reproduce.
But the irradiation of male mosquitoes tends to reduce maritime competitiveness and their survival rate, undermining the effectiveness of this technique.
The IIT method involves a bacterium called Wolbachia. When an infected male mates with an uninfected female mosquito, the egg does not hatch.
This technique does not work if female mosquitoes are infected with the same Wolbachia strain, and successful marriages by mosquitoes that together carry destructive bacteria techniques by producing more Wolbachia-infected female mosquitoes that are resistant to the process.
Preventing the release of Wolbachia-infected female mosquitoes is difficult, with sex sorting techniques usually producing a "female contamination rate" of about 0.3%.
To overcome this, the researchers decided to make mosquitoes infected with the lab in Wolbachia exposed to low levels of radiation, which made the females barren but made the males reproduce.
This allows the team to avoid the burdensome sex screening process and means they can release more mosquitoes simultaneously: in some cases more than 160,000 male mosquitoes per hectare, per week.
Principal researcher Zhiyong Xi, a professor in the department of Microbiology and Molecular Genetics at Michigan State University, compared this technique with "producing insecticides."
"Our goal is to use this technique to build protected areas free of disease," Xi told AFP.
Armbruster, in a review commissioned by the journal Nature which published the study, said the study produced "surprising results."
That trials "almost eliminating vector mosquitoes that are difficult to control very well from the test site are extraordinary," he wrote.
The result is not universal success – populations in more traffic areas, near construction or roads, shrink less than those in isolated zones, possibly because mosquitoes migrate from elsewhere.
But Xi said the technique still promises if "natural barriers" such as highways are used to limit the arrival of outside mosquitoes.
And he said it could be used against mosquitoes that carry diseases, including malaria.
The next step will involve the development of "very effective and practical release strategies" that are suitable for urban settings, he said.