In a time period of only two years, scientists have almost wiped out the most invasive mosquito in the world from two islands in Guangzhou, China. The mosquito species, Asian tiger is a carrier of highly infectious diseases such as Zika, chikungunya and dengue affecting millions of people all over the world. It is very difficult to control.
Over the last forty years, this mosquito has reached to all other continents on Earth excluding Antarctica from its home in Asia. It has caused a heavy impact on public health due to the limited availability of vaccines and treatments for the diseases it spreads. However, with an exciting field test of a mosquito control technique, this can be changed. Researchers used two existing methods to decrease the population of Asian tiger up to 94 percent on the Chinese river islands. In some instances, even one viable egg was not found for 13 weeks. The findings have been published in the Nature journal.
Peter Armbruster, mosquito ecologist while reviewing the work said that the results were quite remarkable and it shows the potential of a new tool to fight infectious diseases that are spread by mosquitoes.
The double combination approach involves a radiation dose for sterilizing the mosquitoes along with a bacterial strain from the Wolbachia genus preventing the hatching of mosquito eggs. When these two methods are applied together on the lab-grown mosquitoes, they work very effectively than when used alone.
Radiation based techniques used at present work with the release of sterile male insects who mate with the females decreasing the population size. However, radiation makes them less competitive sexually and are prone to die quickly. Other methods using bacteria are less harmful but they work only if the male mosquito grown in the lab is infected. When both male and female have a bacterial infection, they cancel each other out producing a healthy offspring.
Sifting through male and female insects is highly painstaking, as although the researchers put all the effort, Wolbachia-infected females get released accidentally 0.3 percent of the time which undermines the whole mission.
However, in the new solution, Wolbachia-infected mosquitoes are reared in the lab who are then subjected to low radiation which makes the females sterile while the males can still reproduce. This not only works theoretically but also works in reality. Getting rid of the sex testing, the team was able to produce and release huge numbers of these mosquitoes grown in the lab, nearly two hundred million in the city having the largest dengue transmission rate in China.
After two years, the team found a decrease of 97 percent in the mosquito bites by the local population. The average number of wild adult females caught per trap reduced by 83 to 94 percent, with none found for a period of six weeks. Authors say the remaining mosquitoes on the island migrated from outside, suggesting that the region would not be free of mosquitoes for a long period of time. However, if the technique is implemented on a larger scale it is possible to make the place free from the Asian tiger mosquitoes.
Zhiyong Xi, a molecular genetics professor at Michigan State University said that their study predicted the total future costs of a completely operational intervention using this approach would be nearly 108 US dollars per hectare per year which is cheaper than other mosquito-control techniques.
Research Paper: https://www.nature.com/articles/s41586-019-1407-9