Sterile males successfully suppress mosquitoes in China

Michigan State University and Sun Yat-Sen University, in partnership with the Wolbaki Biotech Company, the Joint FAO/IAEA Division and others, have successfully suppressed a mosquito vector population in Guangzhou, China, as part of efforts to use a new technique to control the insect that spreads dengue, Zika and other diseases.

The results of this pilot trial were published in the current issue of Nature and show that combining incompatible and sterile insect techniques (IIT/SIT) successfully enable near elimination of field populations of the world’s most invasive mosquito speciesAedes albopictus, or Asian tiger mosquito, on two relatively isolated islands in the Pearl River near Guangzhou over a two-year period.

Almost 200 million irradiated mass-reared adult males of a mosquito line infected with Wolbachia were released. Community support for the IIT/SIT approach strongly increased following mosquito releases, thanks to the decrease in nuisance biting. This successful field pilot demonstrated the feasibility of area-wide application of IIT/SIT for mosquito vector control.

Zhiyong Xi, a microbiology and molecular genetics professor at MSU, leads this international consortium and is the corresponding author of this paper. The field trial in Guangzhou was initially funded by the NIH through the Grand Challenges in Global Health Initiative of the Bill & Melinda Gates Foundation, and subsequently received major fund support by the local government. To run the project, MSU and Sun Yat-sen University established the SYSU-MSU Joint Center of Vector Control for Tropical Diseases, with professor Xi as the director.

The SIT, a form of insect birth control, uses radiation to sterilize male insects, which are then released to mate with wild females. As these do not produce any offspring, the insect population declines over time. Combining it with the cytoplasmic incompatibility conferred to the males by Wolbachia allows a reduced radiation dose to be used, which keeps the males more competitive while sterilizing the incidentally released females to avoid replacement of the target population.

“Our study predicts that the overall future costs of a fully operational intervention using this environmentally friendly approach will be around $108 annually,” Xi said, “which seems cost-effective in comparison with other mosquito control strategies.”

China plans to test the technology in larger urban areas soon using sterile male mosquitoes from the mass-rearing facility operated by the Wolbaki Biotech company. This company uses advanced mosquito mass-rearing and irradiation equipment that has been developed in collaboration with the FAO/IAEA and can produce the required number of mosquitoes.

Success of the field trial in Guangzhou resulted in a broad international collaboration with disease endemic countries including Singapore and Mexico. To combat Zika as public health emergency of international concern in 2016, Xi received support from USAID to establish another mosquito factory in Merida, Mexico, through collaboration with Autonomous University of Yucatan, to develop this technology to control Aedes aegypti. In addition, Xi further worked with Hawaii collaborator by adapting this technology to control Culex quinquefasciatus with a goal to protect endangered native bird species from avian malaria. Xi’s experience has provided a great example how international collaboration can facilitate advance in science and save human life via extending research from the lab bench to the field.

The push for the development of SIT to control mosquitos became more urgent following the recent worldwide Zika epidemic. Moreover, dengue incidence is increasing every year with 390 million new infections estimated yearly.

The SIT has been used for over 60 years to fight agricultural pests such as the Mediterranean fruit fly and has only recently been adapted for disease-transmitting mosquitos. The insect control method can be particularly useful against human disease vectors that are difficult to manage using conventional techniques, or that became resistant to insecticides.

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