Suppressing mosquito population by nuclear technique

Print edition : August 16, 2019

Mosquito larval rearing racks at a mosquito mass-rearing facility at the Wolbaki Biotech Company in Guangzhou, China, in May 2019. Each rack has the capacity to produce about 5,00,000 males a week.

FOR the first time, a combination of the radiation-based nuclear sterile insect technique (SIT) with the incompatible insect technique (IIT) has led to the successful suppression of mosquito populations, a promising step in the control of mosquitoes that transmit devastating diseases. The results of the recent pilot trial in Guangzhou, China, carried out with the support of the International Atomic Energy Agency (IAEA) in cooperation with the Food and Agriculture Organisation (FAO) of the United Nations, were published recently in “Nature”.

SIT is an environmentally friendly insect pest control method involving the mass-rearing and sterilisation of a target pest, followed by the systematic area-wide release of sterile males by air over defined areas. The sterile males mate with wild females, resulting in no offspring and a declining pest population over time.

Although SIT has been successfully used to control a variety of plant and livestock pests such as fruit flies and moths, its effect on mosquito vector control has been limited. The main obstacle in scaling up the use of SIT against various species of mosquitoes has been overcoming several technical challenges with producing and releasing enough sterile males to overwhelm the wild population.

The IIT, which involves exposing the mosquitoes to the Wolbachia bacteria, is a promising alternative, but can be undermined by accidental release of females infected with the same Wolbachia strain as the released males.

Researchers at the Sun Yat-sen University, and its partners, in China, have now addressed these challenges by combining incompatible and sterile insect techniques (IIT–SIT) and have succeeded in near elimination of field populations of the world’s most invasive mosquito species, Aedes albopictus (Asian tiger mosquito).

The bacteria partially sterilise the mosquitoes, which means that less radiation is needed for complete sterilisation. This, in turn, better preserves the sterilised males’ competitiveness for mating. The work was carried out with the support of the Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture, which is leading and coordinating global research in SIT.

The researchers used racks to rear over 5,00,000 mosquitoes per week that were constructed based on models developed at the Joint FAO/IAEA division’s laboratories near Vienna, Austria. A specialised irradiator for treating batches of 1,50,000 mosquito pupae was also developed and validated with close collaboration between the Joint FAO/IAEA division and the researchers. Two hundred million such factory-reared adult males with an artificial triple-Wolbachia infection were released, with prior pupal irradiation of the released mosquitoes to prevent unintentionally released triply infected females from reproducing in the field.

The results of this pilot trial, using SIT in combination with the IIT, demonstrate the near-elimination of field populations of Aedes albopictus. The two-year trial (2016-17) covered a 32.5-hectare area on two relatively isolated islands in the Pearl River in Guangzhou. The method is stated to be cost-effective in comparison with other control strategies. the overall future costs of a fully-operational intervention estimated at $108-163 a hectare per year.

China plans to test the technology in larger urban areas using sterile male mosquitoes from a mass-rearing facility in Guangzhou, said Zhiyong Xi, director of Sun Yat-sen University-Michigan State University’s Joint Centre of Vector Control for Tropical Diseases.

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