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Number of Project Wolbachia mosquitoes released is constantly reviewed to maintain suppression of dengue: NEA

We thank the writer for the letter, “Project Wolbachia: Residents are killing the ‘helpful’ mosquitoes, which can be a nuisance” (Jan 29). Project Wolbachia – Singapore has yielded promising results so far.

Male Wolbachia-aedes aegypti mosquitos being released via a mosquito launcher at a public housing estate test site in Singapore on August 27, 2020.

Male Wolbachia-aedes aegypti mosquitos being released via a mosquito launcher at a public housing estate test site in Singapore on August 27, 2020.

Ng Lee Ching, Group Director, Environmental Health Institute, National Environment Agency

We thank the writer for the letter, “Project Wolbachia: Residents are killing the ‘helpful’ mosquitoes, which can be a nuisance” (Jan 29)

Project Wolbachia – Singapore has yielded promising results so far.

Releases of non-biting male Wolbachia-Aedes mosquitoes have suppressed the urban Aedes aegypti mosquito populations in study sites at Tampines and Yishun by up to 90 per cent, and we have observed 58 to 74 per cent less dengue cases in 2020 in areas where releases have been ongoing for at least a year compared to areas without releases.

However, this does not mean that there will be no dengue cases in the study sites, especially in the initial period, because it takes several months for the releases to bring down the dengue mosquito population.

While some residents at the release sites have noticed more non-biting mosquitoes around their homes, the released male mosquitoes do not bite, and the overall data shows a clear benefit — fewer dengue cases.  

To minimise the inconvenience experienced by some residents, we are continually assessing the situation, and reducing the release numbers in areas where sustained suppression of the dengue mosquito population has been achieved.

We have contacted the letter writer to better understand her situation and determine if release adjustments are needed.

She had suggested studying the population replacement method used in other countries, in which releases of both male non-biting Wolbachia-Aedes mosquitoes and biting female Wolbachia-Aedes mosquitoes are carried out, to replace the wild-type mosquito population.

This is unlike Singapore’s suppression approach, where only non-biting male Wolbachia-Aedes mosquitoes are released, to mate with urban female Aedes mosquitoes and cause their eggs to not hatch.

Before launching Project Wolbachia, NEA had considered and evaluated both approaches.

Through extensive laboratory studies, literature reviews, and consultation with experts, we decided to pursue the population suppression strategy, as this does not require the release of biting female mosquitoes.

Multiple releases of considerable numbers of biting females — required for the replacement method — would be much less socially acceptable to residents.  

As the writer pointed out, it is not possible to sort out male Wolbachia-Aedes mosquitoes for release with 100 per cent accuracy.

However, our stringent quality control processes ensure that only a very small number of female Wolbachia-Aedes mosquitoes are released along with the males.

The number of released females is negligible compared to Singapore’s female urban Aedes aegypti mosquito population.

Project Wolbachia is, however, not a silver bullet, and community support to reduce potential mosquito breeding habitats and lower the risk of dengue transmission remains essential.

Have views on this issue or a news topic you care about? Send your letter to voices [at] mediacorp.com.sg with your full name, address and phone number.

Related topics

Wolbachia dengue Aedes mosquito NEA

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