From July 2020, NEA will gradually expand releases of male Wolbachia-carrying Aedes aegypti (Wolbachia-Aedes) mosquitoes to the entire HDB towns of Yishun and Tampines and cover both towns by March 2022. With this roll-out, NEA will determine if suppression across whole towns can be sustained with fewer male Wolbachia-Aedes mosquitoes.
As of April 2022, releases of male Wolbachia-Aedes mosquitoes have expanded to cover the entire towns of Tampines and Yishun (1,473 blocks, 142,402 households).
The positive outcome of the field studies at Tampines and Yishun show that continued releases of male Wolbachia-Aedes mosquitoes can successfully suppress the female urban Aedes aegypti mosquito population.
- Up to 98% of suppression of the Aedes aegypti mosquito population was observed at the core of study sites. The heat map below shows the “eraser effect”, where previously dark red areas (indicating high Aedes aegypti mosquito population) gradually faded to low mosquito population after releases.
- Up to 88% of reduction in dengue cases was observed at core areas of the study sites with at least one year of releases.
- While most areas at the study sites showed good suppression of the Aedes aegypti mosquito population within three to four months after beginning releases of male Wolbachia-Aedes mosquitoes, environmental factors such as close proximity to non-release areas with persistently high Aedes aegypti mosquitoes populations can delay the effect of such releases.
- With very low Aedes aegypti wild type mosquito populations, the presence of female Wolbachia-Aedes mosquitoes could result in these Wolbachia-Aedes mosquitoes propagating in the field. The eggs from a pair of mated Wolbachia-Aedes mosquitoes are viable and can hatch, resulting in Wolbachia-carrying offspring. These female Wolbachia-Aedes mosquitoes in the community are less harmful than urban Aedes aegypti mosquitoes, because they are partially resistant to dengue infection and do not transmit dengue well. The additional technique of X-ray irradiation was introduced to sterilise the male Wolbachia-Aedes mosquitoes, which successfully reduced the urban Wolbachia-Aedes mosquito population.