In Phase 2, NEA set out to improve our release methods and address challenges identified in Phase 1. Phase 2 was carried out in Tampines West and Nee Soon East, and involved:
- Expansion of release sites and inclusion of buffer zone releases, which counteract migration of females into release sites.
- High-floor releases in addition to ground-floor releases.
- Low-dose X-ray irradiation of sorted pupae to sterilise residual females and prevent establishment of Wolbachia in the urban Aedes aegypti population. Our Impact assessment determined that X-ray irradiation poses no harm to humans or the environment.
Phase 2 findings
- Phase 2 achieved 70-80% suppression of the Aedes aegypti mosquito population in the release sites, an improvement over Phase 1.
- Better results were achieved with the expansion of the release sites and the inclusion of buffer releases, suggesting that larger sites are less affected by the impact of migration.
- High-floor releases resulted in a better vertical distribution of male Wolbachia-Aedes mosquitoes in HDB blocks.
- The use of low-dose X-ray irradiation to sterilise residual females was effective at preventing establishment of Wolbachia in the field.