Wolbachia-Aedes suppression technology
1. How does Project Wolbachia – Singapore work?
Project Wolbachia involves the release of male Wolbachia-carrying Aedes aegypti (Wolbachia-Aedes) mosquitoes to help suppress urban Aedes aegypti mosquito populations, the main vector for dengue. When these male Wolbachia-Aedes mosquitoes mate with female urban Aedes aegypti mosquitoes (without Wolbachia), their resultant eggs do not hatch. Continued releases lead to a decline in the urban Aedes aegypti mosquito population, and therefore, reduce the risk of dengue transmission.
2. Is NEA introducing a new mosquito species into the environment?
NEA is not introducing a new mosquito species into the environment. The male Wolbachia-Aedes mosquitoes released by NEA are of the same Aedes aegypti mosquito species found in the environment. The only difference is that male Wolbachia-Aedes mosquitoes carry the Wolbachia bacterium, which is safe and occurs naturally in more than 60% of insect species.
3. Are Wolbachia-Aedes mosquitoes genetically modified?
Wolbachia-Aedes mosquitoes are not genetically modified, as no changes have been made to their genetic material.
4. Is Wolbachia-Aedes suppression technology safe?
Yes. NEA has carefully studied Wolbachia‑Aedes suppression technology and found it safe, with no risk to human health and no significant impact on the environment. This conclusion is supported by international research and independent reviews. NEA’s rigorous evaluation process involved in-house research, critical reviews of existing knowledge and research, and consultations with various overseas and local experts and stakeholders such as academic researchers, medical and healthcare professionals, and non-governmental organisations.
Following World Health Organization (WHO) guidance, NEA introduced the technology step by step — starting with small trials and gradually expanding — to ensure each phase was based on solid evidence. This phased approach is now the standard recommended by WHO and the International Atomic Energy Agency.
5. How can I recognise male Wolbachia-Aedes mosquitoes?
Male Wolbachia-Aedes mosquitoes look the same as urban male Aedes aegypti mosquitoes in the community. Male mosquitoes tend to be smaller and have more bushy antennae compared to female mosquitoes. Male mosquitoes (regardless of whether they carry Wolbachia) do not bite or transmit disease, and feed only on plant juices such as nectar for survival and energy. On the other hand, female mosquitoes bite as they need blood to produce eggs.
6. Will the release of male Wolbachia-Aedes mosquitoes affect insects other than Aedes aegypti mosquitoes?
The release of male Wolbachia-Aedes mosquitoes is specifically aimed at suppressing urban Aedes aegypti mosquito populations by leveraging Wolbachia, a bacterium that naturally occurs in more than 60% of insect species. When these male mosquitoes mate with urban female Aedes aegypti mosquitoes (without Wolbachia), the resulting eggs do not hatch. This species-specific suppression effect means that other insect species, including other mosquito species, remain unaffected. While studies have shown that mating may occasionally occur naturally between Aedes aegypti and Aedes albopictus mosquitoes, this occurrence is not frequent enough to impact Aedes albopictus mosquito populations.
7. Why does Project Wolbachia only target the Aedes aegypti? Why is the Aedes aegypti considered the primary vector for dengue?
Community vigilance remains essential in preventing mosquito breeding. Residents are reminded to practise the B-L-O-C-K steps regularly:
Project Wolbachia – Singapore field studies
8. Where are the Project Wolbachia – Singapore study sites located?
Click here for more information on all release sites and schedule.
NEA is on track to achieve our target of covering 50% of Singapore's households by the end of 2026. This would be a significant milestone in helping us reduce the risk of major dengue outbreaks in Singapore. NEA will review the need for further expansion thereafter.
9. How were sites chosen for Wolbachia-Aedes releases? Is NEA able to extend Wolbachia-Aedes releases to active dengue clusters and curb dengue transmission as well?
Sites are selected to receive Wolbachia-Aedes mosquito releases based on multiple considerations, including historical dengue risk, Aedes aegypti mosquito population, size and landscape of the area. Historical dengue risk, but not ongoing dengue data, was used for site selection as the dengue situation at existing clusters is dynamic and may not reflect future risks of dengue outbreak in the area.
Since 2025, NEA has been studying the use of Wolbachia-Aedes suppression technology to curtail the growth of existing transmission in large dengue clusters. NEA prioritises deployment based on dengue cluster dynamics - such as the number of cases, growth rate, and local Aedes aegypti population levels. As it typically takes three to six months of releases to achieve significant mosquito population reductions, the technology may not show immediate impact but has the potential to limit the growth of prolonged clusters.
However, Project Wolbachia is just one tool in NEA's integrated approach to dengue control. Curbing dengue transmission in active dengue cluster requires effective environmental management— in eliminating mosquito breeding sites.
To do so, NEA follows an Integrated Pest Management approach, which prioritises prevention while minimising harm to human health and the environment. This means using multiple strategies together: community engagement, removing breeding habitats, biological controls like Project Wolbachia, and targeted use of pesticides only when necessary. This comprehensive approach provides the most effective and sustainable protection against dengue.
10. How long do the releases of male Wolbachia-Aedes mosquitoes need to continue in order for suppression strategy to work?
NEA’s data shows that some areas could achieve good suppression of the urban Aedes aegypti mosquito population about 6 months following releases of male Wolbachia-Aedes mosquitoes. Releases may be reduced or stopped in areas where the urban Aedes aegypti mosquito population has been suppressed to dengue low-risk levels.
However, continued monitoring is essential, and releases may need to resume if mosquito populations recover. In areas where Aedes aegypti mosquitoes may be breeding in hidden or hard to detect sites, it can take longer to see the positive effects of releases or to sustain mosquito population suppression. This underscores the importance of residents regularly practicing the B-L-O-C-K steps to support ongoing efforts to eliminate mosquito breeding habitats.
11. How is NEA measuring the outcomes of the field studies?
NEA’s islandwide network of Gravitraps allows us to monitor mosquito populations across Singapore. We use these Gravitraps to measure Aedes aegypti populations in our study sites, and hence assess the impact of releases of male Wolbachia-Aedes mosquitoes.
NEA also collaborates with the Ministry of Health, the Lee Kong Chian School of Medicine and the School of Biological Sciences of the Nanyang Technological University, the Saw Swee Hock School of Public Health of the National University of Singapore, and the National University Health System to evaluate the impact of the Project on dengue.
12. Why are there still dengue cases in Project Wolbachia – Singapore study sites?
A small number of dengue cases may occasionally be reported within study sites. While Project Wolbachia significantly reduces the Aedes aegypti population by 80-90%, it doesn't completely eliminate all mosquitoes or dengue risk. Nevertheless, the suppressed mosquito population in study sites has resulted in limited dengue transmission and significantly fewer cases compared to areas without releases.
13. Can I kill mosquitoes at the Project Wolbachia – Singapore study sites?
Yes, you can continue with your usual mosquito control measures and kill the mosquitoes as you normally would.
14. Does the release of male Wolbachia-Aedes mosquitoes help to reduce the population of other species of mosquitoes?
No, Project Wolbachia – Singapore is species-specific and only targets Aedes aegypti mosquito, the primary vector for dengue transmission in Singapore. Singapore has many different mosquito species, including Aedes albopictus and Culex quinquefasciatus, with biting females that can cause nuisance. Some of these species are also vectors for other diseases. Project Wolbachia does not affect these other mosquito species, which is why residents may still experience mosquito bites even in Project Wolbachia release sites. This is another reason why it is important for residents living in release sites to remain vigilant and prevent mosquito breeding in your homes and neighbourhood.
15. Why do I still get mosquito bites at Project Wolbachia sites? Is the programme ineffective?
Project Wolbachia is species-specific and only targets Aedes aegypti, the main mosquito responsible for spreading dengue in Singapore. Residents may still encounter bites from other mosquito species that are not affected by the programme.
The programme is highly effective against and has reduced Aedes aegypti populations at release sites by about 80 to 90 per cent, leading to more than 70 per cent reduction in dengue risk. This is achieved by releasing male Wolbachia-carrying Aedes aegypti mosquitoes, which do not bite. When these males mate with urban female Aedes aegypti, their eggs do not hatch, gradually reducing the mosquito population over time.
You may notice more mosquitoes during release days (twice weekly). These are male mosquitoes, which do not bite, but may be attracted to us while searching for female mosquitoes. Residents find that closing doors and windows temporarily during releases helps prevent them from entering homes.
Project Wolbachia is designed to complement - not replace - source reduction efforts Residents should remain vigilant and continue to practice the B-L-O-C-K steps to prevent mosquito breeding and reduce mosquito populations
16. If male mosquitoes do not bite, why are they still landing on me?
Male mosquitoes seek out females, which are likely to be found near people. Thus, although they do not bite, male mosquitoes may still be attracted to (and land on) people. Like females, male mosquitoes are attracted to a variety of cues produced by or associated with humans, including visual cues (e.g. colour and movement); olfactory cues (e.g. carbon dioxide); and thermal cues (temperature and moisture). Click here to find out more.
17. Has Project Wolbachia – Singapore made an impact on dengue cases in the study sites?
Yes, since the start of Project Wolbachia in 2016, the National Environment Agency (NEA) has observed positive outcomes across study sites. The results of a multi-site field study, which started in July 2022, indicate that residents living in these study sites are more than 70% less likely to be infected with dengue. This is the result of an 80 to 90% reduction of the Aedes aegypti mosquito (the primary vector behind dengue transmission) population at the study sites. Residents in adjacent areas are also found to be 45% less likely to contract dengue compared to those with no releases.
18. Does NEA plan to expand Project Wolbachia to cover the whole of Singapore soon?
NEA has been ramping up our male mosquito production and release capacity to enable the expansion of Project Wolbachia and to benefit more households. We are also expanding our repertoire of deployment strategies for different contexts, so as to further increase Wolbachia coverage in a cost-effective and sustainable manner.
As technologies for mass production of Wolbachia-Aedes mosquitoes are still evolving, NEA is working closely with our collaborators to develop solutions which involve the development and maturation of expertise in integrating multi-technical disciplines, including biotechnology, engineering, and data analytics.
There are many lessons that NEA is still learning from the ongoing studies. This includes insights on how best to reduce the number and frequency of mosquito releases without affecting the suppression of urban Aedes aegypti mosquitoes in the community. The ongoing studies will also help NEA to understand the impact of Wolbachia-Aedes technology on reducing dengue cases and to optimise the mosquito production scale that we need. These learnings are essential for ensuring successful expansion. NEA will incorporate these findings in our deployment strategy and share more information about future expansion plans in due course.
19. If I stay within Project Wolbachia study area, does this mean there will not be any thermal fogging or other chemical control activities carried out?
The release of male Wolbachia‑Aedes mosquitoes helps reduce Aedes aegypti populations and should significantly lower the need for chemical control. However, it does not completely eliminate dengue risk. If there are high dengue transmissions or large clusters within release sites, NEA will continue appropriate dengue control operations. When necessary, these may include chemical measures such as thermal fogging. In such cases, NEA will coordinate with relevant stakeholders to avoid overlap between fogging and Wolbachia‑Aedes release schedules.
Risk assessment and mitigation
20. What is the likelihood of accidental release of female Wolbachia-Aedes mosquitoes?
Mosquito production facilities use advanced technology to separate male and female mosquitoes, with stringent quality control checks throughout the sorting process. Due to these stringent measures, the likelihood of female Wolbachia-Aedes mosquitoes being released alongside the males is extremely low.
On the rare occasion of an accidental release of a female mosquito, it still does not pose any public health concern for several reasons. First, the number of accidentally released females would be insignificant compared to the natural female mosquito population already present in the community, so there would be no noticeable increase in biting. Second, even if these few females do bite, their ability to transmit diseases is significantly blocked by the Wolbachia bacteria they carry.
As an additional safeguard, the production process includes exposing all mosquito pupae to low-dose X-ray irradiation. This sterilises any residual females, which means they could not breed with urban male mosquitoes, ensuring that Wolbachia does not establish itself in the wild mosquito population.
21. If Aedes aegypti populations are suppressed or eliminated, will other mosquitoes such as Aedes albopictus be able to take over and proliferate more?
NEA has been studying whether the release of male Wolbachia-Aedes mosquitoes would have any spillover effects on the population of other mosquito species.
Surveillance using Gravitraps has not shown that reducing Aedes aegypti leads to an increase in Aedes albopictus. NEA will continue monitoring closely to detect and respond to any unusual changes in mosquito populations.
22. What happens if residents become less vigilant about checking for and removing breeding habitats?
Wolbachia‑Aedes suppression technology is not a “silver bullet” — it works best alongside community efforts to remove mosquito breeding sites. If residents become less vigilant, the benefits of the releases may be lost and dengue cases could rise. Property owners also have a legal responsibility under the Control of Vectors and Pesticides Act to prevent mosquito breeding. Most importantly, we all need to work together to keep our communities safe. By practising the B-L-O-C-K steps regularly, and combining these actions with Wolbachia technology, we can achieve the strongest protection against mosquitoes and dengue in our neighbourhoods.
Wolbachia programmes in other countries
23. I have read that some countries are releasing female Wolbachia-Aedes mosquitoes. Why is NEA not doing the same?
Wolbachia bacteria can block the ability of Aedes aegypti mosquitoes to carry and transmit dengue viruses. Some countries like Australia, Brazil, Indonesia, Malaysia and Vietnam are leveraging this protective effect by releasing both female and male Wolbachia-carrying mosquitoes in what is known as the replacement strategy.
NEA focuses on the suppression strategy—the release of only male Wolbachia-Aedes mosquitoes to suppress Aedes aegypti populations. The suppression strategy, which does not require the release of biting females, is aligned with our long-held emphasis on source reduction. Click here for more details on NEA’s suppression strategy. Besides Singapore, the Wolbachia-Aedes suppression programme has also been piloted by disease control programmes in China, Thailand, US, and the French Polynesia among other countries.