Wolbachia-Aedes Mosquito Suppression Strategy

Frequently Asked Questions

  1. Wolbachia-Aedes suppression technology
  2. Project Wolbachia – Singapore field studies
  3. Risk assessment and mitigation
  4. Wolbachia pilots in other countries

Wolbachia-Aedes suppression technology

1.    How does Project Wolbachia – Singapore work?

NEA has been conducting field releases of male Wolbachia-carrying Aedes aegypti (Wolbachia-Aedes) mosquitoes to suppress urban Aedes aegypti mosquito populations, the main vector for dengue, in parts of Singapore. 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?  

NEA has conducted a thorough risk assessment of Wolbachia-Aedes suppression technology and has found the technology to be safe, with no identified risk to human health and no significant risk to ecology. The conclusion is consistent with findings from other research groups around the world, and with the findings of an independent research company. 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.

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 are 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.

Project Wolbachia – Singapore field studies

7.   Where are the Project Wolbachia – Singapore study sites located, and how has the project expanded since its inception?

As of Q1 2024, Project Wolbachia covers about 480,000 households, which represents approximately 35% of all households in Singapore. They cover the following studies, each with different objectives to ensure that the tool and deployment tactics are effective in different landscape.

Field studies commenced in 2016 in selected areas of Yishun and Tampines towns, and by April 2022, had expanded to cover the entirety of both towns. In May 2020, NEA initiated a new approach, conducting targeted releases of male Wolbachia-Aedes mosquitoes in dengue high-risk residential areas within Choa Chu Kang and Bukit Batok towns.

Moving beyond HDB residential estates, NEA has also been studying the use of Wolbachia technology for dengue high-risk landed residential estates and construction sites within the study areas since April 2022.

A Multi-Site Field Study to determine the impact of the Project on dengue cases started in July 2022 covering 8 study sites, namely Bedok North, Bedok Reservoir, Geylang - MacPherson, Hougang, Punggol, Sengkang, Woodlands and Yew Tee.

The expansion in Q1 2024 covers five residential sites in the South of Singapore, comprising both HDB and landed estates. The five locations are Bukit Merah – Telok Blangah, Clementi – West Coast, Commonwealth, Holland and Marine Parade – Mountbatten.

Summary of Release Areas

Pilot Sites

Study Sites

No. of Households

(as of 31 Dec 2023)




Releases since 2016, reached full town coverage by April 2022



Releases since 2016, reached full town coverage by April 2022

Choa Chu Kang


Releases since May 2022, targeted high-risk areas

Bukit Batok


Releases since June 2022, targeted high-risk areas

Marine Parade


Releases since April 2022, first landed estate

Multi-Site Field Study (Release since July 2022):

Study Sites

No. of Households

(as of 31 Dec 2023)

Bedok North


Bedok Reservoir


Geylang – MacPherson










Yew Tee


Expansion (Release from Q1 2024):

Study Sites

No. of Households

(as of 31 Dec 2023)

Bukit Merah – Telok Blangah


Clementi – West Coast






Marine Parade – Mountbatten


8.    How were sites chosen for the field studies? What is NEA doing differently at each study site?

Sites are selected based on past dengue data and Aedes aegypti mosquito population in these areas.

NEA is testing different release approaches and tactics, to determine the most optimal strategies for wider deployment and implementation of Project Wolbachia in an effective and sustainable way. At Yishun and Tampines, NEA has adopted a rolling carpet approach in which releases are gradually expanded to eventually cover entire towns. At Choa Chu Kang and Bukit Batok, NEA is testing a more targeted strategy, focusing on neighbourhoods with consistently high Aedes aegypti mosquito populations. The Multi-Site Field Study at the eight selected sites aims to collect more data through larger-scale field trials, to build on our understanding of the impact of Wolbachia technology on reducing dengue cases in Singapore. At Marine Parade landed estate and Tampines study site, NEA, together with our partner Debug by Verily Life Sciences (Verily), is exploring the use of vans equipped with release automation technology to conduct releases. The use of van releases is part of NEA’s efforts to incorporate automation into releases, so that we can cover larger areas more effectively as Project Wolbachia scales up. 

9.    How is the latest expansion in Q1 2024 different from existing study sites?

The latest expansion is no different from existing study sites. All field studies, including the upcoming expansion, help NEA understand the environmental factors that influence efficacy, improve deployment strategy, and enhance cost-effectiveness. Past studies have revealed differences in the persistency of mosquito population amongst sites. While it takes typically 3 to 6 months to achieve a significant reduction in the population of Aedes aegypti mosquitoes, there are areas that require a longer period of release. Continued releases in different types of settings / terrains, and data collection provides insights that will enhance our proficiency in using this novel vector control tool.

10.    There are areas outside the study sites with active dengue clusters, is NEA able to extend Wolbachia-Aedes releases to these areas as well?

The Wolbachia technology is best used for prevention of dengue, and NEA’s data has shown the feasibility. Male Wolbachia-Aedes mosquitoes are not specifically released at existing large dengue clusters as NEA is still assessing the use of the technology as an additional tool to interrupt active dengue clusters. As it impacts the following generations of Aedes aegypti mosquitoes and does not remove existing dengue virus infected ones, its use for outbreak control needs further evaluation.

Project Wolbachia study sites were selected based on past dengue data and Aedes aegypti mosquito population in these areas. Past 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. Hence, planning for expansion of Project Wolbachia is not based on ongoing dengue data.

Project Wolbachia is not a silver bullet solution to stem dengue transmission in Singapore. While the technology has shown to be effective in reducing the Aedes aegypti population and the risk of dengue transmission in a local area, it is a complementary tool for dengue control. The key measures for outbreak or cluster control are the removal of mosquito breeding habitats, as well as the spraying of pesticides to kill the adult Aedes population, including infected mosquitoes. Community action is critical to curb the transmission of dengue.

11.    Are there plans to expand Wolbachia-Aedes releases to condominiums?

There are currently no plans to conduct field studies in condominiums, but residents in condominiums within or adjacent to study sites may see male Wolbachia-Aedes mosquitoes in their area and experience the positive spill-over effects. 

12.    When is the Project Wolbachia field trial going to end? How long will releases of male Wolbachia-Aedes mosquitoes be conducted?

Project Wolbachia is a long-term project with clearly defined objectives in each phase, to enable the study to progress and the technology to be systematically evaluated. NEA’s data shows that some areas could achieve good suppression of the urban Aedes aegypti mosquito population within 3 to 6 months following releases of male Wolbachia-Aedes mosquitoes. Releases may be stopped or reduced in areas where the urban Aedes aegypti mosquito population has been suppressed to dengue low-risk levels. However, in areas where there may be more cryptic Aedes aegypti mosquito breeding in the community, more time may be required to see positive effects of the releases, or for mosquito population suppression to be sustained. This highlights the need for residents to regularly practice the B-L-O-C-K steps to complement ongoing efforts to suppress the presence of breeding habitats.

13.     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.

14.  In some areas, vans are seen releasing Wolbachia-Aedes mosquitoes. Is this a new release strategy?

A combination of van and manual releases is currently used in Tampines and Marine Parade landed study sites with plans for further deployment in new areas in 2024. As Project Wolbachia scales up, the integration of automated release mechanisms such as van releases will enable NEA to efficiently cover larger areas.

15.     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. This could be due to the presence of low-level dengue transmission, or because cases living in the area were infected elsewhere. However, due to the low Aedes aegypti population in the study sites brought about by the releases of male Wolbachia-Aedes, we have seen limited dengue transmission and therefore significantly fewer dengue cases in study sites compared to areas without releases.

16.    Can I kill mosquitoes at the Project Wolbachia – Singapore study sites?

You can continue with your usual mosquito control measures and kill the mosquitoes as you normally would, as it is difficult to tell the male and female mosquitoes apart. To prevent mosquito breeding, it’s important to regularly practice B-L-O-C-K.

17.   If male mosquitoes do not bite, why am I still getting bitten? 

Project Wolbachia – Singapore only targets Aedes aegypti mosquitoes, the primary vectors for dengue transmission in Singapore, but not other mosquito species (such as Aedes albopictus and Culex quinquefasciatus). Hence, you may still be bitten by such mosquitoes or other biting insects. Please remain vigilant and continue to Stop Dengue with B-L-O-C-K even if you are residing in a neighbourhood with Wolbachia coverage.

18.    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 you. Like females, male mosquitoes are attracted to a variety of cues produced by or associated with humans, including visual cues (e.g. light, colour, and movement); olfactory cues (e.g. carbon dioxide, lactic acid, and octenol); and thermal cues (temperature and moisture). Mosquito traps also use these attractants to lure mosquitoes. Click here to find out more.

19.    Has Project Wolbachia – Singapore made an impact on dengue cases in the study sites? 

Aedes aegypti is the primary vector that drives dengue transmission in Singapore. Field studies conducted in Bukit Batok, Choa Chu Kang, Tampines and Yishun have achieved more than 90% suppression of the Aedes aegypti mosquito population. Data from 2019 to 2022 indicates that residents in areas with at least one year of releases were up to 77% less likely to acquire dengue. However, the impact on mosquito population and dengue varied across sites and years.

Preliminary data from the eight study sites (under the multi-site field study) launched in July 2022 also suggested reductions of more than 80% in the dengue mosquito population. NEA continues to collect data from these sites to obtain more definitive results on efficacy of dengue risk reduction.

20.  Why can’t we just deploy Wolbachia technology islandwide? Why are field trials taking so long?

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 such as Debug by Verily Life Sciences (Verily) and Orinno Technology Pte Ltd to develop solutions which involves 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.

21.    Can Wolbachia technology be used to curb the transmission of dengue?

Project Wolbachia is an additional tool but not a silver bullet solution to stem dengue transmission in Singapore.  While the technology has shown to be effective in reducing the Aedes aegypti population and the risk of dengue transmission in a local area, conventional vector control efforts must continue, and the community still needs to be vigilant in doing their part to suppress the presence of breeding habitats.

22.     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? 

Releases of male Wolbachia-Aedes mosquitoes will help in the reduction of Aedes aegypti mosquitoes but will not completely eliminate the dengue risk. In the event of high dengue transmission or large dengue clusters within the study sites, e.g. during the early phase of releases, dengue control operations will be implemented. These operations may include chemical control measures such as thermal fogging. In such cases, NEA will work with relevant stakeholders to deconflict the thermal fogging and Wolbachia-Aedes mosquito release schedules.

Risk assessment and mitigation

23.    How does NEA separate out male Wolbachia-Aedes mosquitoes for release? Are any female Wolbachia-Aedes mosquitoes released and what is the impact of this?

As male mosquito pupae are smaller than female pupae, male and female mosquitoes can be sorted by size at the pupal stage. This is done at our mosquito production facility. After sorting, male Wolbachia-Aedes mosquito pupae are allowed to emerge as adult mosquitoes, which are then ready for release. NEA’s stringent quality control checks ensure that this sorting is done with high accuracy. 

A very small number of female Wolbachia-Aedes mosquitoes may be released along with the males. This will not result in increased biting, as the number of released females is insignificant compared to the natural population in the community. The ability of this small number of released females to transmit disease would also largely be blocked by Wolbachia.

However, female Wolbachia-Aedes mosquito released could produce Wolbachia-carrying offspring in the field. A Wolbachia Aedes population in the field does not increase risk of dengue transmission but could hamper suppression effort due to loss of biological incompatibility between released males and females in the field. NEA takes the additional step of exposing pupae to low-dose X-ray irradiation to sterilise any residual females to prevent Wolbachia from establishing itself in the mosquito population.

24.   How does NEA ensure that large numbers of female Wolbachia-Aedes mosquitoes are not accidentally released? 

NEA’s mosquito production facility implements stringent laboratory security and containment measures. These measures, together with regular quality-control checks of the sex-sorting process, will prevent the unintentional release of large numbers of female Wolbachia-Aedes mosquitoes. 

25.    If Aedes aegypti populations are suppressed or eliminated, will other mosquitoes such as Aedes albopictus be able to take over and proliferate more?

Based on NEA EHI’s study, there is no evidence that the reduction of Aedes aegypti has allowed Aedes albopictus to proliferate more. Nevertheless, NEA continues to monitor Aedes albopictus populations using our Gravitrap surveillance system, which will allow us to pick up any unusual increases. To keep the populations of both Aedes species low, it is critical for the community to continue practising the B-L-O-C-K steps.

26.  What happens if residents become less vigilant about checking for and removing breeding habitats? 

Wolbachia-Aedes suppression technology is not a silver bullet, and is intended to complement, not replace source reduction efforts. Diminished community efforts to reduce mosquito breeding may negate the effect of the releases and can lead to an increase in dengue cases. Under the Control of Vectors and Pesticides Act, anyone found breeding mosquitoes within their premises will be subjected to enforcement action, as they have created, caused or permitted the creation of conditions favourable for the harbouring of vectors. It is therefore critical for the public to remain vigilant and regularly practise the B-L-O-C-K steps, so that our neighbourhoods and homes can be kept free of mosquitoes and dengue.

Wolbachia programmes in other countries

27.    I have read that some countries are releasing female Wolbachia-Aedes mosquitoes. Why is NEA not doing the same? 

Releases of both female and male Wolbachia-carrying mosquitoes are being piloted by disease control programmes in Australia, Brazil, Indonesia, Malaysia, and Vietnam, among other countries. This approach, known as the replacement strategy, aims to replace field mosquito populations with Wolbachia-carrying mosquitoes, which have a reduced ability to transmit diseases such as dengue. 

While NEA continues to monitor the results of these trials, we have after careful evaluation decided to focus on 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 decades of emphasis on source reduction. Click here for more details on why NEA is focusing on the suppression strategy.  

28.    Where else is Wolbachia-Aedes suppression programme being piloted?

Besides Singapore, Wolbachia-Aedes suppression programme has also been piloted by disease control programmes in China, Thailand, US, and the French Polynesia among other countries.

The table below provides examples of past and ongoing pilots of Wolbachia-Aedes suppression programmes. While a number of pilots have been successful, there are as yet no reports of large-scale deployment.



Year of field release

Mosquito species targeted





Culex quinquefasciatus

100% non-viableCulex quinquefasciatuseggs by week 12 [Link]

French Polynesia



Aedes polynesiensis

Reduction inAedes polynesiensispopulation[Link]




Aedes albopictus

Reduction inAedes albopictuspopulation [Link]




Aedes albopictus

83-94% reduction inAedes albopictuspopulation when IIT-SIT is implemented [Link]




Aedes albopictus

Significant reduction in the proportion of viable eggs collected in the field[Link]


Fresno, California


Aedes aegypti

Up to 95.5% reduction in the femaleAedes aegyptipopulation in release areas [Link]


Chachoengsao (East of Bangkok)


Aedes aegypti

Up to 84% reduction inAedes aegyptimosquito population in the wild and up to 97% reduction inAedes aegyptimosquito population in households [Link]


Innisfail, Queensland


Aedes aegypti

80% reduction inAedes aegyptipopulation[Link]


Miami, Florida


Aedes aegypti

Up to 78% reduction in femaleAedes aegypti numbers in release area [Link]


Houston, Texas


Aedes aegypti

Up to 92% reduction in Aedes aegypti female numbers in release area [Link]

Puerto Rico



Aedes aegypti

No substantial entomological impact after a 15-month trial. Issues with the long-distance transport of Wolbachia-Aedes from California to the treatment site resulted in sub-optimal performance from the mosquitoes. [Link]