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 is piloting the use of male Wolbachia-carrying Aedes aegypti (Wolbachia-Aedes) mosquitoes to suppress urban Aedes aegypti mosquito populations in Singapore. Male Wolbachia-Aedes mosquitoes are released regularly at NEA’s study sites to mate with female urban Aedes aegypti mosquitoes. Their resultant eggs do not hatch and no offspring are produced. Continued releases lead to a decline in the urban Aedes aegypti mosquito population, and therefore less 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’s comprehensive risk assessment of Wolbachia-Aedes suppression technology has determined it to be safe, with no 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 comprehensive 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. Nevertheless, male mosquitoes are smaller and have more bushy antennae compared to female mosquitoes. Male mosquitoes (regardless of whether or not 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?

Project Wolbachia – Singapore suppresses urban Aedes aegypti mosquito populations, as eggs produced by matings between released male Wolbachia-Aedes mosquitoes and urban female Aedes aegypti mosquitoes do not hatch. As male Wolbachia-carrying Aedes aegypti mosquitoes mate with Aedes aegypti mosquitoes and not with other insects, this suppression effect is species-specific. Other insect species, including other mosquito species, remain unaffected. Though studies have shown that matings may occasionally occur naturally between Aedes aegypti and Aedes albopictus mosquitoes, this does not happen often enough to affect Aedes albopictus mosquito populations.

Project Wolbachia – Singapore field studies

7.    Where are the Project Wolbachia – Singapore study sites located? Why were these areas selected? 

Since 2016, NEA has been conducting trial releases of male Wolbachia-Aedes mosquitoes at study sites in Yishun and Tampines towns. NEA has gradually expanded these sites over successive phases of the field study. These sites were chosen as they are representative of housing estates in Singapore, and had previously experienced dengue outbreaks and high Aedes aegypti mosquito populations. NEA had also monitored the mosquito populations in these areas for up to three years prior to the start of releases, and had thereby established a baseline against which to evaluate the impact of mosquito releases.

In addition to the gradual roll-out at Yishun and Tampines to eventually cover the entire towns, NEA began testing a different approach of more targeted releases of male Wolbachia-Aedes mosquitoes at dengue high-risk neighbourhoods at Choa Chu Kang and Bukit Batok, in May 2020. With the promising results, NEA expanded releases at more high-risk areas within Choa Chu Kang and Bukit Gombak in October 2021 and May 2022, respectively.

Starting from July 2022, NEA will also be progressively expanding Project Wolbachia to eight more study sites (Bedok North, Bedok Reservoir, Yew Tee, Geylang, Hougang, Punggol, Sengkang and Woodlands), covering an additional 1,400 HDB blocks, as part of a multi-site field study that will help NEA to understand the impact of Wolbachia technology on dengue cases.

Moving beyond HDB residential estates, NEA will also be developing the use of Wolbachia technology for dengue high-risk landed residential estates, and construction sites within the study areas. Marine Parade landed residential estate, being a dengue high-risk neighbourhood with consistently high Aedes aegypti mosquito population, has been selected, and van releases started in April 2022.

8.     How were sites chosen for the multi-site field study?

The multi-site field study was scientifically designed to evaluate the impact of Wolbachia technology on the reduction of dengue cases. Several dengue high-risk HDB areas have been selected to receive releases, based on historical dengue data and Aedes aegypti mosquito populations at these areas between 2016 and 2020. The landscape of these areas and distances between each of the areas were also taken into consideration, to ensure that there are borders such as parks and highways that could serve as natural barriers, to contain each study site and avoid spill-over of the impact across sites. Another factor considered was NEA’s mosquito production and release capacity, which limits the number of sites we can expand to. As Wolbachia technology is not a turn-key solution, constant efforts are required to develop new innovations and engineering solutions, to automate and ramp up mosquito production and release processes.

9.     What is the duration of the releases at the multi-site field study? Will releases stop when dengue cases have reduced?

The multi-site field study will be conducted for a two-year period from July 2022 to 2024. Regular releases are required for the whole duration of the study, in order to ensure robust data collection and evaluation. Plans for use of Wolbachia technology beyond 2024 will depend on findings of the study.

10.     There are other areas with high dengue cases, is NEA able to extend Wolbachia releases to these areas as well?

Additional areas beyond the release sites may be considered, but this is subject to various considerations including capacity constraints. Meanwhile, NEA will continue to monitor the ground situation and work with stakeholders and the community on source reduction efforts in areas with dengue cases. 

11.   
What is NEA doing differently at Tampines and Yishun HDB estates compared to the targeted strategy at Choa Chu Kang and Bukit Batok HDB estates, the multi-site field study at eight HDB estates, and at Marine Parade landed estate?

NEA is testing different release approaches and tactics, to determine the most optimal strategies for future deployment and implementation of Project Wolbachia in an effective and sustainable way.

At Yishun and Tampines, NEA has adopted a rolling approach in which releases are gradually expanded to eventually cover entire towns. Full coverage has been achieved since April 2022.

At Choa Chu Kang and Bukit Batok, NEA is testing a more targeted strategy, zeroing in on neighbourhoods with consistently high Aedes aegypti mosquito populations. NEA will continue to expand the mosquito releases to cover all dengue high-risk areas (i.e. areas with perennially high Aedes aegypti mosquito populations and persistent dengue transmission) within Choa Chu Kang and Bukit Batok towns, by end-2022.

While results from existing trials have been promising thus far, there is a need to collect more data through larger-scale field trials, to conclusively determine the impact of Wolbachia technology on reducing dengue cases in Singapore. NEA’s latest expansion of the project to eight additional sites at HDB estates aims to achieve this.

At Marine Parade landed estate, NEA, together with our partner 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.  

12.     Why are releases still ongoing at Tampines and Yishun study sites while releases have been stopped in parts of Choa Chu Kang and Bukit Batok study sites?

NEA is testing two approaches – rolling and targeted. The rolling approach is tested in Tampines and Yishun study sites whereby releases are gradually expanded to cover entire towns. The targeted approach is tested in Choa Chu Kang and Bukit Batok study sites, focusing on neighbourhoods with consistently high Aedes aegypti mosquito populations. Targeted releases are also carried out at selected construction sites.

Once the Aedes aegypti population is suppressed to a low level, releases can be reduced or stopped. Testing different approaches is important as it allows NEA to determine optimal strategies for future implementation of Project Wolbachia in an effective and sustainable way.

13.     Are there plans to expand Wolbachia release to other landed estates and condominiums?

Since April 2022, Wolbachia releases have been carried out using vans within five square kilometres of landed estate at Marine Parade. This is following small-scale test releases conducted from October to December 2021 at Duku Road and Jalan Baiduri to understand the behaviour of the released non-biting male Wolbachia-Aedes mosquitoes in the field, and working with the community and resident volunteers in the estate to deploy gravitraps to collect data for baseline surveillance.

Although there are currently no plans to conduct field studies in condominiums (other than condominiums within Marine Parade study site), residents in condominiums within or adjacent to study sites may expect to see male Wolbachia-Aedes mosquitoes in their area and also experience the positive spill-over effects. 

14.    How much has Project Wolbachia – Singapore expanded since its inception?

With the success of the Project Wolbachia – Singapore field trials, NEA is working to extend releases of male Wolbachia-Aedes mosquitoes to more areas so that more residents can benefit. We have been developing and incorporating automated technologies into our mosquito production facility to scale up our production and release capacity. This has already allowed us to expand release areas significantly since our initial field studies in 2016:

Gradual roll-out releases in Tampines and Yishun (since 2016): 

Study site  Phase 1
(Oct 2016 -
Jan 2017)
 Phase 2
(Apr 2017 -
Dec 2018) 
  Phase 3
(Feb 2019 -
Nov 2019)
 Phase 4
(Nov 2019 -
Jul 2020) 
 Phase 5
(ongoing;
numbers below
are as of Jun 2022) 
No. of
blocks
No. of
households
No. of
blocks
No. of
households
No. of
blocks
No. of
households
No. of
blocks
No. of
households
No. of
blocks
No. of
households
 Yishun 10 1,000 40 3,581 84 7,950 293 29,700 68669,659
 Tampines 29 2,941 36 3,475 60 5,560 260 26,300 78772,743
 Total 39 3,941 76 7,056 144 13,510 553 56,000 1,473142,402


Targeted releases in Choa Chu Kang and Bukit Batok (as of May 2022):

 Area HDB blocks  Households
 Choa Chu Kang 31830,708
 Bukit Batok 133 12,161


Multi-site field study (from Jul 2022):

AreaHDB blocksHouseholds
Bedok (Bedok North) 219 30,027
Bedok (Bedok Reservoir) 133 12,115
Choa Chu Kang (Yew Tee)
 167 15,350
Geylang 86 11,135
Hougang 183 16,329
Punggol 221 22,558
Sengkang 221 21,599
Woodlands 268 25,493

15.      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 progress 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 4 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 is more 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 shows the synergistic effect of Project Wolbachia with the cooperation of the community in removing mosquito breeding habitats.

16.    How is NEA measuring the outcomes of the field study?

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 to assess the impact of releases of male Wolbachia-Aedes mosquitoes.

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

NEA is conducting trials using van releases to evaluate the behaviour, distribution and longevity of van-released mosquitoes. Van releases have been first piloted in a small area within the Tampines study site, and will be carried out in more areas within Wolbachia study sites. As Project Wolbachia scales up, the use of automated release mechanisms such as van releases will allow NEA to cover larger areas more efficiently.

18.    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 significantly fewer dengue cases in study sites compared to areas without releases.

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

Residents in study sites do not have to do anything differently. You may use NEA-registered insecticides or any gadget to kill mosquitoes as you normally would. Residents must remain vigilant and continue to carry out mosquito control measures, and regularly practise the Mozzie Wipeout to keep the mosquito population low. 

20.    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. Do the Mozzie Wipeout regularly to keep mosquitoes at bay.

21.    If male mosquitoes do not bite, why are they still landing on me? 

Male mosquitoes seek out female mates, which are likely to be found near humans. 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). 

22.    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. We have observed up to 98% suppression of the Aedes aegypti mosquito population and up to 88% reduction in dengue incidence at Tampines and Yishun study sites with at least one year of releases in 2019. Similar observations have been made in the 2022 dengue outbreak where areas have 70% less dengue compared to similar areas without Wolbachia. NEA will need to conduct larger-scale field trials to conclusively show that Wolbachia-Aedes releases are able to reduce dengue transmission in Singapore.

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

To enable the rollout of Wolbachia technology to more areas so that more residents can benefit, NEA has been ramping up our male mosquito production and release capacity. A challenge we face is that Wolbachia technology is nascent, and off-the-shelf commercial solutions for increasing scale are not available. NEA and our collaborators are, therefore, custom-developing innovative engineering solutions to automate production and release, so that the Wolbachia technology can be implemented sustainably and cost-effectively. This process involves the integration of multiple technical disciplines, including biotechnology, engineering, and data analytics, and hence requires considerable time and development of expertise.

In step with the development of automation, NEA is rigorously evaluating the technology in the field via a phased approach, and developing strategies and tactics for effective and sustainable deployment. To date, NEA has expanded releases to cover Tampines and Yishun HDB towns entirely as of April 2022. Data collected will allow us to determine if mosquito population suppression at the town level can be sustained with releases of fewer male Wolbachia-Aedes mosquitoes. This is important to allow Wolbachia technology to be sustainably deployed on a larger scale in the future. NEA has also, since May 2020, been testing a more targeted release strategy in dengue high-risk areas of selected neighbourhoods in Choa Chu Kang and Bukit Batok towns, to pre-emptively suppress high Aedes aegypti mosquito populations in these areas. Since April 2022, NEA has also released male Wolbachia-Aedes mosquitoes in the Marine Parade landed residential estate with the aim of developing deployment tactics in such landscapes. These trials are part of NEA’s efforts to expand our repertoire of potential deployment strategies and determine which are most suitable for different contexts. NEA will continue to work to further increase Wolbachia coverage in a cost-effective and sustainable manner.

24.    Can Wolbachia technology be used to curb the transmission of dengue? Can male Wolbachia-Aedes mosquitoes be deployed in active clusters?

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, conventional vector control efforts must continue and the community still needs to be vigilant in doing their part to suppressing the presence of breeding habitats. NEA is assessing the use of the technology as an additional tool to interrupt active dengue clusters.

25.    If Project Wolbachia – Singapore has been successful, why were dengue cases on the rise in 2022?

NEA’s pilot releases of male Wolbachia-Aedes mosquitoes have successfully suppressed the Aedes aegypti mosquito populations and dengue cases at the Tampines, Yishun, Bukit Batok and Choa Chu Kang study sites. The results have been promising thus far.

In Tampines and Yishun, where there has been more than one year of releases, we have previously observed up to 98% reduction in the dengue mosquito population and up to 88 per cent reduction of dengue cases. Similar observations have been made in the current dengue outbreak where these areas have 70 per cent less dengue compared to similar areas without Wolbachia.

In Choa Chu Kang and Bukit Batok, areas with at least a year of releases show dengue case reductions of up to 53%. However, the current study covers and impact only about 19% of all HDB blocks in Singapore. The expansion will allow the technology to impact more areas in the next months.

26.     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. Dengue control operations, which may include chemical control measures such as thermal fogging, will be carried out in the event of high dengue transmission or large dengue clusters within the study sites. In such cases, NEA will work with relevant stakeholders to deconflict the thermal fogging and Wolbachia-Aedes mosquito release schedules.


Risk assessment and mitigation

27.    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. 

As the sorting is not 100% accurate, we expect a very small number of female Wolbachia-Aedes mosquitoes to be released along with the males. This will not result in increased biting, as the number of released females is much smaller than Singapore’s female urban Aedes aegypti mosquito population. The ability of this small number of released females to transmit disease would also largely be blocked by Wolbachia.

28.    What happens when a female Wolbachia-Aedes mosquito mates with either a male Wolbachia-Aedes mosquito or a male urban Aedes aegypti mosquito?

When a female Wolbachia-Aedes mosquito mates with either a male Wolbachia-Aedes mosquito or a male urban Aedes aegypti mosquito, the resultant eggs will hatch into Wolbachia-carrying offspring. This is due to the loss of biological incompatibility, and as a result of maternal transmission of Wolbachia from mother to offspring. Although this hampers suppression, there is little public health risk, as these mosquitoes are partially resistant to dengue infection and do not transmit dengue well.

29.    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. However, as size-based sex-sorting is about 99.8% accurate, we expect a very small number of female Wolbachia-Aedes mosquitoes to be released along with the males.

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

Based on Gravitraps data and our knowledge of the local context, there is no evidence that Aedes albopictus is taking over the niche left vacant by the suppressed Aedes aegypti mosquito population in the study sites, especially if the community remains vigilant against mosquito breeding. First, although the two species share some common habitats, Aedes aegypti prefers urban spaces while Aedes albopictus prefers natural greenery. Second, our analysis of the population dynamics of the two species shows that decreases in Aedes aegypti numbers are not associated with increases in Aedes albopictus numbers. 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 Mozzie Wipeout.

31.    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 Mozzie Wipeout, so that our neighbourhoods and homes can be kept free of mosquitoes and dengue.

Wolbachia pilots in other countries

32.    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 more suitable for Singapore’s context and is aligned with our decades of emphasis on source reduction. Click here for more details on why NEA is focusing on the suppression strategy.  

33.    Where else is Wolbachia-Aedes suppression technology being piloted?

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

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