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 release of male Wolbachia-carrying Aedes aegypti (Wolbachia-Aedes) mosquitoesto suppress urban Aedes aegypti populations in Singapore. Male Wolbachia-Aedes mosquitoes are released regularly at NEA’s study sites to mate with urban female mosquitoes. Their resultant eggs do not hatch and no offspring are produced. Continued releases lead to a decline in the urban Aedes aegypti population, and therefore less dengue. 

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 species as Aedes aegypti mosquitoes 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 groups around the world, and with the findings of an independent research company. NEA’s comprehensive evaluation process involved 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.    What happens to male Wolbachia-Aedes mosquitoes after they are released? 

Male Wolbachia-Aedes mosquitoes do not bite or transmit disease. After release, male Wolbachia-Aedesmosquitoes will look for female Aedes aegypti to mate with. These matings result in eggs that do not hatch. The males will die soon after release, most within a week. 

6.    How can I recognise male Wolbachia-Aedes mosquitoes?

Male Wolbachia-Aedes mosquitoes have more bushy antennae but the difference between these males and female mosquitoes in the community may not be obvious visually. 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 a blood meal to produce eggs.

7.    Will the release of male Wolbachia-Aedes mosquitoes affect insects other than Aedes aegypti?

Project Wolbachia – Singapore suppresses urban Aedes aegypti populations, as eggs produced by matings between released male Wolbachia-Aedes mosquitoes and urban female Aedes aegypti do not hatch. As male Wolbachia-carrying Aedes aegypti mosquitoes mate with Aedes aegypti 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 between Aedes aegypti and Aedes albopictus naturally, this does not occur often enough to affect Aedes albopictus mosquito populations. 

Project Wolbachia – Singapore field studies

8.    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 in 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 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 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 in dengue high-risk neighbourhoods at Choa Chu Kang and Bukit Batok in May 2020. With the promising results, NEA will continue to expand and carry out releases in more high-risk areas within Choa Chu Kang and Bukit Batok towns by December 2021.

Moving beyond HDB residential estates, NEA will also be developing the use of Wolbachia technology for 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  small-scale field releases will commence from Q4 2021.

9.    What is NEA doing differently in Tampines and Yishun HDB estates as compared to targeted strategy in Choa Chu Kang and Bukit Batok HDB estates, and in Marine Parade landed estate?

In Yishun and Tampines, NEA is gradually expanding the study sites by moving into adjacent neighbourhoods, to eventually cover entire towns. In Choa Chu Kang and Bukit Batok, NEA is testing a more targeted strategy, zeroing in on neighbourhoods with consistently high Aedes aegypti populations. With the promising results, NEA will continue to expand to cover more high-risk areas within Choa Chu Kang and Bukit Batok towns by end 2021. Targeted releases will be conducted in areas with perennially high Aedes aegypti mosquito populations and persistent dengue transmission.

For the latest study at Marine Parade landed estate, NEA, together with our partner Verily Life Sciences (Verily), will explore the use of vans equipped with release automation technology to conduct releases. Trial tests would first be carried out and the data collected would further guide NEA’s deployment strategy for further large scale releases at the estate. 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. 

Testing different approaches is important as it allows NEA to determine the most optimal strategies for future deployments and implementation of Project Wolbachia in an effective and sustainable way.

10.    How are releases at construction sites different from  residential estates?

Releases at construction sites are part of NEA's release strategy to achieve better suppression in the study sites by covering different terrains and landscapes. Releases at residential areas are currently carried out either by NEA or our partner, Verily Life Sciences. For construction sites, NEA is engaging the relevant stakeholders, including construction companies, and will guide them on the surveillance and releases of male Wolbachia-Aedes mosquitoes at such premises

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

With the success of the Project Wolbachia – Singaporefield 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 2021) 
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 29,700 417 40,314
 Tampines 29 2,941 36 3,475 60 5,560 260 26,300 443 40,402
 Total 39 3,941 76 7,056 144 13,510 553 56,000 860 80,716

 

Targeted releases in Choa Chu Kang and Bukit Batok (since May 2020):

 Area HDB blocks  Households
 Choa Chu Kang 59 4830
 Hong Kah North 94 7830
 Keat Hong 54 4890

 

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

Project Wolbachia – Singapore is a long-term project with clearly defined objectives for each phase, so as to progress the study and evaluate the technology systematically. While NEA’s data shows that some areas could achieve good suppression of Aedes population within 3 to 4 months after the release of male Wolbachia-Aedes, there are also instances whereby more time is required to see positive effects or for suppression to be sustained. Releases may be stopped or reduced in areas where the Aedes aegypti mosquito population has been suppressed to dengue low-risk levels.

13.    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.

14.    With NEA’s islandwide network of Gravitraps, why do we still need residents at landed estates to host mosquito traps within their homes?

In addition to existing Gravitrap surveillance, the hosting of traps in residents’ homes will augment the surveillance of Aedes mosquito populations in landed homes. This will allow NEA to assess the distribution and impact of released male Wolbachia-Aedes mosquitoes that will further guide NEA’s  targeted deployment strategy in landed estates.

15.    How does NEA define low-risk mosquito population level?

Islandwide data on mosquito population (from the Gravitrap Surveillance network) has been found to correlate with dengue cases. As the Aedes aegypti mosquito is the primary vector of dengue in Singapore, reduced Aedes aegypti mosquito numbers in an area are associated with a lower risk of dengue. When the Aedes aegypti mosquito population is suppressed to dengue low-risk levels, the risk of a dengue cluster forming is low.  

16.    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.

17.    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. 

18.    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.

19.    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). 

20.    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. NEA will need to conduct larger-scale field trials to conclusively show that Wolbachia-Aedes releases are able to reduce dengue transmission in Singapore.

21.    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. NEA is gradually expanding releases to cover Tampines and Yishun HDB towns entirely by early 2022, allowing 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. Since May 2020, NEA has also 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. From fourth quarter 2021, NEA will also be releasing 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.

22.    Why is NEA not releasing male Wolbachia-Aedes mosquitoes at existing large dengue clusters to reduce dengue transmission?

Project Wolbachia – Singapore is still in its study stage, and we need more information on its impact before we can trial the technology in areas with ongoing high intensity dengue transmission. In its original conception, ProjectWolbachia – Singapore was intended to be used as a preventive tool, and is not primarily designed as a tool to be applied to existing dengue clusters, or as a real-time mosquito management solution.  

23.    If Project Wolbachia – Singapore has been successful, why were dengue cases on the rise in 2020?

NEA’s pilot releases of male Wolbachia-Aedes mosquitoes have successfully suppressed the Aedes aegypti mosquito populations and dengue cases in parts of Tampines, Yishun, Choa Chu Kang and Bukit Batok towns. However, these study sites were still relatively small, covering only about 8% of all HDB blocks in Singapore in 2020. Though the number of dengue cases were significantly reduced within the release sites, they were not expected to significantly impact the dengue outbreak in 2020.

Risk assessment and mitigation

24.    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.

25.    How did the Wolbachia-Aedes mosquitoes propagate in the Tampines study site when there is mitigation in place?

Our study showed that in areas with very low Aedes aegypti mosquito populations, the presence of female Wolbachia-Aedes mosquitoes could result in Wolbachia-Aedes mosquitoes propagating in the field. In June 2020, NEA observed an increase in the Wolbachia-Aedes mosquito population at a small section of the Tampines West study area, where the population of Aedes aegypti mosquito had previously been reduced to very low levels due to Project Wolbachia. As this scenario was anticipated early on in the Project, additional technique of X-ray irradiation was introduced to sterilise the male Wolbachia-Aedes mosquitoes, which successfully reduced the urban Wolbachia-Aedes mosquito population.

26.    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.

27.    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.

28.    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.

29.    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

30.    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.  

31.    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.