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NEA Commences Small-Scale Field Study With Release Of Male Wolbachia-Carrying Aedes Aegypti At Braddell Heights

18 Oct 2016

NEA will also conduct releases at Tampines West and Nee Soon East in coming weeks; and seeks the continued support from residents and local stakeholders

Singapore, 18 October 2016 – The Environmental Health Institute (EHI) of the National Environment Agency (NEA) released the first batch of male Wolbachia-carrying Aedes aegypti mosquitoes today at Braddell Heights, as it embarks on its six-month long small-scale field study. The first release of these mosquitoes at the other two selected sites located at Tampines West and Nee Soon East will be on 28 October 2016 and 15 November 2016, respectively.

2          After six years of laboratory and risk assessment studies on novel tools for dengue control, and four years specifically on Wolbachia-carrying Aedes aegypti mosquitoes, the project has reached a significant milestone, as it enters the second phase of the study. As announced in August this year, NEA is embarking on a six-month long small-scale field study to gain a further understanding of the behaviour of male Wolbachia-carrying Aedes aegypti mosquito population in our urban environment. The small-scale field study involves the release of male Wolbachia-carrying Aedes aegypti mosquitoes on a regular basis at three selected sites located within Braddell Heights, Nee Soon East and Tampines West. These male Wolbachia-carrying Aedes aegypti mosquitoes do not bite or transmit diseases. (Please see Annex A for more information on the small-scale field study and Annex B for the location maps of the three selected sites.)

3          The small-scale field study will help NEA move towards the longer term goal of using male Wolbachia-carrying Aedes aegypti mosquitoes for suppression of Aedes aegypti mosquitoes in the community. Eggs produced from the mating between a male Wolbachia-carrying Aedes aegypti mosquito and a female urban Aedes aegypti mosquito (without Wolbachia) will not hatch. Multiple releases of male Wolbachia-carrying Aedes aegypti mosquitoes over time will thus eventually lead to a reduced urban Aedes aegypti population, and reduce the potential spread of diseases such as dengue. If this small-scale field study and the subsequent suppression trial are successful, NEA hopes to use Wolbachia technology to complement NEA’s existing vector control efforts and reduce the spread of viruses such as dengue.

4          The commencement of the small-scale field study follows a comprehensive risk assessment of Wolbachia technology which has determined it to be safe, with no risk to human health and insignificant risk to ecology. This conclusion is consistent with other international findings and the findings of an independent research company.

5          Dengue Expert Advisory Panel (DEAP) member, Associate Professor Vernon Lee, of the National University of Singapore's Saw Swee Hock School of Public Health said, "The Dengue Expert Advisory Panel fully supports NEA's plan to use this method to reduce the Aedes aegypti population in Singapore and the transmission of diseases spread by this mosquito, such as dengue and Zika. NEA has done an extensive assessment on the safety of this method, and we are satisfied that it is safe. This field release today is critical to help us understand its effectiveness in the Singapore context, through close monitoring of the trial results. The results will help to calibrate the strategy for maximal mosquito suppression and reduction of dengue in Singapore. As no method is 100% effective, it is important to combine this with other existing methods of mosquito control, such as community-based removal of potential breeding habitats. It is therefore important for everyone to play their part to eradicate mosquito breeding habitats in their surroundings."

Engagement and Outreach Efforts

6          NEA’s comprehensive evaluation process, since 2012, involved critical reviews of existing knowledge and research, and consultations with various stakeholders such as academic experts, medical and healthcare professionals and Non-Governmental Organisations (NGOs).

7          Since the announcement of the small-scale field study in August 2016, NEA, together with the Grassroots Advisers and Grassroots Leaders of the three selected study sites, have been reaching out to their residents and stakeholders through various activities, including home/premises visits, block/garden parties, and Project Wolbachia Learning Journey visits to EHI’s mosquito production facility.

8          Thus far, more than 100 engagement sessions have been conducted with stakeholders and members of the community to generate awareness and understanding of the Wolbachia-Aedes technology.

9          The majority of residents at the selected sites are supportive of the small-scale field study. Some have also volunteered to host fan-based mosquito traps in their homes. We are grateful for the strong support that we have received from the residents and local stakeholders of the selected sites thus far, and we seek their continued support as NEA explores the potential of Wolbachia technology.

10        Dr Raman Velayudhan, Coordinator, Vector Ecology and Management, Neglected Tropical Diseases (NTD) Department, World Health Organization (WHO), said: “We hope this trial will produce a long-term sustainable solution for the control of Aedes mosquitoes – the principal vectors of both dengue and Zika. Innovative control measures are absolutely essential for the future.”

Collective Effort Needed to Fight Dengue

11        The co-operation and support from residents and local stakeholders at the selected sites will be crucial in ensuring the success of the small-scale field study. NEA emphasises that during all studies and trials exploring the potential of the Wolbachia-Aedes technology, source eradication of mosquito breeding habitats and spraying of insecticide where necessary to control the adult mosquito population remain essential for dengue prevention in Singapore.

12        Residents do not have to do anything differently, but continue to carry out mosquito control procedures and practise the 5-Step Mozzie Wipeout as normal. We also seek the co-operation of members of the public not to remove or tamper with the mosquito traps.

13        Everyone must continue to play his part to help stem dengue transmission in the environment and reduce the mosquito population. NEA alone cannot eradicate Aedes mosquitoes.

14        We encourage everyone to learn about Wolbachia technology, and share information on Wolbachia technology and the small-scale field study with their family and friends. If successful, Wolbachia technology has the potential to naturally contribute to dengue control in Singapore. Members of the public can find out more about Wolbachia technology by visiting or contact NEA at 1800-CALL-NEA (1800-2255 632) if they have any enquiries.

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For more information, please contact us at 1800-CALL NEA (1800-2255 632) or submit your enquiries electronically via the Online Feedback Form or myENV mobile application.



  • Male Wolbachia-carrying Aedes aegypti mosquitoes will be released at the three selected sites to help us understand how far and high they fly, how long they live and how well they compete with urban male mosquitoes for a mate. These data is required to support the design of a subsequent suppression trial, in which male Wolbachia-carrying Aedes aegypti mosquitoes will be released for further tests on their ability to reduce the mosquito population.

  • The three sites selected for the small-scale field study were based on a number of criteria:
    • These sites represent a cross-section of typical housing estates in Singapore;
    • These estates have seen dengue outbreaks previously and/or have Aedes aegypti mosquitoes present in the environment;
    • NEA has been monitoring the mosquito population in these sites for up to three years, providing a baseline from which to make comparative studies 
  • A total of about 4,200 households are located within the three release sites. Traps will also be placed outside these areas for data collection.

  • An average of one to three male mosquitoes per person will be released regularly[1] at each of the selected sites over the six-month study period. The total number will depend on the baseline data collected (number of urban Aedes aegypti mosquitoes already present at the study sites), number of residents at the study sites, etc. About 3,000 male Wolbachia-carrying Aedes aegypti mosquitoes were released today at Braddell Heights.

  • Currently, releases are planned for every four weeks at a single point at Braddell Heights and Nee Soon East, and weekly at multiple points at Tampines West. However, the study design will be adjusted according to data collected during the course of the small-scale field study.

  • NEA researchers will release the male Wolbachia-carrying Aedes aegypti mosquitoes at public spaces around houses and blocks. Release points may include stairwells, void decks, open spaces between blocks of high-rise homes, and outside landed homes from the streets. Though mosquitoes will not be released directly into homes, residents may notice a temporary increase in mosquitoes one to two days after the release.

  • Three types of traps will be placed within the selected release sites, and in the surrounding areas – Ovitraps, Gravitraps (black cylinder shaped containers) and fan-based traps. Both Ovitraps and Gravitraps will be placed along corridors or backyards around homes. Fan-based traps, which will be placed inside homes, will be used to passively capture male Wolbachia carrying-Aedes mosquitoes to understand their flight range. We seek the co-operation of members of the public not to remove or tamper with the mosquito traps.

  • Data collected from the small-scale field study will support the design of a subsequent suppression trial, in which releases of male Wolbachia-carrying Aedes aegypti 



[1]The frequency of releases is dependent on the number of mosquitoes present, weather conditions and the natural environment at the selected sites. Residents will be informed prior to when releases will take place.



location-map-of-braddell-heights-site (1)

Fig. 1 Location map of Braddell Heights site

Male Wolbachia-carrying Aedes aegypti mosquitoes will be released in the area demarcated in blue.

No. of houses (in release area) – blue solid line:



location-map-of-tampines-west-site (1) 

Fig. 2 Location map of Tampines West site

Male Wolbachia-carrying Aedes aegypti mosquitoes will be released in the area demarcated in blue.

No. of blocks (in release area) – blue solid line:



location-map-of-nee-soon-east-site (1) 

Fig. 3 Location map of Nee Soon East site

Male Wolbachia-carrying Aedes aegypti mosquitoes will be released in the area demarcated in blue. Mosquito traps will be placed in areas demarcated in red and blue to monitor mosquito behaviour.

No. of blocks (in release area) – blue solid line:


No of blocks (in monitoring area outside release area) – red broken line:

B – 16 (South)

C – 9 (East)

D – 12 (West)

E – 6 (North)

Other buildings (in monitoring area outside release area) – red broken line:

4 schools (east & west)

Columbarium (north west)