NEA to test novel way of cutting mosquito numbers
Study using bacteria-infected male mozzies to render females sterile to be held in three areas
By Amelia Teng, The Sunday Times, 28 Aug 2016
From October, some residents might notice more mosquitoes buzzing in their neighbourhoods.
But don't worry, they won't bite.
In fact, these male Aedes mosquitoes do not transmit disease, but are Singapore's latest allies in the fight against dengue. What the male mosquitoes will be armed with is Wolbachia, a naturally occurring bacterium. When these males mate with female mosquitoes, the bacterium causes the females to lay eggs that do not hatch.
Over time, this could lead to a fall in the population of Aedes aegypti mosquitoes, which transmit the viruses that cause dengue fever. These mosquitoes also carry the chikungunya and Zika viruses.
Yesterday, Environment and Water Resources Minister Masagos Zulkifli announced that the National Environment Agency (NEA) will release the bacteria-carrying mosquitoes at three sites as part of a field study. The areas, Yishun Street 21, Tampines Avenue 4 and Jalan Riang/Jalan Sukachita in Braddell Heights, previously had dengue outbreaks and represent a cross-section of typical housing estates here - both high-rise and landed.
The Environmental Health Institute, a public health laboratory at the NEA, has been studying this novel method since 2012 and carrying out risk assessment and research to confirm that it is safe.
Study using bacteria-infected male mozzies to render females sterile to be held in three areas
By Amelia Teng, The Sunday Times, 28 Aug 2016
But don't worry, they won't bite.
In fact, these male Aedes mosquitoes do not transmit disease, but are Singapore's latest allies in the fight against dengue. What the male mosquitoes will be armed with is Wolbachia, a naturally occurring bacterium. When these males mate with female mosquitoes, the bacterium causes the females to lay eggs that do not hatch.
Over time, this could lead to a fall in the population of Aedes aegypti mosquitoes, which transmit the viruses that cause dengue fever. These mosquitoes also carry the chikungunya and Zika viruses.
Yesterday, Environment and Water Resources Minister Masagos Zulkifli announced that the National Environment Agency (NEA) will release the bacteria-carrying mosquitoes at three sites as part of a field study. The areas, Yishun Street 21, Tampines Avenue 4 and Jalan Riang/Jalan Sukachita in Braddell Heights, previously had dengue outbreaks and represent a cross-section of typical housing estates here - both high-rise and landed.
The Environmental Health Institute, a public health laboratory at the NEA, has been studying this novel method since 2012 and carrying out risk assessment and research to confirm that it is safe.
Mr Masagos told reporters that while efforts to reduce the mosquito population have been "fairly successful", Singapore is still susceptible to dengue outbreaks as it is in a region where dengue is endemic.
He said the new method "works together with source eradication". "Whatever we're doing today to ensure that mosquitoes don't have opportunity to breed must continue."
The NEA estimated that an average of one to three male mosquitoes per person will be released at regular intervals at each of the three sites.
The six-month field study aims to understand the behaviour of Wolbachia-carrying Aedes aegypti male mosquitoes in the urban environment, such as how far and high they fly, and how well they compete with counterparts without Wolbachia to mate with females.The NEA estimated that an average of one to three male mosquitoes per person will be released at regular intervals at each of the three sites.
To collect data, NEA will set up traps at locations including public spaces and the homes of resident volunteers. The data will support the planning for a suppression trial, which may start next year.
Experts said that similar trials abroad have had a positive impact.
For instance, a release of Wolbachia-infected mosquitoes led to a more than 90 per cent drop in the mosquito population on an island in Guangzhou, China, under a pilot project starting in March last year.
Professor Ary Hoffmann from the University of Melbourne, who sits on the Dengue Expert Advisory Panel appointed by NEA in 2014, said: "Sterile release has been used against disease vectors and agricultural pests very successfully for many years around the world.
Professor Ary Hoffmann from the University of Melbourne, who sits on the Dengue Expert Advisory Panel appointed by NEA in 2014, said: "Sterile release has been used against disease vectors and agricultural pests very successfully for many years around the world.
"The only difference here is that sterility is being generated through Wolbachia rather than radiation, but Wolbachia bacteria are already present in many insects...and do not pose any risk to humans."
He added that Wolbachia, which can be found in over 60 per cent of insect species including butterflies and dragonflies, cannot be transmitted to mammals, including humans, as the bacteria cannot survive outside insect cells.
Mr Derek Ho, director-general of NEA's Environmental Public Health Division, said residents should continue mosquito-control procedures, such as clearing stagnant water. Associate Professor Vernon Lee, of the National University of Singapore's Saw Swee Hock School of Public Health, said: "Any gains through the Wolbachia method could be negated if residents provide mosquitoes with an abundance of breeding sites."
Housewife Winnie Lim, 49, who lives at one of the Tampines blocks where the field study will be conducted, said the Wolbachia technology sounds like a "good idea".
"Instead of fumigating all the time, this is a long-term effort to wipe out the mosquitoes."
"Instead of fumigating all the time, this is a long-term effort to wipe out the mosquitoes."
Frequently asked questions about Wolbachia
The Sunday Times, 28 Aug 2016
Q Why is the National Environment Agency (NEA) conducting a field study that involves the release of male Wolbachia-carrying Aedes aegypti mosquitoes?
A Such mosquitoes can potentially reduce the Aedes aegypti population, which spreads dengue.
When they mate with their female counterparts, it results in eggs that do not hatch and no offspring.
The field study is needed to ensure this strategy will work in our urban environment.
Q Is a new mosquito species introduced into the environment?
A No. The male Wolbachia-carrying Aedes aegypti mosquito is from the same species as the one in our environment. The only difference is that it is carrying Wolbachia, a naturally-occurring bacterium found in 60 per cent of insect species.
Q How safe is Wolbachia?
A NEA has conducted a comprehensive risk assessment of the method and found it to be safe, with no risk to human health and insignificant risk to ecology.
Q Why were the three sites - within Braddell Heights, Nee Soon East and Tampines West - chosen for the field study?
A They represent a cross-section of typical housing estates and have seen dengue outbreaks previously and/or have Aedes aegypti mosquitoes present. NEA has been monitoring the mosquito population in these sites for up to three years, providing a baseline for comparative studies.
Q Will residents at the sites get more bites?
A They may see a temporary increase in mosquitoes in the first few days after each release. Male mosquitoes may land on humans as they are seeking a mate, which is likely to be near a human, in search ofa meal.Butmalemosquitoesdonot bite or transmit diseases as they feed on plant juices.
Q Do the male mosquitoes draw female ones to the sites?
A No, the male mosquito is attracted to the female, not the other way round.
Source: NEA
The Sunday Times, 28 Aug 2016
Q Why is the National Environment Agency (NEA) conducting a field study that involves the release of male Wolbachia-carrying Aedes aegypti mosquitoes?
A Such mosquitoes can potentially reduce the Aedes aegypti population, which spreads dengue.
When they mate with their female counterparts, it results in eggs that do not hatch and no offspring.
The field study is needed to ensure this strategy will work in our urban environment.
Q Is a new mosquito species introduced into the environment?
A No. The male Wolbachia-carrying Aedes aegypti mosquito is from the same species as the one in our environment. The only difference is that it is carrying Wolbachia, a naturally-occurring bacterium found in 60 per cent of insect species.
Q How safe is Wolbachia?
A NEA has conducted a comprehensive risk assessment of the method and found it to be safe, with no risk to human health and insignificant risk to ecology.
Q Why were the three sites - within Braddell Heights, Nee Soon East and Tampines West - chosen for the field study?
A They represent a cross-section of typical housing estates and have seen dengue outbreaks previously and/or have Aedes aegypti mosquitoes present. NEA has been monitoring the mosquito population in these sites for up to three years, providing a baseline for comparative studies.
Q Will residents at the sites get more bites?
A They may see a temporary increase in mosquitoes in the first few days after each release. Male mosquitoes may land on humans as they are seeking a mate, which is likely to be near a human, in search ofa meal.Butmalemosquitoesdonot bite or transmit diseases as they feed on plant juices.
Q Do the male mosquitoes draw female ones to the sites?
A No, the male mosquito is attracted to the female, not the other way round.
Source: NEA
* NEA to run mosquito control trial next week
Male mozzies modified to inhibit egg hatching to be released in Braddell Heights
By Samantha Boh, The Straits Times, 14 Oct 2016
As part of a trial to control the spread of dengue, male Aedes aegypti mosquitoes carrying Wolbachia bacteria will be released at the Braddell Heights housing estate next Tuesday.
The small-scale trial is the first of three planned by the National Environment Agency (NEA). The other two will be carried out in Nee Soon East and Tampines West within the next month.
When male mosquitoes carrying the naturally occurring Wolbachia mate with females, the bacteria causes the females to produce eggs that do not hatch.
Over time, this could lead to a fall in the Aedes aegypti population; these mosquitoes transmit viruses that cause dengue fever as well as chikungunya and Zika. A trial was first run in Australia five years ago and has shown success in reducing local transmission of dengue.
The authorities here warned earlier that the number of dengue cases this year could exceed 30,000 - higher than the record of 22,170 cases reported in 2013.
NEA said the mosquitoes would be released at regular intervals at each of the three sites. The males do not bite and will not lead to any disease transmission.
The agency has been inviting residents from the three estates to its Environmental Health Institute's mosquito-production facility in Jurong, to learn about the process of rearing these special insects.
Yesterday, about 30 Nee Soon East residents were taken to laboratories there to see what happens up close. In one room, they entered a cage of free-flying male mosquitoes to see for themselves that the males do not bite. Elsewhere, they were shown how male pupae are separated from females.
Male mozzies modified to inhibit egg hatching to be released in Braddell Heights
By Samantha Boh, The Straits Times, 14 Oct 2016
As part of a trial to control the spread of dengue, male Aedes aegypti mosquitoes carrying Wolbachia bacteria will be released at the Braddell Heights housing estate next Tuesday.
The small-scale trial is the first of three planned by the National Environment Agency (NEA). The other two will be carried out in Nee Soon East and Tampines West within the next month.
When male mosquitoes carrying the naturally occurring Wolbachia mate with females, the bacteria causes the females to produce eggs that do not hatch.
Over time, this could lead to a fall in the Aedes aegypti population; these mosquitoes transmit viruses that cause dengue fever as well as chikungunya and Zika. A trial was first run in Australia five years ago and has shown success in reducing local transmission of dengue.
The authorities here warned earlier that the number of dengue cases this year could exceed 30,000 - higher than the record of 22,170 cases reported in 2013.
NEA said the mosquitoes would be released at regular intervals at each of the three sites. The males do not bite and will not lead to any disease transmission.
The agency has been inviting residents from the three estates to its Environmental Health Institute's mosquito-production facility in Jurong, to learn about the process of rearing these special insects.
Yesterday, about 30 Nee Soon East residents were taken to laboratories there to see what happens up close. In one room, they entered a cage of free-flying male mosquitoes to see for themselves that the males do not bite. Elsewhere, they were shown how male pupae are separated from females.
The six-month field study in the three estates aims to understand the behaviour of Wolbachia-carrying Aedes aegypti in the urban environment - for instance, how far and high they fly, and how well they compete with their counterparts without Wolbachia in mating with females.
To collect data, NEA will be setting up traps at various locations, including public spaces and the homes of volunteer residents. The data gathered will support the planning for a suppression trial, which could start next year.
Residents can contribute to the research by volunteering to host fan-based mosquito traps in their homes and on their premises. NEA will compensate them for the electricity used to power the fan-based devices.
Wolbachia-Aedes field study yields valuable data for future suppression trial -8 Feb 2017Residents can contribute to the research by volunteering to host fan-based mosquito traps in their homes and on their premises. NEA will compensate them for the electricity used to power the fan-based devices.
** Braddell Heights 'welcomes' 3,000 mozzies
Male Wolbachia-carrying Aedes aegypti mosquitoes released into estate in study to curb hatching
By Lin Yangchen, The Straits Times, 19 Oct 2016
There was a buzz around Braddell Heights yesterday morning, with a group of people clad mainly in white polo T-shirts out at Jalan Riang playground to welcome the newcomers to the estate.
"Normally, I would welcome new residents. Today, I welcome a different kind of resident... the male Wolbachia-carrying Aedes aegypti mosquito," said the area's MP, Mr Seah Kian Peng, drawing laughter from the crowd.
The MP for Marine Parade GRC welcomed about 3,000 of these "residents" - male Aedes aegypti mosquitoes released into the Braddell Heights estate yesterday by the National Environment Agency (NEA) in a pioneering field study to understand the behaviour of the disease-transmitting mosquito species.
The male mosquitoes, which neither bite humans nor transmit disease, have been artificially infected with Wolbachia bacteria. When they mate with uninfected females, the resulting eggs will not hatch.
Male Wolbachia-carrying Aedes aegypti mosquitoes released into estate in study to curb hatching
By Lin Yangchen, The Straits Times, 19 Oct 2016
There was a buzz around Braddell Heights yesterday morning, with a group of people clad mainly in white polo T-shirts out at Jalan Riang playground to welcome the newcomers to the estate.
"Normally, I would welcome new residents. Today, I welcome a different kind of resident... the male Wolbachia-carrying Aedes aegypti mosquito," said the area's MP, Mr Seah Kian Peng, drawing laughter from the crowd.
The MP for Marine Parade GRC welcomed about 3,000 of these "residents" - male Aedes aegypti mosquitoes released into the Braddell Heights estate yesterday by the National Environment Agency (NEA) in a pioneering field study to understand the behaviour of the disease-transmitting mosquito species.
The male mosquitoes, which neither bite humans nor transmit disease, have been artificially infected with Wolbachia bacteria. When they mate with uninfected females, the resulting eggs will not hatch.
Traps have been placed in public locations and residential premises around the estate to try to recapture the mosquitoes and determine where and how far they fly from the point of release in Jalan Sukachita.
Mr Seah said it was a privilege for Braddell Heights to be part of this study. When he learnt of NEA's plans, he asked the team to "please come to Braddell Heights first".
Behind this adventurous initiative is a team of more than 30 at NEA's Environmental Health Institute (EHI), who plan to release mosquitoes at two more sites: Tampines West on Oct 28 and Nee Soon East on Nov 15.
Regular releases will be made at the three sites over the next six months to accumulate data on the mosquitoes' flight patterns. The data will go into mathematical modelling, helping the researchers design a subsequent study of how effectively Wolbachia can suppress the mosquito population in the field.
If these studies are successful, NEA hopes Wolbachia technology will eventually complement its existing mosquito control efforts.
If these studies are successful, NEA hopes Wolbachia technology will eventually complement its existing mosquito control efforts.
NEA and grassroots leaders have been visiting residents, throwing block parties and conducting other outreach activities to raise awareness of Wolbachia technology.
EHI director Ng Lee Ching thanked residents who have volunteered to keep fan traps at home to capture mosquitoes, so as to track their movements. "The people who host the fan (traps) are one of our most important partners," he said.
Retiree Tan Soo Kon, 78, who has lived in Jalan Girang for 30 years, sees this as a breakthrough initiative worth supporting. He said his fan trap had caught 10 mosquitoes the night before the Wolbachia-carrying mosquitoes were released, adding: "I hope some of these (Wolbachia-carrying) mosquitoes will fly to my house and make it safer."
Associate Professor Vernon Lee, a member of the Dengue Expert Advisory Panel appointed by NEA in 2014, said the field study is essential for understanding the effectiveness of Wolbachia technology in Singapore. He added that the panel is satisfied that the study is safe, given prior risk assessments by NEA.
Dr Raman Velayudhan, coordinator of vector ecology and management at the World Health Organisation's Neglected Tropical Diseases Department, said: "We hope this trial will produce a long- term sustainable solution for the control of Aedes mosquitoes... Innovative control measures are absolutely essential for the future."
While the study is in progress, residents should continue normal mosquito control measures like the five- step Mozzie Wipeout, said NEA.
*** Wolbachia study to control dengue shows promise
Indication is that eggs of female mozzies mating with males carrying the bacteria do not hatch
By Lydia Lam, The Straits Times, 9 Feb 2017
The use of male Aedes aegypti mosquitoes carrying the Wolbachia bacteria to control the spread of dengue in a small-scale field study in three areas in Singapore has shown promise, with valuable data for future suppression trials.
After three months of releases at the Tampines West site, the viability of Aedes mosquito eggs collected from the site has been reduced by about half, the National Environment Agency (NEA) said in a media statement yesterday.
This suggests that the released male Wolbachia-Aedes mosquitoes successfully mated with the urban Aedes aegypti females.
Investigations at the other two sites, Braddell Heights and Nee Soon East, focused mainly on understanding the mate-seeking behaviour and flight ability of the released male Wolbachia-Aedes mosquitoes, as well as how well they survive in the urban environment.
Other data gathered include details on how far and high the mosquitoes fly and how long they live.
Conclusions from the data were derived after a three-day meeting between NEA's Dengue Expert Advisory Panel and NEA's Environmental Health Institute.
In October last year, NEA started the field study at Braddell Heights, followed by Tampines West and Nee Soon East a month later.
When male mosquitoes carrying the naturally occurring Wolbachia bacteria mate with female mosquitoes, the bacteria causes the females to produce eggs that do not hatch.
The aim of this is to reduce the Aedes aegypti population, which transmits the viruses that cause dengue fever. These mosquitoes also carry the chikungunya and Zika viruses.
NEA appointed the panel in June 2014 to provide professional advice on the use of Wolbachia for suppression of the Aedes aegypti mosquito population.
The panel comprises experts from Australia, Singapore, Britain and the United States, with specialised knowledge on vector-borne diseases, entomology, epidemiology, virology and public health.
The panel chairman, Professor Duane Gubler, founding director of the Emerging Infectious Diseases Programme at Duke-NUS Medical School, said: "NEA and the people of Singapore are to be congratulated on the rapid containment of what could have been a major Zika epidemic here."
More data is being collected from the field study to refine the suppression trial design.
NEA, in its release, said the Wolbachia-Aedes technology is promising, but is not the sole strategy for Aedes control.
It must be complemented with a strong integrated vector control programme with community participation, NEA said.
The NEA also urged everyone to be vigilant and practise the five- step Mozzie Wipeout.
"Persons infected with dengue should protect themselves from mosquito bites by applying repellent regularly, and those showing symptoms suggestive of dengue should see their doctors early to be diagnosed," it added.
**** Phase 2 of dengue control study kicks off in April 2018
More Wolbachia-carrying male mosquitoes to be released into Tampines West, Nee Soon East
By Samantha Boh, The Straits Times, 27 Feb 2018
There will be an added buzz in Tampines West and Nee Soon East come April with the release of male Wolbachia-carrying Aedes aegypti mosquitoes into the estates.
It is part of phase two of an ongoing field study into a novel method to curb dengue transmissions in Singapore which has delivered promising results.
The Aedes aegypti mosquitoes, which neither bite humans nor transmit disease, have been artificially infected with Wolbachia bacteria. When they mate with uninfected females, the resulting eggs will not hatch.
Phase two will involve more housing blocks in the two sites and even X-ray treatment. About one to six mosquitoes will be released per person each week, up from one to three mosquitoes previously.
Braddell Heights, which was part of the first phase, will not be involved this time as it does not have high-rise buildings - a focus of phase two.
These estates represent a cross-section of typical housing estates and have seen dengue outbreaks previously.
The National Environment Agency (NEA) has been monitoring the mosquito population in these sites for years, providing a baseline for comparative studies.
While the study is in progress, residents should continue normal mosquito control measures like the five- step Mozzie Wipeout, said NEA.
*** Wolbachia study to control dengue shows promise
Indication is that eggs of female mozzies mating with males carrying the bacteria do not hatch
By Lydia Lam, The Straits Times, 9 Feb 2017
The use of male Aedes aegypti mosquitoes carrying the Wolbachia bacteria to control the spread of dengue in a small-scale field study in three areas in Singapore has shown promise, with valuable data for future suppression trials.
After three months of releases at the Tampines West site, the viability of Aedes mosquito eggs collected from the site has been reduced by about half, the National Environment Agency (NEA) said in a media statement yesterday.
This suggests that the released male Wolbachia-Aedes mosquitoes successfully mated with the urban Aedes aegypti females.
Investigations at the other two sites, Braddell Heights and Nee Soon East, focused mainly on understanding the mate-seeking behaviour and flight ability of the released male Wolbachia-Aedes mosquitoes, as well as how well they survive in the urban environment.
Other data gathered include details on how far and high the mosquitoes fly and how long they live.
Conclusions from the data were derived after a three-day meeting between NEA's Dengue Expert Advisory Panel and NEA's Environmental Health Institute.
In October last year, NEA started the field study at Braddell Heights, followed by Tampines West and Nee Soon East a month later.
When male mosquitoes carrying the naturally occurring Wolbachia bacteria mate with female mosquitoes, the bacteria causes the females to produce eggs that do not hatch.
The aim of this is to reduce the Aedes aegypti population, which transmits the viruses that cause dengue fever. These mosquitoes also carry the chikungunya and Zika viruses.
NEA appointed the panel in June 2014 to provide professional advice on the use of Wolbachia for suppression of the Aedes aegypti mosquito population.
The panel comprises experts from Australia, Singapore, Britain and the United States, with specialised knowledge on vector-borne diseases, entomology, epidemiology, virology and public health.
The panel chairman, Professor Duane Gubler, founding director of the Emerging Infectious Diseases Programme at Duke-NUS Medical School, said: "NEA and the people of Singapore are to be congratulated on the rapid containment of what could have been a major Zika epidemic here."
More data is being collected from the field study to refine the suppression trial design.
NEA, in its release, said the Wolbachia-Aedes technology is promising, but is not the sole strategy for Aedes control.
It must be complemented with a strong integrated vector control programme with community participation, NEA said.
The NEA also urged everyone to be vigilant and practise the five- step Mozzie Wipeout.
"Persons infected with dengue should protect themselves from mosquito bites by applying repellent regularly, and those showing symptoms suggestive of dengue should see their doctors early to be diagnosed," it added.
**** Phase 2 of dengue control study kicks off in April 2018
More Wolbachia-carrying male mosquitoes to be released into Tampines West, Nee Soon East
By Samantha Boh, The Straits Times, 27 Feb 2018
There will be an added buzz in Tampines West and Nee Soon East come April with the release of male Wolbachia-carrying Aedes aegypti mosquitoes into the estates.
It is part of phase two of an ongoing field study into a novel method to curb dengue transmissions in Singapore which has delivered promising results.
The Aedes aegypti mosquitoes, which neither bite humans nor transmit disease, have been artificially infected with Wolbachia bacteria. When they mate with uninfected females, the resulting eggs will not hatch.
Phase two will involve more housing blocks in the two sites and even X-ray treatment. About one to six mosquitoes will be released per person each week, up from one to three mosquitoes previously.
Braddell Heights, which was part of the first phase, will not be involved this time as it does not have high-rise buildings - a focus of phase two.
These estates represent a cross-section of typical housing estates and have seen dengue outbreaks previously.
The National Environment Agency (NEA) has been monitoring the mosquito population in these sites for years, providing a baseline for comparative studies.
In phase one conducted from October 2016 to December last year, NEA found mosquito populations in the study sites were reduced by half.
The phase two study will run till January next year and aims to overcome challenges that cropped up in the earlier study, NEA said yesterday.
The agency said the plan was to embark on a larger suppression trial after phase one. But the first trial threw up unexpected hurdles.
Only 6 per cent of the adult male Wolbachia-carrying mosquitoes released on the ground floor were later found on the ninth-floor level and higher. So in phase two, the mosquitoes will be released on higher floors, in addition to being released on the ground floor.
They will also be released twice a week instead of once a week previously, in order to keep the population up for longer. The earlier study had found that only half of the mosquitoes released lived up to four days.
Containers holding male Wolbachia-carrying mosquito pupae will also be placed at the study sites this time, as the NEA wants to study if they will adapt better to the site conditions.
During phase one, the NEA noted that a small percentage of female Wolbachia-carrying Aedes aegypti mosquitoes were inadvertently released, as they had slipped through the sorting process which is about 99.7 per cent accurate.
While normal female Aedes aegypti mosquitoes that mate with male Wolbachia-carrying mosquitoes lay eggs which do not hatch, female Wolbachia-carrying mosquitoes still go on to have offspring.
These offspring cannot transmit dengue, chikungunya and Zika, but in the long term, they would affect the ability of male Wolbachia-carrying mosquitoes to suppress the urban mosquito population, said NEA.
Hence all batches of Wolbachia-carrying mosquitoes, adult and pupae, will undergo X-ray treatment to ensure that any females present will be made infertile.
Studies show the X-ray treatment does not affect the virility of males.
The chairman of the Dengue Expert Advisory Panel, Professor Duane Gubler of Duke-NUS Medical School, said:"The phase one studies were very successful in helping us understand this ecology. Phase two will build on this knowledge and, hopefully, increase the efficacy of the male release method."
As for the use of X-ray, NEA said it does not harm humans or the environment, and is currently used in a field study in Guangzhou, China.
"Irradiation has been successfully used to sterile other insect species and should increase the efficacy of the trial," added Prof Gubler.
Only 6 per cent of the adult male Wolbachia-carrying mosquitoes released on the ground floor were later found on the ninth-floor level and higher. So in phase two, the mosquitoes will be released on higher floors, in addition to being released on the ground floor.
They will also be released twice a week instead of once a week previously, in order to keep the population up for longer. The earlier study had found that only half of the mosquitoes released lived up to four days.
Containers holding male Wolbachia-carrying mosquito pupae will also be placed at the study sites this time, as the NEA wants to study if they will adapt better to the site conditions.
During phase one, the NEA noted that a small percentage of female Wolbachia-carrying Aedes aegypti mosquitoes were inadvertently released, as they had slipped through the sorting process which is about 99.7 per cent accurate.
While normal female Aedes aegypti mosquitoes that mate with male Wolbachia-carrying mosquitoes lay eggs which do not hatch, female Wolbachia-carrying mosquitoes still go on to have offspring.
These offspring cannot transmit dengue, chikungunya and Zika, but in the long term, they would affect the ability of male Wolbachia-carrying mosquitoes to suppress the urban mosquito population, said NEA.
Hence all batches of Wolbachia-carrying mosquitoes, adult and pupae, will undergo X-ray treatment to ensure that any females present will be made infertile.
Studies show the X-ray treatment does not affect the virility of males.
The chairman of the Dengue Expert Advisory Panel, Professor Duane Gubler of Duke-NUS Medical School, said:"The phase one studies were very successful in helping us understand this ecology. Phase two will build on this knowledge and, hopefully, increase the efficacy of the male release method."
As for the use of X-ray, NEA said it does not harm humans or the environment, and is currently used in a field study in Guangzhou, China.
"Irradiation has been successfully used to sterile other insect species and should increase the efficacy of the trial," added Prof Gubler.
NEA To Commence Phase Two Wolbachia-Aedes Field Study At Three Sites In April 2018
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