Genetically Modified Mosquitoes: Background and Concerns

Aedes aegypti

Aedes aegypti

By Bhavani Prakash

In Dec 2010, 6000 genetically modified (GM) Aedes aegypti sterile male mosquitoes were released in the unhabited forests of Betong, Malaysia, according to the statement by the government run Institute of Medical Research (IMR).  

The GM mosquitoes were developed by the UK biotech company, Oxitec. The purported aim of the company is to work with governments around the world to combat dengue disease caused by the Aedes mosquito. It had already “released 3 million GM male mosquitoes as part of an open release field experiment in the Caymen Islands in 2010,” according to the press release by UK’s Gene Watch entitled, “Oxitec’s genetically-modified mosquitoes: in the public interest?”

The mosquitoes released in Malaysia were genetically engineered in such a way that when they mate with females in the wild, the resulting mosquito larvae die young (although this will only happen in the absence of the antibiotic tetracycline).  Oxitec claims that this will drastically reduce the population of disease causing mosquitoes. However not everybody is of the same view with many scientists arguing that this practice is fundamentally flawed.

Prior to the experiment, Malaysia’s Third World Network (TWN) had already raised concerns and submitted their objections about genetically modified or engineered (GE) mosquitoes. They sought answers to the following concerns:

 1) Could female mosquitoes be accidentally released?

TWN’s concern was about the possibility of an accidental release of female GE mosquitoes that could in turn raise further concerns, as females act as vectors for diseases such as dengue and chikungunya. Their argument was that the sex selection process prior to release may not be fully accurate or effective. They claimed that the available information does not indicate whether the reliability and efficiency of the sex selection process can be guaranteed.

 2) Could GE mosquitoes and GE larvae survive and persist in the environment?

Oxitec mentions that mosquito larvae that are produced after the GE males mate with females will only die if they do not encounter tetracycline in the environment. TWN’s concern is that since Tetracycline is a fairly common antibiotic used in animal husbandry, there is a possibility of the larvae surviving. TWN claims that the available information provided does not indicate whether the use, presence and persistence of tetracycline in the environment at the proposed release sites have been assessed.

In addition, TWN is also concerned that about the possibility that the conditional lethality trait may not be 100 percent effective, meaning some of the GE larvae produced will not die.

All this implies that it is reasonable to expect at least some GE mosquitoes to persist beyond the first generation in the environment. While the number may be small, a proportion of these would be female, and thus capable of transmitting disease. TWN is concerned that there is a risk of an increase in the disease burden of the communities at the inhabited release sites.

3) Could there be a surge of other disease-transmitting mosquito species if Aedes aegypti populations are suppressed?

Aedes aegypti is not native to Malaysia, but is an introduced, invasive species. Nonetheless, it has become part of Malaysia’s complex ecological ecosystem. It would be important to consider the implications on other species that interact with Aedes aegypti in the receiving environment.

Aedes albopictus is an indigenous species of mosquito to Malaysia, which also transmits dengue, as well as chikungunya. If the GE Aedes aegypti mosquitoes successfully achieve their aim of suppressing wild populations, there could be a surge in Aedes albopictus, with potential increase in incidences of chikungunya and possibly also dengue.

There may also be other ecological implications of long-term suppression of Aedes aegypti populations. This could include effects on food webs and ecological functioning or impacts on the abundance of other species that feed on mosquitoes. The available information provided does not indicate whether there are baseline ecological data on mosquito and other ecology in the proposed release sites that could inform the assessment.

 4) Could there be gene flow and effects on non-target organisms?

 While the available information suggests that gene flow through mating of closely related species (Aedes albopictus) will not produce fertile offspring, the possibility of gene flow between different Aedes aegypti populations and perhaps other mosquito species cannot be absolutely discounted.

This possibility may vary depending on the genetic elements used in the specific modification, which may to a greater or lesser extent be genetically unstable, especially under field conditions. If horizontal gene flow happens, non-target species may be adversely affected by sterility-inducing genetic elements, increasing the risk of ecological harm.

5) Are the monitoring and control measures proposed adequate?

While the applicant has proposed control measures to prevent the GE mosquitoes from persisting in the environment, the monitoring of these mosquitoes is dependent on the adequate functioning of the fluorescence marker gene. Because genetic expression can vary, the production of the fluorescent marker may be diminished and some GE mosquitoes may not be identifiable by fluorescence. If this happens, the GE mosquitoes may persist in the environment without our knowledge.

Furthermore, given the possibility that some GE mosquitoes could persist beyond the first generation in the environment (see point 2), the proposed period of one month for application of the control measures may not be long enough.

Therefore, an assessment must also be made as to whether the monitoring plan as proposed by the applicant is adequate and whether complete removal of GE mosquitoes and larvae from the field release sites is possible.

 6) Has the prior informed consent of local communities at the release sites been obtained?

As the experiments are also proposed for inhabited sites, local communities living in these areas have the right to be specifically informed, consulted and their consent obtained before any field release occurs. This is especially given the possibility of the risks as highlighted, particularly in relation to disease transmission.

 7) Is there sufficient risk assessment and regulatory experience?

The only reported environmental release of GE insects to date has been in the United States, of a transgenic pink bollworm, an agricultural pest that is not involved in intimate contact with humans or disease transmission as Aedes aegypti is. There may have already been field experiments with GE mosquitoes, but little information is available; however, this proposed release would be certainly be one of the first such releases in the world.


The experiment drew flak from several organizations in Malaysia. Following the news of the release of the GM mosquitoes in Malaysia in December 2010, a coalition comprising of 21 NGOs demanded that the government disclose full details of the trial release and its results and to identify the existence of any adverse effects. They also “criticized the government for “silently” conducting the experiment despite making a public announcement that the trial had been postponed pending public consultation.”

Following the experiment, the MP of Sungai Siput, Dr D Jeyakumar, who is also a respiratory physician called the using of laboratory mosquitoes to fight dengue “a catastrophic mistake” in this article by Free Malaysia Today.  Some of the points he raised were:

  • the release of large numbers of genetically modified (GM) mosquitoes into the environment could cause the transformation of the mosquitoes  or even some other insects in some unanticipated manner that might be difficult to control.
  • the process of producing the male GM mosquitoes was not foolproof and that  3% to 4% of them would be female which could copy the role of the wild female Aedes to spread dengue. (This is also raised in Consumer Association of Penang’s Memorandum dated Dec 20, 2010 titled, ” Malaysia’s Planned Release of Aedes Mosquito: ethical, legal and human rights concern)
  • the means of biological suppression cannot completely eliminate the species from the environment and the government would have to go on purchasing, releasing and killing the GM mosquitoes. “We would need billions of these transgenic mosquitoes for an average sized city. Wouldn’t it be more logical and productive if that same sum were spent in improving the drains and sewerage systems in our urban areas?”


On January 12 2012 , civil society groups  Friends of the Earth U.S., GeneWatch UK and Third World Network in a joint press release titled, “Genetically modified mosquitoes survival rate concealed,”  revealed a confidential internal document by Oxitec that showed that genetically modified mosquitoes described by the company “as “sterile” are in fact not sterile and their offspring have a 15 percent survival rate in the presence of the common antibiotic tetracycline.

The antibiotic tetracycline is widely used in agriculture and is present in sewage as well as in industrially farmed meat. Mosquitoes that carry dengue fever are known to breed in environments contaminated with sewage where they are likely to encounter widespread tetracycline contamination.

Even in the absence of tetracycline contamination, the GM mosquitoes are known to survive in the laboratory at rates of around 3 percent. In the field, this would translate into large numbers of survivors, given that continual releases of millions of GM mosquitoes would be needed to sustain the goals of population suppression.”

In January 2012, the US delayed the release of genetically engineered mosquitoes, according to FOE’s press release. Eric Hoffman, FOE’s biotechnology policy campaigner said:

“This delay is welcome and prudent given the risks that genetically engineered mosquitoes pose. Introducing genetically engineered mosquitoes into the environment could destabilize ecosystems, harm human health and scare away tourists, endangering the Florida Keys economy. These potential impacts must be evaluated through a serious and thorough environmental impacts review process. We are confident that any truly impartial, science-based review will lead to the cancellation of this risky experiment.”

It is to be expected that Oxitec will endeavour to rope in more nations into this experiment with GM mosquitoes. The issue is of particular concern to the public in neighbouring countries such as Singapore, and the rest of tropical Asia where there is a prevalence of dengue. Many questions are raised from the way the experiment was conducted in Malaysia and Cayman Islands. Has the public been involved and sufficiently consulted in the process? Aren’t there other non-invasive ways to attack the dengue issue, rather than doing an irreversible experiment with nature, especially when there are several unanswered concerns?



About the Writer:

Bhavani Prakash is the Founder of Eco WALK the Talk .com.  She is a sustainability speaker, trainer and writer can be contacted at bhavani[at]ecowalkthetalk.com. Follow Eco WALK the Talk on Facebook, Twitter and YouTube



Further links you may be interested in: 

Friends of the Earth U.S., GeneWatch UK and Third World Network’s Joint Press Release: “Genetically modified mosquitoes survival rate concealed,


Consumer Association of Penang’s Memorandum dated Dec 20, 2010 titled, “ Malaysia’s Planned Release of Aedes Mosquito: ethical, legal and human rights concern

UK’s Gene Watch :”Oxitec’s genetically-modified mosquitoes: in the public interest?”

Free Malaysia Today: GM mosquitoes Horror story in the making?


On GM Food: 

EWTT:  China suspends commercialisation of genetically engineered rice and wheat

EWTT:  Better labelling of GM Food in Singapore essential

EWTT: Lim Li Ching: GMO Free

EWTT:  India’s GM Bill: Anti-people, Anti-nature

EWTT: Go GM Free in Australia

EWTTDr Vandana Shiva: Traditional Knowledge, Biodiversity and Sustainable Development

EWTTDr Mira Shiva: Health Effects of GM Food




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Posted by on Apr 6 2012. Filed under Animals/Wildlife, Biodiversity, Health, Human wellbeing, Sustainable Agriculture/GMO/Organic. You can follow any responses to this entry through the RSS 2.0. You can leave a response or trackback to this entry

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