ANALYSIS: Are we being told the full truth about GM mosquitoes?

Promotion of GM mosquitoes as a way to tackle a tropical disease is simply part of a PR strategy intended to pave the way to a new global business selling GM agricultural pests, says Helen Wallace

In November 2010, Oxford University spin-out company Oxitec announced it had released 3 million genetically modified (GM) male mosquitoes in the Cayman Islands. Shock and surprise was muted by enthusiastic press coverage of its claims to have reduced the wild population of the Aedes aegypti species of mosquitoes by 80 per cent. This is one of two species of mosquito that can transmit the tropical disease dengue fever. In January 2011, the company submitted its results to the journal Science. This week – two years after completing the experiments – the findings have finally been published as Correspondence to the Editor of journal Nature Biotechnology.

Oxitec reports several different estimates of the temporary reduction in the wild population of mosquitoes, ranging from 60 per cent to 85 per cent. There is no baseline data on mosquito populations at the site. At different times, Oxitec moved mosquito traps from one location to another and changed the size of the release site. It is unstandable then that a succession of peer reviewers have rejected its results.

To achieve the claimed effect, Oxitec had to significantly increase the number of adult GM mosquitoes it released each week and focus on a 500m by 200m area where it added GM pupae at locations spaced 70 to 90m apart. The release ratio of 25 GM mosquitoes to one wild one means that adult GM males are very inefficient at finding and mating with wild females. Preliminary unpublished results from Brazil are even worse: a release ratio of 54 was needed. The well-established public health approach of removing the flower pots and water containers where mosquitoes breed is likely to be more effective and has the added benefit of reducing both mosquito species that spread dengue, not just one of them.

Ethical standards in the paper are as poor as scientific ones. Oxitec failed to send the required risk assessment which meets European standards to the EU and UK authorities before exporting GM mosquito eggs to the Cayman Islands. Informed consent is not possible without a published risk assessment, which did not exist. Scientists, as well as environmental groups, have criticised the company for conducting its first experiments in a British Overseas territory which has no biosafety law, and for not meeting these legal and ethical requirements.

Oxitec’s GM mosquitoes are not “sterile”: they mate with wild mosquitoes and produce offspring which survive to the late larval or pupal stage. Some 3-4 per cent of these survive to adulthood and this can rise to 15% in the presence of the common antibiotic tetracycline: information which Oxitec tried to conceal from public scrutiny. When Oxitec was forced to release a risk assessment, following the trials, scientists from the Max Planck Institute published a critique arguing that the risk of releasing GM biting females, and the survival of GM mosquito offspring, should have been properly considered.

It is hard to justify planned commercial releases based on these results. Poorly effective approaches to reducing mosquito populations can actually increase the risk of the more severe form of dengue in dengue-endemic countries (such as Brazil), due to the loss of cross-immunity to different dengue virus serotypes. Other risks include a possible increase in the numbers of the Asian Tiger mosquito, which also transmits dengue; and increases in the number of surviving GM mosquitoes over time.

Back in 2010, Oxitec’s exaggerated claims that it had a GM solution to the dengue virus were widely reported despite no published results. A Nature News blog even stated that the company had wiped-out the disease although dengue is not endemic in the Cayman Islands and no tests have ever been conducted of the impacts on the illness. The effect of suppressing mosquito populations on the incidence of dengue is poorly understood and may be very limited. Plans to scale-up releases of GM mosquitoes in Brazil to 2.5 million a week may still go ahead regardless, following a 2007 agreement between the Brazilian and UK governments. UK Trade and Investment is targeting developing countries as potential markets to help Oxitec commercialise its patents, and helping Brazil to secure venture capital investment. Experiments are also planned in Florida and Panama.

Oxitec’s funders include the multinational pesticide and GM seed company Syngenta. Most of its management team and consultants are ex-Syngenta staff. Promotion of GM mosquitoes as a way to tackle a tropical disease is part of a PR strategy intended to pave the way to a new global business selling GM agricultural pests. GM olive flies, tomato borers, diamond back moths (which eat cabbages and broccoli), fruit flies and pink bollworms (cotton pests) will be just the start. Other ideas for the future include GM pesticide-resistant bees.

Oxitec’s GM insects could soon end up in your food. The European Food Safety Authority (EFSA)’s new Guidance on risk assessments for GM animals could be adopted as early as December, opening the door for large-scale commercial releases of GM insects in the EU. Oxitec has indicated that it wishes dead and surviving GM larvae, pupae and adult insects on food crops to be treated as “technically unavoidable”: allowing them to enter the food chain without any labelling. If used commercially, many GM pests will die as larvae inside olives and tomatoes, as well as on the outside of some other crops. Ecosystem impacts are poorly understood and surviving GM pests could spread across national borders and into sensitive environments and organic crops.  

Concerned individuals should - urgently - be thinking about contacting their MPs and MEPs and writing to supermarkets to ask them not to stock such products.

Helen Wallace is Director of GeneWatch UK


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