Frequently asked questions
Q1. What exactly is the Sterile Insect Technique (‘SIT’)?
The Sterile Insect Technique (SIT) is an environment-friendly, species-specific method of insect control, which has been described as ‘birth control for insects’. SIT works by releasing sterile insects of a target species. The sterile males compete with the wild males for female insects. If a female mates with a sterile male then it will have no offspring, thus reducing the next generation’s population. Repeated release of insects can eventually reduce the insect population to very low levels and hence reduce the damage or spread of disease.
SIT has been used very successfully in agriculture for over 50 years but is currently restricted by the need to irradiate the insects to sterilize them. For some species, for example mosquitoes, the dose required to sterilize the males also damages their fitness to the extent that SIT cannot be used.
Q2. What is the difference between conventional SIT and Oxitec’s approach?
Conventional SIT uses radiation to sterilize the insects and frequently both sterilized males and females are released. The radiation dose must be fine tuned providing enough radiation to sterilize the insect without damaging it to the extent that it does not mate in the wild.
Oxitec’s technology was developed using genetics rather than radiation. This means that, for the first time, the Sterile Insect Technique, which has been extremely successful in agriculture, can be applied to mosquitoes that spread disease. Also, Oxitec only release male insects of a species that do not spread disease or (in agriculture) cause crop damage. Further, in comparison to programmes where radiation can be used the use of a genetic approach can circumvent the fitness penalty associated with radiation.
Q3. Why is this approach necessary in control of vector-borne disease?
Because dengue fever is rapidly increasing and current control methods are tools are not adequate to stop this growth. New approaches are needed
Dengue fever is transmitted by the bite of an Aedes aegypti mosquito infected with any one of the four versions of the dengue virus. Symptoms appear in 3–14 days (average 4–7 days) after the infective bite. Dengue fever is a severe, flu-like illness that affects infants, young children and adults. There is neither specific medicine nor vaccine for dengue fever. Dengue hemorrhagic fever is a potentially lethal complication, particularly in children, and early clinical diagnosis and careful clinical management by experienced physicians and nurses is necessary to reduce the number of fatalities.
The Aedes aegypti mosquito has spread itself around the world, largely in the last 50 years and, as it has done so, dengue fever has increased dramatically.
More than 70% of the global disease burden is in South-East Asia, Asia and the Western Pacific area. In Latin America and the Caribbean, the incidence and severity of disease are increasing rapidly. The USA, Europe and the Eastern Mediterranean are much less affected. In total the WHO state that over 2.5 billion people are at risk from dengue.
Q4. Do all mosquitoes spread dengue?
No. The Aedes aegypti female mosquito spreads dengue. Males do not bite or spread disease (in fact males cannot bite: they do not have the mouthparts to do so!) Another species, Aedes albopictus, can also spread dengue but Aedes aegypti is the main vector. Other mosquito species bite but do not spread dengue.
Q5. Is Oxitec’s mosquito genetically modified?
Q6. What is a GMO?
A genetically modified organism (GMO) is an organism whose genetic make up has been altered using techniques in genetics generally known as recombinant DNA technology.
Q7. Is genetic modification unsafe?
No, genetic modification (or recombinant DNA technology as it is sometimes called) is a scientific tool or technique. GM approaches are now used, for example, in the production of pharmaceutical drugs and vaccines, new medical approaches (gene therapy) in industry (production of enzymes) and in new biofuel approaches.
Q8. What are the benefits of using Oxitec mosquitoes over other control methods?
There are several benefits:
This is the only currently available approach that has the potential to reduce the Aedes aegypti population to a level below which disease is not transmitted. (The use of insecticides or community actions is often impractical or not cost effective due to the variety and locations of potential breeding sites).
It also reduces the threat of chikungunya and yellow fever diseases which are also spread by Aedes aegypti mosquitoes.
The Oxitec mosquitoes that are released are all males and hence do not bite or spread disease
It is a method of biological control and is likely to be less costly and more effective than using humans with chemical sprays or fogging devices to kill the biting females as it harnesses the natural instinct of the male mosquito to actively seek female mosquitoes of its own species.
It is an environmentally friendly approach (no toxic chemicals are used): the sterile male mosquitoes released will only mate with their own species and hence no other species is affected (unlike, say, where a general insecticide is used).
Q9. What are the likely impacts on the environment and on humans?
Aedes aegypti originated in Africa and only achieved pan-tropical distribution in the 1930s. Therefore in most countries it is not a native species. There are no birds, fish or other insects that feed exclusively on it and therefore reducing the number of Aedes aegypti is most unlikely to have negative impacts on the environment. Additionally, the released mosquitoes will die in the environment and their progeny will die so this is a ‘self limiting’ approach, i.e. there is no permanent change to the wild mosquito population.
Q10. What is actually killing the mosquito larvae/what genetic modification has been made?
The gene that has been introduced into the mosquito inhibits the cell’s ability to function normally. This means that all the progeny die at the larval stage, making the male ‘sterile’. When a ‘sterile’ male mates with a wild (non sterile) female all the progeny will inherit this gene and none will survive. This approach is not toxic but it stops the larvae from developing so no adult mosquito emerges. It works only by inheritance and does not affect other insects, or predators such as fish or birds that might eat a mosquito.