One way scientists are looking to fight mosquitoes and the diseases they carry is an insect pest birth control method known as the sterile insect technique (SIT). SIT is a proven method using nuclear techniques for controlling agricultural insect pests such as fruit flies, moths and tsetse flies and shows potential for use on mosquitoes. In line with global efforts to ‘End Malaria for Good’ — the theme of World Malaria Day today — the IAEA supports research and development to help find new solutions and strategies to continue the fight against malaria. SIT, as part of an integrated vector management approach, is one of these promising innovations.
Here is snapshot look at SIT, malaria and how they fit together.
What exactly is SIT?
SIT is a method that uses ionizing radiation to sterilize male insects mass-produced in special rearing facilities. The sterilized male mosquitoes are then released over affected areas, where they will compete with wild males and mate with wild female mosquitoes, which in turn then do not produce any offspring. Gradually the number of sterile males surpasses the fertile ones, which leads to a significant reduction of the insect pest population and therefore the spread of disease. Other, non-target insects remain unaffected.
The IAEA, in partnership with the Food and Agriculture Organization of the United Nations (FAO), spearheads global research in the development and application of the SIT.
What is malaria, and how is it affecting the world?
Malaria is an infectious disease transmitted by infected female Anopheles mosquitoes. As the female mosquito bites, it delivers a parasite through its saliva into people, leading to a range of adverse health symptoms and, in some cases, death. Almost half of the world’s population remains at risk of the disease, and in 2015 alone, malaria was the cause of almost half a million deaths, around 80 percent of which occurred in Africa, according to the World Health Organization (WHO).
Through an increased international push toward reducing incidence and mortality from malaria by at least 90 percent, new cases have dropped by more than one-third since 2000. It is estimated that between 2001 and 2015 more than six million deaths have been averted as a result of these collaborative efforts. However, there is still much work to be done to eliminate the disease.
Learn more about malaria and its impact on the world here.
Where does SIT fit into the fight against malaria, and how is the IAEA helping?
One of the major challenges in the fight against malaria is insecticide resistance. Insecticide sprays and bed nets treated with insecticides are used to keep mosquitoes at bay by either killing them at the larval or adult stage. While these have been effective methods in the fight against malaria to date, malaria-carrying mosquitoes are developing an increasing resistance to these chemicals.
Scientists are now looking for complementary biologically-based ways to address this challenge and continue the momentum toward reducing malaria. SIT, which does not rely on insecticides, can offer a viable option. It is among the safest and most environmentally friendly, and therefore sustainable, insect pest control methods available, and is usually applied as part of integrated campaigns to suppress insect pest populations.
While good progress has been made in developing mass-rearing and sterilization procedures for Aedes mosquitoes, which transmit Chikungunya, dengue fever and Zika viruses, research is still in an earlier phase for Anopheles mosquitoes that transmit malaria.
One potential hurdle in applying the SIT to Anopheles mosquitoes is its swarming behaviour: scientists were unsure the sterile males would be competitive enough to integrate and mate with females in the swarm. Fortunately, field experiments done in Sudan with IAEA support have confirmed the ability of the sterile males to join naturally occurring swarms or to start new ones. This will undergo further testing and evaluation as Sudan constructs its new mass rearing facility to increase its capacities and the scale of its SIT pilot project.
Another major challenge with this type of mosquito has been to accurately separate male from female mosquitoes on a large scale in the rearing facilities. This is essential so that only sterile males are released, which are the ones that do not bite and therefore cannot spread any disease. Scientists at the Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture are now refining methods, such as separating mosquito pupae by size or infusing blood meals with toxins, to target and eliminate females from the mass-reared mosquitoes.
Check out this photo essay to see more about Preventing Procreation: The IAEA’s Research for Mosquito Control.
Several projects are in progress or being implemented to provide equipment, expertise, and training, and to further develop suitable methods for applying SIT to different disease-carrying mosquitoes. These are ongoing in China, Pakistan, Philippines, Sri Lanka, South Africa, Sudan and Thailand, among others.
Learn more about the scientific progress being made in using the SIT against mosquitoes in Back to the future: the sterile insect technique against mosquito disease vectors.