What is the Sterile Insect Technique or SIT?
The
SIT
is an environment-friendly insect pest management method by which (male) insects
are made infertile through irradiation and mass released into a target area.
When these sterile males mate with wild females, there are no offspring. The
systematic and repeated release of sterile males reduces the target wild insect
population over time.
Are there other techniques similar to SIT?
There are other techniques similar in concept and aim, but the mechanism by which sterility is induced in the target insect population is different. Sterility can be induced by transgenesis, or by infecting the insects with a certain bacterium (Wolbachia). The SIT
method used by the FAO/IAEA uses controlled irradiation to sterilize insects and does not involve genetic engineering.
How does SIT differ from mosquito population replacement?
Population replacement aims at replacing the local mosquito population by one that may limit the transmission of diseases under certain conditions.
How are the mosquitoes sterilized?
The insects are exposed to radiation,
either gamma- or X-rays which stops the production of viable reproductive cells,
making them infertile.
Is it dangerous? What impact does it have on humans?
The irradiated insects do not become radioactive and do not pose a danger to people, animals and the environment. The radiation dose applied induces sterility in the mosquito.
Where in the world is this being used?
The SIT was developed in the late 1950s
and has been used in many countries in the management of agricultural pests,
such as the Mediterranean fruit fly, the false codling moth, the New World
screwworm and tsetse flies, among others. The technique is now being refined for
use against disease-transmitting mosquitoes and being tested in several
countries, including Brazil, Cuba, Germany, Greece, Italy, Mauritius Mexico,
Spain and the USA.
Why is the IAEA working on mosquito control?
The IAEA is the world’s centre for cooperation in the nuclear field and works to help countries in the use of peaceful applications of nuclear techniques that contribute to human health,
food and agriculture, among others. Through the Joint FAO/IAEA Programme, the
IAEA has been working for decades on the application of the sterile insect technique to combat various agricultural pests. The technique is now being extended for use against disease-transmitting mosquitoes.
What are the advantages of this method over others?
The SIT is an environment-friendly and a species-specific pest control method that can be particularly useful against
vectors that are difficult to manage using conventional techniques, such as
traps, nets or insecticides. It is also an option for managing insects that have
widely distributed larval sites, or when there is a need to reduce the use of
insecticides for environmental and human health reasons and also when the wild
mosquito populations developed insecticide resistance.
Is SIT a stand-alone technique?
The SIT works best when combined with
other vector control tools. Before releasing sterile males, for example, it is
generally necessary to reduce mosquito population density by removing larval
sites or using insecticides, in order to reduce the number of sterile males to
be released.
How can SIT reduce disease transmission?
Female mosquitoes bite people and transmit diseases. The SIT aims at reducing the population of female mosquitoes. (Males
cannot bite).
Why do you only release males?
Male mosquitoes don’t bite and therefore don’t transmit diseases. The sterile mosquitoes are also unable to produce offspring, so will not contribute to mosquito population growth. Releasing sterile male mosquitoes poses no risk to human health or the environment.
How are the mosquitoes released?
Sterile insects are generally released by
ground (by foot, or vehicle) or by air (via drones).
What is a mark-release-recapture study?
The study involves the release and recapture of a known number of marked – dusted with a colour – male mosquitoes in a defined area. The number of recaptured mosquitoes provide information about the size of the wild mosquito population, the distance the mosquitoes can travel, and how long they can survive in nature. This information also helps to determine the area and number of sterile mosquitoes to be released.
When do you plan to carry out these studies, and how long will they last?
Give accurate times and dates and be honest and transparent about your planned activities.
Who is funding this study?
Note: Any funding agencies and stakeholders should be mentioned to maintain transparency. This is specific to
each programme- explain.
Who is involved in the study?
Note: Often, the vector control unit
within the Ministry of Health, or other health authorities are involved in the
project, as well as the affected communities, and sometimes universities and
NGOs. However, this is specific to each programme- explain.
Where do the mass-reared mosquitoes come from?
Mosquitoes are collected from the local wild population to create a colony in a production facility. The mosquitoes are then mass-reared, separated into male and female, and the males are sterilized before they are released in the target area.
What regulatory permissions did you need to obtain?
Each project should follow the regulatory framework of his Country or Region. However, the SIT Does not require any
regulatory approvals.
How are you engaging with the community?
It is advised that the programme is
transparent, and the stakeholders are well informed about the technique, what to
expect, planned activities, and the programme (eg.,
http://www-naweb.iaea.org/nafa/ipc/public/SIT-Trifold_20170310.pdf). However,
the means of disseminating information are numerous and are specific to each
programme- explain
What happens after the releases ended?
When the release of sterile males stops,
and eradication has not been achieved, the relic fertile population will gradually return to its original size. It is therefore important to continue to take measures to limit the mosquito population.
How are you monitoring the study/programme?
We monitor the programme by setting traps to collect mosquitoes to determine the number of adults in the trial area and whether this number is declining. Ovitraps are also placed to attract females to lay eggs in them in order to collect information on the level of sterility that has been achieved. If the wild females mated with our sterile males, this will be confirmed by the non-hatching eggs found in these traps. The number of eggs
laid in the ovitraps also provides information on the density of wild females,
and whether this number is declining.
How many and how often are you releasing male mosquitoes?
The number of sterile males released and the frequency of releases depend on several factors, such as the density of the wild population and the mating capacity and longevity of the sterile mosquitoes.
Does this mean I can stop taking the same precautions against mosquito bites?
No, there are other mosquito species in the area- some of which also bite people and some which may be vectors of other diseases. Also, even if the population of the target species were to decrease
during the trial, there would be some females left that could transmit diseases.
In this regard, you should continue to use your usual precautions against mosquito bites.
I see more mosquitoes in my neighbourhood – is this harmful
to me and my family?
You may see an increase in mosquito numbers when sterile male mosquitoes are released. These sterile males are not
harmful to you, your family and pets nor to the environment as male mosquitoes do not bite, and sterile mosquitoes cannot reproduce.
Will my neighbourhood be affected?
Your neighbourhood may be affected positively if the sterile males successfully mate with wild females and reduce the mosquito population size. You will also see our team members in the neighbourhood more often as they will be releasing the sterile male mosquitoes periodically. They will be available for any questions that you may have.
Will I still get mosquito bites if I live in the release area?
You probably will still get mosquito bites
as there are also other species of mosquitoes living in the area, and the
effects of the sterile male releases will need time to become apparent, i.e.
reduction of the target population.
Will I have to do anything?
You don’t have to do anything for the SIT
component itself. However, you should still implement your usual methods to protect yourself against mosquitoes. Moreover, removing standing water is a very important part of mosquito control strategies and it would be appreciated that you do so in your property to help us reach our goals.
How can I help the SIT programme?
You can help the programme by supporting
our activities or allowing us to place a trap on your property, or disseminating
our information leaflets
Will reducing the mosquito population harm bats and birds
(e.g., food deprivation)? What impacts will this programme have on the
environment?
Reducing the number of one (invasive)
mosquito species will not affect the environment, nor other animals. There are over 3500 species of mosquitoes that serve as food for animals and other insects. Moreover, the released sterile male can also serve as food for mosquito predators, which would not suffer any harm by ingesting these. Eliminating an invasive species of mosquito can also help to restore the ecosystem. So far,
none of the SIT programmes over the past 70 years were reported to have negative
impact on the environment and SIT is considered as an environment-friendly
technology.
What if other animals eat the irradiated male mosquitoes?
The mosquitoes do not become harmful or turn radioactive after they have been irradiated. Ingesting an irradiated mosquito is not different from ingesting a non-irradiated mosquito.
Will this have any effect on my pets?
The release of sterile male mosquitoes will have no effect on your pets. Reducing the number of Aedes aegypti or
Aedes albopictus may even protect your pets from veterinary diseases such as heartworm.
Insect Pest Control Section | Joint
FAO/IAEA Centre
