Sterile insect technique

Image:AnophelesGambiaemosquito.jpg

Sterile insect technique is a method of biological control, whereby millions of sterileinsectsare released. The released insects are normally maleas it is the femalethat causes the damage, usually by laying eggs in the crop. The sterilemales compete with the wild males for female insects. If a female mates with a sterile male then it will have no offspring, thus the next generation's populationis reduced. Repeated release of insects can eventually wipe out a population, though it is often more useful to consider controlling the population rather than eradicating it.

The technique has successfully been used to eradicate the Screwwormfly(Cochliomyia hominivorax) in areas of North America. There have also been many successes in controlling species of fruit flies, most particularly the Medfly(ceratitis capitata).

Insects are sterilised with radiation, which can weaken the newly sterilized insects making them less able to compete with wild males.

Success stories

• Screwwormfly - Eradicated from the United States, Mexico, Guatemala, Belizeand most of Panama.
• MedflyCeratitis capitata - successful control in Israel, California, Central America etc.

Current Targets

• Anophelesmosquito- Malariavector
• Tsetse fly(Glossina spp) - sleeping sicknessvector.

Painted apple moth (Lep: Lymantriidae) in Auckland, New Zealand

Drawbacks

• Repeated treatment is required to exterminate the population.
• Sex separation is difficult for some species (though can be easily performed on Medfly, for example).
• Radiation treatment affects the health of males, so sterilized insects are at a disadvantage when competing for females.
• The technique is species specific: there are 22 species of Tsetse flyin Africa, for instance, and the technique must be implemented separately for each.
• Many fertile pest insects must be grown before sterilisation and must be housed securely to prevent their escape or release: in February 2003, the irradiation machinery at a plant in Mexico failed and 4 million fertile screwworms were released before the problem was spotted.

Genetic modification

A method using recombinantDNA technology to create genetically modifiedinsects called RIDL (Release of Insects carrying a Dominant Lethal) is under development. The method works by introducing a "Dominant Lethal" gene into the insects in such a way that the gene is expressed only in females, and the gene's effect can be countered in the controlled insect manufacturing environments, fx by giving a food additive. The insects can also be given genetic markers, such as fluorescence, that make monitoring the progress of eradication easier.

The released males are not sterile, but any female offspring their mates produce will have the dominant lethal gene expressed, and so will die. The number of females in the wild population will therefore decline.

The advantages of the RIDL technique are that the male insects can be separated from the females for release simply by withdrawing the factor in the controlled manufacturing environment that kept the females alive, fx removing a food additive. Using RIDL also means that the males will not have to be sterilized by radiation before release, making the males more healthy when they need to compete with the wild males for mates.

Progress towards applying this technique to mosquitos has been made by researchers at Imperial College Londonwho created the world's first transgenic malaria mosquito.

A similar technique is the daughterless carp, a genetically modified organismproduced in Australiaby the CSIROin the hope of eradicating the introduced carpfrom the Murray Riversystem. As of 2005, it was undergoing tests to assess the risks of releasing it into the wild.

External links

• Sterile insect technique
• CleanFruit project
• InSecta Ltd

This article is licensed under the GNU Free Documentation License.
It uses material from the http://en.wikipedia.org/wiki/Sterile+insect+technique Wikipedia article Sterile insect technique.