Sterile Insect Technique - Genetic Modification

Genetic Modification

A method using recombinant DNA technology to create genetically modified insects called RIDL (Release of Insects carrying a Dominant Lethal) is under development by a company called Oxford Insect Technologies (Oxitec), UK. The method works by introducing a repressible "Dominant Lethal" gene into the insects. This gene kills the insects but it can be repressed by an external additive, which allows the insects to be reared in manufacturing facilities. This external additive is commonly administered orally, and so can be an additive to the insect food. The insects can also be given genetic markers, such as DsRED fluorescence, that make monitoring the progress of eradication easier, preferably under the field conditions.

There are potentially several types of RIDL, but the more advanced forms have a female-specific dominant lethal gene. This avoids the need for a separate sex separation step, as the repressor can be withdrawn from the final stage of rearing, leaving only males.

These males are then released in large numbers into the affected region. 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, causing the overall population to decline.

Using RIDL 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 London who created the world's first transgenic malaria mosquito.

A similar technique is the daughterless carp, a genetically modified organism produced in Australia by the CSIRO in the hope of eradicating the introduced carp from the Murray River system. As of 2005, it was undergoing tests to assess the risks of releasing it into the wild.