Genetically-modified fruit flies could control wild populations by producing only sons

Mediterranean fruit flies are responsible for extensive damage to fruit and vegetable crops, not only in the Mediterranean region but also in Australia, North and South America. While existing methods of controlling them include the use of insecticides and sterilization, the University of East Anglia and biotech company Oxitec are pioneering what they claim is a greener and less expensive approach –  they're genetically modifying male fruit flies to produce only male viable offspring.

In the existing sterilization approach, radiation is used to render captive male "medflies" sterile – it's known as the Sterile Insect Technique (SIT). When those flies are released into wild populations, they mate with females that would otherwise be mating with wild males. Because the SIT males are sterile, however, those couplings don't result in any fertile eggs, thus lowering the population.

One of the problems with SIT, however, is that the irradiation process weakens the flies, lessening their ability to mate properly. That's where the UEA/Oxitec process, called RIDL (Release of Insects Containing a Dominant Lethal), comes in.

It doesn't involve radiation, but instead introduces a gene that keeps male flies' female offspring from reaching the reproductive stage. The treated males are said to be healthier than those subjected to SIT, and will readily mate with wild females once they're released. Those females will in turn lay fertile eggs, but all of the resulting female babies will die before they're able to produce offspring of their own.

In lab tests conducted in medfly-containing greenhouses at the University of Crete, RIDL reportedly resulted in a "rapid population collapse." UEA and Oxitec are now seeking approval for open-field trials of the technology.

Previously, Oxitec has collaborated with the University of California, Irvine, on a system in which genetically-modified male mosquitoes produce female offspring that lack wings. These flightless females can't reach humans, and are easy pickings for predators.

A paper on the RIDL research was published this Wednesday in the journal Proceedings of the Royal Society B.

Sources: University of East Anglia, Oxitec