The sterile insect technique, or SIT, has been used for decades to control insects such as the Mediterranean fruit fly. Basically, insects are exposed to radiation, which makes them sterile, and then they’re released into the wild to mate. However, since they’re sterile, no viable offspring are produced.
Now a new method of sterilization — one that involves genetically modifying the insects instead of irradiating them — is being tested. New research published by scientists at the University of East Anglia and Oxitec Ltd. in the journal Proceedings of the Royal Society B reveals how the release of genetically engineered male fruit flies could be used as an effective population suppression method, saving crops around the world.
The Mediterranean fruit fly is a serious agricultural pest which causes extensive damage to crops. Researchers simulated a wild environment within greenhouses in Crete and studied the impact of releasing Oxitec flies.
“Of all of the current techniques used to control these flies, SIT is considered the most environmentally friendly as it uses sterile males to interrupt matings between wild males and females. The down side is that these males don’t tend to mate as well in the wild because the irradiation method used for sterilization weakens them,” said lead researcher Dr Philip Leftwich. “Our research looked at whether releasing Oxitec flies, which are genetically engineered so that only male fly offspring survive, could provide a better alternative.”
“The genetically engineered flies are not sterile, but they are only capable of producing male offspring after mating with local pest females — which rapidly reduces the number of crop-damaging females in the population,” he continued. “Using this method means that the males do not have to be sterilized by radiation before release, and we have shown they are healthier than the flies traditionally used for SIT. We simulated a wild environment within secure eight-meter greenhouses containing lemon trees at the University of Crete. When we tested the release of the genetically modified male flies, we found that they were capable of producing rapid population collapse in our closed system. This method presents a cheap and effective alternative to irradiation. We believe this is a promising new tool to deal with insects which is both environmentally friendly and effective.”
The Oxitec method works by introducing a female-specific gene into the insects that interrupts development before females reach a reproductive stage. Populations of healthy males and females can be produced in controlled environments by the addition of a chemical repressor. If the chemical repressor is absent in the genetically engineered flies’ diet, only males survive. The surviving males are released, mate with local wild pest females and pass the female specific self-limiting trait onto the progeny resulting in no viable female offspring. The next stage of the research will be to gain approval for open-field studies.
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