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Monday, 3 April, 2000, 07:37 GMT 08:37 UK
Lethal 'switch' kills pests
The research was carried out on fruit flies
Scientists have found a novel way to kill an insect that involves throwing a lethal "switch" hidden in its genes.

The pest remains perfectly healthy and can reproduce only so long as it has a particular food in its diet. When this is removed, a repressed gene gets turned on and the creature is killed by a toxic chemical produced in its own body.

The technology has been developed at Oxford and Manchester Universities. It is intended for use in pest control programmes that control wild populations by releasing hundreds of millions of sterile male insects into the environment.

Significant proportions of the introduced males win the affections of females but because of their infertility father no offspring. It is an approach that, over time, can bring down pest numbers.

Irradiated males

However, the sterile insect technique (SIT) is not an easy strategy to implement. Separating males from females is difficult and inevitably some females will also be released. This is undesirable because it is usually the females of the species that cause disease or damage crops by laying their eggs in plant tissue.

Also, the sterilisation of the males involves irradiation and, although this prevents them from producing offspring, it means they are not as fit as the wild pests with which are supposed compete.

The Oxford and Manchester team hope their new method can overcome all the shortcomings of the standard SIT. They made a modification to the genetics of fruit flies (Drosophila melanogaster) which collapsed only the females' ability to process and store nutrients and run an effective immune system.

This fatal modification was designed to lay dormant for as long as the antibiotic tetracycline was included in the diet. When the team removed the food additive, all the females in their experiment died.

The males also carried the modification but were unaffected by it. However, none of their daughters could survive the toxic effects of the genetic changes.

Major pests

"The big challenge is getting this to work in a real pest species like Medfly, (Ceratitis capitata)," Luke Alphey of the Zoology Department at Oxford University told BBC News Online. "We used Drosophila simply because it is a good lab tool. But we deliberately didn't use any genetic tricks that are only available in Drosophila. So we think all the necessary components are available in other species.

"We are now working on the medfly and the yellow fever mosquito, Aedes aegypti. The first is a crop pest, the second is a disease vector. They are both relatively simple and easy to grow in the lab.

"However, there is the issue of getting all this to work on a factory scale. Error rates we cannot measure in the lab could become apparent when things are massively scaled up."

The Oxford and Manchester research was published in the journal Science.

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