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environment general science genetics health and medicine space technology February 28, 2003 
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Elsewhere on the web

Permit application - Field Release of a Transgenic Pink Bollworm

Center for Food Safety news release

Transgenic arthropodes - Genetic Engineering Newsletter, July 2000

Sterile Insect Release Method and Other Genetic Control Strategies

California Department of Food and Agriculture S.I.T. program

Research aimed at fighting a major cotton pest is igniting a battle over genetically modified insects. Scientists plan this summer to conduct the first-ever confined release of a genetically altered bug.

As this ScienCentral News video reports, environmental groups are threatening to go to court to block such an experiment.

How do you breed an entire population of sterile insects?

No, they’re not being cloned.

A genetic switch called a "conditional lethal gene"—nicknamed the "terminator gene"—controls the fertility of these genetically engineered insects. Genetic switches are scientists’ way of controlling when a transgenic, or genetically engineered, organism expresses whatever traits have been added to it. Certain conditions must be met in the organism’s environment before the gene switch turns on.

With the new type of pink bollworm, two conditions must be met before it becomes infertile. First, the temperature around the bollworms must be in a certain range. Second, the insects—normally raised on a diet that includes the common antibiotic tetracycline—stop taking their medicine. As soon as the tetracycline levels in their systems drop, the genetic switch kicks on, and the "lethal gene" is activated, making the insect unable to produce offspring.

The advantage, though, is that they should still mate and behave normally with wild pink bollworms, who don’t know their new mates are sterile. This means the wild population mates at the same rate, but the number of offspring produced by the population should plummet, meaning fewer pests to munch on cotton.

So while it seems counterproductive to breed a population of sterile insects, the mechanics of it are as simple as a switch. Keep them warm, feed them tetracycline, and let them breed until you have the desired number of insects. Then take away their tetracycline, set them loose, and watch those studs become duds.

What other genetically engineered bugs are in the works?

•Transgenic Mediterranean fruit flies (major citrus pest) for population control

•Transgenic silkworms that produce more and stronger silk

•Transgenic mosquitoes to combat malaria and yellow fever

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