Hope for transgenic medflies comes alive.

Genetic engineering of everything from plants to mice may seem commonplace nowadays, but scientists have only recently succeeded in genetically engineering any insects other than Drosophila, the fruit fly long favored in laboratory experiments.

The hope of genetically disarming important pests, however, just got a little brighter. Scientists have successfully altered the genetic makeup of the Mediterranean fruit fly (Ceratitis capitata), which destroys fruit and coffee crops worldwide, report Thanasis G. Loukeris and his colleagues at the Foundation for Research and Technology in Heraklion, Greece.

The researchers have yet to diminish the insect's bite, but they have taken the first step in using genetics to achieve that goal, they report in the Dec. 22 Science.

"Will the successful transformation of the medfly result in better methods to control this pest? Yes, in the long run," predicts Michael Ashburner of the University of Cambridge in England in an accompanying commentary. The result should also "relieve the frustration of those trying to transform other insects . . . [and] allow us to learn much more about the basic biology of this beast," notes Ashburner.

After learning how to engineer Drosophila in the early 1980s, scientists had thought that the medfly would pose a fairly easy target, says Charalambos Savakis, who led the Greek group. The medfly resembles Drosophila in key ways, including the simplicity of its genome. But discovering how to modify the Drosophila techniques took many years, he notes.

Scientists needed a new transposable element, a sequence of DNA that can transport a new gene into unsuspecting hosts' sperm and egg cells, which impart it to the offspring. Savakis and his colleagues eventually succeeded with an element called minos, taken from another fruit fly, Drosophila hydei.

Like other transposable elements, minos has two important characteristics: It can replicate inside its host's chromosomes, and it produces an enzyme, transposase, that enables it to jump into different chromosomes in its host.

Using tools developed for Drosophila, the Greek scientists combined two minos elements into a package that they used to carry a marker gene called white. Despite its name, white produces eyes of a normal red color. The investigators used the white gene to find out whether their technique works before they try inserting genes expected to be useful in pest control. They injected the white gene package into the embryos of almost 4,000 medflies.

They used mutant medflies that, thanks to a genetic whim of nature, have white eyes and normally produce white-eyed descendants. When they gazed into the eyes of their flies' descendants, the researchers knew that white had penetrated the sperm and egg cells. The white marker gene made some of the white-eyed insects produce offspring with the normal red eye color, the team reports.

The medfly white gene came from Laurence J. Zwiebel of the European Molecular Biology Laboratory in Heidelberg, Germany, and his colleagues. They recently isolated and made copies of the gene for the first time, they report in the Dec. 22 issue of Science.

A lack of genetic markers has proved a "substantial obstacle" to genetically engineering insects other than Drosophila, they note.

In Drosophila, the white gene also serves frequently as a marker gene. It gained some notoriety when scientists linked it to male-male courtship in Drosophila (SN: 7/1/95, p.13).