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Science, Sex, Superflies

VIENNA 8 tsl Medfly

Mediterranean Fruit Fly (Medfly), also known as Ceratitis capitata. (Photo: Scott Bauer/USDA)

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A spin-off of nuclear science and technology has changed the dynamics of a complex mating game. Along the way, it has spawned success stories - some small, some large - from Asia to Africa to the Americas during the IAEA´s first half century.

Vienna, Austria -- They call the latest one VIENNA 8 tsl, designed to yield what an outsider might simply describe as a macho sex agent of science and technology. A veritable superfly bred for mating... and birth control.

VIENNA 8 tsl is a genetic sexing strain of Ceratitis capitata, the scientific name of the Mediterranean fruit fly, or Medfly. Tsl stands for "temperature sensitive lethal", which despite the connotation is a desirable mutation when it comes to mass-rearing and sterilizing Medflies at production centres. The trait coupled with a colour-coded genetic marker enables producing only the males, and that turns out to be a good thing.

The Medfly is on the most unwanted list of farmers and food inspectors in about 80 countries. If not controlled, the pest can nest in more than 300 fruit and vegetable crops - from Granny Smith to Beurre D´Anjou - and ravage them.

VIENNA 8 tsl is tailor-made to yield only male flies that stay strong enough after gamma sterilization to become virile agents of Medfly family planning. Once the sterile males are released into the wild, their mission is to compete in the mating game and win over willing females. The union is, of course, fruitless, and the outdoor fly population falls to nothing when systematically targeted over time. Biological birth control.

The genetic sexing strain is a 21st-century feature of the sterile insect technique (SIT). The technology has spawned success stories in unlikely places during the IAEA´s first half century as the world´s "atoms for peace" organization. What started out in the 1950s and 1960s on a small laboratory scale has peacefully "mushroomed" into a multi-million dollar affair that continues to attract more and more players.

VIENNA 8 tsl is among advances registered through the IAEA´s joint work since 1964 with the Food and Agriculture Organization (FAO) and delivered through technical cooperation channels. At any given moment, more than four billion sterile insects - 3.5 billion of them Medflies bred using genetic sexing strains - are being reared for weekly use at 30 SIT facilities worldwide. Among the latest are mass-rearing plants in Bahia, Brazil, and Valencia, Spain.

All the SIT facilities supply pest eradication, suppression and prevention programmes against various insect pests. A main common goal: to protect the quality of food and agricultural products, including livestock, that the pests can attack and destroy.

Successes include winning battles from the Americas to Africa to Asia to Australia - against screwworm flies endangering cattle herds, tsetse flies killing livestock and humans, moths ruining crops and orchards, and fruit flies threatening entire harvests. Future applications target mosquitoes that transmit malaria and viral diseases, with research taking place through IAEA/FAO channels in Sudan and other countries.

In richer countries, the benefits of success are valued in tens of billions of dollars for fruit exporters, national economies, and public health authorities. In poorer countries, success means life for farming families reliant on their animals and crops.

"Fruit flies live in 178 countries and islands," Mr. Pablo Gómez Riera, an expert at Argentina´s National Institute of Agricultural Technology, reports. Of these, he says, 20 species, including the Medfly, are the most harmful, triggering quarantine measures on food and agricultural products coming from infested areas. "That restricts their international trade significantly," he says.

Quarantines are lifted only after certification that products are grown and shipped from clean areas. "Newly adopted food safety and phytosanitary standards require the establishment of either low prevalence or entirely fruit-fly-free areas," he explains.

The Medfly has been eradicated from the continental United States, Mexico, and Chile, and effectively suppressed in many other countries - all with the help of the SIT in combination with other strategic area-wide measures.

In South Africa, for example, fruit fly suppression targets the Hex River Valley. Progress is impressive. "In one season, the number of cartons rejected for export because of fruit fly damage halved from 8% to 4%, the lowest it has ever been," says Brian Barnes, the scientist coordinating efforts.

Genetic sexing strains like VIENNA 8 tsl look to be the future for species-specific biological pest control. Other strains are in some stage of research and development, experts say, being designed to help combat various species of fruit flies and insects. At SIT rearing facilities, the production of only males is a step that saves considerable time and money.

"The latest genetic strain opens more doors for the SIT. It can become a part of routine Medfly suppression rather than only for big eradication or barrier programmes," explains Mr. Jorge Hendrichs, who heads the FAO/IAEA Insect Pest Control Sub-Programme. "That means no burdensome quarantines and less spraying of insecticides to meet requirements."

Though genetic research can be controversial, that has not been the case with the SIT so far. "Since the insects are sterile, they cannot become established in ecosystems, and carry no potential to adversely affect the environment," says Mr. Walther Enkerlin, an entomologist who works with Dr. Hendrichs. "The SIT is generally regarded as a ´clean and green´ pest-control tool."

While the latest steps are welcome, there´s still a good way to go, entomologists say. The future is tied even more closely to genetic research and development, and advances in other fields of science and technology.

"Sterilized males still don´t perform as well sexually as their competitors in the wild," says Mr. Hendrichs, a recognized expert on Medfly mating and sexual behaviour. "That means to win in the wild, so many sterile males have to be produced and released that they far outnumber the competition." The FAO/IAEA last year launched a multinational Medfly research programme to learn more about the interplay between mass-rearing operations, radiation sterilization, and the performance of male fruit flies.

SIT advances complement other technologies at play.

In the United States, where invasive insects are on a hit list of transboundary threats, sterile male Medflies are being released in high-risk areas to prevent the pest´s establishment. Scientists track the origin of Medfly outbreaks using genetic code. DNA samples have been collected from captured Medflies worldwide by Dr. Bruce McPheron and teams at Penn State University in the USA.

One of the last times the USA detected a Medfly outbreak in imported fruit, Dr. McPheron´s team kicked in. They tapped genetic data on record that told them exactly where the pest had come from overseas. Food safety inspectors quickly moved to block the fruit sales - and to shut down the imports from the sending country. -- Lothar Wedekind, IAEA Division of Public Information

For more technical reports, see the Sterile Insect Technique, Principles and Practice in Area-Wide Integrated Pest Management, the definitive book on the SIT edited by FAO/IAEA experts Arnold Dyck, Jorge Hendrichs, and Alan Robinson.