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At Mexico-Guatemala Border, Sterile Insect Technique has Controlled the Northward March of Medflies Since 1982

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At Mexico-Guatemala Border, Sterile Insect Technique has Controlled the Northward March of Medflies Since 1982

(Photo: J. Reyes/IAEA)

Imagine an area of nearly 200 000 km2 that needs to be monitored on a daily basis – monitored for the presence of a destructive insect smaller than a fingernail. It has been more than four decades since the governments of Mexico, Guatemala and the United States agreed to work together to stop the spread of the Mediterranean fruit fly – an agreement which evolved from three bilateral agreements signed in 1975 and 1981 into the one single Trinational Moscamed Cooperative Agreement signed by the three governments in 2015 plus a memorandum of understanding with Belize. In their years of working together, the countries have kept the medflies out of their orchards and fields but also, with the support of the Joint FAO/IAEA Division, have continued to improve the technology, including the use of the sterile insect technique (SIT), insecticide-bait applications and on-the-ground surveillance. It is all done with annual financial contributions by the three countries and significant numbers of trained personnel who work in the mass-rearing and sterilization facilities and in the field to keep the four countries safe from what could amount to billions of dollars in annual damages to production and trade – if the insects were allowed a foothold.

No one really knows for sure when or how the medfly began its odyssey from its original homeland in East Africa to become one of the most reviled and feared insect pests on the planet. Theories include Ethiopian coffee traders who inadvertently took the flies to North Africa, and sailors who purchased fly-inundated citrus fruits in North Africa and brought them to Europe.

As for the Americas, medflies arrived in Brazil in 1901, possibly through trade with Portugal and, in subsequent years, invaded most of South America. In 1955, they reached Costa Rica in Central America, possibly through trade with West African colonies, and then spread to southern Guatemala in 1976, on a northward trajectory that put the high value fruit and vegetable industry of Mexico, the United States, Guatemala and Belize in their sight.

At the same time, the Joint Division was developing and testing a daring method for medfly control. Known as the sterile insect technique (SIT), it had been used since the 1950s for the suppression and eradication of screw-worm flies but never for medflies. The Joint Division initiated research to use the SIT technique for medflies at its laboratories in Seibersdorf, Austria, where it reared and sterilized the number of insects needed for field testing. In 1969, pilot testing was undertaken on two Mediterranean islands off the coast of Italy, Procida and Anacapri, releasing the sterilized male insects to mate with wild females – and thus produce no progeny. The pilot was declared a success in 1971.

Although still a visionary idea, by the time medflies were detected at the border of Guatemala and El Salvador, the countries were able to transfer the technology from Seibersdorf and adopt it in an attempt to quash potential disaster. A medfly mass rearing and sterilization facility was constructed in Metapa, Chiapas, in southern Mexico, with the first sterile fly releases in 1978. Four years later, after releasing billions of sterilized flies, the medfly was proclaimed eradicated from approximately 1 millionhectares of Chiapas, a state on Mexico’s South Pacific Coast that borders Guatemala. Years later, a second and larger rearing facility, El Pino, was constructed in Guatemala, which greatly contributed to the goal of protecting the medfly-free areas in Guatemala and preventing the northern spread of the pest.

Building from success, focus switched from eradication to maintaining a containment barrier on Guatemalan territory away from the Mexican border and to the gradual medfly eradication from Guatemala. Today, that biological barrier has served its purpose and the programme continues to release sterilized male medflies – as many as 1.3 billion each week – to maintain it.

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