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Sterile Insect Technique Curtails Pest Threat to Mexico’s Opuntia Cactus Sector


When a cactus moth lays its eggs on an Opuntia cactus, it creates one of nature’s most effective camouflages. The eggs emerge as what is called an “egg stick”, because they look like the cactus spine. The problem is that when the larvae emerge from the dozens of eggs that make up the egg stick, they survive by eating – and destroying – the cactus leaf pads. The cactus moth is an invasive species native to South America, including northern Argentina, Uruguay, Paraguay and southern Brazil, but after its initial introduction to the Caribbean for research purposes, it expanded its range to the Caribbean islands and eventually to the Florida Keys off the US Gulf Coast. It also infested two islands off the Yucatan Peninsula, from which it threatened Mexico’s enormous commercial cultivations of Opuntia as well as the arid ecosystems of the area that depend on Opuntia cactus for soil and wildlife conservation. The threat was enough to bring Mexico’s Ministry of Agriculture, the US Department of Agriculture (USDA), the Joint FAO/IAEA Division and IAEA’s Technical Cooperation Department together to implement an eradication programme to curtail the Yucatan infestation. However, despite its success, the moth threat remains.

The Opuntia cactus can be fried as a vegetable, eaten raw as a fruit, used as forage for livestock, added as an ingredient in botanical medicines, planted in rows as border hedges, or left to propagate in arid areas where it contributes to soil conservation and serves as a water or food source for wildlife. In Mexico, where this cactus is considered a staple food, some 300 000 tonnes are produced for consumption each year by 30 000 producers and another 28 000 are employed in processing and packing facilities.

Thus, when one invasive cactus moth was found in an Opuntia cactus on Mujeres Island off the coast of the State of Quintana Roo on the Yucatan Peninsula in 2006, alarm bells went off in Mexico City. Plant protection authorities immediately surveyed the island and found most Opuntia plants infested. Further inspection of the neighbouring Contoy Island also found infestations. Armed with this information, the Mexican Ministry of Agriculture took immediate steps to initiate an eradication programme before the moths could reach the mainland.

As it happened, there was already an existing technological package, including surveillance tools and the sterile insect technology, set to deploy. In the late 1980s, the United States had faced a similar infestation when the cactus moth was found in the Florida Keys – probably the result of an infested shipment of ornamental plants that had arrived from the Caribbean into mainland USA. When the moth was found in Florida, Mexico knew that its extremely important Opuntia cactus sector could be in the sight of the pest, so it joined forces with the USDA to combat an invasive pest outside Mexico’s borders. It signed an agreement with the USA that included contributing financial resources toward efforts to combat the cactus moth in Florida and, in turn, keep the moth from moving along the Gulf Coast to Texas where it would pose a direct threat to Mexico.

Mexico adopts pest control measures used in Florida

The containment programme in Florida had been a success, so Mexico determined to follow a similar plan on the islands off Yucatan. This called for defining the area of the outbreak, setting out baited traps within the area, cutting back any infested cactus and eliminating Opuntia plants that could act as hosts to the moths, replacing them with ornamental plants. These initial steps served to greatly suppress the moth population on the two islands, after which the campaign employed the sterile insect technique (SIT). This meant bringing to Mexico sterilized moths that had been reared in Florida for the US cactus moth containment campaign. The moths, which had been sterilized by exposure to gamma irradiation, were released over the infested areas in the islands. With SIT, the sterilized males mate with the wild females and produce no offspring, which is the final step of a pest eradication process.

By October 2009, when three life cycles of the pest had passed without any further detection, the cactus moth was officially declared eradicated. The work of the Mexican Ministry of Agriculture, the USDA, the Joint FAO/IAEA Division and IAEA’s Technical Cooperation Department avoided significant damage to the economically important cactus and prickly pear industries, and to the Opuntia arid ecosystems. If the moths had made it to the mainland – where some 150 000 ha of cacti are cultivated for fodder, 60 000 ha for production of prickly pear fruit, 10 500 ha for the Opuntia leaf vegetable and another 3 million hectares are covered with wild Opuntia – the results would have been economically, socially and environmentally devastating.

Since the eradication was declared, Mexico has continued the comprehensive surveillance programme at high-risk points of entry, which puts it in a good position for early detection and emergency response if the cactus moth enters Mexican territory again. Mexico has also continued its cooperation with USDA to prevent entry into Texas and to the north-eastern states of Mexico. The USA concluded its SIT release programme in 2012 but remains vigilant in efforts to contain any further spread of this potentially devastating invasive pest.

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