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Released Sterile Flies Free the Dominican Republic of Medfly Infestation


Twice a week, from October 2015 until April 2017, plant protection officials of the Dominican Republic went to the airport to meet a plane bringing a unique cargo from Guatemala. The planes were carrying boxes containing the pupae of up to 82 million sterilized male Mediterranean fruit flies (medflies). The pupae were transported to an emergence centre where they were held for few days, with sugar and corn flour fed to the emerging adults before their field release. Adult flies were chilled to immobilize them, placed in temperature controlled boxes loaded into planes and released in medfly infested areas. This scenario is a typical operation in what is known as the sterile insect technique (SIT), a technology used over many decades that controls and can eradicate pests by sterilizing males and releasing them in infested areas to mate with wild females who then produce no offspring. In the Dominican Republic, the arrival of the sterilized medfly pupae and adult release to initiate SIT was the final step in a programme to eradicate a medfly infestation that had shut down the country’s horticulture trade.

The Caribbean Region had always been free of the invasive and destructive Mediterranean fruit fly –until March of 2015, when one medfly was spotted in a lone almond tree in the eastern region of the Dominican Republic. It, apparently, all started when a cruise ship docked at Punta Cana, a popular tourist destination at the island’s eastern tip, carrying fruit infested with the dreaded medfly. When its presence was discovered, the Ministry of Agriculture, through its plant protection authorities, took steps to assess the size of the infestation and to contain the outbreak.

This is a pest that harms fruit and vegetable production. It also interrupts trade, because importing countries that are free of the pest often restrict horticulture imports from countries where the medfly is present. Although the Dominican Republic had taken initial action, when its efforts proved insufficient to stop the infestation, the national authorities requested support in setting up a country-wide surveillance network and an eradication campaign. Immediate support was provided by FAO and IAEA through their Joint FAO/IAEA Division and the IAEA’s Technical Cooperation Department, as well as by the US Department of Agriculture (USDA) and the Guatemala-Mexico-USA Moscamed Programme. Other organizations, including Organismo Internacional Regional de Sanidad Agropecuaria (OIRSA) and the Instituto Interamericano de Cooperación para la Agricultura (IICA) also provided valuable support.

Although the government reacted when the first medflies were found, so did the country’s trading partners. Within a week of the government’s alert that the medfly had been detected in the country, its main trading partner, the USA, had banned imports of 18 agricultural products, including avocado, tomato, bell pepper and mangoes. The ban stayed in force while the agricultural authorities, together with the collaborators, set up and implemented their eradication campaign.

Surveillance identifies 2 000 km2 medfly infested area

The campaign began by setting up a surveillance network with traps around the epicentre of the fly find, extending geographically until it found the perimeter of the infestation. Although it identified an infestation of more than 2 000 km2, this area was approximately 200 km from the nearest horticulture production site. The surveillance network revealed that the rest of the country was clean. So the eradication campaign targeted the infested area in the eastern part of the country.

First step was to suppress the medfly population, using ground bait sprays and bait stations placed on trees. Any host fruits where the medflies might lay eggs were collected and disposed of, and the almond trees that had hosted the first indication of medflies – the primary medfly host – were heavily pruned. SIT was used as the final step of the medfly eradication process – a clean-up operation to eliminate any populations that remained.

SIT works most efficiently if the pest population has already been suppressed, because the sterilized male flies mate with the remaining wild females. It would be prohibitively expensive and less effective to apply SIT when the population is high.

So, starting in October 2015 and ending in April 2017, each week up to 82 million sterilized flies were shipped to the Dominican Republic from their rearing facility in Guatemala. The campaign went so well that in January 2016, trade reopened with the USA, while the SIT eradication was still underway. However, as an illustration of the economic devastation that accompanies a medfly infestation, in the initial nine months Dominican producers had already lost 40 million dollars due to their inability to export to the USA.

As a preventive measure, the sterile fly release continued for several more months. If at any point, the presence of the medfly had been detected, the export ban would have been reintroduced. Once the sterile fly release stopped, surveillance continued another three months – three medfly life cycles – to make sure no flies were left.

A surveillance network against invasive non-native fruit flies, including medfly, has now been established at high-risk points of entry and quarantine actions have been strengthened. This will enable early detection and immediate response to any pest incursion, safeguarding the country’s horticultural industry and the livelihoods of its farmers.

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