A Pest That Knows No Borders: Balkan States Consider Sterile Insect Technique Against Mediterranean Fruit Fly

The female can produce up to 800 offspring per season. The larvae or worms feed on the pulp of fruits, tunnelling through it, and reducing the fruit to an inedible mush.

The battle waged by farmers in Croatia and Bosnia and Herzegovina against the Medfly has been fought since the 1940s with insecticides. But the growing export market in the European Union imposes strict rules on pesticide residue limits in food.

So in 2007 Croatia turned to the IAEA for help to apply the most environmentally friendly alternative to insecticide - the Sterile Insect Technique (SIT). There are plans to start implementation next year.

SIT involves the sterilization of factory-reared male insects by irradiation. Millions of sterile males are hatched and then released into infested areas. When they mate with females in the wild, no offspring are produced, thereby gradually reducing and in some situations even eradicating the population. The technique is particularly effective in a confined area such as the Neretva Valley, which runs across the borders of Croatia and Bosnia and Herzegovina, where the migration of flies from outside into the valley is reduced.

This valley produces 80 percent of Croatia´s clementines for export. Thirty percent of them are infested by Medflies. Across the border Bosnia´s small farmers who grow peaches and plums also struggle with Medfly infestation.

"National borders mean nothing to the Medfly, so these two countries are working together on this control project which has an SIT component," says Rui Cardoso Pereira an Entomologist in the IAEA´s Insect Pest Control Section.

The Medfly, which is slightly smaller than a common housefly, originated in Africa and is now a global pest found in over 85 countries in tropical and subtropical regions.

It infests some 50 different types of fruit in the Neretva River Valley. "This area is what we call the northern limit," says Mr. Pereira. "It´s close enough to the coastal areas where the winter temperatures aren´t low enough to kill the Medfly. And this helps sustain the population, which has been wreaking havoc on plants here since the 1940s."

SIT, when integrated with other control measures, has proven to be an effective weapon against the Medfly, resulting in total eradication of this pest in Mexico, Chile and the USA. Southern Argentina, parts of Guatemala and Southern Peru have also been declared Medfly-free as a result of using this technique. Increasingly, SIT is also being used to suppress Medfly populations to acceptable levels in many regions around the world.

In the Neretva Valley project suppression is the objective as well. SIT implementation will not only dramatically cut the use of pesticides, but increase yields and the quality of available produce.

But it isn´t a quick-fix.

"Implementing this technology takes longer than insecticide application," says Mr. Pereira. "Croatia took the first two years just to collect baseline data. Not only do we need to collect statistics and do feasibility studies, but we also need to test whether or not the wild females will mate with the sterile males we are going to release. Also, to find out when the first flies appear after each winter period is key to engaging in well-oriented suppression of this pest," he said. Bosnia and Herzegovina began feasibility assessments into its Medfly population in January 2009.

"With the full involvement of the fruit industry in the valley, our counterparts in Croatia plan to begin releasing some sterile Medflies into the area in 2010," Mr. Pereira says. "Our efforts will be a success if we bring down the infestation rate in Croatia in 2011 and if crop yields increase for the poor small farmers in Bosnia and Herzegovina who are still recovering from the war."