Five million irradiated fruit flies burst out of white boxes every Saturday and race to stop female flies from breeding larvae-filled eggs in Trok Nong, a small rural town in eastern Thailand. Their mission: protect premium export fruits like durian and mangosteen. Thanks in part to these swarms of flies produced with the sterile insect technique (SIT), farmers in Chanthaburi province now have a steady supply of fruit for lucrative export markets.
But these Thai farmers didn't always have these unusual allies.
"For years our community struggled to export even 50 tons of fruit. So we tried to use more and more pesticides and had some success, but the chemicals made a lot of us sick. We couldn't control the fruit flies well enough to eliminate many of the trade barriers, so our community was under constant stress," said Chanapol Hoharn, a farmer and head of the farming community leading the local SIT programme supported by the country's Department of Agricultural Extension (DOAE), the Thailand Institute of Nuclear Technology (TINT) and the IAEA, in cooperation with the Food and Agriculture Organization of the United Nations (FAO).
The orchards in this community of 855 farming families were under attack by one of the world's most invasive fruit fly species: the Oriental fruit fly. These fruit flies are known for infesting more than 470 different fruits. After they lay their eggs inside the fruit, the larvae emerge and live there, feeding on its flesh as fuel for transforming into an adult. The result is hundreds of millions of dollars' worth of damaged fruit each year and a hard-to-break cycle of fruit fly reproduction.
In Chanthaburi province, the flies only target the soft-skinned fruits, like longkong, mango, guava and rose apple that are primarily sold around Thailand. But with so many fruit flies in the area, their presence alone made it virtually impossible for the farmers to export their premium fruits.
"Durian and mangosteen have tough skin so the fruit flies can't penetrate them, but many countries won't accept any or very few fruits if they know fruit flies are a problem in the growing area or if they detect fruit flies in any stage of their life cycle," said Suksom Chinvinijkul, Head of the Irradiation for Plant Pest Management Section in the DOAE. "Some countries also ban fruits when they detect an overuse of the chemicals that keep the flies away."
"After we added sterile flies to our insect control methods, it only took a few years for us to meet export standards and then we started exporting around 300 to 500 tons of fruit per year," said Preecha Kanayat, Chief of the Trok Nong Subdistrict Agricultural Technology Transfer and Service Center. "Today we're exporting as much as 4000 tons of high-quality fruits each year, and because we don't need to use pesticides, we are considered eco-friendly and have access to markets we would never have been able to get before."
Introducing the sterile insect technique to control fruit flies
Farmers and local government officials in Chanthaburi province first heard about SIT (see Sterile insect technique and area-wide integrated insect pest management) in 2005 from scientists at the Thailand Institute of Nuclear Technology (TINT) that were carrying out a research project involving SIT.
In 2013, shortly after the project finished, the DOAE, which is responsible for the practical application of new methods and technologies in agriculture, teamed up with the Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture, through the IAEA's technical cooperation programme, to find new ways to address the fruit fly problem around the country. The DOAE first reached out to the district and then subdistricts' administrative organizations that helped them approach the local community. Together they set up the area-wide integrated insect pest management (see The Science box) programme in a 2590-hectare area. Farmers now receive 5 000 000 pupae each week from a facility in Pathumthani province about 290 kilometers away.
After each shipment, the farming community works to repackage the pupae into boxes and distribute them so that when the adult flies are ready, they fly out of the boxes and seek out wild females.
Farmers lead the way for the sterile insect technique
The plan is now to expand the buffer zone of the target area by 640 hectares in all directions.
"Fruit flies don't operate within boundaries. They can fly as far as 30 kilometers. This means that getting a programme to work depends on the farmers in the entire area actively participating in pest management. If just one farmer doesn't do his or her part, it can jeopardize the whole area," Chinvinijkul said.
That's where leaders in the farming community come in. They are using their understanding of local farming culture and their experience with SIT to help the expansion get off the ground.
"We can talk farmer to farmer and help them see how this programme changed things for us and can change things for them too," said Hoharn. "My approach is that I tell them the advantages of the programme, like not needing pesticides and how it can help them reach new markets. Then when they ask how it works, I tell them it's done with radiation. I use X-rays as an example because they know about the good of that in medicine and then they can more easily see how radiation can be used in many good ways."
Sterile insect technique and area-wide integrated insect pest management
The sterile insect technique (SIT) is a form of insect pest control that uses ionizing radiation to sterilize male insects that are mass produced in special rearing facilities. As large quantities of sterile male insects are released systematically from the ground or by air, they mate with wild females in nature. The result is that no new offspring are produced. Over time, this brings the insect population down or, in some cases, eradicates an entire population. SIT is among the most environmentally friendly control tactics available. It has been successfully used on insects such as fruit flies and tsetse flies, and scientists continue to research its use on other insects such as disease-carrying mosquitoes.
SIT is usually applied as the final component of an area-wide integrated insect pest management programme — a cost-effective and sustainable approach that proactively coordinates and combines control methods to target an entire insect pest population.
If only one method is used or efforts are uncoordinated, insects can more easily repopulate or move from an untreated area to a treated area, which would make it a temporary and unsustainable approach. Integrating techniques over a certain timeframe and an entire pest population is a proactive, long-term way to help address the ecological, environmental and economic dimensions of insect pest management.