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Costa Rica Aims to Eradicate Harmful Flies with the Help of Wasps and Nuclear Technology

Just about the same size as the common housefly, the stable fly bites and causes stress in the cattle it attacks, provoking anaemia, weight loss and reduced milk production. (Photo: L. Gil/IAEA)

A group of Costa Rican experts has demonstrated that using a tiny wasp and nuclear technology can control the stable fly, a pest that is causing losses to pineapple producers and cattle breeders in Costa Rica and beyond. The pilot project was supported by the IAEA and the Food and Agriculture Organization of the United Nations (FAO).

Just about the same size as the common housefly, the stable fly bites and causes stress in the cattle it attacks, provoking anaemia, weight loss and reduced milk production. It breeds among others in pineapple residue, which is abundant in Costa Rica, the world’s number one pineapple producer.

“The pest is having an economic impact, because it’s affecting the health of cattle; a social impact, because the population blames the pineapple producers; and an environmental impact, because the pineapple producers apply more and more pesticide and plastic traps to control it,” said Arturo Solórzano, an entomologist at Costa Rica’s Institute of Agricultural Technology Research (INTA-MAG).

The solution that INTA-MAG has identified to control the fly is simple: a wasp. It’s the result of research on area-wide insect pest management, an approach that often includes the use of radiation to sterilize insects before they are released. In this case, another nuclear application proved more effective.

Spalangia endius wasps, natural enemies of the stable fly. (Photo: L. Gil/IAEA)

“It is extremely hard to get rid of the fly,” Solórzano said. “Its populations are indestructible. So it’s important to attack the fly before populations explode, which is what the wasp does by stinging the pupae.”

The Spalangia endius wasp is a parasitoid, an insect that attacks other insects. A natural enemy of the stable fly, it lays its eggs in the fly’s pupae and feeds on it. Upon hatching, the wasp larvae consume the pupae and, when the adult wasp is born, no fly emerges. It all happens naturally, which is why the wasp is called a biocontrol agent. And as for the wasp itself, it neither stings nor bites.

With support from the IAEA’s technical cooperation programme, experts at INTA-MAG established a pilot facility in 2012 to rear Spalangia wasps. When the wasps mature into adults, they mass release them in cattle farms in Eastern Costa Rica. The wasps seek out stable fly pupae to lay their eggs in, reducing the fly population. See this photo essay to learn more about their work in Costa Rica.

The wasp, it has turned out, can kill up to 70 per cent of the stable flies, Solórzano said, over twice as many as initially expected.

Sterilizing pupae

But there is a loophole in this process. Rearing wasps requires bringing a colony of stable flies, or Mediterranean fruit flies into the facility and using its pupae: If a pupa does not have wasp eggs in it, it can develop as an adult stable fly — and be released, causing damage to cattle.

Here is where nuclear technology comes in. In order to make sure that adult flies from these pupae do not get released, the flies are sterilized with X rays at the larval stage. “This way, even if a few adult flies emerge, they are sterile and produce no offspring,” said Walther Enkerlin, an entomologist at the Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture.

Affected: farmers and producers

This has provided a safe and cost-effective solution to an escalating problem for Costa Rica. It is also a good alternative to using costly chemical insecticides, which harm the environment and are becoming less and less effective.

“The fly is developing resistance. One of the three types of pesticides we apply no longer works on it,” said Olivier Vargas, manager at Dole, one of the major pineapple producing companies in the country. For the time being, Dole is destroying pineapple residue right after harvest to minimize the breeding ground for the fly. This is a costly process, as the country generates over 6 million tonnes of pineapple residue per year.

With a production of over 2.5 million tonnes per year, Costa Rica is the top producer of fresh pineapple in the world. It supplies 60 per cent of global exports. Dole alone produces about 25 million pineapples a year, which it exports to the US and Europe. Indirectly, according to Vargas, the company generates employment to around 15 000 people.

Olivier Vargas (left), manager at pineapple producing company Dole, examines pineapple plant leftover with Arturo Solórzano (right), entomologist at Costa Rica’s Institute of Agricultural Technology Research (INTA-MAG).

Cattle breeders are also affected by the stable fly. “The flies are growing in the areas with more pineapple,” said Marco Antonio Fallas, Project Head at Cattle Foundation CORFOGA. “Farmers are seeing their animals lose appetite and die, in front of their eyes. Cows, bulls, even horses.”

“The fly is a serious national problem,” said Óscar Arias, President of Agribiotecnología (AgriBio), a Costa Rican agricultural citrus and pineapple company that is working with INTA-MAG to control the pest. “And it is getting worse.”  According to 2015 and 2016 findings by INTA-MAG, the fly has started to breed in coffee, oil palm and citrus fruit residue as well as in rice straw.

Experts at Costa Rica’s Ministry of Agriculture and Livestock are analysing the results of the pilot study to prepare a national action plan. Both farmers and producers hope science will solve their problem.

“We trust that scientists will make sure this does not stay at the research level,” Arias added. “We want to apply it at a wider scale, across the country. I am positive that this work in progress will help reduce the fly population.”

With a production of over 2.5 million tonnes per year, Costa Rica is the top producer of fresh pineapple in the world. (L. Gil/IAEA)