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

“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 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 into 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 harvesting 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 USA and Europe. Indirectly, according to Vargas, the company generates employment for around 15 000 people.

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 the Stockbreeding Promotion Corporation 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 to control the pest. “And it is getting worse.”  According to 2015 and 2016 findings by INTA, 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.”