<p>Just about the same size as the common housefly, the stable fly is a pest that is causing losses to cattle breeders in Costa Rica and beyond.</p>
<p>Photo: C. Brenes/SENASA MAG</p>
The stable fly can wreak havoc on cattle and affect its productivity, provoking anaemia, weight loss and reduced milk production as cattle stops eating when stressed by the biting flies.
The stable fly breeds among others in pineapple residue, which is abundant in Costa Rica, the world’s number one pineapple producer.
In an effort to control the fly without resorting to chemical sprays, a group of Costa Rican entomologists has identified another way to do the job — using a tiny wasp as a biocontrol agent.
<p>This tiny wasp, called Spalangia endius, is a parasitoid — an insect that attacks other insects. Parasitoids feed on living hosts that are eventually killed before producing offspring. A natural enemy of the stable fly, the adult female wasp lays its eggs in the fly’s pupae.</p>
<p>Photo: A. Solórzano/INTA</p>
<p>Upon hatching, the wasp larvae consume the pupae and kill the host to fully develop into an adult wasp, which comes out of the puparium shell instead of the fly. When the adult wasp is born, no fly emerges. It all happens naturally, which is why the wasp is called a biocontrol agent.</p>
<p>Photo: A. Solórzano/INTA-MAG</p>
With support from the IAEA’s technical cooperation programme and the Joint FAO/IAEA Programme, experts at Costa Rica’s National Institute of Agricultural Technology Innovation and Transfer (INTA) established a pilot facility in 2012 to rear Spalangia wasps.
To rear the wasps, experts need to bring a colony of stable flies, or Mediterranean fruit flies, into a facility and use its pupae.
<p>But if a fly pupa does not have wasp eggs in it (has not been parasitized), it can develop as an adult fly and be released, causing damage to cattle or crops.</p>
<p>Photo: D. Taylor/USDA<p>
<p>Here is where nuclear technology comes in. Experts use X-rays to irradiate all of the flies at the larval stage. This way, even if a few adult flies emerge they are sterile and produce no offspring.</p>
<p>Infographic: F. Nessim/IAEA<p>
When the wasps mature into adults, they will be mass-released in cattle farms and pineapple fields in eastern Costa Rica. Once wasps lay their eggs in stable fly pupae, the fly population will be reduced.
This could provide 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 because the flies are growing resistance to them.
<p>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 pineapple producers hope science will solve their problem.</p>
<p>Photos and text: L. Gil/IAEA</p>
