Next time you drizzle olive oil on your salad, give a thought to the larvae of the olive fly, which love olives as much as you do. Every year in Catalonia, Spain, farmers have to fight these pests so they don’t ruin the year’s crop. The customary method is to spray with insecticides, but in recent years a simpler weapon has gained favor: the olive fly trap.
The female olive fly is slightly larger than the male, and can be spotted by the spike at the end of its abdomen. This spike is used to inject eggs into the olive flesh while they are still on the tree. When the eggs hatch, the young feed on the olive pulp.
These flies are endemic to the Baix Ebre and the Montsià regions of Catalonia. In 2014, 40% of the harvest was lost to olive flies and drought. Spraying can be effective, but is a big job, has to be repeated, and is less effective when it’s windy because the spray just blows away. This year, 400,000 traps were deployed to try a different approach.
The trap is as simple as it gets. Supplied as flat sheets of plastic, the traps are twisted into a cone shape on site and hung from trees. Instead of the usual liquid bait, these traps use a solid attractant (mostly diammonium phosphate) contained in a sachet made of a porous membrane. Imagine those little sachets of desiccant you find in your new electronics and you’ll be close enough. These packets are moistened overnight by dew, ready to bait flies in the morning. The traps work all season long, and keep going through the winter which, thanks to the pleasant local climate, isn’t always cold enough to kill off the flies.
Holes on the top let flies walk in, but they can’t fly back out. And that’s it. Farmers like them because they work in the wind, and once you’ve hung it on the tree it keeps going. The traps are effective too, if they’re deployed properly. To work most successfully, the majority of an area must be blanketed by traps. In a trial in June of this year, technician Quique Pedret managed to cover 20,000 of the 27,000 hectares in the test area, partly due to the fact that farmers are enthusiastic about the low-maintenance traps.
This is corroborated by Jordi Roig of Probodelt, the company that manufactures these traps. In a trial at a farm in Montsià, Probodelt found the traps to be more effective than spraying. Thanks to their long life, the traps can be spread over huge areas, and Roig estimates that just one trap per four trees gives optimum protection if the entire area is covered. “
“This does’t means that the entire population is eliminated,” Roig told Barcelona’s Vanguardia newspaper. “The treatment will reduce the fly population.”
But can these traps replace pesticide spraying by plane? Not completely, but they form an important part of the fight against olive flies.
“It’s important to remember that the traps don’t replace other methods,” Jaume Gregori Puñet, a retired sustainable agriculture expert in the government of the Generalitat of Catalunya told Co.Exist. ”In the case of very intense attack of the pest, crop spraying is necessary to achieve a satisfactory solution.”
New government supplements are available to farmers who use the traps, which will help their popularity. But it’s also possible to make your own traps. In fact, when I started to research this article, the majority of the results were for DIY versions using old soft-drinks bottles, proving that some things–like farmers’ ingenuity and their drive never to waste anything–never change.