The olive fly is one of the main pests threatening the quality and viability of olive oil in the region. Due to the damage it does, decreasing the weight and quantity of the fruit, and the increasing the acidity of the oil, growers have been "hunting" this insect for decades. Through Integrated Pest Management (IPM), damage control is sought with a reduction in the use of chemically synthesized insecticides. To do this, the first step is to monitor the population to determine the best time to carry out control actions.
The problem is that "the current population monitoring system for the olive fly is obsolete and has no scientific basis," explains researcher Meelad Yousef, who, together with the team formed by Enrique Quesada, Flora Moreno, and Pablo Valverde, with the Agricultural Entomology Group at the University of Córdoba, has carried out a study identifying the most effective method to monitor the olive fly.
After two years of field trials in the provinces of Córdoba and Cádiz, the team managed to determine that small double-sided yellow adhesive panels (10 × 25 cm) are the most efficient traps to gauge olive fly numbers. The ideal distribution, according to the tests, is 15 adhesive panels per hectare, for greater accuracy, but it was also concluded that 4 traps per hectare allow for an effective estimation of the population. This would make it possible to update, with scientific evidence, Spain's Integrated Pest Management Guide, which established 6 traps for a reference plot of 300 hectares, and did not stipulate the best trap for this insect.
"Among the traps studied (6 different ones), the yellow adhesive panels and the McPhail traps (very common for this purpose) outperformed the rest in terms of flies captured, but we selected the yellow adhesive panels because the McPhail traps also captured many natural enemies, in addition to the fly," Meelad Yousef explains. Once the type of trap was selected, they tried different colors: yellow, green, white and blue. The flies were more attracted to the yellow one.
In terms of size, contrary to what one might assume, the smaller trap (10x25cm) was actually more effective than the larger one (20x25); though it captured the same numbers of flies, but fewer beneficial insects. Size-related information is also absent from the current guide.
In addition, researcher Flora Moreno continued, "we proposed the distribution of traps, and the optimal distance between them to obtain the data allowing us to decide precisely when to treat the crops, reducing costs by not applying treatments at the wrong times."
Variety matters
This work is pioneering in that it relates the damage caused by the olive fly to its populations and the variety of olive tree in question. It was found that the variety of tree is a key factor to predict what damage a certain population will do "because 10 flies do not affect the different varieties in the same way." For example, with a similar number of flies on the Frantoio and Empeltre varieties, the latter suffered greater damage.
This work lays the foundations for more effective monitoring, in turn leading to better decision-making regarding the control of the olive fly, and is key to the development of electronic traps that will send data in real time to growers and technicians, a technology that the Agricultural Entomology group is currently working on.
Reference:
Flora Moreno-Alcaide, Enrique Quesada-Moraga, Pablo Valverde-García, Meelad Yousef-Yousef, Optimizing decision-making potential, cost, and environmental impact of traps for monitoring olive fruit fly Bactroceraoleae (Rossi) (Diptera: Tephritidae), Journal of Economic Entomology, Volume 118, Issue 1, February 2025, Pages 219–228, https://doi.org/10.1093/jee/toae296