Commercially farmed olives in the Western Cape have several major insect pests, with the olive fruit fly (Bactrocera oleae), being indigenous to sub-Saharan Africa. The Mediterranean olive industry experiences significant losses due to the olive fruit fly, which negatively affects the production of table olives as well as olive oil. In South Africa, this fly only becomes economically significant when serious infestations of olive groves occur, usually every few years. It is thought that either population suppression by natural enemies, or more probably climate, affects the development and size of olive fruit fly populations.
Monitoring pest populations of olive fruit fly is the first step in developing a management strategy. Monitoring is done by means of trapping the olive fruit fly by using traps, lures and retention systems to keep the trapped flies from escaping. Mediterranean olive farmers have advanced monitoring systems in place which use both trapping and climate information. In order to create a statistically based monitoring system with measurable thresholds in South Africa, where none exists for olive fruit fly, determining the best monitoring method is key. In order to determine which trapping system should be used for monitoring, two different traps were compared, using the same attractants in both trap types. Olive fruit fly sex pheromones and the product of protein decomposition, ammonium bicarbonate were used as an attractant, as this combination attracts both male and female flies. The two trap types used in the comparison are both currently available to South African farmers. South African olive farmers currently use yellow delta traps for monitoring olive fruit flies, but its efficacy had not yet been assessed. Yellow bucket traps, on the other hand, have been used by Mediterranean olive farmers for decades.
The trial was conducted in Stellenbosch, Somerset West and Paarl on 20 pre-harvest commercial olive groves, during the autumn of 2013, which is when fruit are mature. The 20 groves had mixed cultivars of Favolosa, Kalamata and Nocellara olives. When comparing the results of the trapping, it was found that the trap currently in use, the delta trap, performed better than the bucket trap. Factors taken into consideration were variable abundances of olive fruit fly, with Somerset West showing the highest population levels, sexual maturity of the flies, as well as the dispersal of the lure odours. The overall conclusion was that the trapping system currently in use by Western Cape olive farmers was satisfactory. This finding now allows for further research to commence. Economic thresholds and management practices for control of olive fruit fly can now be determined and olive farmers may mitigate damage caused by this pest.
These findings were published in Bekker, Addison & Addison. 2017. Comparison of two trap types for monitoring Bactrocera oleae (Rossi) (Diptera: Tephritidae) in commercial olive groves of the Western Cape Province, South Africa. African Entomology 25(1):98-107. doi: http://dx.doi.org/10.4001/003.025.0098
