Bactrocera (Dacus) oleae is an insect of the order Diptera and of the Tephritidae family. It has a geographic presence in the whole of the Mediterranean area, west Asia and east and south-east Africa.
Typically, it hibernates in winter in pupae form buried a few centimetres below the soil surface, although in areas with a temperate climate, it can also spend the winter in its adult form in sheltered places. In spring, when the temperatures are above 7ºC, the first adults emerge which feed on nitrogenous and sugary substances. From approximately June onwards, depending on the climate, and three days after mating, they begin laying eggs on the olives. Using its ovipositor, the female deposits only one egg on each olive, below the epidermis. High temperatures and low relative humidity can cause the death of the eggs. After a few days (2-3 in summer or 8-10 in autumn-winter) the eggs hatch and the larvae emerge, which feed on the olive and create larval tunnels in its interior. At the end of its development, the larva breaks the epidermis and then transforms into a pupa in the interior of the fruit. The duration of this period depends on climatic conditions and once complete, an adult emerges which will repeat the same cycle.
During the autumn, Bactrocera oleae becomes more active with an increase in the number of punctured olives, the number of individuals in each stage of development and an overlapping of generations. There can be between two or three generations per year depending on the climatic conditions, even reaching four in very favourable conditions. The duration of the cycle is 35 to 40 days for summer generations and can reach 60 in the case of autumn generations.
B. oleae only causes damage to the fruit.
In the case of the table olive, the fruit is rejected for sale due to the mark left behind by the female when laying the egg and the destruction of the pulp by the larva.
In the case of olives for the production of oil, the fruit that has been punctured early (between June and August), matures prematurely and falls to the ground prior to harvesting. However, any olives that have been punctured late in the season (September to November) remain on the tree until harvested, but the larval tunnels created by the larvae during their development are a means of entry for fungus and bacteria, which affect the final quality of the oil due to an increase in acidity and a deterioration of the organoleptic properties.
Bearing in mind that the insect begins to cause damage from when the stone begins to harden, there are two options for action:
- Bait spraying against the adult forms by treating one square meter of the south face of each tree using a mixture of an attractant lure and an authorised insecticide. Patch spraying is applied when the level of infestation is low and there are no recent puncture marks or when it is observed that there are quite a few exit holes.
- Cover spray, to eliminate the larvae by spraying the whole plantation with an authorised insecticide. These treatments are on occasion necessary, but it is worth remembering that when doing so, useful fauna that controls this and other infestations is being eliminated, therefore it is not unusual that they increase over time, especially when application ceases, black scale (Saisetia oleae) populations, for example.
The mass trapping has a less drastic effect compared to insecticides when employed, but their effect is continuous: traps, throughout the useful life of the attractant, continue to capture the adults emerging from the area to be controlled or from bordering areas, without interruption. Therefore, as large scale trapping reduces the population in a continuous manner, it guarantees the prevention of damage as a result of any unexpected sharp increases in populations.
The main factors that we must take into account when applying the large scale trapping technique are as follows:
- The trap. It must be designed to trap the maximum number of adults possible, easy to enter and difficult to exit. We have trap designs for liquid attractants (Conetrap and Maxitrap UV). (Hemitrap 2180 and Maxitrap UV XL) and solid attractants (Conetrap y Maxitrap UV).
- The attractant. To make a good, efficient use of this technique, food-based attractants must be used, which will mainly capture the females responsible for the damage to the fruit. PROBODELT has liquid (Bactrotrap) and solid attractants (Amphos-Dacus). The effectiveness is good in both cases, but the liquid needs to be refilled approximately every month, whereas the solid will last the whole season, which will ultimately lead to savings and ensures continued effectiveness.
The solid attractants require that there is a small amount of insecticide in the interior in order to kill the captured adults. A suitable trap limits the risks of the fly developing a resistance to the insecticides used, given that it prevents adults with a nonlethal dose from escaping.
- When to place traps. In order to obtain the best results from large scale olive fruit fly trapping, place the traps in the field towards the end of June or beginning of July and keep them active until after the harvest. In this instance, the most suitable trap and attractant is Conetrap baited with Amphos-Dacus, as this permits it to be employed in the field at the optimum time and maintain its efficiency until harvest without the need for maintenance.
Evaluate the option of an early olive harvest for oil production in order to reduce the percentage of affected fruit. This way, a higher quality oil can be obtained as there will be less affected fruit, however, the output will be lower.