The olive fruit fly (Bactrocera oleae Rossi, 1790) is one of the most relevant pests of the olive grove. The use of traps and the application of treatments for the control of the olive fruit fly is frequent in the Spanish olive grove.
Phases of the biological cycle, olive fly: Egg, larvae, pupa and adult
Egg: It has elongated and cylindrical shape with approximate dimensions of 0.7×0.2 mm. The female of the olive fruit fly, deposits the eggs under the skin of the olive, in a small chamber that she performs with the oviscapto. The small incision made on the skin of the olive forms a small brown spot. This spot is visible to the naked eye and is known as “fly bite“.
Larvae: similar to that of other dipterans, is transparent-white, with spindle shape, with very small head and the end of the broad abdomen. At the end of its development it reaches a size of 7-8 mm.
Pupa: reddish brown-brown and similar to that of a barrel of wood.
Adult: The olive fly has a length of only 4-5 mm and is somewhat smaller in size of the common fly. The body features a varied range of brown tones with a light colored triangle on the back somewhat yellowish.
The size of the females is larger than that of the males and they have a oviscapto (organ used by the fly to bite or lay) very appreciable.
Olive fruit fly: Biological Cycle
The olive fruit fly begins to make the first bites in the olives during the month of June. Once the olive bone has hardened, the fly can begin to act. Depending on the environmental conditions the laying will be important or scarce.
Olive fly eggs suffer very high mortality with high temperatures and low humidity environmental. However, mild temperatures and high humidity favor the multiplication of the olive fruit fly.
Normally the olives affected are scarce during June. However, the farmer must remain fully alert and detect the existence of favorable conditions.
The hot and dry summers are the best defense of the farmer against the olive fly. When the fly has good conditions to spread in the initial phase of olive development, the number of adults soars in autumn and the plague becomes more virulent.
With the rains of late summer and especially during the fall, the activity of the fly increases considerably. The final number of generations depends on the weather and temperature.
Once the egg hatches, the larvae feeds on the pulp of the olive for a time that varies with temperature.
After feeding, the larvae becomes a pupa, it can pass this phase inside the olive or buried in the ground. In just a few days the pupa becomes an adult that if the conditions are favorable it will give way to a new generation of fly.
Damage caused by olive fruit fly
The damages can be divided according to whether they affect the green olive or impair the olive oil production.
Green olives (table olives): suffer direct and indirect damage. The direct are due to the scar product of the fly bite and the galleries that the larva performs during its development. The indirect are a consequence of fungi as the gusset that usually appear in olive fruit fly bites parasitized by Prolasioptera berlesiana.
Oil production: fruits chopped in June-August ripen early and fall to the ground before harvesting. The chopped olive during the fall does not usually fall and the quality is still good if it is processed quickly after harvesting. However, the oil quality is low when the olive is stored without grinding or is collected from the ground.
Olive fly treatment and control
The climatic factors and to a lesser extent the predators of the olive fruit fly can control the pest without the need for phytosanitary treatments.
Climate fly control
The high temperatures summers above 35ºC begin to eliminate fly larvae and are lethal when they reach 39-40ºC. Eggs are more sensitive and are also affected by low ambient humidity conditions.
Olive fly predators
Some insects present in the olive grove prey or parasitize the olive fly. This helps to control fly populations while climatic conditions are not favorable for their development and these insects are overwhelmed.
The following species may prey to a greater or lesser extent on fly populations: Cyrtoptyx latipes, Eurytoma Martelli, Eupelmus urozonus, Lasioptera berlesiana, Pnigalio mediterraneus and Psyttalia concolor.
Increasing the populations of predators favors the ecological fight against this plague.
Cultural measures (olive fruit fly traps)
You can buy sophisticated olive fly traps or make homemade traps by transparent plastic bottle recycling . The most famous and used homemade trap against olive fly is the olipe trap. This trap has very low cost and high efficiency. To the olipe trap, food attractants (wine vinegar, hydrolysable proteins…), sexual attractants are added (pheromones) or diammonium phosphate.
It is very important that the holes made are less than 5 mm so that beneficial insects cannot enter.
In organic olive groves, the use of olive fruit fly traps is one of the most common solutions. The placement of traps to massively capture olive flies is a good way to control the populations of Dacus oleae and reduce the application of treatments. In addition, they help us control the activity of the fly and know when to deal with the olive fly.
Phytosanitary treatments against the olive fly
Although, at present, the “biological warfare” against this plague is being used. The insecticide treatments of authorized application are still common against the olive fly.
Products authorized by the Map (2019).
The biological warfare consists of the application of entomopathogenic fungi on the soil of the olive tree.
The treatments with systemic insecticides are effective and can be applied partially or totally. The time of treatment will depend on the evolution of the pest, greatly influenced by the annual climatic conditions and previous existing populations.
The partial treatment is applied by performing patch of insecticide and food attractant. Patching is the most commonly used technique when the Bactrocera oleae population is not very high.
For the application of total treatment the use of attractant is unnecessary. This application can be made when with the first generations 1% of olives chopped in green and 2-3% for olive oil mills are exceeded.
Before applying, we must take into account the security deadlines, which in some cases are very high (40 or more days). We must also inform ourselves that the phytosanitary product for olive fly remains authorized at the time of application.
Bactrocera oleae resistant olive varieties
There are less palatable olive varieties for olive fly. The fly usually prefers large olives, with high oil content and good pulp / bone ratio.
They are fly sensitive: Alfafara, Arbequina, Gordal Sevillana, Verdial de Badajoz, Villalonga, Morisca, Manzanilla Sevillana, Blanqueta, Farga, Picudo, Empeltre, Lemon Peak, Ocal, Itrana, Carolea, Leccino, Frantoio, Cornicabra.
The varieties of olives may be apparently more or less sensitive to olive fly attacks. This depends on the preferences of Bactrocera oleae for the olive varieties in the growing area.
We have translated the information on our website from Spanish to English. Note that some words may have seen their meaning altered during their translation.