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Bactrocera oleae is the scientific name of the most dangerous parasite for olive cultivation, an enemy that if not fought in time, acts undisturbed destroying large amounts of olives. The olive fly is in the form very similar to the flies that strike other types of fruit and is easily recognizable because of the black dot that is found on the tip of each of the two wings.
For the development of the olive fly, the climate plays a fundamental role. The ideal temperatures for the development of this insect are those between 22 and 30 degrees centigrade. Adult flies become active when the temperature starts to exceed 14 degrees and stop when temperatures begin to exceed 33 degrees. The conditions of hot summers, with absent rains and low humidity, cause a high degree of mortality both in adult flies and in any larvae still present in the fruits. Taking the example of the region of Tuscany, where there is a large number of fields planted with olive groves, the olive fly is more present, and particularly aggressive, in the area near the coast, while it is almost absent going towards the interior of the region . On the coast, in fact, the climate is milder, winters are less harsh and summers less torrid, compared to the more internal area, in particular the more oriental areas of Arezzo and Florence. It is close to the coast that the plants are more vigorous and less suffering from drought, but also more prone to attack by the olive fly, which finds here the ideal conditions for living.
In the winter season the olive fly remains almost in the pupal state, the stage following the larva stage and the fly stage, inserted in the olives that have remained on the ground or on the plant. Depending on the region you are in, the first flies can begin to form and already in the months of April - May. Pupae can survive in this state for up to seven months, depending on the weather conditions. The laying of the eggs, by the female, occurs when the olive core begins to harden, that is to say, when the fruit reaches the diameter of 7-8 millimeters,
The egg is laid by a puncture made with the olive and a single egg is left here. The hatching period of the egg and the consequent formation of the larva, is very variable and closely related to the climatic conditions and can range from two, three days, up to about ten days. The warmer the climate the faster the egg hatching times are.
The birth of the larva is the moment when the decay of the fruit begins. Before turning into a fly, the larva begins to feed and grow by digging tunnels inside the pulp, feeding on it. When the adult olive fly comes out of the fruit, the exit hole allows the air to come into contact with the already weakened pulp, oxidize it and make it even weaker. In summary, the harmful effects caused by the olive fly are: destruction of the pulp that feeds the larvae, falling of the fruits, otherwise known as drop and finally an alteration of the quality of the olives which greatly reduce their ability to produce oil.
Olive fly:
To counter the attack of the olive fly, there are three different types of treatment: chemical treatment, biological and integrated control and finally biotechnical control. The time to perform one of the aforementioned treatments is when the presence of olives containing eggs or larvae reaches about ten percent. To check a reliable sample of plants, you can take ten olives from ten different plants and check for fertile stings. The type of treatment to be carried out, to counteract the presence of the olive fly, depends on the extent of the attack and it is therefore important to make a careful evaluation of the phenomenon, based on the presence of adult flies and the type of bites present on the fruits.
Biotechnical control is recommended if the attack of the olive fly is of a late and limited intensity type. It is a question of keeping the population level low by capturing adult flies through traps that must be positioned as soon as the first adult subjects begin to appear. Biotechnical control is effective for large olive groves with a surface area of more than four hectares.
The use of chemical products for the fight against the olive fly is to be taken into consideration when its presence is very high. In the case of organic farming, natural pesticides must be used or in any case admitted by the rules related to the production of organic olive oil. A remedy with low environmental impact, which proved to be of good efficacy, if used in a timely manner, is based on the use of copper and propolis in combination with phytosanitary devices with low environmental impact and known for the fight against olive fly , which are dimethoate and deltamine.
Finally, research into the fight against olive fly has revealed how this can be fought by using antagonist insects. Psytallia concolor, and Fopius Arisanus have proven to be very effective antagonists. Research in this area will have to evaluate the effects of the introduction of these insects into the environment, in order to find natural solutions that are less and less impacting on the environment.
