Olive fly: the fight against the olive tree parasite

A feared parasite,  but one less dangerous than the Xylella fastidiosa for the survival of individual plants and species is the Olive Fly (Bactrocera Oleae), endemic throughout the Mediterranean 

The damage caused by the Olive Fly is limited to the deterioration and loss of fruit; the fly punctures the ripening fruit before inserting an egg inside, as such, spreading  the disease. A larva quickly develops from the egg which grows by eating the pulp, rich in oil; in just a couple of days it turns first into a pupa and then a grown adult that is able to repeat the cycle. Since a single fly can lay from tens to hundreds of eggs each time, if the environmental conditions allow it, the disease is a real biological bomb that, within three to four weeks, is able to attack the whole plantation harvest.

In severe cases of infestation, the damage causes the loss of the crop, which is left on the plant; if collected, it results in a quantitative loss since the larvae eat an important part of the fruit pulp, and in a serious drop in the quality of the oil obtained, which is not only affected by the presence of the insect, but is also strongly oxidised due to a fungus (formed by the parasite) within the fruit, which determines an increase in free acidity and peroxides, so what is obtained must be considered a priori lampante olive oil.

In the past, this insect has caused famines in southern Italy, becoming such an important problem that in the second half of the nineteenth century, when the infestation was so high, farmers couldn’t even produce lampante olive oil.

At the end of the 1930s, in order to produce even small quantities of edible oil, thoughts turned to the harvest of the passerine olives present in the Coratina variety. These olives are very small and round, resulting from a simple enlargement of the ovary of the non-fertilised olive flower which, in general, delays ripening: these characteristics (smaller size and early stage of maturation) protect the plant from the parasite

Traps and defence methods against the olive fly

Until the early 1970s the only means of defence were traps poisoned with arsenates, and it is only following this decade that extremely efficient synthesis products have been developed against the flies, but with negative characteristics for the presence of residues in the oil.

Since then a wide spectrum of effective pesticides available both for conventional and organic agriculture has been introduced, starting with simple traps laden with attractive substances.

The real problem is the timeline of the intervention: whilst regions do monitor the progress of the disease, it is up to the individual to decide when to intervene. 

It can happen that climatic trends favourable to the olive fly (mild temperature and high humidity) in July-August lead to a mostly predictable advance of the attack, but often farmers are not prepared and cannot resist the temptation to postpone treatment, with serious qualitative and quantitative losses to both their own production, and that of their neighbours.