Predisposing Factors
The predisposition to the flies' attacks is tied to several factors, both intrinsic and extrinsic. The main ones are climatic (temperature and rainfall), so marked differences can occur from year to year. However, other genetic or agronomic factors should not be overlooked.
Ultimately, the environmental conditions favorable to fly attacks are:
- Conditions of moderate heat, with temperatures not exceeding 32-34°C
- A humid climate
- Premature cultivation
- Mass or dual purpose cultivation
- Cultivation under irrigation
Because of these factors, the incidence of olive fruit fly attacks increase, passing from the southern to northern areas, and coastal to inland regions. As for the season in general, the summer infestations are usually contained with the exception of cooler environment and more susceptible cultivars. On the other hand, infestation peaks happen from the months of September until cold weather arrives, especially with a rainy climate.
Another unique factor is the relationship between the alternation of production, a phenomenon in which the olive tree is particularly susceptible, and the intensity of the attacks. The attacks are usually most intense in years of low production and high production. The cause of this behaviour is partly biological, partly agricultural.
In low seasons following a high one, usually, a significant amount of olive residue is left on the plants from the previous year, so it has a higher population at its production peak in spring, and a higher reproductive potential occurring with more intense and earlier attacks. The attacked olives fall early in autumn and this causes a higher incidence of mortality during the winter.
In the subsequent good year for the population of first generation olives, production is quite low, with modest reproductive potential. The attacks will therefore be later and help a mass-production.
Read more about this topic: Olive Fruit Fly
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