The olive fruit fly is a phyto-phagus species, whose caterpillar feeds on the olive fruit. It is a very dangerous pest of the olives and has a severe economic threat for olive growers, with significant effects on the amount and quality of production. It came from Eastern Africa, where the wild olive trees have more natural enemies. Records show that there are olive fruit infestations since the third century BC. In the Mediterranean region it has been a problem for many-many hundreds of years.
The fruit fly lays its eggs under the skin of the olive fruit during the summer, when the olive fruit is about 8mm in diameter, puncturing the skin and leaving its eggs in the hole below. The hatching of the eggs takes a few days, depending on weather conditions. The eggs become caterpillars that feed from the olive flesh, opening tunnels on the surface of the skin and going deeper into the core. When the caterpillar matures, it becomes pupa, exits the olive fruit and drops onto the ground where it pupates.
The olive fruit fly has high longevity and about 2 to 5 generations occur through the year. If it is not controlled, the whole crop may be seriously damaged. The visible damage occurs during the months of September and October with the appearance of small spots on the skin of the olive fruit. When the olive is cut open, maggots in brown tunnels are visible. The only place the olive fruit fly reproduces, is the olive fruit.
Infested olive fruit should not be left on the olive tree or on the ground, because the fruit flies are going to continue their dirty work in the spring.
The development cycle of the olive fruit fly depends on the environmental conditions. The development of the egg takes from 2 to 10 days, the caterpillar 10 to 25 and the pupa 20 days to up to 5 months when the temperature is below 0 C. Adults take several months. Temperatures 20 C to 35 C with humidity are most favorable.
In the summer heat the caterpillar migrates deeper into the olive and avoids the effects of the high temperatures. Environmental conditions like 30 C to 35 C temperatures with high humidity are increasing the olive fruit fly attacks. An unusual and unique phenomenon in which the olive tree is susceptible to the attacks, is during the grafting period.
The olive fruit fly damages the olives qualitatively and quantitatively. The infested olives deteriorate and the extracted olive oil is of poor quality.
The adult fruit fly is attracted to sweet nitrogenous substances. Their behavior is used to develop programs for their control. These substances that are used as bait to attract the flies, are protein hydrolysates full of poisoned organophosphate insecticides.
Treatments with chemicals are implemented against the caterpillar by spraying the olive trees with insecticides to destroy the adults, also traps can be hung from the trees, with main target the massive trapping of the fruit fly. Traps are better environmentally.