Dacos (Dacus olea Cmel.) is the most harmful insect for the olive tree. It attacks domestic and wild olive trees. In places where the fructification is late and there are not wild olive trees, the spreading of the insect is limited.
When the tree gets attacked, the production and the quality of the olive oil and table olives, decrease significantly. Sometimes when the olives remain on the olive trees, because either their picking is difficult, or there are varieties of olives with early or late fructification, the growth of the insect is favorable, because of the existence of the olive fruit for longer period.
In the Southern and warmer places of Greece, the attacks start when the olives start to develop, about June-July. In July and August the attacks lower because of the high temperatures and low atmospheric moisture. They start increasing again when the time of the picking of the olives is approaching. The ideal temperatures for the growth of the Dacos are 24C and 28C.
The female of Dacos is a small fly which lays its eggs on the olive. The table olives are the ones which are getting attacked first. The insect opens a small hole on the olive and lays an egg in it. In about 3-4 days, depending on the temperature, the eggs are hutching and the caterpillars are getting fed from the olive flesh until their complete growth that takes about a month.
In favorable weather conditions, the Dacos can generate up to 7 times a year. Hot weather and drought effects negatively its growth.
The caterpillars of the Dacos have their enemies also, which are other insects. The Prolasioptera beriesiana is a parasite that destroys a big part of the Dacos population.
To fight this insect is very costly and heavy duty insecticides are used, which are destroying the caterpillar and the insect. The spraying of the olive trees starts from June and can continue into September and October. They should stop a month before the picking, because that’s how long the insectisides stay on the olive tree. The spraying should start from the ground, because with the aero-spraying, it is difficult to control where the liquid is going and it is possible to damage people and honey bees.
Another way to fight this insect is with decoys. Bottles hung from the olive trees filled with insecticides, attract the insect with a sweet essence, like molasses. This is a safer way.
The chemical fighting against Dacos has unfavorable results for the environment, because the insecticides contaminate it, kill useful insects and poison animals and water streams.
There is a safe method for the fighting of this insect and its offered by Biotechnology. This method is based on the fact that the insects, to respond to their daily needs and the deposit of their eggs, they are taking signal from chemical essences, produced by the insects of the opposite sex, or the environment.
For the fight against Dacos with this method, traps are made from plywood, are hanged from the olive trees. These traps are soaked with insecticides and sticky substances, so the insects when they get near the trap, they stick and die on it.