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BACTROCERA OLEAE

Biocontrol of the Olive fruit fly

Common name: Olive fruit fly
Scientific name: Bactrocera oleae
Order: Diptera
Affects: Olive trees
Main season: Spring, Summer and Autumn

General information

This species is associated with plants of the Olea genus and in particular to the olive tree. It is found throughout the Mediterranean Basin, South Africa, Canary Islands, India and Western Asia. In the Western hemisphere, it is only found in California. It is considered to be the most damaging pest of olive trees in the regions where it is present, even conditioning the quantity and quality of most crops.

Its attacks tend to increase in wetter and colder areas, with great variability depending on the variety of olives cultivated. It is less noticeable in areas with dry and hot summers.

Morphology and biology

The adult insect is a reddish-grey or orange colour which is highlighted by black spots.

It has transparent, iridescent wings and the lower part of its thorax is yellow. Its eggs are elongated and white. The larva is apodous and also white. The pupa is elongated and has a yellowish colour, that darkens as it grows.

On average, two to three generations can be observed every year, depending on the climate conditions. They usually overwinter in pupal stage which is located underground at little depth, although individuals can be found at all stages of development.

The adults of the first generation appear in March or April and spend some time feeding on sugary substances, such as the honeydew from some Homopterans, until they reach sexual maturity and begin to lay eggs. The female lays her eggs under the skin of the chosen olive. The olive should have the correct level of ripeness and must not be occupied by another egg. It is common for this insect to lay only one egg per olive.

After hatching, the larva feeds on the olive by excavating a small and torturous gallery. Once the larva has finished growing, it pupates inside the fruit near the epidermis.

Flight activity of the Olive fruit fly reaches its highest peaks in July and October. However, there is a greater increase in flight activity during October.

Damages

There are two types of damage caused by the Olive fruit fly: quantitative and qualitative.

Quantitative damage is caused by second stage larvae and especially third stage larvae. They consume an important amount of the olive’s pulp, which as a result, reduces the quality of the oil. Part of the production is lost because the olives that have been attacked fall prematurely from the tree. In olives used to produce oil, damage caused by the bite marks and first stage larvae do not have a significant economic impact. However, for table olives, the bite marks depreciate the value of the product.

However, for table olives, the bite marks depreciate the value of the product.

In terms of quality, it should be considered that olives with a high percentage of this pest produce oil of poorer quality, particularly if they are third stage larvae. The oil extracted from these olives may have an acidity level (expressed in oleic acid) from 2% to 10% depending on the percentage of infestation. It is also less possible to preserve these oils because they contain a higher percentage of peroxide.

Third stage larva

Third stage larva
© Giancarlo Dessi

Olive with a fresh bite mark

Olive with a fresh bite mark
of Dacus (Bactrocera) oleae

Exit holes created by the Olive fruit fly

Exit holes created by the Olive fruit fly
© Giancarlo Dessi

Due to the attacks from this fly, secondary qualitative damage also occurs. The remains left behind by the larva inside the fruit, produce fungi that deteriorate the quality of the oil extracted. This secondary damage in quality is more obvious in oils extracted from olives that have been attacked, then picked from the ground or they may also have been stored for many days before being crushed in the olive press.

Detection and monitoring

1 to 2 traps per hectare should be placed depending on the location and uniformity of the plots.

The traps should be installed 3 months before harvesting, on the south side of the olive trees at 1.5 to 2 metres high.

Mass trapping

10 to 20 traps per hectare should be placed depending on the location and uniformity of the plots. One trap controls an area of 500 m² to 1.000 m².

The traps should be installed as soon as there are captures and 3 months before harvesting. The traps should be placed on the south side of the olive trees at 1.5 to 2 metres high.

On the borders of the plots, it will be necessary to set a barrier of traps separated 10 to 15 metres apart from each other.

Period of use

To obtain good control of the Olive fruit fly, it is advisable to combine two methods: detection and monitoring; and mass trapping.

At the beginning of summer, 1 trap per hectare should be placed to detect the pest and observe its population levels. Through tolerance thresholds established in each area, the moment to adopt control measures is later defined, in this case mass trapping.

The tolerance threshold for Dacus (Bactrocera) oleae is very low and varies depending on the area. In general, there are between 1 and 5 captures per trap, per day.

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