One of the most harmful pests for olive groves is the olive moth. It is present everywhere in the olive groves, especially in the areas overlooking the sea. This parasite, also known as Prays oleaehas a very complex life cycle, in which several generations are distinguished. It is important to know the differences that exist between one generation and another, in order to understand exactly when to intervene with the methods allowed in organic farming.
Of course, the first thing to do is careful monitoring to check for the presence of the insect on our olives.
In this article we will look at all these different aspects.
Description of the olive moth
There Prays oleae is an insect of the order of Lepidopterafamily of Hyponoumeutides.
Due to its small size as an adult butterfly it is considered a micro-moth, as well as the best known absoluta suit of the tomato.
Attach the olive tree crops, and when fully ripe it looks like a butterfly with a wingspan of about 14 mm. With the wings closed it is long, more or less, 7 mm.
It has a very particular livery, easy to recognize. The color is silvery gray, with evident black spots on the front wings.
Moth eggs
The eggs of this olive moth they are tiny. They measure approximately 0.5mm in diameter and are oval in shape.
Moth larvae
The moth larvae, the ones that cause damage on olives, are 7-8 mm long when fully developed. They are greenish-brown in color, tending towards light.
On the back they have greenish bands, while on the side they have 2 yellowish bands.
The head has a variable color from brown to black. Before reaching full development, the larva goes through 5 growth stages, in which its head gets bigger.
The chrysalis of the moth
Finally, the chrysalises, up to 6 mm long, brown in color and sub-conical in shape.
Life stages of the olive moth
Monophagous insects are those that grow and feed on the damage of a single plant species. The olive moth is a species that belongs to this category. Obviously, the plant affected by this parasite is the olive tree.
The moth turns 3 generations in a yeareach of which completes its cycle on a different vegetative organ.
Here’s what they are:
- First generation antofogaborne by the flowers;
- Second generation carpophagusto the detriment of the fruits;
- Third generation phyllofogawintering on olive leaves.
The adults overwinter at the chrysalis stage and begin to flicker in spring, when the tree differentiates the flower buds.
First generation
At this stage, the moths lay eggs on the calyx of the flower and after 10-15 days the first larvae emerge. These enter the flowers, remove the pollen and, in the last stage of development, penetrate the internal organs. They are very active and attack up to 15 flowers, wrapping them with a thin silk thread. This makes the affected flower very visible.
The first generation larva completes its development in about a month. Then it cryss into the tree’s tissues and flickers after 10-15 days, kicking off the second generation.
Second generation
This generation of olive moth is the most harmful for oil production, as it occurs in the fruit growth phase, putting the olive harvest.
The adult butterflies ovide on the calyx of the small fruits, near the peduncle.
After less than 1 week, the new larvae are born, which penetrate deep into the olive.
Once their development is finished, a further crysalidation takes place, which often takes place inside the olives.
Third generation
In September, the adults of the last generation of olive moth, the wintering one, flicker. These butterflies lay their eggs on the upper side of the leaves, within which they go through the 5 stages of development. This causes considerable erosions on the canopy.
The damage of the moth on olive trees
Damage of the olive moth
There olive moth causes damage can be evaluated differently, depending on the intensity of the infestation. In addition, the damage also varies depending on the generation that does it.
The damage of the first generation
The attack of the generation of antofoga olive tree moth (the one that affects the flowers), varies from a few flowers attached to the field, up to values of up to 90%. It is easy to understand how the extent of the damage is very variable.
The damage of the second generation
The attack of the larvae of the generation of carpophagous olive moth (the one that damages the fruit) are the most feared. This is especially true as they cause the olives to drop early. This happens in two distinct moments:
- from June to July, when the larva enters the fruit;
- and from September to October, when the moth larva becomes crystalline.
In the first phase, it is necessary to understand if the drop is due to the attacks of the moth or to natural thinning. The phenomenon could in fact depend, for example, on high temperatures and long periods of drought.
In the second period, the olives close to harvest fall. In this phase, the concern of the olive grower is high, since it is difficult to intervene with decisive treatments.
The damage of the third generation
The third generation larva, the olive moth phyllofoga (the wintering one that erodes the leaves), causes damage to the vegetation by limiting the photo-synthetic activity. From an operational point of view, it does not raise concerns such as to justify defense interventions. However, as it is easy to guess, it is the basis of future problems.
Natural factors that hinder the development of the olive moth
The olive moth, in its various phases, develops in mild climatic conditions.
In very hot summer seasons, with daytime temperatures always above 30 ° C and high humidity, there is the natural death of eggs and larvae.
The chrysalises, on the other hand, manage to survive even above 40 ° C.
Another natural limiting factor is observed in the carpofoga generation of the olive moth. As mentioned, the small attached olives fall off. With the death of the fruit, however, also the larva inside it perishes.
The predators of the moth that affects the olive tree
There olive moth has numerous natural enemieswhich we can define beneficial insects in the olive grove system. I’m several studies which demonstrate its effectiveness.
Unfortunately, the use of chemical pesticides, so widespread in conventional agriculture, limits the presence of this moth’s natural predators. And this makes their action insufficient.
List of antagonistic insects of the olive moth
Let’s see thelist of antagonistic insects of the olive moth:
- Hymenoptera Clelonus elaphilus And Ageniaspis fuscicollis var. praysincola. They are able to parasitize the eggs of all 3 generations of the moth.
- Hymenoptera Apantheles xantostigma, Elasmus stefani And Itoplectis alternans. They too parasitize a high number of eggs.
- Chrysopid Chrysoperla carnea. It is a predator of moth larvae.
Monitor the olive moth
Chrysalis of Prays oleae
As we have seen for the oil flythe monitoring of the olive moth it can be done thanks to pheromone traps. These traps intercept the males of the species and give us indications on the flight curves of the different generations.
The problem, in the case of our parasite, is that the sex pheromone trap method does not give an exact indication of the total number of the population present. Not having good precision, therefore, this technique cannot be used for mass trapping. In fact, where it has been tested, it has given poor results.
Anyway, pheromone trap like this one it gives us knowledge of the presence of the moth, and therefore it is appropriate to use it.
The monitoring of the moth on olives it can also be done visually, especially in the case of the carpophagous generation.
Fruits can be sampled in two ways:
- evaluating the early drop;
- by transversely cutting a small sample of olives on the tree suspected of being attacked by the moth. This way you can tell if there are eggs or larvae in the olive.
How to prevent olive moth
Unfortunately for prevent olive moth there aren’t many roads to take.
When planting a new olive grove, in an area where we know that the insect is present, we must choose small drupe varieties. The small olives, in fact, make life more difficult for the moth. Furthermore, the attack has less impact on the total number of olives present on the tree.
For soil management, the technique ofgrassing to processing., so as to favor the presence of useful insects.
There olive tree pruning it must not be too intense in areas at risk of attack. This is because, otherwise, the few olives on the tree, in the season following pruning, are exposed to a greater possibility of infestation.
Pruning, therefore, must always be balanced, to meet both the production needs and those of pest defense.
Fighting the olive moth with Bacillus thuringiensis
There fight against olive moth is carried out with the use of bacillus thuringiensisbiological insecticide we have already told you about.
The most effective strains against this insect are:
It is usually not recommended to intervene on the antofoga generation of moth, unless the percentage of infested flowers is not higher than 45%.
It is the carpofoga generation that is the most harmful and against which action must be taken.
The intervention threshold, in this case, is fixed in 15% of the infested fruit. The best time to operate is that of the hatching of the eggs, when the small larvae have not yet entered the fruit.
Once inside, in fact, everything is ineffective, as Bacillus thuringiensis acts only by ingestion.
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