The olive moth, Prays oleae, is a phytohagous insect that adapts to its host, which is almost certainly an example of insect-plant co-evolution. It produces three generations a year, each one specialised in the exploitation of different parts of the plant. The nutritional value of these “menus” together with other determinants allows the insect a faster or slower rate of development, whichever is necessary for perfect synchronisation with the phenology of the tree.
MORPHOLOGY AND BIOLOGY
The adult is grey with silvery tones. The wingspan is 13-14 mm wide and 6 mm long. The egg is lentil-shaped and flat, measuring 0.5 mm diameter. Recently laid it is a whitish colour, but then turns a yellowish colour when it hatches. The larva can grow to a maximum length of 8 mm. Its colour varies, mainly brown and green, but always in light shades. The chrysalis, which has no specific morphological features, is protected by silks and plants and earthen remains on the ground as well as in the stem, depending on the generation.
The three generations that take place throughout the season are perfectly synchronised with the phenological evolution of the olive tree.
Antophagous generation: In April and May, the adults that come from the previous generation lay the eggs in the closed flower buds but have a strong preference for the calyx.
The neonate larvae enter inside the bud and mainly feed on the anthers and stigma. It pupates on the fertile shoots by protecting itself with the remains of pressed flowers, which are joined together by silk threads. This generation grows much faster than the others, it lasts a month and a half.
Carpophagous generation: The adults that appear from May to June lay their eggs in small fruits, mainly in the calyx. When the larvae are born, they perforate the fruit directly and enter inside the olive before the stone hardens.
They feed on the seed until mid-September when they exit the olive. Then, they pupate in the ground up to the end of October. The new adults lay the eggs on the leaves (October), beginning the phyllophagous generation again.
Phyllophagous generation: The adults lay their eggs on the leaves during October and November; and the newborn larvae remain in interior galleries throughout the winter. Their activity increases in February. They change leaf several times and finally they feed outside on buds and leaves. They mainly pupate on the underside of the leaf, inside a silky cocoon, although they can do the same in a stem or in the ground.
DETECTION AND MONITORING
For the detection and monitoring of Prays oleae, 1 trap per hectare should be placed at the same height as the crops. Traps can also be placed on a specific support. They should be placed before the first generation appears.
The males of this species are mostly captured in order to reduce mating, meaning that the unfertilised females will lay unviable eggs. This greatly reduces the pest population.
For mass trapping, the amount of traps per surface area must be increased, depending on the location and homogeneity of the plots. One trap controls a surface area between 500 and 1.000 m2. This means a density of 10 to 20 traps per hectare.
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PERIOD OF USE
To obtain good control of the Prays oleae it is advisable to combine two methods: detection and monitoring; and mass trapping.
In spring, 1 trap per hectare can be placed for the detection of the pest and the observation of its population levels. With tolerance thresholds established in each area, the moment to adopt control measures, in this case mass trapping, can be later defined.
The tolerance threshold for Prays oleae is very low and varies depending on the area. In general, it is between 7 and 21 captures per trap and per week. For mass trapping, traps should be placed throughout the plots.
Antophagous generation: The damage produced by this generation is very difficult to calculate. A larva can destroy from 20 to 30 flowers but, in an olive tree, for every 100 flowers only 2 or 3 fruits ripen. In addition, the olive tree compensates the loss of flowers with a larger blossom. Only in the case of poor flowering and high population of Prays oleae, could there be an important decrease in production.
Carpophagous generation: It is the most harmful because it causes the fruit to fall. The first fall (June) is very difficult to assess because the tree compensates the loss by increasing the size of the remaining olives. In many cases, during the harvest of the olive, this can be beneficial. However, the second fall (autumn) is very important because the olive has already grown and the tree does not have time to compensate for any losses.
Phyllophagous generation: The adult trees do not produce economic damage. Buds can only be destroyed in plant nurseries and growing trees, which can affect the future of the tree.
FACTORS THAT INFLUENCE THE NUMBER OF TRAPS NEEDED
The pest population, the bordering crops, the level of control required, etc….
One important factor is the size of the crops. In small and irregular crops, a greater number of traps are required than in larger and more uniform plots.
Another important factor is the distance between plots that have the same pest. In these cases, the borders of the plots must be reinforced, so it could be necessary to place up to 20 traps per hectare or even more for mass trapping.
If specialists or farmers use the traps and pheromones correctly, as previously described, especially during the early stages when the adults of the first generation appear, then the effectiveness of this monitoring system is very good and with a very low level of damage. A level of control of more than 95% is very common, especially in large areas of crops.
A limiting factor of this system could be when there are small plots distributed all around and the neighbours have a high level of infestation of this pest.
Despite some important basic rules for the effective monitoring of Prays oleae, farmers or specialists have to find their own system to achieve it. They can experiment with this system, even establishing their own tolerance thresholds.
Corrugated cardboard box of 3.000 units (150 packs of 20 units)
Box size: 0.60×0.40×0.35 m (length x width x height)
Box weight: 9.8 kg.
No. of boxes per pallet: 20.
Pallet size: 1.20×0.80×1.90 m (length x width x height).
Pallet weight: 203 kg.
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