Among the insects that attack the olive tree, the olive moth (Prays oleae) – belonging to the order of Lepidoptera and the family Iponomeutidae (not Pyralidae, as erroneously reported) – plays a particularly important role. Also known as “olive moth” in English, this complete species three generational cycles each year: Ant-phagous (on the flowers), carpophagous (on the fruits) and phyllophagous (on the leaves).
The adult has a wingspan of 13 to 14 mm. The forewings are greyish, with silvery reflections and dark spots. Females lay eggs of about 0,5 x 0,4 mm, initially white and then dark. The larvae hatch from the eggs, up to 8 mm long, with a light green body and a red-brown back crossed by irregular lines. The prothorax, also light green, has reddish spots. The pupal stage, about 6 mm long, shows colors that vary from yellow-brown to dark brown.
Biological cycle
Le larvae of the three generationsThey develop on different parts of the plant: the anthophagous generation lays eggs on the flower buds, and the larvae feed on the flowers; in late spring the adults appear, which give rise to the carpophagous generation, whose larvae penetrate the fruit and feed on the seed; at the end of summer, the third generation (phyllophagous) develops from the eggs laid on the leaves, where the larvae dig leaf galleries and overwinter until the following spring.
Population sizes vary significantly depending on climate, agronomic practices, cultivated variety and the presence of natural enemies. Temperatures above 30°C and relative humidity below 50% significantly reduce the survival of eggs and young larvae of the carpophagous generation.
A complex of about 40 species of parasitoids, which mainly attack larvae and pupae of the anthophagous generation, can cause mortality of up to 60%. Among these we can distinguish: egg parasitoids of the genus Trichogramma; and others, such as Ageniaspis fuscicollis e Chelonus eleaphilus, which affect both eggs and larvae.
The eggs of the carpophagous generation are also preyed upon by anthocorids, mirids and chrysopids, among which the most notable are: Chrysoperla carnea. Recent observations also signal the significant presence of ants and mites that prey on the young stages of the Lepidoptera.
The damages
I greater economic damage are caused by the Anthophagous and carpophagous generationsVarieties with high flower production and low fruit set are generally less susceptible to the anthophagous generation.
In Italy, the damage is considered economically significant if the infestation exceeds 40% of the flowers in the oil varieties and 10% in the table varieties. In Portugal, the threshold is lower: 4-6% in high-yield years, and 8-11% in low-yield years, especially for small-fruited varieties. Table cultivars with large fruits are more vulnerable to attacks by the carpophagous generation.
The feeding habits of adults are not yet fully known, but it is believed that they may feed on nectar and honeydew. A study conducted in Portugal (Villa et al., 2017) identified among the most favorable food sources:
the honeydew of saissetia oleae e Euphyllura olivine; spontaneous flowers such as malva sylvestris, Trifolium repens, Conium maculatum. The S. oleae honeydew and the flowers of M. sylvestris have been shown to be particularly beneficial to the survival and reproduction of the insect.
Polyphenols play a crucial role in plant defense against parasites and pathogens. Studies such as that of El Boustani et al. (1998) have highlighted an increase in flavones and phenols in response to Verticillium dahliae infections. Infected leaves show an accumulation of phenolic compounds that could limit the spread of infection. Ilias F. (2017) found that the presence of rutin, a phenolic compound, is associated with resistance to olive green moth.
Effective control of the moth requires careful monitoring of adult flight to determine the optimal time for intervention. According to Caponero (2015), the intervention thresholds are:
– 10-15% of drupes affected for oil cultivars;
– 2-3% for table cultivars.
I Treatments should be carried out after the peak of flight and before the core hardens..
In conventional agriculture, insecticides are used such as cypermethrin, lambda-cyhalothrin, esfenvalerate and spinetoram. Alternatively, the Bacillus thuringiensis var. kurstaki It represents a valid biological option against anthophagous larvae, acting by ingestion.
In the two-year period 2019–2020, experiments were conducted in Three olive groves in Andalusia to evaluate the effectiveness of sexual confusion (Mating Disruption) in controlling the moth throughout all its generations.
Fruit infestation, male captures with pheromone traps and the number of affected inflorescences were compared in treated and untreated plots. The use of one or two aerosol dispensers/ha was also tested.
In both years, the mean number of males caught in traps in plots with mating confusion was significantly lower (>75%) than in controls. reductions of infested fruits they were of the80% in two olive groves, of the 40% in the third.
Installing two dispensers per hectare reduced damage to less than 20%, except in one case, where a 71% reduction was still observed in 2019.
Although most comparisons did not show significant differences between one and two dispensers per hectare in terms of captures and infested fruits, significant differences emerged in the number of affected inflorescences, suggesting comparable performances between the two densities (Ortiz A. et al., 2021).
