Innovative Research: Use of Micro-Computed Tomography to Study Pest Damage in Olives
A recent study published in the journal Scientific Reports (Nature), conducted by Professors Javier Alba-Tercedor and Francisca Ruano from the Department of Zoology at the University of Granada, has revealed surprising findings on the damage caused to olive fruits by the olive fly, the olive moth, and the shield. For the first time, the innovative technique of micro-computed tomography (micro-CT) was applied in this study. This technology has enabled a three-dimensional reconstruction of the internal damage caused by these insects, including oviposition marks, entry and exit galleries, and cavities generated by fungal infections.
In the case of the olive fly, the researchers managed to completely map the galleries, differentiating them by color according to the size of the larval stages. While feeding, the larvae create a «rosary» pattern in the tunnels they excavate, indicating their consumption of olive pulp.
On the other hand, the study on the olive moth confirmed that larvae feed exclusively on olive pits, leaving the pulp intact. Additionally, a fascinating evolutionary adaptation was discovered: the larvae construct zigzag entry galleries, making it difficult for parasitoids that might threaten them to attack.
Introduction: The Importance of Olive Production in Mediterranean Countries
Olive production is a fundamental pillar of the economy in Mediterranean countries, where some of the best olive oils in the world are produced. This sector not only provides employment to thousands of people but is also a symbol of the region’s culture and gastronomy. However, olive trees face serious challenges due to various pests that threaten the quality and quantity of olive tree production. Among these pests, the olive fly (Bactrocera oleae), the olive moth (Prays oleae), and the olive fruit rot (little shield), caused by fungi transmitted by the cecidomyiid fly (Lasioptera berlesiana), which is an active consumer of olive fly eggs, stand out in our region. These pests reduce olive production and affect oil quality.
Observations on the Olive Fly and Olive Moth
Although it has been previously noted that the olive fly produces a single puncture per olive, it has been observed that this can increase in situations of low yield and fruit scarcity. In the studied olive fruit, five oviposition punctures were detected, of which only three continued with galleries and two reached the adult stage (two pupal skins). In recent years, there has been a significant decrease in crop yields in some areas, attributed to drought caused by climate change, which justifies the high infestation rate.
Some oviposition punctures do not correspond to laid eggs, as females with immature ovaries also attempt to oviposit. Many authors refer to these as live, non-live, or false punctures, as they may be due to undeveloped eggs or a puncture without egg laying. In our study, some punctures in fruits infested by B. oleae must have been sterile, as no gallery developed. Additionally, an egg mortality rate of 2.6%–16.6% was reported. Some of these damaged eggs may have been caused by L. berlesiana. However, in this study, fruits affected by L. berlesiana did not show remnants of B. oleae galleries, excrement, or exuviae. This means that the destruction of the olive fly egg should occur almost immediately after oviposition.
Regarding the damage caused by B. oleae to olives, a concave external necrotic depression was observed that was not directly linked to the pupal chamber or feeding galleries. This finding suggests that the depression was caused by a high accumulation of secondary metabolites around the pupal galleries, and not by fungal proliferation, as previously suggested.
A single short external gallery was found in the fruits attacked by olive moths. This gallery exhibits alternating angles forming a zigzag tunnel, which may hinder some parasitoids’ access to the larvae. P. oleae individuals use the same gallery to enter and exit the olive seed, thereby enlarging the exit gallery and causing the fruit to fall. In any case, the larva remained exclusively in the olive pit, revealing that the pulp was not affected and that the entire internal part of the pit was consumed.
In the study of olive fruit rot, in addition to the evidence of fungal filaments (hyphae) and reproductive organs, two oviposition cavities were observed near the external opening, corresponding to B. oleae (the larger one) and the smaller one to L. berlesiana. Therefore, a single external opening should correspond to the exit hole of L. berlesiana larvae, which immediately after leaving the olive fruit, pupate in the soil.
In conclusion, this study revealed the effects of pests inside olives in a way never observed before. It provides not only high-resolution 3D images of great beauty and provides supplementary videos that will serve as valuable tools for future research and educational resources. The findings highlight the importance of micro-CT in understanding pest-crop interactions, opening new avenues for the protection of olive trees and olive oil production.
Reference:
Alba-Tercedor, J. & Ruano, F. Use of micro-computed tomography to monitor olive fruit damage caused by three insect pests. Scientific Reports 14, 1–10 (2024). https://www.nature.com/articles/s41598-024-72029-3
PLATES
VIDEOS
1.- Observing the galleries of the olive fruit fly Bactrocera oleae inside the olive using micro-CT.
https://www.youtube.com/watch?v=NEeBN35Ltg8
2.- Microtomographic study of an olive with a gallery of the olive moth - Prays oleae (Bernard, 1788).
https://www.youtube.com/watch?v=2r_1TIRBFwQ
3.- Micro-CT study of the destructive effects of the olive fruit rot shield fungal disease in the olives.
https://www.youtube.com/watch?v=TDWH86wfs1A
Contact:
Javier Alba-Tercedor
Emeritus Professor
Department of Zoology
Faculty of Sciences
University of Granada (Spain)
Email: @email
Francisca Ruano
Department of Zoology
Faculty of Sciences
University of Granada (Spain)
Email: @email
