Exploring Morphological Structure and VOC Emissions in Olive Fruits: Potential Interactions with Bactrocera oleae Infestation

Giovanni Spinelli ¹, Cosimo Taiti ¹, Elisa Masi ¹, Luciana Renna ¹, Marta Beccaluva ², Stefano Mancuso ³, Giovanni Stefano ²

Department of Agricultural, Food, Environmental and Forestry Sciences and Technologies (DAGRI) University of Florence ¹, Department of Biology, University of Florence ², Department of Agricultural, Food, Environmental and Forestry Sciences and Technologies (DAGRI) University of Florence, Foundation for the Future of Cities (FFC) ³

The olive fruit fly (Bactrocera oleae) represents the most significant threat to olive cultivation. Current pest management methods still largely rely on chemical treatments, which are harmful to the environment and subject to increasingly stringent regulations. However, morphological characteristics such as fruit size, firmness, and cuticle thickness play a crucial role in pest resistance. A thicker cuticle may act as a physical barrier against oviposition, while smaller and firmer fruits have been associated with lower infestation rates. Additionally, olive fruits emit volatile organic compounds (VOCs) that influence the behavior of the olive fruit fly, acting as either attractants or repellents. This study aimed to investigate these factors in relation to B. oleae infestation across different olive cultivars and ripening stages, with the goal of promoting sustainable pest control strategies. Four olive cultivars (Arbequina, Canino, Coratina, Nocellara messinese) were analyzed at two ripening stages: early (August) and advanced (November). Samples were collected from the CREA OFA’s International Olive World Germplasm Bank, an ideal site for studying the insect’s preferences among a diverse range of cultivars. Morphological data and ripening indices were recorded. The degree of infestation by B. oleae was assessed by examining the fruits for insect punctures, categorized into three groups: active, sterile, and dead. Cuticle thickness was evaluated using Nile Red staining, with fruit sections observed under a confocal microscope to obtain data on cuticle thickness and composition. VOCs were analyzed using a Proton Transfer Reaction-Mass Spectrometer (PTR-MS-TOF). Volatile emissions were measured directly from the fruits after simulating insect punctures to identify emission profiles relevant to pest behavior. Larger fruits demonstrated higher levels of infestation but also exhibited a higher proportion of sterile punctures. In contrast, smaller fruits (Arbequina, Canino) showed lower infestation rates. This observation suggests that identifying varieties with small drupes that are nonetheless highly targeted by B. oleae could provide valuable insights into the insect's selection dynamics for oviposition. Nile Red staining revealed that cuticle thickness varies among cultivars and developmental stages. Infested fruits often exhibited thicker cuticles, which likely function as a physical barrier to further infestation, reducing the fruit’s vulnerability to injury. The VOC analysis indicated that while the types of VOCs emitted were not distinct among cultivars, there were significant differences in the quantities and distribution of specific compounds. Some substances appeared to be particularly relevant to the insect's behavioral preferences. These results suggest that fruit size, cuticle characteristics, and VOC emissions collectively influence olive susceptibility to B. oleae. Further studies are needed on a broader range of cultivars with comparable drupe sizes and ripening periods to better identify the plant’s defense mechanisms.

Main author career stage: Master student

Contribution type: Poster

First choice session: 2. Ecology

Second choice session: 3. Biodiversity and global change