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Type of thesis
Dasineura oleae (Angelini, 1831): damage and chemical ecology in a tritrophic context
Scientific disciplinary sector
Istituto di Scienze della Vita - AGROBIOSCIENCES
relatore PETACCHI, RUGGERO
- cuticular hydrocarbons
- Dasineura oleae
- Olea europaea
Exam session start date
Cecidomyiid outbreaks generally last few years, that are preceded and followed by long periods of latency. During the outbreak, the severity of midge attacks may involve crops production, interfering with yield quantity and quality. However, knowing the causes of this phenomenon is generally very complicated, because except during the period of strong infestation, the relations among midge, host plant, and natural enemies are not much investigated. This research focuses on the relationship between Dasineura oleae (Diptera: Cecidomyiidae) and its unique host, Olea europaea, in a tritrophic scenario. Dasineura oleae, known as the olive leaf gall midge, feeds on tender leaflets at larval stages causing malformation and swellings and complete tree defoliation when the infestation is strong. In this Ph.D. thesis, the damage caused by the midge has been studied from different points of view, starting from the origin of the gall-inducing stimulus. As a consequence of the larval feeding action, the olive leaves showed modifications of the leaf blade shape, that became 6-fold greater because of structural alterations of the spongy parenchymal tissue. In turn, damages on leaf physiology, such as minor efficacy concerning some photosynthetic parameters, were recorded (stomatal conductance (−28%) and net photosynthesis (−35%)). Parenchymal alteration may have a role in inducing plant defense response, as the emission of herbivore-induced plant volatiles (HIPVs), that play an important role in the recruitment of herbivore natural enemies. In this thesis, the first characterization of HIPVs released from infested olive leaves is proposed. A blend of 12 volatiles was emitted from olive trees infested by D. oleae. Following the insect attack, the emission amount of some volatiles increased significantly (germacrene-D, (E,E)-α-farnesene, and (Z,E)-α-farnesene, α-copaene, DMNT, (E)-β-guaiene and heptadecane), while other HIPVs were not present in control plants and appeared only after the infestation (β-copaene, β-ocimene, cosmene, unknown 1 and unknown 3). This dissertation aims to improve the knowledge of the relationship between D. oleae and its natural enemies, in order to lay the foundation for eco-friendly control methods. Furthermore, since insect cuticular hydrocarbons (CHCs) can be involved in chemical communication, D. oleae cuticular extracts were investigated as the first work on a cecidomyiid. Dasineura oleae males and females at different ages from emergence (0-12 h; 12-24 h; 24-36 h) and distinct mating conditions (virgin and mated) were considered. A total of 49 compounds were detected, and among them, 18 compounds showed significant differences between groups, inducing to suppose a potential role in intraspecific communication. Even if further behavioral tests are required to assign ecological roles both to HIPVs and cuticular extracts, the obtained preliminary results encourage new outlooks for the Integrated Pest Management (IPM) of D. oleae.
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