[Thesis defence] 16/12/2025 – Louna Rizzi: «Effect of the introduction and management of service plants on volatile organic compound emissions and aphid control in fruit growing» (UR PSH)

Ms Louna RIZZI will publicly defend her thesis entitled: «Effect of the introduction and management of service plants on volatile organic compound emissions and aphid control in fruit growing», supervised by Ms Hélène GAUTIER, on Tuesday 16 December 2025.

Laboratory

UR1115 – Research Unit for Horticultural Plants and Cultivation Systems

Composition of the jury

Mrs Hélène GAUTIER	Avignon University	Thesis supervisor
Ms Anne-Marie CORTESERO	University of Rennes	Rapporteur
Mr Arnaud AMELINE	Picardy Jules Verne University	Rapporteur
Mrs Blanche COLLARD	AgroParisTech	Examiner

Summary

Reducing pesticide use is a major challenge for the sustainability of the arboriculture sector. Among the agroecological levers explored, the introduction of service plants (SPs) represents a promising alternative for regulating populations of green apple aphids (Dysaphis plantaginea) in apple orchards. Some SPs emit volatile organic compounds (VOCs) that can act directly on aphids (bottom-up effects) or indirectly by recruiting their natural enemies (NEs) (top-down effects). This thesis aimed to identify PdS species that are effective in limiting D. plantaginea by combining these two mechanisms, and to assess the extent to which certain cultural practices can amplify their effects. To answer these questions, experiments were conducted in orchards, where different PdS, planted in pots or directly at the foot of trees, and their effects were monitored in spring and autumn. The populations of D. plantaginea and their associated ENs were counted, and the VOCs emitted by the PdS were characterised at different seasons and at different heights in the canopy. At the same time, two cultivation practices, reduction of nitrogen fertilisation and application of UV-C flashes, were applied in a greenhouse on Ocimum basilicum to assess their ability to increase its VOC emissions and their direct effects on the performance of D. plantaginea and Myzus persicae. The results show variable effects depending on the species, year and season. Tagetes patula appears to be most effective in spring, with early attraction of hoverflies and a reduction in the lifespan of D. plantaginea colonies. O. basilicum may have a repellent effect on aphids in autumn during their return flight. Foeniculum vulgare acts as a bank plant at the flowering stage, but too late to effectively regulate colonies, and Mentha × piperita has a delayed phenological cycle that limits its effectiveness. Under controlled conditions, a period of reduced nitrogen fertilisation increased terpene emissions from O. basilicum, reduced aphid fertility and altered their feeding behaviour, with UV-C flashes having more transient effects. This work shows that PdS alone does not provide sufficient control, but combining it with nitrogen restriction offers promising potential. Longer-term monitoring of these combinations in orchards will be necessary to confirm these effects and guide the choice of practices to be implemented. In the future, the use of VOC diffusers could make it possible to deliver effective semiochemical mixtures at key times (early spring and autumn return flight), which would facilitate the development of these chemical ecology practices in orchards.

Keywords : service plants, arboriculture, aphids, olfactory landscape, beneficial insects, agronomic levers