de Benedetta, Flavia (2025) Interactions between Stinkbug damage and Fruit Phenology in Hazelnut (Corylus avellana L.): Effects on kernel composition and quality and insights for sustainable pest management. [Tesi di dottorato]

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Abstract

Stink bug damage to hazelnuts (Corylus avellana L.) has been a persistent issue in orchards worldwide. While several species, such as Gonocerus acuteangulatus, Nezara viridula, and Palomena prasina, contribute to this damage, Halyomorpha halys, the invasive brown marmorated stink bug has proven particularly harmful. Stink bug feeding activity causes various types of damage (i.e. blank, shriveled, and cimiciato) depending on the developmental stage of fruits. Cimiciato damage results from a complex process involving mechanical injury from the insect's piercing-sucking mouthparts and the injection of salivary enzymes during feeding activity. This initial damage triggers a cascade of effects, including tissue disruption, oxidative stress, lipid alterations, reduced phytosterol content, and activation of plant defense mechanisms. These changes make the kernels more susceptible to rancidity and fungal infections. The cimiciato defect negatively affects hazelnut quality, manifesting as off-flavors, aesthetic imperfections, and physiological symptoms significantly reducing the crop's commercial value. The biochemical processes triggered after insect feeding remain largely unknown, and a detailed characterization of the cimiciato defect is necessary to enhance pest management and understanding of the metabolic processes involved. This study seeks to explore these aspects in greater depth. This thesis is divided into two main chapters. The first chapter analyses the relationship between the phenology of two hazelnut cultivars (San Giovanni and Tonda Romana) and the incidence of stinkbug damage in Italian orchards managed either with integrated pest management (IPM) or without treatments. Specifically, the study involved detailed monitoring of stink bug populations, fruit development stages, and hazelnut damage. Results showed that untreated orchards experienced a significantly higher incidence of cimiciato than treated orchards. Furthermore, the San Giovanni cultivar suffered greater damage than Tonda Romana, particularly in untreated plots. This greater susceptibility is likely explained by its earlier phenological development with critical stages of kernel development coinciding with the peak feeding activity of H. halys, leading to a higher incidence of cimiciato. IPM treatments were only partially effective in reducing cimiciato incidence, indicating that phenological timing is critical for optimizing treatment strategies. The second chapter provide an extensive evaluation H. halys feeding on hazelnuts over two growing seasons (2022 and 2023) in Italy, utilizing cage experimentation. This assessment considered the climatic conditions and phenological development of four hazelnut cultivars (San Giovanni, Tonda Romana, Tonda di Giffoni, and Mortarella) and, subsequently, the metabolomic and sensory impact of the pest on the final product. The results highlighted that the extent and severity of damage vary with the developmental stage of the fruit. Early feeding causes blank nuts and embryo abortion, mid-stage feeding leads to shriveled nuts, and mid-to-late-stage feeding results in cimiciato of varying severity (brown, white-brown, and white spots). Damage occurred after phenological stage 6.4 led to white spots, which were less detrimental to flavor and overall sensory quality. Metabolomic analysis revealed that damaged nuts exhibit elevated levels of specific secondary metabolites, such as Carpinontriol B and Giffonin P, which can serve as damage biomarkers. Sensory analysis indicated that hazelnuts with brown and white-brown spots had the lowest but did not perceive a significant difference between healthy nuts and those with white spots. This suggests that while some late-stage damage has less impact on marketability, early interventions are crucial for maintaining high-quality produce. In conclusion, this research underscores the importance of cultivar-specific responses and phenological timing in managing stink bug damage. Targeted pest control strategies, focusing on early and mid-stage fruit development, can significantly reduce the impact of stink bug feeding on hazelnut quality. The findings suggest that chemical treatments applied after phenological stage 6.4 may be unnecessary, offering valuable insights for more sustainable pest management practices in hazelnut cultivation.

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