Metabolomic characterization of stink bug–damaged hazelnuts: Cultivar-specific defense responses and associated chemical signatures

Stink bug feeding severely compromises hazelnut quality, causing economic losses and food waste. To elucidate the biochemical responses, four cultivars grown under identical conditions in Southern Italy were analyzed using untargeted and targeted metabolomics. Kernels were classified as healthy or cimiciato to identify metabolic alterations associated with insect feeding. Damaged nuts showed higher levels of diarylheptanoids, whereas healthy kernels contained more flavonoids, including catechin and myricitrin, with cultivar-dependent differences. Lipid-derived metabolites including oxylipins, free fatty acids, and fungal glycolipids were also altered. The Mortarella cultivar exhibited a distinctive profile, with limited accumulation of bitter compounds and higher lipid content, suggesting alternative defense responses. Because all cultivars were grown under the same conditions, these differences likely reflect genetic factors. Overall, stink bug damage triggers complex, cultivar-dependent metabolic reprogramming and metabolomic signatures consistent with a possible microbial contribution, offering insights for breeding and quality monitoring strategies.