Detecting bug damage on hazelnut

Insect species that belong to Coreidae and Pentatomidae families in the Hemiptera order are responsible for severe damage to hazelnut, causing alterations in qualitative traits of kernels during their feeding. Currently, the most harmful species on hazelnut in Italy are the invasive brown marmorated stink bug, Halyomorpha halys, which has recently colonized many hazelnut production areas, and the native box bug Gonocerus acuteangulatus. However, studies on the correlation between numbers of G. acuteangulatus sampled in the hazelnut orchards and numbers of corked kernels, as well as on characteristics of corked kernels, are still scarce. Therefore, the injury of G. acuteangulatus, in terms of damaged kernels per individual and alterations of kernel characteristics, was assessed by caging single G. acuteangulatus on hazelnut branches. The potential suitability of an electronic nose, texture analysis and sensory analysis for discerning between undamaged and damaged kernels was evaluated. The electronic nose was also tested to distinguish kernels damaged by different bug species. The damage rate caused by G. acuteangulatus was confirmed to be still unpredictable, due to the high variability between individuals, some of which damaged all the nuts inside the cage and others not even one. This variability may be due to behavioral or physiological factors (e.g., salivary enzyme characteristics) which deserve further investigation. Damaged and undamaged hazelnuts can be discriminated with all the techniques proposed. In particular, the roasting process was very important in the sensory analysis, and after roasting, damaged hazelnut kernels differed greatly from undamaged ones. In the texture analysis, the hardness and Joung module values were higher for undamaged hazelnuts. The electronic nose was able to discern between undamaged and damaged kernels, and between kernels damaged by different species. Therefore, after an appropriate training, it could be used both in the field to monitor the presence of bug species and in the storehouse to detect damaged hazelnuts.