Impact of Halyomorpha halys (Hemiptera: Pentatomidae) on Persian walnut in northern Italy

The brown marmorated stink bug, Halyomorpha halys (Hemiptera: Pentatomidae), is a highly polyphagous agricultural pest resident in Italy since 2012, where it has become a major pest on many crops. The presence of this pest was frequently observed in Persian walnut Juglans regia L. orchard in northern Italy, but little is known on its impact on this crop. Here, we conducted a field study in three walnut orchards northern Italy to investigate H. halys seasonal population dynamics and assess its impact on walnut production. For damage assessment, insect-proof net cages were installed, including J. regia branches with nuts after fruit set. Halyomorpha halys was detected in the orchards throughout the season, and the highest numbers were observed in June. The presence of H. halys juveniles was high in the lower part of the plant, while adults were more abundant in the higher part. Nut quality decreased following H. halys infestation: overall, cages infested by H. halys showed lighter nuts compared to the zero-infestation treatment, and more damaged nuts (both pericarp and seed lesions) were detected in infested cages. In addition, dropped nuts were more abundant in cages with H. halys adults. The results obtained in this work suggest that H. halys can exhibit considerable damage potential for Persian walnut production and the definition of effective management practices on this crop are required.