Halyomorpha halys invasion: a new issue for hazelnut crop in northwestern Italy and western Georgia?
Some bug species (Heteroptera: Coreidae and Pentatomidae) are well known as main hazelnut pests, causing fruit alterations with their feeding, evident only on kernels (e.g., superficial whitish to brownish spots), and are highly detrimental to nut quality. Generally, Gonocerus acuteangulatus, Nezara viridula and Palomena prasina are the primary insect pests of hazelnut in several areas, even though the species composition and abundance can change in relation to the geographic area. Recently, the invasive exotic species Halyomorpha halys has also been recorded on this crop, and it has been found to damage nuts throughout the entire period of kernel development as the other hazelnut bugs. Therefore, field surveys were conducted in NW Italy and W Georgia, two important hazelnut-cropping areas, to assess the presence and abundance of the common bug species and the new invasive one, and evaluate the severity of damage at harvest. Monitoring was carried out by plant beating on hazelnut plants, along the borders and in the centre, in five orchards (three in NW Italy, Piedmont region, and two in W Georgia, Samegrelo region), in 2015-2016. In NW Italy, G. acuteangulatus, P. prasina and N. viridula were mainly collected, even if in different amounts, whereas H. halys was found only in 2016, when it represented 3% of total sampled bug specimens. In W Georgia, besides the other three species, H. halys was always sampled, and turned out to be the most abundant species, reaching 70 and 84% of the total collected bugs in 2015 and 2016, respectively. Results on the distribution and abundance of hazelnut bug species in the surveyed orchards are here discussed, as well as the relationship between species composition and damage severity.