Citizen science and early detection of invasive species: phenology of first occurrences of Halyomorpha halys in Southern Europe

Early detection of invasive alien species and the ability to track their spread are critical for undertaking appropriate management decisions. Citizen science surveys are potentially valuable tools for quickly obtaining information on biodiversity and species distributions. The Asian brown marmorated stink bug, Halyomorpha halys, is an invasive pest of agricultural crops and a dwelling nuisance. Halyomorpha halys was first recorded in Italy in 2012 in Emilia Romagna, one of the most important fruit producing regions of Europe. To rapidly obtain data on its distribution in the newly invaded area, a survey that combined citizen science and active search was set up using multimedia channels. Data concerning when, where and how the bugs were spotted were collected, together with photographs and specimens. The survey detected established breeding populations in different areas of Northern Italy and Southern Switzerland, indicating a potentially high risk for crop damage that extends beyond the territories of first detection. Furthermore, new data on H. halys phenology, host plants, voltinism and behaviour were obtained. The importance of citizen science in early detection of introduced pest species is highlighted. This paper also provides a picture-based key to recognize H. halys from similar pentatomids in the world.