Patterns of Vespa velutina invasion in Portugal using crowdsourced data

Abstract

Abstract The invasive yellow‐legged hornet (Vespa velutina) was first detected in mainland Portugal in September 2011. The lack of information regarding the processes of species spread has hampered the development of adequate measures to mitigate the potential impact of this invasive predator. Crowdsourced data, i.e., information opportunistically reported by citizens, can facilitate the collection of numerous species occurrence records over large spatial scales, which can be valuable to understand the expansion of invasive species. Here, using validated crowdsourced data on the precise location of 49 013 nests, we: (i) update information regarding V. velutina distribution in Portugal; (ii) estimate the species expansion rate; and (iii) analyse the patterns of nests distribution at national and local scales. The species is currently distributed over an area of approximately 57 000 km2, which corresponds to 62% of mainland Portugal. We estimated an average rate of 37.4 ± 13.2 km/year for V. velutina expansion. Vespa velutina nests presented an aggregated distribution and nest density at the urban local‐scale was estimated in 5.4 ± 3.3 nests/km2. The observed decrease in the nearest‐neighbour nest distance over the years suggests that the density of nests has not reached its limit. We advocate that the development of a cheap and rapid method for nest detection and the study of fine‐scale mechanisms leading to V. velutina dispersal are important steps to identify colonisation pathways and plan management approaches aiming to halt species spread and impact in apiaries.