Spread of the invasive yellow-legged hornet Vespa velutina (Hymenoptera: Vespidae) in Italy

The yellow-legged hornet Vespa velutina Lepeletier 1836, accidentally introduced into France in 2004, is rapidly colonizing other European countries. In Italy the species is spreading throughout the northwest part of the country. Setting up management plans for controlling invasive alien species requires an understanding of the spread modalities and distribution range of the species, information currently not available for the yellow-legged hornet in Italy. The aims of this work are to reconstruct the spread of the yellow-legged hornet from its first arrival in the country, evaluating its distribution range and spread modalities. The area occupied by the species increased from 205 km2 in 2013 to 930 km2 in 2015. In 2015 the frontline of the species was at 55 km along the coast from the French border, with a linear spread of 18.3 ± 3.3 km/year. A human-mediated dispersion could be recognized in different occasions. A cluster analysis of the range allowed the identification of 17 core areas used by the species, with a mean nest density of 2.9–3.5 nests/km2. These details are fundamental to improve control plans and to establish an early warning and rapid response system for the yellow-legged hornet in Italy and, therefore, setup an effective management plan for the species.