Vespa velutina Lepeletier (Hymenoptera Vespidae): a first assessment two years after its arrival in Italy

Vespa velutina nigrithorax is an invasive alien social wasp species known as harmful for its effective prey pressure on Apis mellifera. The aim of this work was to assess the presence of V. v. nigrithorax two years after the first capture in North West Italy, to evaluate its relative abundance and dominance in the social wasp communities sampled by means of bait-traps, and to describe some biological and nesting activity. V. v. nigrithorax was trapped or observed in 4 localities in Piedmont and in 10 localities in Liguria, from 20 m a.s.l. up to 1100 m a.s.l. Five embryo and eight developed nests were counted in eight different localities. V. v. nigrithorax was a subdominant species in the social wasp community trapped at Giardini Hanbury (Liguria). At present, V. v. nigrithorax is spreading in North West of Italy at a rate of 10-20 Km per year and measures for its spatial containment should be urgently implemented .