Social wasp trapping in north west Italy: comparison of different bait-traps and first detection of Vespa velutina.

Twelve bait-traps were tested and compared in order to find the best lure for studying social wasp populations in North West Italy. Polistes associus Kohl, Polistes dominula (Christ), Polistes gallicus (L.), Polistes nimpha (Christ), Vespa crabro L., Vespa velutina Lepeletier, Vespula germanica (F.), Vespula vulgaris (L.), and Dolichovespula media (Retzius) were trapped for a total of 5,077 specimens in the period 2007-2012. V. velutina was captured at Loano (Liguria) for the first time in Italy by means of a yellow cap trap filled with beer. V. crabro, V. germanica and V. vulgaris were the most abundant species in the social wasp communities studied. Beer in clear, colourless and transparent, 1.5 l polyethylene bottles with yellow and white coloured caps was a good bait-trap combinations for all social wasp species, while it trapped only some Bombus terrestris (L.) specimens. A white cap trap filled with commercial mint syrup solution was a good combination for trapping Bombus argillaceus (Scopoli) and a yellow cap trap filled with a solution of vinegar, sugar and honey was the best combination for trapping Apis mellifera L.