Effects of trap baits and height on stag beetle and flower chafer monitoring: ecological and conservation implications

The implementation of conservation actions requires a reliable assessment of presence and/or abundance of targeted species. This is particularly difficult for rare and elusive species. In this study the use of bottle traps and the effects of two potential baits in relation to height in the trees were tested to detect presence and assess abundance of stag beetles (Lucanidae) and flower chafers (Scarabaeidae, Cetoniinae), an important component of forest biodiversity. The study was carried out in a flood-plain forest of northern Italy. Forty-eight handcrafted traps were assigned to two height categories (1.5-2 m and 10-20 m) and three kinds of bait: (i) red wine, white wine and sugar, (ii) red wine, beer and mashed banana, (iii) no bait, as control. Fieldwork lasted 8 weeks, with 32 surveys, from May to July. Overall, we recorded 399 captures of the following species: Dorcus parallelipipedus, Lucanus cervus, Cetonia aurata, Protaetia speciosissima, P.affinis, P. morio and P. cuprea. Traps baited with red wine, white wine and sugar showed the highest detection probabilities for all the species. A clear preference for the canopy layer (traps between 10 and 20 m high) was shown by all species except for D. parallelipipedus which was mostly captured between 1.5 and 2 m of height. The study period was long enough to improve ecological knowledge on species phenology, but not enough to include the whole phenology for all of them. The method allowed the assessment of population size only for flower chafers as the number of stag beetles captures was too low.