Using odour traps for population monitoring and dispersal analysis of the threatened saproxylic beetles Osmoderma eremita and Elater ferrugineus in central Italy

Pheromone-based monitoring could be a very efficient method to assess the conservation status of rare and elusive insect species, but there are still few studies for which pheromone traps have been used to obtain information on presence, abundance, phenology and movements of such insects. We performed a mark-recapture study of two threatened saproxylic beetles, Osmoderma eremita (Scarabaeidae) and its predator Elater ferrugineus (Elateridae), in two beech forests of central Italy using pheromone baited window traps and unbaited pitfall traps. Two lures were used: (1) the male-produced sex pheromone of O. eremita (racemic γ-decalactone) to attract females of both species, and (2) the female-produced sex pheromone of E. ferrugineus (7-methyloctyl (Z)-4-decenoate), to attract conspecific males. In total, 13 O. eremita and 1,247 E. ferrugineus individuals were trapped. For E. ferrugineus, males were detected earlier than females, and 7-methyloctyl (Z)-4-decenoate was much more efficient lure compared to racemic γ-decalactone in detecting its presence. The population size at the two sites were estimated to 520 and 1,369 individuals, respectively. Our model suggests a sampling effort of ten traps checked for 3 days being sufficient to detect the presence of E. ferrugineus at a given site. The distribution of dispersal distances for the predator was best described by the negative exponential function with 1 % of the individuals dispersing farther than 1,600 m from their natal site. In contrast to studies on these beetles in Northern Europe, the activity pattern of the two beetle species was not influenced by variation in temperature during the season