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

Abstract:
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 c-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 c-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.