Monitoring the saproxylic longhorn beetle Morimus asper: investigating season, time of the day, dead wood characteristics and odour traps

Monitoring of rare or localized saproxylic species is essential for assessing species extinction risk and to investigate the ecological integrity of forests. Morimus asper (Sulzer, 1776) (Coleoptera, Cerambycidae) is a longhorn beetle for which many aspects of its biology are still unknown and this hampers the development of a standard monitoring protocol. Here we investigated two different systems to attract M. asper in the Reserve Bosco della Fontana (Italy): freshly cut log piles (FCLPs) and pitfall traps baited with selected chemical compounds. The FCLPs were composed from logs of two tree species (Quercus robur L. or Carpinus betulus L.) utilizing wood of three diameter classes (small: 5-12 cm; medium: 13-30 cm; large: 31-60 cm). The occurrence and the detection of M. asper varied during the season and during the time of the day. M. asper was more common in the first half of the season and was more frequently detected at 20:00. Occupancy models did not show a clear influence of log diameter and tree species on species occupancy. In contrast, when analysing the abundance data, a significantly higher number of individuals was intercepted on FCLPs made from Q. robur and on those with a diameter above 13 cm. The baited pitfall traps did not catch any M. asper, even though some of the substances tested are known to attract other species belonging to the same subfamily (Lamiinae).