Relationship between tree-related microhabitats and the captures obtained using different trap methods for large threatened saproxylic beetles

Osmoderma eremita and Cerambyx cerdo are saproxylic beetle species, included in the IUCN Red List and inthe EU/92 Habitats Directive. Their occurrence has been recorded, through appropriate traps, in several localitiesin Italy, including urban and peri-urban parks, mostly associated with veteran trees.In this study, traps were tested over 17 veteran oak trees in the Castelporziano Presidential Estate (Latium,Rome province, central Italy) and the abundance of sampled saproxylic beetles was related to the growing stockvolume (GSV) and the abundance of microhabitats. Moreover, we compared three different trapping methods: atrap designed to monitor C. cerdo (CC), and two traps designed for monitoring O. eremita, i.e., the Black CrossWindow Trap (BCWT) and the Black Bottle Traps (BBT).We found that larger trees hosted a great variety of microhabitats, in particular cavities, which abundance wascorrelated with the number of specimens sampled, especially O. eremita species. Both classic traps (i.e., CC trapsand BCWT) and the herein-introduced BBT variants were effective for capturing large saproxylic beetles.In this work, we underline the importance of the preservation of veteran trees to the occurrence of threatenedsaproxylic beetles, and we contributed to (i) extending general knowledge of the habitat preferences of saproxylicbeetles and (ii) improving new cost-effective trapping system variants.