Distribution patterns and population analysis of threatened longhorn beetles in forest habitats of central Italy

Abstract

Morimus asper and Rosalia alpina are two saproxylophagous longhorn beetles associated to mature broadleaf forests. Both are threatened by local fragmentation and micro-habitat loss due to dead wood removal by forest management practice. Our two years mark-recapture study, revealed new information on population dynamics and habitat preference of M. asper and R. alpina in different beech forests of central Italy Dispersal was recorded in few individuals for both species. The sampling method performed, allowed to get population size estimates for the two species. Both species showed preference for old huge trees in a medium decay class. M. asper proved to be sensitive to temperature effect and it resulted to prefer lying dead trees, coarse woody debris and high canopy closure in the surroundings. Sun-exposed huge trees resulted to be preferred plants for R. alpina and for oviposition of M. asper. Probably, for M. asper the standing dying trees, still owning a part of tree foliage, provide a good compromise between larval development in sunexposed parts and adult activity in shady parts. “Key trees” for population viability of the two species were identified in the study areas. Forest management practices should promote the maintenance of old and huge trees as “stepping stones” to preserve the habitat connectivity and favour genetic flow in both the species. Overwintering ability was observed for M. asper adults, both males and females, with a very long lifespan (282-409 days). Sexual dimorphism in M. asper was detected in several morphological traits, and the scaling relationship between antennal length and body size divided the male population into two groups, smaller and larger males, which showed different mating frequencies. Regarding R. alpina, the computer-aided photographic identification resulted a reliable and less invasive capture-mark-recapture method, and we provided suggestion to standardize and facilitate the procedure.