Factors associated with occurrence, potential distribution and conservation of Polyphylla ragusae, an endemic Scarabaeidae (Melolonthinae) from Sicily

Polyphylla ragusae (Coleoptera Scarabaeidae) is an endemic beetle restricted to the island of Sicily (Italy). This species is among the most threatened invertebrates in Italy. Currently, scientific knowledge of the distribution and habitat selection of P. ragusae is scarce, though anecdotal observations suggest that the species is primarily found in intact dune systems associated with river mouths with rich riparian vegetation and reeds. We assembled data between 2012 and 2021on the species' distribution and activity from direct collections and observations of beetles throughout the island. We also included additional distribution data from published literature. Our results showed that: (i) there was a significant skewed sex-ratio in specimens; (ii) there were differences in flying behaviour between the sexes, and (iii) habitat selection was non-random. We also analysed (i) the relationship between the occurrence of P. ragusae and CORINE landcover variables in Sicily and (ii) built a potential distribution map using MAXENT. We showed that the species occurrence was correlated with areas with more permanent freshwater waterbodies and less with those areas with more shrubs and croplands, indicating that P. ragusae could be a habitat specialist. These habitat features are common along coastal areas in Sicily, often linked to relatively unaltered dune environments. The degradation of these habitats is therefore likely to have caused the decline of the species in Sicily. We suggest that P. ragusae should be used as a flag species to attract attention for the protection of Sicilian dune systems.