Emergence trap, a new method to survey Limoniscus violaceus (Coleoptera: Elateridae) from hollow trees

The study of insects inhabiting basal hollow trees presents a methodological challenge inducing the fact that there is very little research done on fauna of this habitat. Many endangered saproxylic species only develop in cavities located at ground level. One of the most emblematic species of the kind is the Violet Click Beetle (Limoniscus violaceus), included in Annex II of the UE Habitats Directive. Surveys have been conducted in five Natura 2000 areas using a new method to monitor L. violaceus: the emergence traps. A total of 376 beetle species, including 239 saproxylics, have been identified. Five are considered threatened and are registered on the European Red List of saproxylic beetles and three are included in Annex II of the Habitats Directive. Among 191 trees studied, 33 revealed the presence of L. violaceus. Sampling efforts required to detect at least one specimen have been evaluated. Our results show that sampling a minimum of 20 hollow trees in April and May with emergence traps is recommended to obtain a meaningful survey on the presence of the Violet Click Beetle.