Distribution of a residual population of the Dytiscid Graphoderus bilineatus (de Geer, 1774) in the Grande Caricaie nature reserves, Switzerland

Currently, the distribution of diving beetles in Switzerland is poorly known making it difficult to determine conservation priorities for species with small and/or declining populations. In order to establish conservation priorities, in 2018, we surveyed diving beetles of the genus Gmphoderus in the Grande Caricaie reserves with special consideration for the Red Listed G. bilineatus. While G. bilineatus and G. cinereus showed high habitat niche overlap, the distribution of G. bilineatus was limited to mainly one of the eight reserves. When comparing our results to available historical data, the habitat of G. bilineatus has likely diminished during the last 40 years. Our study provides the first comprehensive documentation of the distribution of Graphoderus species in the Grande Caricaie. We further highlight the importance for improving the knowledge of G. bilineatus distribution in Switzerland to develop policy for conservation of this globally threatened species.