Distribution of a residual population of the Dytiscid Graphoderus bilineatus (de Geer, 1774) in the Grande Cariçaie 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 genusGraphoderusin the Grande Cariçaie reserves with special consideration for the Red ListedG.bilineatus. WhileG.bilineatusandG.cinereusshowed high habitat niche overlap, the distribution ofG.bilineatuswas limited to mainly one of the eight reserves. When comparing our results to available historical data, the habitat ofG.bilineatushas likely diminished during the last 40 years. Our study provides the first comprehensive documentation of the distribution ofGraphoderusspecies in the Grande Cariçaie. We further highlight the importance for improving the knowledge ofG.bilineatusdistribution in Switzerland to develop policy for conservation of this globally threatened species.