New records of the oleander seed bug Caenocoris nerii (Germar, 1847) (Insecta: Hemiptera) in Bulgaria and notes on its hosts in the Black Sea region

The oleander seed bug Caenocoris nerii (Germar, 1847) is a Mediterranean species associated primarily with Apocynaceae host plants that has been expanding its range northward in recent decades. We report new records of C. nerii in Bulgaria and discuss the distribution and the hosts of the species in the Black Sea region. Analysis of regional occurrence data revealed a clear northward range expansion since 2000, with very recent records from Croatia, Bosnia-Herzegovina, Serbia, and Romania. In Bulgaria, reproduction appears limited to areas where the primary host plant Periploca graeca occurs in suitable density, particularly in Black Sea wooded dunes and Flooded forests of Common alder (Alnus glutinosa). The timing and pattern of establishment suggest climate-mediated range expansion, as rising winter temperatures progressively remove thermal barriers that historically confined the species to the Mediterranean region. Our findings indicate that C. nerii is likely to continue spreading northward across the Danube River and Thracian lowland in areas with both suitable climatic conditions and host plant availability.