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Phytopathogens are responsible for devastating plant diseases threatening agriculture and food security worldwide. Phloem-restricted bacterial plant pathogens belonging to the classes mollicutes (‘Candidatus Phytoplasma’, Spiroplasma), α-proteobacteria, and γ-proteobacteria have a significant impact on several high-value crops. These bacteria are obligate parasites, depending on their plant and insect hosts. Inside the plants, they are restricted to the phloem, which is a source of primary and secondary plant metabolites representing a suitable niche for them. Additionally, phloem sap is utilized for nutrition by multiple Hemipterans and several species within the leafhopper, planthopper, and psyllid taxa, which can acquire and transmit the phloem-dwelling bacteria during feeding. The present review aims at providing an overview of interactions between phloem-restricted bacterial plant pathogens and their vector insects, which are mediated by primary and secondary plant metabolites. The overview is organized in two sections describing the current knowledge of phloem and volatile metabolite mediated interactions between pathogens, their host plants, their vector insects, and where information is available, the antagonists of vectors. This bibliographic oriented part is followed by a comprehensive synthesis of the reviewed literature and important research gaps were identified. The evolution of plant – pathogen – vector systems and novel trends on pest management strategies of phloemrestricted bacteria, in which semiochemicals are applied, are discussed. Finally, an outlook on future prospects is given. [ABSTRACT FROM AUTHOR]

Plant-emitted volatile organic compounds play an important role in plant–insect interactions. Thanks to plant-emitted volatiles, herbivores are able to find suitable hosts. Recognition and location of host plants are a key challenge for successful survival and reproduction of migrating insects, such as the plum psyllid Cacopsylla pruni. This psyllid migrates between Prunus spp. for reproduction and conifers for overwintering. C. pruni also is the only known vector of 'Candidatus Phytoplasma prunorum', a plant pathogen causing the European Stone Fruit Yellows, a severe plant disease. The preference of C. pruni for different Prunus species was monitored in the field. The sampling revealed a high abundance of C. pruni on Prunus spinosa, the natural host, as well as on different Prunus rootstock suckers. To investigate the influence of volatile profiles from different plants on the host preferences of C. pruni, the volatiles of two reproduction hosts and one overwintering host were sampled and analyzed by gas chromatography and mass spectrometry. The volatile compositions were compared, and important components that lead to the differentiation between plant species and growth stages were identified. Antennal responses of C. pruni females were elicited by eleven plant species and growth stage-specific volatiles, detected by electroantennography. The role of host plant volatiles on the migration behavior and the use of synthetic components in alternative control strategies are discussed. [ABSTRACT FROM AUTHOR]