Phloem Metabolites of Prunus Sp. Rather than Infection with Candidatus Phytoplasma Prunorum Influence Feeding Behavior of Cacopsylla pruni Nymphs

Phytoplasmas are specialized small bacteria restricted to the phloem tissue and spread by hemipterans feeding on plant sieve tube elements. As for many other plant pathogens, it is known that phytoplasmas alter the chemistry of their hosts. Most research on phytoplasma-plant interactions focused on the induction of plant volatiles and phytohormones. Little is known about the influence of phytoplasma infections on the nutritional composition of phloem and consequences on vector behavior and development. The plum psyllidCacopsylla prunitransmits 'CandidatusPhytoplasma prunorum', the causing agent of European Stone Fruit Yellows (ESFY). While severalPrunusspecies are susceptible for psyllid feeding, they show different responses to the pathogen. We studied the possible modulation of plant-insect interactions by bacteria-induced changes in phloem sap chemistry. Therefore, we sampled phloem sap from phytoplasma-infected and non-infectedPrunus persicaandPrunus insititiaplants, which differ in their susceptibility to ESFY and psyllid feeding. Furthermore, the feeding behavior and development ofC. pruninymphs was compared on infected and non-infectedP. persicaandP. insititiaplants. Phytoplasma infection did not affect phloem consumption byC. pruninymphs nor their development time. In contrast, the study revealed significant differences betweenP. insititiaandP. persicain terms of both phloem chemistry and feeding behavior ofC. pruninymphs.Phloem feeding phases were four times longer onP. insititiathan onP. persica, resulting in a decreased development time and higher mortality of vector insects onP. persicaplants. These findings explain the low infestation rates of peach cultivars with plum psyllids commonly found in field surveys.