Systematic Characterization of Cacopsylla chinensis as a Potential Vector of Erwinia amylovora on Korla Fragrant Pear in Xinjiang, China

Pear fire blight, caused by the bacterium Erwinia amylovora, is a destructive disease affecting Rosaceae plants. Although insect transmission is well-documented, most studies have focused on pollinators, with limited attention to psyllids. Chinese pear psyllid (Cacopsylla chinensis) is a major piercing–sucking pest of pear trees, yet its role in the transmission of E. amylovora remains unclear. Here, we investigated the distribution of E. amylovora in and on C. chinensis and the synergistic damage (i.e., C. chinensis creates invasion wounds and nutrient-rich niches for E. amylovora via piercing–sucking feeding, while the pathogen enhances the vector’s fitness to promote disease spread). Field and laboratory assays confirmed severe synergistic symptoms. E. amylovora was isolated from all life stages and body parts of C. chinensis, with significantly higher pathogen loads and virulence in internally harbored strains compared to external ones. Specifically, E. amylovora loads in nymphs were significantly higher than those in adults, and strains from the digestive system and female reproductive organs caused a 3- to 9-fold higher disease index on pear leaves at 7 days post-inoculation compared to body surface isolates. This study provides evidence that C. chinensis acts as a crucial vector for E. amylovora in Xinjiang, laying a theoretical basis for the precise integrated management of this pest–disease complex.