Bee-mediated delivery of bacteriophage for biocontrol of the cherry canker pathogen Pseudomonas syringae pv. syringae

• Developed a bee-vectored phage delivery system to control floral crop diseases. • Confirmed phage stability in bee feed for effective field applications. • Achieved high-efficiency phage delivery to flowers via bumblebees in glasshouse trials. • Significantly suppressed Pseudomonas syringae pv. syringae (cherry canker). • Offers a sustainable, pollinator-driven alternative to chemical disease control. Bacteriophages, phages or viruses that specifically infect bacteria, have shown promise for the biocontrol of bacterial plant diseases. However, one of the main challenges of using phages in agricultural systems is their precision application, being able to deliver an effective dose to the site of bacterial infection. In this study, a series of artificial and real cherry flower experiments was conducted to test whether commercially managed bumblebees ( Bombus terrestris audax ) could deliver phage effective against the cherry canker pathogen Pseudomonas syringae pv. syringae ( Pss ). Freeze-dried phage powder was formulated with powdered-skimmed milk and when tested, was found to retain viability for seven days in artificial bee feed after storage at 4 °C, room temperature or under glasshouse conditions. In both artificial and cherry flower experiments, bees successfully transferred the formulated phage from their hive to up to 88 % of flowers, resulting in significant reduction in Pss populations. Bees were also able to transfer phage between cherry flowers. The application of phages disrupted the cycle of Pss transmission by bees. These results highlight the potential of bee-mediated phage delivery as an effective biocontrol strategy against floral pathogens like Pss .