Bacterial Communities in Aphid Honeydew Provide Species-Specific Functional Chemical Cues in Aphid-Predator Interactions.

The role of microbial communities in aphid honeydew in shaping multitrophic interactions remains uncertain, while bacterial diversity and its variation among aphid species and ageing are still underexplored. This study investigated variations in bacterial community structure and VOC profiles of honeydew between two aphid species (Aphis fabae, Acyrthosiphon pisum), across time from fresh to 72-hour aged. We also assessed the behavioral responses of a natural enemy of aphids, the hoverfly Episyrphus balteatus, to different honeydew combinations. Aphis fabae honeydew harbored a more diverse bacterial taxonomic richness than A. pisum, including a significant shift in bacterial community composition over time that also extended to the semiochemical profiles. Further, 24-hour-aged honeydew from A. fabae emitted a higher concentration of volatile compounds than A. pisum. We assessed E. balteatus preferences for aged honeydew from both aphid species using wind tunnel assays, revealing a strong attraction to 48-hour-old A. pisum honeydew resulting in higher egg-laying activity. These findings underscore the role of microbial succession in aphid honeydew in shaping multitrophic interactions, suggesting potential biocontrol strategies by modulating microbial influences on aphidophagous beneficial behavior.