Bacterial communities in aphid honeydew provide species-specific functional chemical cues in aphid-hoverfly 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 aphid predator (i.e., 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. Hence, 24-hour-aged honeydew from A. fabae emitted a higher concentration of volatile compounds than A. pisum. Wind tunnel assays, assessing E. balteatus preferences for aged honeydew from both aphid species, revealed a strong attraction to 48-hour-old A. pisum honeydew stimulated 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.