Field persistence of entomopathogenic fungi and network-level associations within the soil microbial community as biocontrol agents

The effects of entomopathogenic fungi (EPF) on native soil microbiota are poorly understood. Here, we investigated the persistence of the EPF Metarhizium brunneum and Beauveria bassiana as preventive treatments for date palms against the red palm weevil, Rhynchophorus ferrugineus, and monitored the microbial community within the palms. We assessed the changes in the soil microbiota of the palms following application by fungal soil isolation techniques, high-throughput metagenomics, EPF persistence assays, and accompanied that with a continuous monitoring of date palm health. EPF preemptive treatments significantly improved palm protection against the weevil. While both EPF species persisted for 180 days post-application, their effectiveness diverged, with B. bassiana providing longer palm protection. Overall microbial community composition showed no major changes following EPF applications; however, transient alterations increased the relative abundance of local EPF genera, with dominant taxa being more likely to persist. Both EPF treatments enhanced the relative abundance of nitrogen-fixing bacteria, organic matter decomposers, and ammonia-oxidizing archaea, suggesting potential implications for nutrient cycling that require further validation through direct functional measurements. B. bassiana induced the strongest temporal effects on diversity indices, while M. brunneum was more persistent but showed no significant changes in diversity indices compared to the control. These results highlight EPF as a multifunctional biocontrol agent - moderately shaping soil microbiomes for beneficial ecosystem functions.