Immune Response and Gut Microbiota Shift in the Red Palm Weevil (Rhynchophorus ferrugineus) Infected With Entomopathogenic Fungus, Beauveria bassiana, Reveal Host-Pathogen Interactions

Abstract

The red palm weevil (RPW), Rhynchophorus ferrugineus (Oliver), is a major pest of palm plants. Entomopathogenic fungi (EPF) are considered promising biocontrol agents against RPW. This study investigated the changes in immune-related gene expression and gut microbiota of RPW larvae infected with Beauveria bassiana (Bb-NCHU-155). In infected larvae, fungal genome copy numbers in the midgut and hindgut were lower than those detected in the fat body, suggesting that infection primarily occurs via the cuticle rather than the digestive tract. Immune-related gene expression in the fat body increased steadily from 3 days post-inoculation (dpi), reflecting a typical host response, whereas digestive tissues exhibited fluctuating patterns. The midgut showed peak induction of C-type lysozyme at 3 dpi and C-type lectin at 6 dpi, while the hindgut displayed the highest expression of serine protease-like protein at 3 dpi. Despite an overall downregulation of immune-related genes, these results indicate tissue-specific immune responses. Although B. bassiana may not infect hosts through the digestive system, gut microbiota composition differed significantly between infected and control groups, with higher relative abundances of Acetobacteraceae, Lactobacillaceae, and Streptococcaceae in the infected larvae. These shifts co-varied with the expression of immune-related genes, such as defensin and C-type lectin, suggesting potential functional links between gut microbiota and host immunity. This study provides fundamental insights into the effects of EPF on gut microbiota and immune gene expression in RPW, supporting further research into the complex interactions underlying microbial control.