Insect-microbe-fungus interplay in citrus agro-ecosystems: Cuticular symbionts mediate <em>Diaphorina citri</em> resistance to <em>Beauveria bassiana</em>

Microbial symbionts are critical in insect ecology, notably for mediating host–pathogen interactions that influence pest population dynamics in agro-ecosystems. The Asian citrus psyllid (Diaphorina citri), a key vector of Huanglongbing, depends on such microbial associations; however, how its cuticular microbiota responds to fungal infection remains unclear. This study examined changes in the cuticular bacterial community of D. citri following Beauveria bassiana infection and identified protective symbionts that alter host susceptibility. Using 16S rRNA sequencing, we detected significant shifts in bacterial diversity and composition on the psyllid cuticle after fungal exposure. From the cuticle, we isolated two bacterial strains, Bacillus albus (CQC‑1) and Shouchella miscanthi (CQC‑32), which showed strong antifungal activity, inhibiting B. bassiana spore germination by 94.53 % and 73.50 %, respectively. In bioassays, these strains increased psyllid survival under fungal challenge to 71.3 % and 65.2 %, compared with 16.4 % in controls. Our results highlight the functional role of cuticular bacteria in host–pathogen interactions and suggest their potential use in sustainable management of D. citri. These findings further clarify how cuticular microbial communities respond to entomopathogenic fungi and modulate insect defense, with implications for microbial ecology and integrated pest management in citrus agro-ecosystems.