Immune responses of Galleria mellonella L. (Lepidoptera: Pyralidae) to Beauveria bassiana infection: hemolymph antimicrobial activity and total Hemocyte Count)

Beauveria bassiana is a widely used entomopathogenic fungus and an eco-friendly alternative to chemical pesticides in sustainable pest management. Although its efficacy as a biopesticide is well established, early immune responses of insect hosts to B. bassiana infection remain poorly understood. In this study, the short-term innate immune response of Galleria mellonella larvae following topical exposure to a naturally isolated B. bassiana strain was investigated. The fungus was obtained using the Galleria trap method and identified by morphological traits and ITS rDNA sequencing. Larvae were exposed to different conidial concentrations, and humoral and cellular immune responses were evaluated at 24 and 48 hours post-infection. Humoral immunity was assessed by measuring the antimicrobial activity of hemolymph against Gram-positive and Gram-negative bacteria and Candida albicans, while cellular responses were evaluated by total hemocyte count (THC). Infected larvae showed significantly enhanced antimicrobial activity compared to controls, with dose-, time-, and microorganism-dependent effects. Lower conidial doses increased THC, indicating immune activation, whereas higher doses caused a marked reduction in hemocyte numbers, suggesting immune suppression during infection progression. Overall, G. mellonella exhibited a dynamic innate immune response involving both humoral and cellular components. These findings provide new insights into early host–pathogen interactions during entomopathogenic fungal infection and support the use of G. mellonella as a reliable in vivo model for biocontrol research.