Host immunology and pathogen-bacteriophage interactions in Black Soldier Fly Larvae (BSFL; Hermetia illucens)

Abstract

The Black Soldier Fly (Hermetia illucens) has emerged as a sustainable bioconversion species with considerable potential for a circular economy. While extensively studied for waste management and protein production, its innate immune system remains comparatively underexplored. This thesis aims to establish and optimise experimental and molecular approaches to investigate host immune responses and bacteriophage-pathogen interactions in H. illucens, providing new insight into its immunological potential and implications for sustainable disease control.

Methodological optimisation included refining larval rearing conditions, bioactive administration, and RNA extraction techniques tailored to the physiological characteristics of H. illucens. Using pathogen-associated molecular patterns (PAMPS), lipopolysaccharide (LPS) and polyinosinic:polycytidylic [Poly (I:C)], the dose-dependent induction of pattern-recognition receptors and antimicrobial peptide genes was quantified through qPCR analysis. Responses showed thresholds and paralogue-specific expression profiles, indicating scalable innate activation.

A directional poly (A) RNA-seq transcriptome was generated from pooled whole-body larvae and subjected to genome-guided, orthology-informed annotation to produce a curated immune gene database. Canonical innate immune pathways, including Toll, IMD, JAK/STAT and JNK signalling, were characterised through Gene Ontology, KEGG, Reactome, and STRING protein-protein interaction analyses, providing a comprehensive molecular framework for future functional and comparative studies.

Finally, prophylactic administration of bacteriophage SPFM14 significantly reduced Salmonella enterica serovar Typhimurium (SL1344) colonisation in H. illucens, supporting the potential of phage-based biocontrol as an alternative to antibiotics in insect production systems. Time-course experiments further demonstrated rapid phage shedding from the larval gut, providing important context for interpreting in vivo phage persistence and bacteriophage-mediated bacterial control.