Immune activation and metabolic suppression: resource reallocation in Hermetia illucens (Diptera: Stratiomyidae) larvae fed on aquaculture sludge.

The bioconversion of aquaculture sludge using Hermetia illucens larvae represents a promising strategy for sustainable waste management; however, the physiological impact of such complex matrices on the insects remains poorly understood. This study investigated the temporal dynamics of the cellular stress response (heat shock protein 70, HSP70) and metabolic vigor (vitellogenin, VTG) in relation to the functional antimicrobial activity of the hemolymph against the fish pathogen Aeromonas salmonicida. Larvae were exposed to a standard control diet, a 50% sludge blend, and 100% undiluted sludge. Our results show an immediate antimicrobial activation, resulting in the complete inhibition of bacterial viability within 4 h (T1) of exposure to the 100% sludge substrate. Conversely, molecular analysis revealed a significant transcriptional downregulation of VTG by 24 h (T2) across sludge-exposed groups. In the 100% sludge cohort, this metabolic crash coincided with a delayed upregulation of HSP70 and a 15% mortality rate. These findings suggest a potential physiological resource reallocation, where acute immune activation and cytoprotective mechanisms suppress anabolic pathways, indicating that while complex waste streams can boost acute immunological defenses, the severe subchronic metabolic costs establish strict biological limits for their acute utilization.