Forged in iron: molecular insights into iron tolerance in Hermetia illucens.

Black soldier fly (BSF) larvae are increasingly valued as a sustainable source of proteins and essential minerals in animal feed and potentially food, yet their physiological response to substrate iron fortification is poorly defined. Here, integrated transcriptomic, proteomic, and tissue iron detection approaches were used to characterize responses of BSF larvae reared on diets containing 323 (control), 1255, and 6970 mg Fe/kg dry matter (DM). Larval growth at day 12 was unaffected, while prepupal emergence after 15 days showed a statistically non-significant increase at the highest iron level, suggesting only subtle developmental effects. Prussian blue staining showed a dose-dependent iron accumulation in the midgut epithelium, consistent with known insect iron responsive regions of entoferritin-based sequestration. An elevated iron signal in the peritrophic matrix indicated a complementary defensive barrier. Multi-omics profiling revealed oxidative stress responses, suppression of mitochondrial and translational pathways, and activation of exoskeleton biosynthesis. Entoferritin levels rose by ~70% for both protein subunits despite insignificant transcript changes, pointing to a post-transcriptional regulation mechanism. These results suggest a gut-centered "accumulate-and-store" physiological strategy enabling BSF larvae to tolerate high dietary iron. This entoferritin-based high iron accumulation capacity highlights the potential of this insect as a sustainable source of a protein bound iron in feeds.