Influence of Cr and Cd accumulation and excretion on growth and gut microbiota in black soldier fly larvae (Diptera: Stratiomyidae)

Black soldier fly larvae (BSFL) are widely used in livestock manure treatment; however, heavy metal contamination in manure poses risks to their growth and application, limiting their practical promotion. However, existing studies have predominantly focused on the effects of individual heavy metals on BSFL, whereas the combined effects of Cr and Cd remain unclear. Furthermore, the underlying mechanisms by which Cr and Cd affect BSFL growth through gut microbiota regulation remain poorly understood. This study aimed to evaluate the effects of Cr and Cd accumulation and excretion on larval growth and gut microbiota and to clarify the related regulatory mechanisms. BSFL were reared on feed mixtures with different ratios of Cd and Cr exposure. The Cr and Cd contents in larval bodies and frass, as well as larval growth performance, behavior, nutrient composition, gut damage, and gut microbial community structure, were measured and analyzed. The results showed that Cr and Cd accumulation in larval bodies and frass increased significantly with increasing exposure concentration, and Cd was more readily accumulated (60.4–86.8%) than Cr (