ABSTRACT Black soldier flies (BSF, Hermetia illucens ( L .) Diptera: Stratiomyidae) are increasingly used for sustainable protein production. However, production waste from BSF processing, particularly chitin‐rich byproducts, remains underutilized. Chitin‐rich byproducts (including frass, pupal cases, and deceased adults) may serve as valuable fertilizers due to their positive effects on plant health. Therefore, this study aimed to investigate the effects of adding BSF byproducts to commercial potting soil on the growth of fungus gnats ( Bradysia ocellaris Comstock , 1882 Diptera: Sciaridae), which are pests of several greenhouse crops. Specifically, we determined the chitin content of several BSF life stages using an optimized analytical procedure for chitin measurement. In three experiments, we compared the performance of fungus gnats grown in soils containing various BSF byproducts: frass (a mixture of larval excrements, undigested feed residues, and small amounts of deceased larvae), sanitized frass (autoclaved), and unsanitized frass enriched with adults and pupal cases. Notably, the addition of byproduct mixture, sanitized frass, and unsanitized frass substrates significantly decreased fungus gnat population by 93%, 80%, and 77%, respectively, compared with that in the commercial potting soil. Maternal oviposition preference partially explained the reduced populations in byproduct‐amended soils, as it was significantly lower in sanitized frass and byproduct‐mixed substrates. In contrast, no significant difference was observed in oviposition between the unsanitized frass and commercial potting soil groups. An increasing trend in juvenile mortality was observed in the pure potting soil and byproduct mixture groups, possibly due to resource limitations in the pure potting soil and the higher chitin content in the byproduct mixture substrate, which may have increased soil suppressiveness. In conclusion, these results demonstrate that BSF byproducts show promise for application in plant protection for controlling pests in horticulture and agriculture.
Gärttling et al. (Thu,) studied this question.