Abstract Amid growing concerns over environmental change and increasing food demand, the development of sustainable agricultural practices is becoming increasingly urgent. Black soldier fly (BSF), Hermetia illucens (L.) (Diptera: Stratiomyidae) is widely recognized for its ability to convert organic waste into high-value protein for animal feed. However, the potential of BSF by-products, including frass/exuviae, as soil amendments remains insufficiently studied. This study aimed to evaluate the effects of different BSF by-products on plant growth, photosynthesis, pest performance, and defense-related hormone dynamics. We tested BSF frass/exuviae subjected to fermentation and granulation, alongside unprocessed materials, using bok choy (Brassica rapa L. subsp. chinensis cv. Chun Xiu) and its pest, the green peach aphid, Myzus persicae (Sulzer) (Hemiptera: Aphididae), as a model system. Plant performance, photosynthetic traits, aphid population growth, defense gene expression, and hormone levels were measured across treatments. Processing by fermentation or granulation did not alter plant growth or photosynthetic performance compared with unprocessed BSF by-products. Across treatments, BSF by-products promoted lower overall plant growth than conventional chemical fertilizers but significantly increased the root-to-shoot ratio. Aphid population growth and several defense-related genes were not significantly affected. However, salicylic acid (SA) levels were elevated in treated plants even in the absence of herbivory, indicating activation of defense pathways. Our findings indicate that black BSF frass/exuviae represent functionally relevant insect-derived inputs capable of contributing to crop protection. By altering plant biomass allocation and inducing SA-associated defenses, these by-products may indirectly affect herbivore performance.
Liao et al. (Thu,) studied this question.