Resource Valorization of Beetle Larval Frass Using Powder Technology

Abstract

In this study, we investigated a mild cellulose valorization approach that combines microbial fermentation with insect digestion, focusing on the digestive and powder-forming functions of beetle larvae. White-rot fungi were used to control the degree of fermentation of lignocellulosic substrates, and the resulting substrates were fed to larvae. The growth behavior of larvae and the physicochemical properties of the excreted feces were systematically evaluated from a powder engineering perspective. The results indicated that while the degree of fermentation alone did not directly determine cellulose extraction efficiency, the larval digestion process significantly influenced feces disintegration behavior and responsiveness to subsequent bleaching treatments. Time-dependent changes in larval body weight suggested that fermentation degree affects post-feeding digestion, metabolism, and nutrient assimilation dynamics, highlighting the importance of both feeding timing and feces collection timing. Elution tests further suggested that hydrophobic surface components on feces inhibit chemical reagent penetration, and that neutral detergent pretreatment is effective for improving cellulose extraction. XRD and XRF analyses revealed the presence of inorganic components, mainly Si-based particles, with possible sex-dependent differences in feces composition. This study demonstrates that beetle larval feces can be regarded as functionalized biomass powder produced through natural decomposition processes, providing a basis for low-environmental-impact cellulose resource utilization.

Graphical Abstract

Time-course observation of beetle larvae and feces during mushroom substrate feeding. Following a buffer period, larvae were fed different substrates, including leaf mold and spent mushroom substrates, and changes in larval appearance and feces were compared.