Evaluation of nutritional composition of natural and artificial diets for feed optimization for cantharides larvae

Cantharides is a general term for cantharidin-rich beetles and an insect-derived medicine as listed in the Chinese Pharmacopoeia . Cantharides larvae feed exclusively on locust eggs in nature, posing significant challenges for their artificial rearing. The current artificial feed is effective for rearing older instars but exhibits lower fitness for earlier ones. This study analyzed the nutritional content of natural food (locust eggs) and a basic artificial feed (BAF), revealing that the BAF had higher total sugar content but lacked sufficient protein and fat. Based on these findings, we developed an improved artificial feed (IAF) with enhanced protein and lipid content. The larvae fed the IAF exhibited higher survival rates and food conversion efficiency than those fed the BAF; however, these metrics remained inferior to those in larvae fed locust eggs. Mass spectrometry analysis revealed that 1425 proteins and 683 lipids were significantly more abundant in the IAF than in locust eggs, whereas 21 proteins and 378 lipids were less abundant. Proteins and lipids with higher amounts in IAF than in locust eggs positively correlated with larval food utilization and growth, but were inversely associated with survival rates. Conversely, compounds absent from IAF exhibited an opposite trend. This study identified critical nutritional disparities between the IAF and locust eggs, indicating potential impact on the growth and development of cantharides larvae. These findings provide scientific insights into the feeding plasticity of cantharides larvae and suggest potential strategies for optimizing artificial feed formulation for cantharides larvae.