Interactive effects of dietary leucine and isoleucine on the nutrient deposition and immune performance of Apis mellifera ligustica

Bees, as vital pollinators, are currently confronting numerous survival threats. Balanced amino acid nutrient have a positive impact on helping bees to resist pathogens and pesticides. This study aims to explore the interaction between leucine (Leu) and isoleucine (Ile) on key physiological parameters of Apis mellifera ligustica (Apidae: Hymenoptera) colony. The experiment was designed into four distinct dietary groups, including control diet (CK): 6.8 g/kg Leu + 3.9 g/kg Ile; high Ile diet: 6.8 g/kg Leu + 21.9 g/kg Ile; high Leu diet: 43.8 g/kg Leu + 3.9 g/kg Ile; diet with both high L-I: 43.8 g/kg Leu + 21.9 g/kg Ile. The results showed that Leu and Ile, to a considerable extent, promote the growth and vitality of the bee colony, with Ile mitigating Leu-induced absorption inhibition. Leu and Ile synergistically reduced haemolymph triglyceride via upregulated activities of fatty acid synthase and acetyl-CoA carboxylase, and expression of Lipase 1 and adipokinetic hormone receptor compared with CK. Furthermore, L-I treatment increased key activities of immune enzymes like phenol oxidase, lysozyme, glucose oxidase, and altered expression of antimicrobial peptides ( abaecin, apidaecin, and defensin 1 ), indicating coordinated immunomodulation. In conclusion, within the context of this study, 43.8 g/kg Leu and 21.9 g/kg Ile in the artificial pollen substitute feed prove to be beneficial for the nutrient deposition and immunity of individual bees. This work provides a framework for optimising artificial pollen diets, offering experimental guidance towards more effective strategies in sustainable beekeeping.