Diet Quality Shapes Metabolic and Immune Transcriptional Responses of Honey Bees Under Acute Heat Stress

Climate warming increasingly threatens honey bee health, yet diet-associated molecular patterns under thermal stress remain poorly understood. In this study, newly emerged honey bees were fed eight dietary treatments, including natural diets (honey and bee bread) and artificial diets (sugar syrup and pollen substitute diets), for 5 days before exposure to acute heat stress (45 °C for 4 h). Transcriptional responses were quantified by quantitative real-time PCR (qRT-PCR) using genes associated with nutrient sensing, metabolism, immunity, and stress responses, and the resulting expression profiles were analyzed using principal component analysis, hierarchical clustering, and univariate statistical analyses. Distinct diet-associated transcriptional patterns were observed under both baseline and heat-stress conditions. Under baseline conditions, transcriptional variation was primarily associated with nutrient-sensing and metabolic pathways, whereas under heat-stress conditions, metabolic and stress-response pathways contributed more strongly to transcriptional variation. Sugar syrup-fed honey bees exhibited elevated expression of several immune-related genes following heat stress, suggesting greater physiological disturbance. In contrast, honey- and bee bread-based diets exhibited more coordinated regulation of nutrient-sensing and metabolic pathways and comparatively lower expression of selected immune-related genes. These findings demonstrate that dietary quality is associated with distinct molecular profiles under thermal stress and provide mechanistic insights into the relationship between nutrition and gene expression under heat-stress conditions, supporting the development of nutrition-based strategies for promoting honey bee health under climate warming.