Melatonin Enhances Thermal Resilience and Extends Worker Lifespan in Apis cerana via Redox-Metabolic Reprogramming

Area of Science:

• Apiculture Science
• Insect Physiology
• Environmental Stress Biology

Background:

• Honey bee colonies, particularly *Apis cerana*, face significant losses during summer heatwaves in Southern China.
• Effective strategies are needed to improve colony survival and productivity under increasing thermal stress.

Purpose of the Study:

• To investigate the efficacy of dietary melatonin supplementation in enhancing thermal tolerance and lifespan of *Apis cerana* workers under heat stress.
• To elucidate the molecular mechanisms underlying melatonin's protective effects against heat-induced damage.

Main Methods:

• Laboratory bioassays and field trials were conducted to assess worker survival, colony weight gain, and physiological responses.
• Gene expression analysis (RNA-seq) was used to identify molecular pathways affected by melatonin under heat stress.
• Measurements included heat shock proteins, detoxification enzymes, reactive oxygen species (ROS), and proboscis extension response (PER).

Main Results:

• Melatonin supplementation (20 µg/mL) significantly improved *A. cerana* worker survival at 35 °C and 37 °C, with greater effect at 37 °C.
• Melatonin-treated colonies exhibited significantly higher weight gain during summer heatwaves compared to controls.
• Melatonin induced a biphasic adaptive response, upregulating heat shock proteins, detoxification enzymes, and lipid metabolism pathways, while reducing ROS and preserving sensory function.

Conclusions:

• Dietary melatonin acts as a potent nutritional intervention to mitigate heat-induced damage in *Apis cerana*.
• Melatonin reprograms redox and metabolic networks, enhancing antioxidant capacity, reducing oxidative damage, and extending worker longevity.
• Melatonin shows promise as a practical tool to improve honey bee colony health and productivity under climate warming.