Metabolomics reveals the key role of oxygen metabolism in heat susceptibility of an alpine-dwelling ghost moth, Thitarodes xiaojinensis (Lepidoptera: Hepialidae).

Ghost moths inhabiting the alpine meadows of the Tibetan Plateau are cold-adapted stenothermal organisms that are susceptible to heat (dead within 7 days at 27 °C exposure). Exploring the metabolic basis of their heat susceptibility would extend our understanding of the thermal biology of alpine-dwelling invertebrates. Here, gas chromatography-mass spectrometry-based metabolomics was combined with physiological and transcriptional approaches to determine the metabolic mechanisms of heat susceptibility in Thitarodes xiaojinensis larvae. The metabolomics results showed that 27 °C heat stress impaired the Krebs cycle and lipolysis in T. xiaojinensis larvae, as demonstrated by the accumulation of intermediary metabolites. In addition, carbohydrate reserves were highly and exclusively consumed, and an anaerobic product, lactate, accumulated. This evidence suggested a strong reliance on glycolysis to anaerobically generate energy. The respiration rate and enzymatic activity test results indicated a deficiency in O metabolism; in addition, the Krebs cycle capacity was not decreased, and the metabolic flux through aerobic pathways was limited. These findings were further supported by the occurrence of hypoxia symptoms in midgut mitochondria (vacuolation and swelling) and increased transcription of hypoxia-induced factor 1-α. Overall, heat stress caused O limitation and depressed the overall intensity of aerobic metabolism in ghost moths, and less efficient anaerobic glycolysis was activated to sustain their energy supply. As carbohydrates were depleted, the energy supply became deficient. Our study presents a comprehensive metabolic explanation for the heat susceptibility of ghost moths and reveals the relationship between O metabolism and heat susceptibility in these larvae.