Diapause is a deep resting stage facilitating temporal avoidance of unfavourable environmental conditions that is used by many insects to adapt their life cycle to seasonal variation. Although considerable work has been invested in trying to understand each of the major diapause stages (induction, maintenance and termination), we know very little about the transitions between stages, especially diapause termination. Understanding diapause termination is critical for modelling and predicting spring emergence and winter physiology of insects, including many pest insects. In order to gain these insights we investigated metabolome dynamics across diapause development in pupae of the butterfly Pieris napi, which exhibits adaptive latitudinal variation in the length of endogenous diapause that is uniquely well characterized. By employing a time-series experiment we show that the whole-body metabolome is highly dynamic throughout diapause and differs between pupae kept at a diapause-terminating (low), or at a diapause-maintaining (high) temperature. We show major physiological transitions through diapause, separated temperature-dependent from temperature-independent processes and identified significant patterns of metabolite accumulation and degradation. Together the data show that while the general diapause phenotype (suppressed metabolism, increased cold tolerance) is established in a temperature-independent fashion, diapause termination is temperature-dependent and requires a cold signal. This revealed several metabolites that are only accumulated in diapause terminating conditions and degraded in a temperature-unrelated fashion during diapause termination. In conclusion, our findings indicate that some metabolites, in addition to functioning as e.g. cryoprotectants, are candidates for having regulatory roles as metabolic clocks or time-keepers during diapause.

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