【目的】 本研究旨在探究光周期对小菜蛾Plutella xylostella (Linn.)羽化节律的调控作用，为小菜蛾的季节性种群动态预测提供理论基础。【方法】 在自然光周期和逆转光周期条件下，观察小菜蛾每日的羽化情况。【结果】 在自然光周期和逆转光周期条件下，小菜蛾蛹在24 h均可以羽化。正常光周期下，羽化行为表现为近似抛物线形昼夜节律，雌成虫通常在黑暗阶段羽化（18:00-6:00），而雄成虫大多在光照阶段羽化（6:00-18:00）。在逆转光周期下，小菜蛾蛹的羽化无明显规律。在正常光周期下，雌成虫的羽化频率在光期和暗期没有显著差异，但是，相比于暗期，雄成虫在光期羽化率较高；在逆转光周期后，雌成虫在暗期（6:00-18:00）的羽化数量比光期（18:00-6:00）高，雄成虫暗期的羽化数量比光期低。【结论】 光周期逆转后小菜蛾雌成虫和雄成虫的羽化节律明显改变，这将有助于阐明害虫光周期变化与生物钟之间的关系。

[Objectives]  To investigate the effect of photoperiod on the timing of eclosion in the diamondback moth (DBM), Plutella xylostella (Linn.). [Methods]  Daily eclosion activity was recorded under natural and reversed photoperiod conditions to investigate the temporal frequency of eclosion. [Results]  Adults emerged throughout the day. Eclosion had an approximately parabolic circadian rhythm; females emerged mainly during the dark phase (18:00-6:00), whereas males emerged mostly during the light phase (6:00-18:00). Reversing the photophase and scotophase disrupted the approximately parabolic eclosion rhythm resulting in no obvious pattern. No significant differences were observed in the frequency of female eclosion between the photophase and scotophase in the control group but a higher rate of male eclosion was found in the photophase than in the scotophase. After the photoperiod was reversed, more females emerged during the scotophase (06:00-18:00) than during the photophase (18:00-06:00), but fewer males emerged during the scotophase than during the photophase. [Conclusion]  Reversing the photoperiod changed the timing of eclosion of male and female DBM. These results help illustrate the relationship between photoperiod and the circadian clock in an insect pest.