Harmonia axyridis (Pallas) is an important natural enemy insect. Using fourth-instar larvae, we investigated whether changing temperature (5, 15 and 25°C) can enhance the cold tolerance of H. axyridis and determined optimal storage temperature conditions. Larvae were exposed to five altering temperature regimes:15/5 (15°C/12 h:5°C/24 h), 5/15/5 (5°C/12 h:15°C/12 h:5°C/24 h), 15/25/5 (15°C/12 h:25°C/12 h:5°C/24 h), 15/5/25/5 (15°C/12 h:5°C/12 h:25°C/12 h:5°C/24 h), and 5/25/15/5 (5°C/12 h:25°C/12 h:15°C/12 h:5°C/24 h). Compared with the larvae of control treatment (5°C/24 h), the larvae had lower supercooling points (SCPs) in the 15/25/5 and 5/25/15/5 groups, higher glycerol content in all treated groups (except for group 5/15/5), lower fat content in the 15/5/25/5 group, lower water content in the 15/25/5 and 15/5/25/5 groups, higher trehalose content in the 15/5, 15/25/5, and 15/5/25/5 groups, higher glucose content in the 15/25/5 group, and higher glycogen content in the 15/25/5, 15/5/25/5, and 5/25/15/5 groups. Compared with the control larvae, TRE1 activity of all treated larvae was significantly enhanced except for those in the 5/15/5 group. Also, the expression levels of three soluble trehalase genes (TRE1-1, TRE1-2 and TRE1-3) and one membrane-bound trehalase gene (TRE2) increased after the changing temperature treatment, whereas TRE1-4, TRE1-5, and one membrane-bound like trehalase gene (TRE2-like) mRNA expression levels were very low. These results suggest that fourth-instar H. axyridis larvae exposed to a succession of different temperatures, including low temperatures, survived by reducing the SCP, accumulating carbohydrates and glycerol, and consuming fat. The temperature combination 15/25/5°C provided optimal storage conditions. These findings provide valuable insights for further elucidation of the cold resistance mechanism of ladybeetles and for obtaining an extended shelf life under low-temperature storage.

中文翻译：

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温度变化对异色瓢虫幼虫生理生化特性的影响

异色和谐木（Pallas）是重要的天敌昆虫。我们使用四龄幼虫，研究了改变温度（5、15和25°C）是否可以增强木乃伊菌的耐寒性，并确定了最佳的储存温度条件。幼虫暴露于五个变化的温度范围：15/5（15°C / 12 h：5°C / 24 h），5/15/5（5°C / 12 h：15°C / 12 h：5° C / 24小时），15/25/5（15°C / 12小时：25°C / 12小时：5°C / 24小时），15/5/25/5（15°C / 12小时：5 °C / 12 h：25°C / 12 h：5°C / 24 h）和5/25/15/5（5°C / 12 h：25°C / 12 h：15°C / 12 h ：5℃/ 24小时）。与对照组的幼虫相比（5°C / 24 h），在15/25/5和5/25/15/5组中幼虫的过冷点（SCP）较低，所有处理组中的甘油含量较高（除5/15/5组外），15/5/25/5组中的脂肪含量较低，15/25/5和15/5/25/5组中的水分含量较低，15 / 5、15 / 25/5和15/5/25/5组的海藻糖含量较高，15/25/5组的葡萄糖含量较高，15/25 / 5、15组的糖原含量较高/ 5/25/5和5/25/15/5组。与对照幼虫相比，除5/15/5组外，所有处理过的幼虫的TRE1活性均显着增强。此外，温度变化后，三种可溶性海藻糖酶基因（TRE1-1，TRE1-2和TRE1-3）和一种膜结合海藻糖酶基因（TRE2）的表达水平增加，而TRE1-4，TRE1-5和一种膜结合海藻糖酶基因（TRE2样）的mRNA表达水平很低。这些结果表明，暴露于一系列不同温度（包括低温）下的四龄x虫幼虫能够通过降低SCP，积累碳水化合物和甘油并消耗脂肪来生存。15/25/5°C的温度组合提供了最佳的存储条件。这些发现为进一步阐明瓢虫的抗寒机制和在低温储存条件下延长货架寿命提供了宝贵的见解。