United States Department of Agriculture, Edward T. Schafer Agricultural Research Center, Biosciences Research Laboratory, 1605 Albrecht Boulevard North, Fargo, ND 58102-2765, USA.
Department of Biological Sciences, Stevens Hall, P.O. Box 6050, North Dakota State University, Fargo, ND 58108, USA.
Integr Comp Biol. 2019 Oct 1;59(4):1089-1102. doi: 10.1093/icb/icz126.
Insects exposed to low temperature stress can experience chill injury, but incorporating fluctuating thermoprofiles increases survival and blocks the development of sub-lethal effects. The specific parameters required for a protective thermoprofile are poorly understood, because most studies test a limited range of thermoprofiles. For example, thermoprofiles with a wave profile may perform better than a square profile, but these two profiles are rarely compared. In this study, two developmental stages of the alfalfa leafcutting bee, Megachile rotundata, eye-pigmented pupae, and emergence-ready adults, were exposed to one of eight thermoprofiles for up to 8 weeks. All the thermoprofiles had a base of 6°C and a peak temperature of either 12°C or 18°C. The duration at peak temperature varied depending on the shape of the thermoprofile, either square or wave form. Two other treatments acted as controls, a constant 6°C and a fluctuating thermal regime (FTR) with a base temperature of 6°C that was interrupted daily by a single, 1-h pulse at 20°C. Compared with constant 6°C, all the test thermoprofiles significantly improved survival. Compared with the FTR control, the thermoprofiles with a peak temperature of 18°C outperformed the 12°C profiles. Bees in the eye-pigmented stage exposed to the 18°C profiles separated into two groups based on the shape of the profile, with higher survival in the square profiles compared with the wave profiles. Bees in the emergence-ready stage exposed to 18°C profiles all had significantly higher survival than bees in the FTR controls. Counter to expectations, the least ecologically relevant thermoprofiles (square) had the highest survival rates and blocked the development of sub-lethal effects (delayed emergence).
昆虫在低温胁迫下会遭受冷害，但采用波动温度曲线可以提高存活率并阻止亚致死效应的发展。目前，对于保护温度曲线所需的具体参数还知之甚少，因为大多数研究都只测试了有限的温度曲线范围。例如，具有波浪形温度曲线的温度曲线可能比方形温度曲线表现更好，但这两种温度曲线很少被比较。在这项研究中，我们对苜蓿切叶蜂（Megachile rotundata）的两个发育阶段，即眼斑化蛹和出房成虫，分别暴露于八种温度曲线中的一种，最长可达 8 周。所有温度曲线的基础温度均为 6°C，峰值温度分别为 12°C 或 18°C。峰值温度的持续时间取决于温度曲线的形状，即方形或波浪形。另外两种处理方式作为对照，一种是恒定的 6°C，另一种是波动的热环境（FTR），其基础温度为 6°C，每天通过 1 小时 20°C 的单次脉冲中断。与恒定的 6°C 相比，所有测试温度曲线都显著提高了存活率。与 FTR 对照相比，峰值温度为 18°C 的温度曲线优于 12°C 的温度曲线。处于眼斑化阶段的蜜蜂根据温度曲线的形状分为两组，方形温度曲线的存活率明显高于波浪形温度曲线。处于出房准备阶段的蜜蜂暴露于 18°C 温度曲线下的存活率均显著高于 FTR 对照组的蜜蜂。与预期相反，最不具有生态相关性的温度曲线（方形）的存活率最高，并阻止了亚致死效应（延迟出房）的发展。
