Department of Zoology and Physiology and Program in Ecology, University of Wyoming, Laramie, WY, 82071, USA.
Department of Zoology and Physiology and Program in Ecology, University of Wyoming, Laramie, WY, 82071, USA.
J Therm Biol. 2022 Feb;104:103196. doi: 10.1016/j.jtherbio.2022.103196. Epub 2022 Jan 25.
Bumble bees thrive in cold climates including high latitude and high altitude regions around the world, yet cold tolerance strategies are largely unknown for most species. To determine bumble bee cold tolerance strategy, we exposed bumble bees to a range of low temperatures and measured survival 72 h post-exposure. All bees that froze died within 72 h while only one bee died without freezing, suggesting that bumble bees are generally freeze-avoiding insects and may be slightly chill susceptible. We then assessed whether temperatures that cause internal ice formation (supercooling points, SCP) varied among bumble bee castes (drones, workers, and queens), or across queen life stages, collection elevation, species, or season. Males froze at significantly lower temperatures than workers or queens. Queens in pre-overwintering or overwintering states froze at significantly lower temperatures than queens stimulated to initiate ovary development by CO narcosis (i.e., "spring" queens). We also tested whether the presence of water (i.e., wet or dry) or ramping rate affected SCP. As expected, queens inoculated with water froze at significantly higher temperatures than dry queens. SCP tended to be lower, but not significantly so, at faster ramping rates (0.5 °C/min vs 0.25 °C/min). We also found no differences in SCP between queen bumble bees collected in spring and fall, between queens collected at two sites differing in elevation by 1100 m, or between three field-caught bumble bee species. Bumble bees appear to have relatively high, invariable SCPs, likely making them highly susceptible to freezing across all seasons. As bumble bees are not freeze-tolerant and appear to lack the ability to prevent freezing at temperatures much below 0 °C, they may rely on season- and caste-specific micro-habitat selection to thrive in cold climates.
大黄蜂在包括世界各地高纬度和高海拔地区在内的寒冷气候中茁壮成长，但大多数物种的耐寒策略在很大程度上尚不清楚。为了确定大黄蜂的耐寒策略，我们将大黄蜂暴露在一系列低温环境中，并在暴露后 72 小时测量其存活率。所有冻死的蜜蜂在 72 小时内死亡，而没有冻死的只有一只，这表明大黄蜂通常是避免冻结的昆虫，可能稍微容易受到冷刺激。然后，我们评估了导致内部结冰（过冷点，SCP）的温度是否因大黄蜂的蜂型（雄蜂、工蜂和蜂王）、蜂王生命阶段、采集海拔、物种或季节而有所不同。雄蜂的冻结温度明显低于工蜂或蜂王。处于预越冬或越冬状态的蜂王的冻结温度明显低于因 CO 麻醉而被刺激开始卵巢发育的蜂王（即“春季”蜂王）。我们还测试了水（即湿或干）或升温速率是否会影响 SCP。不出所料，与干燥的蜂王相比，接种水的蜂王冻结温度明显更高。以 0.5°C/min 与 0.25°C/min 的较快升温速率，SCP 趋于降低，但没有显著差异。我们还发现春季和秋季采集的蜂王之间、海拔相差 1100 米的两个采集地点之间的蜂王之间，以及三种野外捕获的大黄蜂物种之间的 SCP 没有差异。大黄蜂的 SCP 似乎相对较高且不变，这可能使它们在所有季节都极易受到冻结的影响。由于大黄蜂不耐冻，并且似乎无法在远低于 0°C 的温度下防止冻结，它们可能依赖于季节性和蜂型特定的微生境选择来在寒冷气候中茁壮成长。
