Laboratoire de Lutte Biologique, Département des Sciences Biologiques, Université du Québec à Montréal, Case Postale 8888, Succursale Centre-Ville, Montréal (Qc), H3C 3P8, Canada.
Sciences de l'agriculture et de l'alimentation, Pavillon Paul-Comtois, 2425 rue de l'Agriculture (Qc), Canada, G1V 0A6.
J Therm Biol. 2024 Aug;124:103940. doi: 10.1016/j.jtherbio.2024.103940. Epub 2024 Aug 8.
When overwintering, most endoparasitoids are protected from the cold inside their hosts. However, some endoparasitoids, along with ectoparasitoids, fall into the category called outside-hosts-overwintering parasitoids (OHOP) at immature or adult stages. We compared the cold-hardiness capacity and strategy between adult OHOP and their hosts (HOST) by examining their supercooling points (SCP), with acclimation periods and acclimation temperatures, and their lower lethal temperatures at 50% mortality (LLT50). We hypothesized that OHOP are more cold-hardy than their HOST, with lower SCP and LLT50.
Throughout the summers of 2020, 2021, and 2022, adult cabbage seedpod weevils (HOST) were sampled with a sweep net at the canola pod stage, and thousands of pods were collected and placed in emergence boxes to retrieve the adult OHOP Trichomalus perfectus. Regarding SCP measures, OHOP and HOST were separated according to various treatments. Each treatment considered a target exposure temperature (5, 10, or 20 °C) or a target exposure period (5, 15 or 25 days) at 5 °C. Regarding LLT measures, OHOP and HOST were categorized into five treatments, each corresponding to a specific exposure temperature (-5, -10, -15, -20 or -25 °C).
Acclimations to a lower temperature (5 °C) and a longer period (25 days) led to a significantly lower SCP of OHOP than HOST. Regarding OHOP, the average SCP was -19.71 °C when the acclimation temperature was 20 °C and significantly decreased to -23.20 °C when it was 5 °C. The average SCP was -18.82 °C when the acclimation period was five days and significantly decreased to -23.20 °C when it was 25 days. Conversely, the average SCP for HOST was never below -20 °C. At 20 °C acclimation temperature, HOST exhibited a significantly higher SCP of -14.64 °C compared to acclimations at 5 °C (-19.19 °C) and 10 °C (-20.00 °C), but there were no significant differences between 5 and 10 °C nor between acclimation periods. Therefore, the adult OHOP is more cold-hardy than its HOST. OHOP also exhibited a lower LLT50 than HOST, with -19.20 °C versus -17.59 °C. Finally, OHOP and HOST employ the same freeze-avoidance strategy, as evidenced by their SCP values (-19.57 °C versus -16.80 °C) which closely align with their respective LLT50. Adult OHOP better survive winter than their HOST in cold environments.
当越冬时，大多数内寄生蜂在其宿主体内受到寒冷的保护。然而，一些内寄生蜂和外寄生蜂一起属于称为“体外宿主越冬寄生蜂（OHOP）”的类别，处于未成熟或成虫阶段。我们通过检查超冷点（SCP）、驯化期和驯化温度以及 50%死亡率的致死低温（LLT50），比较了成虫 OHOP 和它们的宿主（HOST）的耐寒能力和策略。我们假设 OHOP 比 HOST 更耐寒，SCP 和 LLT50 更低。
在 2020 年、2021 年和 2022 年的夏季，使用捕虫网在油菜荚阶段采集成年白菜种荚象鼻虫（HOST），收集数千个豆荚并将其放入羽化盒中以获取成虫 OHOP Trichomalus perfectus。关于 SCP 测量，根据不同的处理将 OHOP 和 HOST 分开。每个处理都考虑了目标暴露温度（5、10 或 20°C）或目标暴露时间（5、15 或 25 天）在 5°C。关于 LLT 测量，将 OHOP 和 HOST 分为五个处理，每个处理对应于特定的暴露温度（-5、-10、-15、-20 或-25°C）。
在较低温度（5°C）和较长时间（25 天）的驯化导致 OHOP 的 SCP 明显低于 HOST。对于 OHOP，当驯化温度为 20°C 时，平均 SCP 为-19.71°C，当驯化温度为 5°C 时，平均 SCP 显著下降至-23.20°C。当驯化期为 5 天时，平均 SCP 为-18.82°C，当驯化期为 25 天时，平均 SCP 显著下降至-23.20°C。相比之下，HOST 的平均 SCP 从未低于-20°C。在 20°C 的驯化温度下，与驯化温度为 5°C（-19.19°C）和 10°C（-20.00°C）相比，HOST 表现出明显更高的 SCP，为-14.64°C，但 5°C 和 10°C 之间以及驯化期之间没有显著差异。因此，成虫 OHOP 比其 HOST 更耐寒。OHOP 还表现出比 HOST 更低的 LLT50，为-19.20°C 对-17.59°C。最后，OHOP 和 HOST 采用相同的防冻策略，这一点从它们的 SCP 值（-19.57°C 对-16.80°C）得到证明，这与各自的 LLT50 非常吻合。与宿主相比，成虫 OHOP 在寒冷环境中越冬时具有更好的生存能力。
