The red palm weevil (RPW), Rhynchophorus ferrugineus, is one of the worst palm pests worldwide. Our study aims to assess its internal and external morphological response to a sudden but transient decrease in the environmental temperature. Wild pre-pupae were subjected for 7 days to either low (5.0 ± 0.5 °C) or ambient temperature (23 ± 1 °C). Such conditions mimic a thermal anomaly happening in the larval stage most exposed to environmental factors. We quantified the changes undergone at: 1) the internal morphology, by X-Ray Computer Tomography (CT); 2) the 3-D integument' architecture, by Digital Holographic Microscopy (DHM); and 3) the glucose in hemolymph as a potential endogenous cryoprotectant. From X-ray CT we found that both pre-pupae subjected to cold and those remaining at ambient temperature follow a development where their fat body content decreases while a thick and dense cuticle is formed. There was no difference between both groups in the rate of change of fat body/dense tissues. Nevertheless, the cold group presents a slight developmental delay at the level of hemolymph content. Through DHM we again obtained that pre-pupae subjected to cold have not experienced a stop in their development. However, a more obvious developmental delay is now observed in this group at the level of the integumental roughness. Finally, regarding glucose, we found similar levels in control and ambient temperature larvae, while it was clearly increased in 51,7% of those subjected to cold. Our whole results provide morphological and biochemical evidence showing that the larval-pupal transition of the RPW continues almost undisturbed even during the quiescent state induced by a sudden and severe cold event. Nevertheless, a certain developmental delay is observed in both internal and external morphology. Additionally, the increased glucose level only found in the cold group suggests that glucose is part of the RPW cold tolerance strategy.

中文翻译：

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通过计算机断层扫描和全息显微镜分析的红棕象鼻虫，Rhynchophorus ferrugineus，对瞬态低温的形态响应

红棕象鼻虫 (RPW) Rhynchophorus ferrugineus 是世界上最严重的棕榈害虫之一。我们的研究旨在评估其对环境温度突然但短暂下降的内部和外部形态响应。野生前蛹经受了 7 天的低温 (5.0 ± 0.5 °C) 或环境温度 (23 ± 1 °C)。这种条件模拟了最暴露于环境因素的幼虫阶段发生的热异常。我们量化了在以下方面发生的变化：1) 内部形态，通过 X 射线计算机断层扫描 (CT)；2) 数字全息显微镜 (DHM) 的 3-D 外皮结构；3) 血淋巴中的葡萄糖作为潜在的内源性冷冻保护剂。从 X 射线 CT 中，我们发现经受寒冷的前蛹和保持在环境温度下的蛹都遵循一个发展过程，即它们的脂肪含量减少，同时形成厚而致密的角质层。两组间脂肪体/致密组织的变化率没有差异。尽管如此，冷组在血淋巴含量水平上呈现出轻微的发育延迟。通过 DHM，我们再次获得了经受寒冷的前蛹在其发育过程中没有经历过停止。然而，现在在该组中在珠被粗糙度水平上观察到更明显的发育延迟。最后，关于葡萄糖，我们发现对照和环境温度幼虫的葡萄糖水平相似，而在受冷的幼虫中，51.7% 的葡萄糖水平明显增加。我们的整个结果提供了形态学和生化证据，表明即使在突然和严重的寒冷事件引起的静止状态下，RPW 的幼虫-蛹转变也几乎不受干扰。然而，在内部和外部形态中都观察到了一定的发育延迟。此外，仅在寒冷组中发现的升高的葡萄糖水平表明葡萄糖是 RPW 耐寒策略的一部分。