Transcriptome Analyses of the Honeybee Response to <i>Nosema ceranae</i> and Insecticides

Honeybees (Apis mellifera) are constantly exposed to a wide variety of environmental stressors such as parasites and pesticides. Among them, Nosema ceranae and neurotoxic insecticides might act in combination and lead to a higher honeybee mortality. We investigated the molecular response of honeybees exposed to N. ceranae, to insecticides (fipronil or imidacloprid), and to a combination of both stressors. Midgut transcriptional changes induced by these stressors were measured in two independent experiments combining a global RNA-Seq transcriptomic approach with the screening of the expression of selected genes by quantitative RT-PCR. Although N. ceranae-insecticide combinations induced a significant increase in honeybee mortality, we observed that they did not lead to a synergistic effect. According to gene expression profiles, chronic exposure to insecticides had no significant impact on detoxifying genes but repressed the expression of immunity-related genes. Honeybees treated with N. ceranae, alone or in combination with an insecticide, showed a strong alteration of midgut immunity together with modifications affecting cuticle coatings and trehalose metabolism. An increasing impact of treatments on gene expression profiles with time was identified suggesting an absence of stress recovery which could be linked to the higher mortality rates observed.西方蜜蜂（Apis mellifera）持续暴露于各类环境胁迫因子，诸如寄生虫与杀虫剂。其中，蜂房微孢子虫（Nosema ceranae）与神经毒性杀虫剂可能产生复合作用，进而升高蜜蜂死亡率。本研究对暴露于蜂房微孢子虫（Nosema ceranae）、杀虫剂（氟虫腈（fipronil）或吡虫啉（imidacloprid））以及两种胁迫因子联合处理的西方蜜蜂的分子响应进行了探究。通过两项独立实验，结合全局RNA测序（RNA-Seq）转录组学方法与实时定量反转录聚合酶链式反应（quantitative RT-PCR）筛选选定基因表达的方案，研究测定了这些胁迫因子诱导的蜜蜂中肠转录变化。尽管蜂房微孢子虫与杀虫剂的复合处理显著提升了蜜蜂死亡率，但并未观测到协同效应。根据基因表达谱分析结果，长期暴露于杀虫剂对蜜蜂的解毒基因无显著影响，但会抑制免疫相关基因的表达。单独或联合杀虫剂处理的蜂房微孢子虫感染蜜蜂，其中肠免疫功能出现显著改变，同时伴随表皮涂层与海藻糖代谢相关的修饰变化。研究还发现，随着时间推移，不同处理对基因表达谱的影响逐渐增强，这表明蜜蜂未能实现胁迫恢复，该现象或与观测到的更高死亡率存在关联。