Chemoreception in insects is crucial for many aspects related to food seeking, enemy avoidance, and reproduction. Different families of receptors and binding proteins interact with chemical stimuli, including odorant receptors (ORs), ionotropic receptors (IRs), gustatory receptors (GRs), odorant binding proteins (OBPs) and chemosensory proteins (CSPs). In this work, we describe the chemosensory-related gene repertoire of the worldwide spread pest Spodoptera exigua (Lepidoptera: Noctuide) focusing on the transcripts expressed in larvae, which feed on many horticultural crops producing yield losses. A comprehensive de novo assembly that includes reads from chemosensory organs of larvae and adults, and other larval tissues, enabled us to annotate 200 candidate chemosensory-related genes encoding 63 ORs, 28 IRs, 38 GRs, 48 OBPs and 23 CSPs. Of them, 51 transcripts are new annotations. RNA-seq and reverse transcription PCR analyses show that 50 ORs are expressed in larval heads, and 14 OBPs are larva-specific. To identify candidate ecologically-relevant odours for S. exigua larvae, we set up behavioural experiments with different volatile organic compounds (VOCs). 1-hexanol triggers attraction at the three timepoints tested and linalool repels larvae at any timepoints. Other five VOCs elicit behavioural response at single timepoint. Lastly, we tested if pre-exposure to single VOCs influence the expression patterns of selected ORs and pheromone binding proteins (PBPs), showing a massive and general up-regulation of some ORs after 24h exposure. This work sets the basis for the study of chemosensation in S. exigua larvae, boosting further studies aimed to characterize chemosensory-related genes that underlie ecologically-relevant behaviours of larval stage.

中文翻译：

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转录组学和行为的结合揭示了斜纹夜蛾幼虫的嗅觉系统

昆虫的化学感受对于与寻找食物，避免敌人和繁殖有关的许多方面至关重要。受体和结合蛋白的不同家族与化学刺激相互作用，包括气味受体（OR），离子型受体（IR），味觉受体（GRs），气味结合蛋白（OBP）和化学感应蛋白（CSP）。在这项工作中，我们描述了全世界传播的害虫Spodoptera exigua（鳞翅目：Noctuide）与化学感官相关的基因库，重点是幼虫中表达的转录本，这些转录本以许多园艺作物为食，导致产量下降。全面的从头包括从幼虫和成虫的化学感觉器官以及其他幼虫组织读取的汇编，使我们能够注释200个候选化学相关的基因，这些基因编码63个OR，28个IR，38个GR，48个OBP和23个CSP。其中，有51个笔录是新的注释。RNA-seq和逆转录PCR分析表明，在幼虫头部表达了50个OR，而14个OBP是幼虫特异性的。识别S. exigua与生态相关的候选气味幼虫，我们建立了不同挥发性有机化合物（VOC）的行为实验。1-己醇在测试的三个时间点触发吸引力，芳樟醇在任何时间点排斥幼虫。其他五个VOC在单个时间点引发行为响应。最后，我们测试了预先暴露于单个VOC是否会影响所选OR和信息素结合蛋白（PBP）的表达模式，从而显示24小时暴露后某些OR的大量普遍上调。这项工作为研究S. exigua幼虫的化学感觉奠定了基础，促进了旨在表征与幼虫阶段生态相关行为基础的化学传感相关基因的进一步研究。