Changes in plant secondary metabolism due to insect galls are one of the frontiers in knowledge of plant-insect interactions, especially concerning volatile organic compounds (VOCs). Here we studied the in vivo VOCs released from healthy apical branches of Haplopappus foliosus DC. (Asteraceae) and compared these volatiles to the VOCs obtained from apical bud galls produced in this host plant when attacked by the gall midge Haplopappusmyiia gregaria (Cecidomyiidae). We field-collected VOCs by dynamic headspace and identified them by gas chromatography coupled to mass spectrometry. We found changes in the relative proportions of different classes of VOC in apical branches vs. apical bud galls. H. foliosus VOCs had mainly monoterpene hydrocarbons such as p-cymene, a recognized herbivore deterrent. We also found oxygenated monoterpenes and sesquiterpenes in the H. foliosus volatile mixture. H. foliosus modifies its fragrance composition when parasitized by gall midges, showing an increased proportion of some monoterpene hydrocarbons, e.g. limonene and camphene, while others such as α-thujene, p-cymene and γ-terpinene were down-expressed in apical bud gall VOCs. We discuss these results considering gall signaling and chemical ecology hypotheses, including the potential role of plant defenses as well as gall midge-derived modification for host plant VOCs, and comment on the ecological relevance of our findings.

由虫瘿引起的植物次生代谢变化是植物-昆虫相互作用知识的前沿之一，尤其是关于挥发性有机化合物 (VOC)。在这里，我们研究了从Haplopappus foliosus DC 的健康顶端分支释放的体内VOC 。(Asteraceae) 并将这些挥发物与从这种寄主植物被瘿蚊Haplopappusmyiia gregaria ( Cecidomyiidae )攻击时产生的顶端芽瘿中获得的 VOC 进行比较。我们通过动态顶空现场收集 VOC，并通过气相色谱与质谱联用对其进行鉴定。我们发现顶枝与顶芽瘿中不同类别 VOC 的相对比例发生变化。H. foliosusVOC 主要含有单萜碳氢化合物，如对伞花烃，这是一种公认​​的草食动物威慑剂。我们还在H. foliosus挥发性混合物中发现了含氧单萜和倍半萜。H. foliosus在被瘿蠓寄生时会改变其香味成分，显示某些单萜碳氢化合物的比例增加，例如。柠檬烯和莰烯，而其他如 α-thujene、p-cymene 和 γ-terpinene 在顶芽瘿 VOCs 中被下调。我们在考虑瘿信号和化学生态学假设的情况下讨论这些结果，包括植物防御的潜在作用以及瘿蚊衍生的宿主植物 VOC 修饰，并评论我们的研究结果的生态相关性。