Plants Attract Parasitic Wasps to Defend Themselves against Insect Pests by Releasing Hexenol

BackgroundPlant volatiles play an important role in defending plants against insect attacks by attracting their natural enemies. For example, green leaf volatiles (GLVs) and terpenoids emitted from herbivore-damaged plants were found to be important in the host location of parasitic wasps. However, evidence of the functional roles and mechanisms of these semio-chemicals from a system of multiple plants in prey location by the parasitoid is limited. Little is known about the potential evolutionary trends between herbivore-induced host plant volatiles and the host location of their parasitoids.
Methodology/Principal FindingsThe present study includes hierarchical cluster analyses of plant volatile profiles from seven families of host and non-host plants of pea leafminer, Liriomyza huidobrensis, and behavioral responses of a naive parasitic wasp, Opius dissitus, to some principal volatile compounds. Here we show that plants can effectively pull wasps, O. dissitus, towards them by releasing a universally induced compound, (Z)-3-hexenol, and potentially keep these plants safe from parasitic assaults by leafminer pests, L. huidobrensis. Specifically, we found that volatile profiles from healthy plants revealed a partly phylogenetic signal, while the inducible compounds of the infested-plants did not result from the fact that the induced plant volatiles dominate most of the volatile blends of the host and non-host plants of the leafminer pests. We further show that the parasitoids are capable of distinguishing the damaged host plant from the non-host plant of the leafminers.
Conclusions/SignificanceOur results suggest that, as the most passive scenario of plant involvement, leafminers and mechanical damages evoke similar semio-chemicals. Using ubiquitous compounds, such as hexenol, for host location by general parasitoids could be an adaptation of the most conservative evolution of tritrophic interaction. Although for this, other compounds may be used to improve the precision of the host location by the parasitoids.

研究背景
植物挥发性物质通过吸引昆虫天敌，在植物抵御虫害侵袭过程中发挥关键作用。例如，植食性昆虫为害的植物所释放的绿叶挥发物（green leaf volatiles，GLVs）与萜类化合物，已被证实对寄生蜂的寄主定位具有重要意义。然而，针对多植物系统中，信息化合物在寄生蜂猎物定位过程中的功能角色与作用机制的相关研究证据仍较为有限；目前学界对于植食性昆虫诱导的寄主植物挥发性物质与其寄生蜂寄主定位之间的潜在进化趋势，尚缺乏足够了解。
方法/主要发现
本研究针对豌豆斑潜蝇（Liriomyza huidobrensis）的寄主与非寄主植物共7个科的挥发性物质谱开展层级聚类分析，并检测了未经历过寄主搜寻的寄生蜂（Opius dissitus）对部分主要挥发性化合物的行为响应。本研究证实，植物可通过释放普遍诱导产生的化合物(Z)-3-己烯醇，有效吸引寄生蜂O. dissitus，从而帮助植物抵御斑潜蝇害虫L. huidobrensis的寄生侵害。具体而言，健康植物的挥发性物质谱呈现部分系统发育信号，而受虫害植物的诱导型化合物并非源于：诱导型植物挥发性物质主导了斑潜蝇寄主与非寄主植物的绝大多数挥发性混合组分。我们进一步发现，寄生蜂能够区分受虫害的斑潜蝇寄主植物与非寄主植物。
结论与意义
本研究结果表明，就植物参与的最被动模式而言，斑潜蝇为害与机械损伤均可诱发相似的信息化合物。对于广食性寄生蜂而言，借助己烯醇等广谱存在的化合物开展寄主定位，可能是三营养级互作最保守的进化适应策略。尽管如此，寄生蜂仍可利用其他化合物以提升寄主定位的精准度。