Martini Xavier, Hughes Marc A, Killiny Nabil, George Justin, Lapointe Stephen L, Smith Jason A, Stelinski Lukasz L
Entomology and Nematology Department, North Florida Research and Education Center, University of Florida, 155 Experiment Road, Quincy, FL, 32351, USA.
Entomology and Nematology Department, Citrus Research and Education Center, University of Florida, 700 Experiment Station Rd, Lake Alfred, FL, 33850, USA.
J Chem Ecol. 2017 May;43(5):519-531. doi: 10.1007/s10886-017-0843-y. Epub 2017 Apr 28.
The redbay ambrosia beetle Xyleborus glabratus is the vector of the symbiotic fungus, Raffaelea lauricola that causes laurel wilt, a highly lethal disease to members of the Lauraceae family. Pioneer X. glabratus beetles infect live trees with R. lauricola, and only when tree health starts declining more X. glabratus are attracted to the infected tree. Until now this sequence of events was not well understood. In this study, we investigated the temporal patterns of host volatiles and phytohormone production and vector attraction in relation to laurel wilt symptomology. Following inoculations with R. lauricola, volatile collections and behavioral tests were performed at different time points. Three days after infection (DAI), we found significant repellency of X. glabratus by leaf odors of infected swamp bay Persea palustris as compared with controls. However, at 10 and 20 DAI, X. glabratus were more attracted to leaf odors from infected than non-infected host plants. GC-MS analysis revealed an increase in methyl salicylate (MeSA) 3 DAI, whereas an increase of sesquiterpenes and leaf aldehydes was observed 10 and 20 DAI in leaf volatiles. MeSA was the only behaviorally active repellent of X. glabratus in laboratory bioassays. In contrast, X. glabratus did not prefer infected wood over healthy wood, and there was no associated significant difference in their volatile profiles. Analyses of phytohormone profiles revealed an initial increase in the amount of salicylic acid (SA) in leaf tissues following fungal infection, suggesting that the SA pathway was activated by R. lauricola infection, and this activation caused increased release of MeSA. Overall, our findings provide a better understanding of X. glabratus ecology and underline chemical interactions with its symbiotic fungus. Our work also demonstrates how the laurel wilt pathosystem alters host defenses to impact vector behavior and suggests manipulation of host odor by the fungus that attract more vectors.
红脂大小蠹Xyleborus glabratus是共生真菌劳雷尔散斑壳Raffaelea lauricola的传播媒介，该真菌会引发月桂枯萎病，这是一种对樟科植物具有高度致死性的疾病。先锋红脂大小蠹甲虫会用劳雷尔散斑壳感染活树，并且只有当树木健康状况开始下降时，才会有更多的红脂大小蠹被吸引到受感染的树上。到目前为止，这一系列事件还没有得到很好的理解。在本研究中，我们调查了宿主挥发物和植物激素产生的时间模式以及与月桂枯萎病症状相关的媒介吸引力。在用劳雷尔散斑壳接种后，在不同时间点进行了挥发物收集和行为测试。感染后三天（DAI），我们发现与对照相比，受感染的沼地月桂Persea palustris的叶片气味对红脂大小蠹具有显著的驱避作用。然而，在感染后10天和20天，红脂大小蠹对受感染宿主植物的叶片气味比未受感染的宿主植物更具吸引力。气相色谱 - 质谱分析显示，感染后3天甲基水杨酸（MeSA）增加，而在感染后10天和20天，叶片挥发物中倍半萜和叶醛增加。在实验室生物测定中，MeSA是红脂大小蠹唯一具有行为活性的驱避剂。相比之下，红脂大小蠹并不更喜欢受感染的木材而非健康木材，并且它们的挥发物谱没有相关的显著差异。植物激素谱分析显示，真菌感染后叶片组织中水杨酸（SA）的含量最初会增加，这表明SA途径被劳雷尔散斑壳感染激活，并且这种激活导致MeSA释放增加。总体而言，我们的研究结果有助于更好地理解红脂大小蠹的生态学，并强调了其与共生真菌的化学相互作用。我们的工作还展示了月桂枯萎病病理系统如何改变宿主防御以影响媒介行为，并表明真菌对宿主气味的操纵会吸引更多的媒介。
