USDA Forest Service, Pacific Northwest Research Station, Corvallis, OR 97331, USA.
J Chem Ecol. 2013 Apr;39(4):494-506. doi: 10.1007/s10886-013-0271-6. Epub 2013 Mar 24.
Ethanol in sapwood was analyzed along vertical transects, through small spot cankers and larger basal cankers, of Phytophthora ramorum-infected stems of Quercus agrifolia at three sites in California. Trees with large basal cankers, known to attract scolytid beetles, had a 4.3 times higher ethanol level than trees with spot cankers that attract fewer beetles. Ethanol concentrations inside cankers, where scolytid beetles preferentially attack, varied by about four orders of magnitude among samples, with a median level of 16.0 μg.g(-1) fresh mass. This concentration was 4.3 and 15.5 times greater, respectively, than the concentrations at 1 cm or 15-30 cm outside the canker boundaries. In the laboratory, we demonstrated that ethanol escaped through the bark of a Q. garryana log just 3 days after it was added to the sapwood. At the three study sites, traps baited with ethanol captured more Xyleborinus saxesenii, Pseudopityophthorus pubipennis, and Monarthrum dentiger (all Coleoptera: Curculionidae: Scolytinae) than traps baited with ethanol plus (-)-α-pinene, or ethanol plus 4-allylanisole (4AA). Logs of Q. agrifolia with a 50 % ethanol solution added to the sapwood were placed at the study sites, with or without additional bark treatments above the ethanol. The number of scolytid beetle gallery holes above the ethanol-infused sapwood was 4.4 times greater than that on the opposite side of the log where no ethanol was added. Attachment of ultra-high release (-)-α-pinene pouches to the bark surface above the 50 % ethanol solution reduced scolytid attacks to a density of 19.1 % that of logs without this treatment. We conclude that ethanol in P. ramorum cankers functions as a primary host attractant for scolytid beetles and is an important link in colonization of these cankers and accelerated mortality of Q. agrifolia. The results of this research shed light on the chemical ecology behind the focused scolytid attacks on P. ramorum-infected coast live oaks, and lay the groundwork for future efforts to prolong the survival of individual trees of this keystone species.
在加利福尼亚州的三个地点，对感染疫霉的三叶杨树干进行了分析，这些树干的边材中含有乙醇，并沿垂直的横切面穿过小的点状溃疡和较大的基部溃疡。已知吸引刻梢小蠹的大树基部溃疡，其乙醇水平比吸引较少刻梢小蠹的点状溃疡高出 4.3 倍。在刻梢小蠹优先攻击的溃疡内部，乙醇浓度在样本之间变化约四个数量级，中位数为 16.0 μg.g(-1)新鲜质量。与溃疡边界 1 cm 或 15-30 cm 外的浓度相比，这一浓度分别高出 4.3 和 15.5 倍。在实验室中，我们证明乙醇仅在添加到边材后 3 天就从灰柏原木的树皮中逸出。在三个研究地点，用乙醇诱饵捕获的 Xyleborinus saxesenii、Pseudopityophthorus pubipennis 和 Monarthrum dentiger（鞘翅目：象甲科：小蠹科）比用乙醇加（-）-α-蒎烯或乙醇加 4-丙烯基茴香醚（4AA）诱饵捕获的多。将灰柏原木的边材中加入 50%乙醇溶液，然后放置在研究地点，在乙醇上方的树皮上进行或不进行额外处理。在注入乙醇的边材上方有雕刻甲虫画廊孔的数量是原木另一侧的 4.4 倍，而另一侧没有注入乙醇。将超高释放（-）-α-蒎烯袋附着在 50%乙醇溶液上方的树皮表面上，将雕刻小蠹的攻击密度降低到未进行这种处理的原木的 19.1%。我们得出的结论是，疫霉菌溃疡中的乙醇是雕刻小蠹的主要宿主引诱剂，是这些溃疡的定殖和加速三叶杨死亡的重要环节。这项研究的结果揭示了疫霉菌感染的海岸红杉受聚焦性刻梢小蠹攻击的化学生态，并为未来延长这种关键物种的个体树木生存的努力奠定了基础。
