Thick bark has been shown to protect trees from wildfires, but can it protect trees from an ambrosia beetle attack? We addressed this question by examining the distribution of holes of the invasive Kuroshio Shot Hole Borer (KSHB, Euwallacea kuroshio; Coleoptera: Scolytinae) in the bark of Goodding’s black willow (Salix gooddingii), one of the KSHB’s most-preferred hosts. The study was conducted in the Tijuana River Valley, California, in 2016–17, during the peak of the KSHB infestation there. Using detailed measurements of bark samples cut from 27 infested trees, we tested and found support for two related hypotheses: (1) bark thickness influences KSHB attack densities and attack locations, i.e., the KSHB bores abundantly through thin bark and avoids boring through thick bark; and (2) bark thickness influences KSHB impacts, i.e., the KSHB causes more damage to thinner-barked trees than to thicker-barked trees. Our results indicate that thick bark protects trees because it limits the density of KSHB entry points and thereby limits internal structural damage to low, survivable levels. This is the first study to identify bark thickness as a factor that influences the density of KSHB—or any ambrosia beetle—in its host tree, and the first to link bark thickness to rates of host tree mortality.

中文翻译：

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浓厚的树皮可以保护树木免受严重的甲虫侵袭

已经证明，浓密的树皮可以保护树木免受野火的侵害，但是它可以保护树木免受甲虫侵袭吗？我们通过检查侵入性黑潮子Shot孔虫（KSHB，Euwallacea kuroshio;鞘翅目：Scolytinae）在Goodding的黑柳树（Salix gooddingii）的树皮中的孔的分布来解决这个问题，黑柳树是KSHB最受欢迎的寄主之一。该研究于2016-17年在加利福尼亚的蒂华纳河谷进行，当时那里的KSHB感染高峰。通过对27种受侵染树木的树皮样本进行详细测量，我们测试并发现了两个相关假设的支持：（1）树皮厚度影响KSHB的攻击密度和攻击位置，即KSHB在细皮上大量钻孔并且避免了在粗皮上钻孔; （2）树皮厚度会影响KSHB的影响，即 KSHB对树皮较细的树木造成的损害要大于树皮较厚的树木。我们的结果表明，较厚的树皮可以保护树木，因为它限制了KSHB入口点的密度，从而将内部结构破坏限制在较低的可存活水平。这是第一个将树皮厚度确定为影响其寄主树中KSHB或任何沙棘甲虫密度的因素的研究，也是第一个将树皮厚度与寄主树死亡率联系起来的研究。