Host preference of a tree-killing bark beetle across a geographic boundary separating host species

<p><span>The life cycles of bark beetles are intimately linked to their host species. Therefore, bark beetle species are expected to show traits that vary among different host species and across geographic ranges. The taxonomic proximity of host tree species can also influence host selection. <em>Abies</em> species native to Japan are genetically classified into three phylogenetic groups. Their natural distributions are separated by a </span><span>distinct biogeographic boundary in Japan (i.e. the Tsugaru Strait, also referred to as Blakiston's Line)</span><span>. Especially, <em>A. sachalinensis</em> is the only species native to Hokkaido, north of the </span><span>Tsugaru Strait</span><span>. I, therefore, investigated the host preference of <em>Polygraphus proximus</em> Blandford within four allopatrically distributed <em>Abies</em> species across the north and south of the Tsugaru Strait</span> <span>through field surveys and field choice experiments</span><span>.</span> <span>Field observations and field host-choice bioassays showed that <em>A. sachalinensis</em> was less severely attacked by <em>P. proximus</em> than was <em>A. veitchii</em> on both sides of the Tsugaru Strait.</span><span> The beetles also </span><span>preferred to attack <em>A. firma</em> (which </span><span>belongs to a genetically distinct group (i.e., the section <em>Momi</em>) from that of <em>A. veitchii</em> and <em>A. sachalinensis</em> (i.e., the section <em>Balsamea</em>)), over </span><em><span>A</span></em><span><em>. sachalinensis</em> in both Hokkaido and Honshu</span><span>. Although </span><em><span><span>A</span><span>.</span></span><span>homolepis</span></em><span> also belongs to the section <em>Momi</em>,</span> <em><span>A</span></em><span><em>. firma</em> and </span><em><span>A</span></em><span><em>. veitchii</em> had more attacks t</span><span>han </span><em><span><span><span>A</span><span>. </span></span><span>homolepis</span></span></em>. <span>Th</span><span>e res</span><span>ults provide evidence that </span><em><span>P</span><span>. proximus</span></em><span> does not show specialization across the different parts of their geographic range where the host species are different, and there is no positive correlation between taxonomic proximity and host preference for </span><em><span>P</span><span>. proximus</span></em><span>.</span></p>