Colonisation success of a tree-killing bark beetle: Geographic variation and mismatch with host preference

<p><span>The preference–performance hypothesis (PPH) predicts that female insects maximise their fitness by ovipositing on hosts where their offspring perform the best. The preference–performance relationships in bark beetles are complex because before offspring development can occur in the phloem, adult bark beetles must first successfully invade host trees, and then construct galleries beneath the bark. Therefore, a positive correlation between host preference and successful colonisation is necessary for the PPH in bark beetles to hold (i.e., the preference–colonisation hypothesis in bark beetles).<br>In this study, through field choice experiments, I investigated the successful colonisation of the bark beetle,<em> Polygraphus proximus</em>, within four allopatrically distributed Abies species across a distinct biogeographic boundary in Japan.<br>The results of this study showed that the biogeographic boundary did not limit the successful colonisation by<em> P. proximus</em>. I observed that successful colonization was low in <em>A. firma</em>, despite it being an exotic species and the most preferred at the study sites, indicating a mismatch between preference and colonization success. Additionally, I observed that <em>A. sachalinensis</em> had a high colonization success rate, even though it was the least preferred species at the study sites.<br>The results suggest that the host preference of <em>P. proximus</em> has not been adjusted by colonisation success through natural selection. The absence of significant differences in colonisation success across the Tsugaru Strait, and the preference–colonisation mismatches imply that genetic factors do not contribute to host specialisation.</span></p>