From glacial echoes to timber pathways: Climatic–historical drivers and timber‐trade influence on the phylogeography of Ips sexdentatus in the Basque Country

Ips sexdentatus is a major pine‐infesting bark beetle in southern Europe whose range is expanding as climate warming increases habitat suitability. In the Basque Country, this species has the ability to kill trees at early stages of decline, including Pinus sylvestris , P. radiata , P. nigra and P. pinaster, and serves as a vector of the quarantine pathogen Fusarium circinatum , the causal agent of pine pitch canker. By creating infection courts and carrying fungal propagules, the beetle accelerates pathogen transmission and contributes to pine decline. This study aims to characterize the genetic diversity and population structure of I. sexdentatus across Europe, with particular emphasis on Basque populations, and to assess the influence of historical processes, host availability and timber‐transport networks on its dispersal. Mitochondrial COI sequences from 668 individuals representing 69 populations were analysed to evaluate haplotype diversity, phylogeographic structure and spatial genetic patterns. A total of 106 haplotypes were identified, including several newly described ones concentrated in Iberian populations, confirming this region as a hotspot of genetic diversity. The coexistence of widespread haplotypes with rare, localized variants reflects both long‐term refugial persistence and more recent expansion. Basque populations exhibited an almost panmictic structure, with weak spatial differentiation and no significant association between host diversity and haplotype richness. The absence of host‐associated structure aligns with the species' broad host range across Pinus spp., which limits host‐driven divergence. Overall, the results indicate that climatic suitability and historical demographic processes are key determinants of genetic patterns in I. sexdentatus .