Species diversity and Host Plant Associations of Scolytine Ambrosia Beetle (Curculionidae: Scolytinae) in Southeast Asian Tropical Forests in Laos and Vietnam, revealed by DNA barcoding

1. The weevil subfamily Scolytinae represents a highly diverse group of beetles, comprising over 6,000 described species classified into 26 tribes and 246 genera. These beetles are predominantly found in forests worldwide, with their highest diversity occurring in tropical forests of Asia.2. Despite their economic and ecological importance, knowledge of their host plant diversity remains limited. Accurate host plant data are essential for pest risk assessment, monitoring invasive species, and mitigating their introduction through international plant and wood trade.3. Therefore, this study establishes a DNA barcoding framework to elucidate the host plant diversity associated with ambrosia beetle diversity, sampled directly from their host trees in the tropical forests of Laos and Vietnam.4. In this study, we included 130 ambrosia sequence samples representing 27 species and 16 genera based on mitochondrial cytochrome oxidase I (COI) gene sequences. We also analyzed 30 host plant species representing 17 different plant families using nuclear ribosomal internal transcribed spacer (ITS) and the chloroplast maturase K (<i>matK</i>) sequences.5. We observed substantial variation in host specificity and dominance among ambrosia beetle taxa. <i>Xylosandrus crassiusculus</i> emerged as the most frequently recorded and dominant generalist species, associated with 19 host plant species across 12 families, accounting for 63% of all host plant records. Phylogenetic analysis indicated that closely related beetle species tend to utilize similar host plant families.6. On the other hand, polyphyletic genera exhibited complex evolutionary histories, and shared host use among distantly related clades pointed to ecological convergence. Interestingly, most of the host plant associations documented in this study represent the first recorded hosts for ambrosia beetles in tropical forests of Southeast Asia.