The ambrosia beetle Euwallacea fornicatus Eichhoff sensu lato is a complex of genetically divergent emerging pests responsible for damages to tree industries and ecosystems around the world. All lineages within the species complex are currently considered morphologically identical, presenting problems for their delineation and highlighting the shortcomings of species concepts based solely on type-specimen morphology. The objectives of this work were to 1) broaden the geographic sampling of the E. fornicatus complex in Asia, 2) reconstruct relationships between clades and populations, 3) find morphological characters or combinations of characters which are useful in delimiting the genetic lineages of the E. fornicatus species complex, and 4) propose taxonomic delimitation of species where morphology and phylogenetic identity correlate. Our integrated approach using molecular and morphological evidence suggests four clades that differ morphologically, but with overlap, therefore, cytochrome oxidase c subunit I (COI) barcoding remains necessary for assigning specimens to a clade. The following taxonomic changes are proposed: E. fornicatus (Eichhoff 1868) (= ‘Tea Shot Hole Borer Clade a’); E. fornicatior (Eggers 1923), stat. rev. (= ‘Tea Shot Hole Borer Clade b’); E. whitfordiodendrus (Schedl 1942), stat. rev. (= ‘Polyphagous Shot Hole Borer’); and E. kuroshio Gomez and Hulcr, sp. nov. (= ‘Kuroshio Shot Hole Borer’). This approach delivers a practical, evidence-based guidance for species delineation that can address overlapping variation in morphological characters of an emerging pest species complex.

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