1 The ambrosia beetle morphologically identified as Euwallacea fornicatus consists of several cryptic species that exhibit large differences in the DNA sequences of several nuclear and mitochondrial gene regions. 2 Based on these differences, we suggest that there are at least three different species each with distinct phylogeography. 3 Members of this cryptic species complex have invaded many areas outside their native range and cause substantial damage to both agriculture (avocado in particular) and other tree species. 4 Three of these cryptic species have invaded the USA: two species in California and a third species in both Florida and Hawaii. 5 Identification of their native range allows directed search for their natural enemies that may be used in biological control of these tree pests.

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.

DNA holds great potential for species identification and efforts to create a DNA database of all animals and plants currently contains >7.5 million sequences representing Cognato et al. Taxonomic Expertise Improves Beetle DNA-Identification species was poor. In a demonstration of iterative taxonomy, we constructed parsimonybased phylogenies using COI and CAD sequences for two genera. Although not all clades were resolved or supported, we provided better explanations for species boundaries in light of morphological and DNA sequence differences. Confident species identifications demonstrated <3% COI and <1% CAD difference and recognition of new species became more probable when there was >10-12% COI and/or >2-3% CAD. Involvement of taxonomic experts from the start of this project was essential for the creation of a stable foundation for the DNA identification of xyleborine species. In general, their role in DNA barcoding cannot be underestimated and is further discussed.

The present state of knowledge of the scolytine ambrosia beetles of Thailand is summarised to provide a basis for future studies of the fauna and its economic importance in forestry, timber production and crop tree plantations. A checklist of the fauna is provided with information on local and world distribution, host trees, biology and taxonomy. Six faunal elements based on geographical distribution, and the host tree and altitudinal preferences of species are discussed. One hundred and sixty-one species are recorded from Thailand, 67 of them for the first time. The following new synonym is proposed: Euwallacea wallacei (Blandford) (= Xyleborus barbatomorphus Schedl n.syn.). The following new combinations are given: Ambrosiophilus cristatulus (Schedl), Ambrosiophilus latisulcatus (Eggers), Beaverium dihingensis (Eggers), Beaverium lantanae (Eggers) and Immanus desectus (Eggers) are transferred from their present position in Ambrosiodmus; Ancipitis depressus (Eggers) and Ancipitis punctatissimus (Eichhoff) are transferred from Leptoxyleborus; Cyclorhipidion armipenne (Schedl), Cyclorhipidion inarmatum (Eggers), Euwallacea semiermis (Schedl), Fortiborus macropterus (Schedl), Microperus nudibrevis (Schedl) and Wallacellus minutus (Blandford) are transferred from Xyleborus.

Ten species of ambrosia beetles of the tribe Xyleborini,Amasabeesoni(Eggers, 1930),Amasaopalescens(Schedl, 1937),Amasacylindrotomica(Schedl, 1939),ArixyleborushirsutulusSchedl, 1969,Beaveriumlatus(Eggers, 1923),Cnestusprotensus(Eggers, 1930),Coptodryasquadricostata(Schedl, 1942),CryptoxyleborusconfususBrowne, 1950,Cryptoxyleboruspercuneolus(Schedl, 1951) andCyclorhipidionvigilans(Schedl, 1939), are recorded here for the first time in Thailand. Diagnostic characters, illustrations, distribution and biological data are provided for each species.Xylosandrusramulorum(Schedl, 1957),stat. res.is removed from synonymy withAmasacylindrotomicaand reinstated as a valid species.