Genetic Variability Among Xyleborus glabratus Populations Native to Southeast Asia (Coleoptera: Curculionidae: Scolytinae: Xyleborini) and the Description of Two Related Species

The Essential Role of Taxonomic Expertise in the Creation of DNA Databases for the Identification and Delimitation of Southeast Asian Ambrosia Beetle Species (Curculionidae: Scolytinae: Xyleborini)

“…Most of the morphologically defined species for all genera exhibit 10-12% difference; thus, we contend that this observation is not the result of rampant cryptic speciation that one would expect given a 2% standard sequence divergence between species as promoted by the Barcode initiative (Hebert et al, 2003b; Ashfaq and Hebert, 2016). Cryptic species are evident at intraspecific differences ∼13%, such as in the E. fornicatus species complex and other lineages (Gomez et al, 2018;Cognato et al, 2019;Smith et al, in preparation). Our sequence data shows no evidence of Wolbachia or pseudogenes.…”

“…Anticipating the issue of high COI nucleotide divergence we tested the species identification potential of an alternative locus-in this case CAD. Although, any other gene locus could potentially provide species diagnostic DNA sequences such as, 28S rDNA, preliminary rDNA data suggested that the species level nucleotide variation of this locus was not consistant among scolytine taxa (Jordal and Kambestad, 2014;Cognato et al, 2019). We compare tree-based and DNA match methods for the identification of species and demonstrate the use of DNA barcodes for the discovery of species.…”

“…For the tree-based method, COI and CAD sequences were assembled in separate NEXUS files using the software PAUP version 4.0a (build 161) (Swofford, 2002). Previously published sequences were also included from studies in which we could verify the species status of vouchers (Cognato et al, 2011(Cognato et al, , 2015(Cognato et al, , 2019. These specimens provided a global context as many of these species occurred outside the study area.…”

“…Although there are potential issues and limitations of DNA barcoding using COI, preliminary data suggest the feasibility of identification and delimiting xyleborine species (Dole et al, 2010;Cognato et al, 2011Cognato et al, , 2015Cognato et al, , 2019Jordal and Kambestad, 2014;Stouthamer et al, 2017;Gomez et al, 2018). Studies of a few closely related species of different genera demonstrated: (1) The universal or scolytine specific barcoding COI primers produce PCR products and DNA sequences for most species; (2) nonmonophyletic species; (3) high intraspecific nucleotide difference (> 10% as compared to 2-3% for outbreeding scolytines) (4) the use of nuclear genes as alternative diagnostic loci; and (5) the results of a few studies identified new species (Gomez et al, 2018;Cognato et al, 2019). In addition, there are currently overlapping generations of scolytine taxonomists that can identify specimens to species and can interpret the DNA results in reference to these identifications.…”

Host density dependence and environmental factors affecting laurel wilt invasion

“…Although R. lauricola has been detected in X. glabratus in Asia (Dreaden et al 2019;Harrington et al 2011), laurel wilt disease has not been found in the US prior to the appearance of the X. glabratus (Ploetz et al 2013). R. lauricola populations are quite diverse in East Asia, but the pathogen and its vector seem to be clonal in the US (Cognato et al 2019;Dreaden et al 2019;Hughes et al 2017;Wuest et al 2017). This suggests that both were introduced in a single event, possibly being carried to the port of entry in untreated packing material Ploetz et al 2017).…”