Recognition of the Pseudocryptic Species Xylosandrus declivigranulatus (Schedl) as Distinct from Xylosandrus crassiusculus (Motschulsky) (Coleoptera: Curculionidae: Scolytinae: Xyleborini)

Abstract Xylosandrus crassiusculus (Motschulsky, 1866) occupies worldwide temperate to tropical forests and suburban areas within its natural and non-native range as a result of human introductions. Given its pest status, several studies of population genetics have been conducted. As a result of an ongoing study, several smaller individuals from southern Thailand exhibited nucleotide differences that were dissimilar to the remaining individuals, thus calling into question the species status of these individuals. We performed a phylogenetic analysis of X. crassiusculus individuals from widely dispersed locations, including an individual from southern Thailand, and a robust sampling of other Xylosandrus Reitter, 1913 species using xyleborine diagnostic genes mtDNA COI and nucDNA CAD. The smaller individual from southern Thailand was sister to the remaining X. crassiusculus individuals and demonstrated >13% and >3% nucleotide difference in COI and CAD sequences, respectively. Upon the examination of type specimens, we confirmed that these smaller X. crassiusculus individuals were indeed Xylosandrus declivigranulatus (Schedl, 1936), status restored, which we resurrect. Its smaller size and pronotum as long as wide diagnose this pseudocryptic species from X. crassiusculus.