The red-necked longhorn beetle (RLB; Aromia bungii [Faldermann, 1835]) is an emerging invasive pest. From its native range of East Asia, it invaded Europe and Japan in the early 2010s. Despite its increasing importance, the molecular resources of RLB are scarce, and its invasive dynamics are largely unknown. In the present study, we carried out the first analysis of its population genetic structure in South Korea, which is part of its native range, using 1248 bp cytochrome oxidase subunit I (COI) sequences of 199 individuals from 18 localities. We found that in South Korea, RLB has a moderate population genetic structure and can be divided into three geographical subgroups: central, southeastern, and southwestern subgroup. Comparative analyses with two Chinese, one German, and ten Italian RLB sequences yielded non-significant results because of largely missing genetic data from other native areas. Nevertheless, as it provided the first population genetic data for this invasive alien species (IAS) whose range is increasing, our research is a crucial molecular resource for future invasive dynamics research.

Monochamus alternatus Hope, 1842, is a major forest pest that hosts the pathogenic pinewood nematode (PWN), Bursaphelenchus xylophilus (Steiner and Buhrer, 1934) Nickle 1970. Taxonomically, M. alternatus is currently divided into two subspecies, based on morphology and geography: Monochamus alternatus alternatus Hope, 1842 in China, Taiwan, Tibet, Vietnam, and Laos and Monochamus alternatus endai Makihara, 2004 in South Korea and Japan. Despite their economic importance, the subspecies taxonomy of M. alternatus has never been tested after the first description. In this study, we aimed to reassess the subspecies taxonomy of M. alternatus using molecular and morphological data. For morphological analysis, we examined three major morphological characters (pronotal longitudinal band, granulation on humeri, and elytral proximomedial spine) from 191 individuals from China, Korea, and Taiwan. Population genetic structures were examined using 85 de novo sequences and 82 public COI sequences from China, Korea, Japan, Malaysia, Taiwan, and a few intercepted specimens from the United States. All the genetic data were aligned as three different multiple sequence alignments. Individuals from each subspecies were morphologically and genetically scattered, not clustered according to subspecies in any of the analyses. Therefore, a new synonymy is proposed: Monochamus alternatus Hope, 1842 = Monochamus alternatus endai, syn. n. This study suggests a more robust classification of M. alternatus for the first time and ultimately will pose a substantial impact on implementing quarantine or forestry policies.