Genetic Diversity and Phenotypic Variation in Korean Populations of the Japanese Rhinoceros Beetle Trypoxylus dichotomus (Linnaeus, 1771)

Abstract

The Japanese rhinoceros beetle Trypoxylus dichotomus (Linnaeus, 1771) is an important industrial insect in Korea. However, recent market stagnation and declining consumer demand emphasize the importance of assessing the genetic diversity of domestic stocks, providing a foundation for selective breeding and resource management. In this study, we compared phenotypic traits and mitochondrial genetic diversity among seven regional populations (referred to as SH, YD, YW, OC, SC, YI, and AS), all obtained from commercial insect farms. We detected substantial phenotypic variation under standardized laboratory conditions. The SH population exhibited superior larval growth (particularly in males) and larger adult size traits, whereas AS and YI consistently showed lower performance. Fecundity displayed high within-population variance and no significant differences among populations. A mitochondrial cytochrome oxidase I (COI) analysis revealed eight haplotypes with extremely low divergence (0.1%–0.3%), with no clear geographic structure and the dominance of a single haplotype across populations. Bayesian clustering (BAPS) and principal coordinate analysis (PCoA) indicated that SH and YW formed distinct clusters, clearly separated from other populations. Based on phenotypic and genetic data, SH was identified as a promising candidate for selective breeding. The overall lack of genetic variability raises concerns about population resilience against pathogens and environmental stressors. Diversifying genetic resources, incorporating nuclear and genome-wide markers, and developing crossbreeding strategies will be essential for ensuring the sustainable development of Trypoxylus dichotomus stocks in Korea.