2018 Volume 100 Issue 4 Pages 116-123
Mass mortality of oak by Japanese oak wilt disease is caused by an ambrosia beetle vector, Platypus quercivorus. In northern Gunma Prefecture, a geographically isolated mass mortality occurred in Minakami in 2010 for the first time. We hypothesized three origins of the beetle population causing the isolated mass mortality: (1) a population recently migrated naturally or artificially from near or neighboring prefectures, which might exhibit a low genetic diversity due to founder effect; (2) a recently artificially migrated population from a distant area, which might have genetically different lineages and a low genetic diversity due to founder effect; and (3) an indigenous population, which exhibits a relatively high genetic diversity. We examined these hypotheses using variations of nuclear ribosomal DNA (rDNA), mitochondrial DNA (mtDNA), and nuclear microsatellite (nSSR) for Gunma and six other neighboring or nearby prefecture populations. Genetic structures of rDNA and nSSR showed that the Gunma population belonged to a northeastern Japanese Sea of Japan-side lineage, as had neighboring prefecture populations, indicating that the Gunma population did not recently migrate from a distant area with different lineages through human activity. Genetic diversity of mtDNA and nSSR indicated that the Gunma population exhibited a moderate genetic diversity, similar to the other populations. Therefore, we concluded that the Gunma population might have originated from an indigenous population.