Abstract
The ambrosia beetle, Platypus quercivorus, is an insect vector of the Ascomycete fungus, Raffaelea quercivora, the causal agent of Japanese oak wilt disease. In this study, we compared the nucleotide sequences (937–955 bp) of the nuclear 28S rDNA fragment, including the D1 and D2 expansion segment, among local populations of the beetle in Japan. Sequence analysis of 81 beetles from 32 collection sites ranging from the Ryukyu Islands to northern Honshu Island showed seven types of sequences, many of which were separated among different geographic areas. Phylogenetic analysis showed that these sequence types were separated between two deeply divergent genetic groups, suggesting the necessity for taxonomic reexamination of this species. DNA typing of beetles and oak wilt status at the collection sites indicated that several genetically divergent beetle populations are associated with the incidence of the disease. This is the first investigation of genetic variation in the ambrosia beetle across Japan.
