Volume 41 (2006) Issue 1 Pages 123-128
Adult Platypus quercivorus beetles were artificially inoculated into Japanese oak trees (Quercus crispula). Two inoculation methods were used: uniform inoculation through pipette tips, and random inoculation by release into netting. Four of the five trees that were inoculated uniformly died, as did all five trees that were inoculated at random. Seven of the nine dead trees showed the same wilting symptoms seen in the current mass mortality of oak trees. Raffaelea quercivora, which has been confirmed to be the pathogenic fungus that causes wilt disease and is usually isolated from the mycangia of P. quercivorus, was isolated from all of the inoculated dying trees. Trees that died faster showed a higher density of beetle galleries that succeeded in producing offspring. We found positive relationships between the density of beetle galleries that succeeded in producing offspring and the rate of discoloration in the sapwood and the isolation rate of R. quercivora. Therefore, we clearly demonstrated that P. quercivorus is a vector of R. quercivora, and that the mass mortality of Japanese oak trees is caused by mass attacks of P. quercivorus.