Wilt Disease of Fagaceae Trees Caused by Platypus quercivorus (Murayama) (Coleoptera : Platypodidae) and the Associated Fungus

Aim Is to Clarify the Damage Factor

Abstract

Wilt disease of Fagacea trees bored by Platypus quercivorus has increased in various districts in Japan. We collated information on the damage and discussed the damage factor. It is proved that Raffaelea quercivora isolated frequently from damaged trees is a pathogen, and P. quercivorus is the vector of the pathogen. Trees are killed by the spreading of discolored areas in sapwood where the tracheary function is lost. The loss of the tracheary function is caused by R. quercivora which is carried in large quantities by themass attack of P. quercivorus and spreads around the beetle's galleries. The mass attack of P. quercivorus is induced by aggregation pheromones emitted fromunmated male beetles, and this occurs easily when the population density of the beetles is high. P. quercivorus prefers large trees or fallen trees, because the former have large breeding capacity and high water content maintained for along time, and the latter discharge hardly any sap inhibiting the reproduction of the beetles. Such suitable hosts increase the population density of the beetles. Investigations of the damaged forests indicate that the damage beginsjust after trees are felled or blown down by wind in stands with many large trees. This information suggests that the increase of large trees caused by the neglect of fuel wood forests is occurring everywhere, and in this situation, thefirst damage was caused by the infestation of a large population of P. quercivorus that reproduced using windfall trees or felled trees.