New vectors: Scolytus chikisanii and S. japonicus (Scolytidae) associated with Dutch elm disease in Hokkaido, Japan

Scolytus esuriens is a vector of Dutch elm disease (DED) in Japan. However, small holes that were presumed to be irruption or flight holes of bark beetle species other than S. esuriens were observed at dead small branches of Japanese elms in Sapporo City, Hokkaido, Japan. In this study, bark beetles that use small branches of elm trees for breeding were surveyed as candidate DED vectors. It was determined if the causal fungi of DED, Ophiostoma ulmi and O. novo-ulmi, could be acquired from adult beetles. Two bark beetles were determined as new vectors: Scolytus chikisanii and S. japonicus. The morphology of feeding wounds on the crotches of living twigs by each vector species was investigated. Subsequently, the relative frequency of feeding wounds made by each bark beetle species was estimated based on the morphological type of feeding wounds on wilting twigs in the field. S. chikisanii and S. japonicus may have contributed more to the spread of infection than S. esuriens in the study area.