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

<i>Scolytus esuriens</i> 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 <i>S. esuriens</i> 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, <i>Ophiostoma ulmi</i> and <i>O. novo-ulmi</i>, could be acquired from adult beetles. Two bark beetles were determined as new vectors: <i>Scolytus chikisanii</i> and <i>S. japonicus</i>. 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. <i>S. chikisanii</i> and <i>S. japonicus</i> may have contributed more to the spread of infection than <i>S. esuriens</i> in the study area.