Seasonal variation in ambrosia and bark beetle assemblages in two forest types in southern Japan

Ambrosia and bark beetles have been widely studied in both tropical and temperate forest regions. However, studies on their diversity across different forest types and their seasonal variation in the warm-temperate forest of Japan remains limited. We investigated the diversity and seasonal variation of ambrosia and bark beetles across two forest types in southern Japan. We collected ambrosia and bark beetles using flight interception traps set in Japanese cedar forests and secondary broadleaf forests across four seasons in Kagoshima Prefecture, Japan. We collected a total of 2,728 specimens representing 41 species, comprising 34 ambrosia beetle species and seven bark beetle species. Forest type had no significant effect on the abundance and species richness of ambrosia and bark beetles, while seasonal variation clearly shaped their assemblages, and both abundance and species richness were highest in spring. The similarity of ambrosia and bark beetle species composition observed in Japanese cedar forests and secondary broadleaf forests further suggests that both forest types may contribute to maintaining beetle assemblages in warm-temperate mixed forest landscapes in southern Japan. Furthermore, differences in ambrosia and bark beetle assemblages among seasons indicate the importance of multi-season monitoring to support the conservation of these beetles, given their ecological roles in wood decomposition within forest ecosystems. Implications for insect conservation: These findings suggest that both Japanese cedar forests and secondary broadleaf forests may provide important habitats for maintaining ambrosia and bark beetle diversity in warm-temperate mixed forest landscapes of southern Japan. Furthermore, multi-season monitoring is needed to accurately assess ambrosia and bark beetle diversity and to support biodiversity conservation and forest management, given their roles in wood decomposition although some species are significant pests.