Wild bee surveys across 60 years reveal remarkable reduction of bee abundance in urban green areas in northern Japan

Abstract

Long-term monitoring of wild bee communities at fixed locations using a consistent sampling procedure has been rare, although declines in their diversity and abundance due to anthropogenic impacts are a major concern. At two sites in urban green areas in Sapporo city, northern Japan, where wild bee surveys were conducted in 1959, 1979, 1989, 2018, and 2019, the number of individuals of bee genera was recorded. Patterns of seasonal changes in bee abundance collected at weekly censuses differed between 1979–1989 and 2018–2019. The total bee abundance collected in annual surveys consisting of standardized censuses demonstrated 50% and 41% declines at the two sites from 1959–1989 to 2018–2019. Among the 16 genera found in the surveys, 3 abundant genera, Andrena, Lasioglossum, and Ceratina, always exhibited lower abundance in 2018–2019 than in 1959–1989 at both sites. The remarkable declines in wild bee abundance should be examined in relation to various possible factors of anthropogenic impacts.