Crop-specialized pollinator drives bee and floral community response to urbanization on small squash farms

Abstract Cities can support diverse wild bee communities through managed green spaces. Urban farms, specifically, provide important habitat and resources for wild bee communities in cities. However, the influence of urbanization on specific crop-pollinating bee communities has received little attention. Here we examined how urbanization influences squash-pollinating bee communities across 24 farms that grow squash along an urban gradient in Michigan, USA. We assessed whether forage and nesting resources along this urban gradient influenced bee community abundance and visitation, and their associated functional trait composition. We documented 11 genera and 30 species visiting squash, with the hoary squash bee ( Xenoglossa pruinosa ), a cucurbit specialist pollinator, as the most abundant species with the highest number of squash flower visitations. We found that squash bees were the most abundant on suburban and urban farms compared to rural farms. Oligolectic and ground-nesting bees were most abundant in suburban farms, which mirrored squash bee trends. Cavity-nesting bees were most abundant on rural farms. However, there was no relationship between urbanization and in-farm ground cover. Weed floral diversity, but not surrounding plant diversity, was positively correlated with urbanization. Interestingly, floral diversity had a negative relationship with bee diversity, regardless of urbanization, possibly due to the dominance of the hoary squash bee in the community. Bee community composition largely overlapped, although suburban and urban communities were more heterogeneous. Our results suggest that both urban and suburban farms can support abundant and diverse bee communities.