Wild and managed bee communities in canola respond to landscape context and farm management

Pollinating bees promote greater yield and quality of oilseed crops like canola. Canola acreage has grown over 300% in the past decade in the Pacific Northwest region of the US, providing seasonal pulses of nectar and pollen resources that may affect bee abundance and community structure. However, because pollination by insects does not limit canola seed production, few studies have examined the biodiversity of pollinators that use these resources, or the floral traits of canola that affect pollinators. Here, we conducted surveys at canola farms across the inland Northwest USA to assess how bee biodiversity and abundance varied based on canola production practices and floral traits of canola varieties. We show that mining bees (Adrenidae) were more abundant earlier in the season and sweat bees (Halictidae) later in the season, and that bees were more abundant on farms with less floral nectar and on those in less developed landscapes. Floral traits such as larger petal size and increased nectar were correlated with lower bee abundance and diversity. However, this may reflect that petal size was associated with canola type, and that more abundant and diverse bee communities may have been more effective at removing floral nectar. While we did not find a direct effect of canola type on bees, we did find that winter canola had larger petals but lower nectar volume, which indirectly affected bee diversity and abundance. This research provides information for canola growers and land managers interested in pollinator conservation and offers a framework for future research in pollinator management.