title: Reduced abundance and earlier collection of bumble bee workers under intensive cultivation of a mass-flowering prairie crop.
abstract: One of the most commonly seeded crops in Canada is canola, a cultivar of oilseed rape (Brassica napus). As a mass-flowering crop grown intensively throughout the Canadian Prairies, canola has the potential to influence pollinator success across tens of thousands of square kilometers of cropland. Bumble bees (Bombussp.) are efficient pollinators of many types of native and crop plants. We measured the influence of this mass-flowering crop on the abundance and phenology of bumble bees, and on another species of social bee (a sweat bee;Halictus rubicundus), by continuously deploying traps at different levels of canola cultivation intensity, spanning the start and end of canola bloom. Queen bumble bees were more abundant in areas with more canola cover, indicating that this crop is attractive to queens. However, bumble bee workers were significantly fewer in these locations later in the season, suggesting reduced colony success. The median collection dates of workers of three bumble bee species were earlier near canola fields, suggesting a dynamic response of colonies to the increased floral resources. Different species experienced this shift to different extents. The sweat bee was not affected by canola cultivation intensity. Our findings suggest that mass-flowering crops such as canola are attractive to bumble bee queens and therefore may lead to higher rates of colony establishment, but also that colonies established near this crop may be less successful. We propose that the effect on bumble bees can be mitigated by spacing the crop more evenly with respect to alternate floral resources.
authors.affiliation: Faculty of Environmental Design University of Calgary Calgary AB Canada; Department of Biological Sciences University of Calgary Calgary AB Canada.
authors.forename: Paul
authors.identifier: 0000-0003-0099-3981
authors.initials: P
authors.lastname: Galpern
authors.affiliation: Department of Biological Sciences University of Calgary Calgary AB Canada.
authors.forename: Sarah A
authors.initials: SA
authors.lastname: Johnson
authors.affiliation: Department of Biological Sciences University of Calgary Calgary AB Canada.
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Retzlaff
authors.affiliation: Department of Biological Sciences University of Calgary Calgary AB Canada.
authors.forename: Danielle
authors.initials: D
authors.lastname: Chang
authors.affiliation: Department of Biological Sciences University of Calgary Calgary AB Canada.
authors.forename: John
authors.initials: J
authors.lastname: Swann
keywords: Bombus; Canadian Prairies; agricultural intensification; bumble bee; canola; mass‐flowering crop; oilseed rape; phenology; pollinator conservation