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Reduced abundance and earlier collection of bumble bee workers under intensive cultivation of a mass ‐ flowering prairie crop

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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 (Bombus sp.) 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.

No MeSH data available.


Study area near Calgary, Alberta, Canada, indicating locations of 15 sites adjacent to canola (canola‐present; 20%–95% canola cover within 250 m) and 15 sites not adjacent to canola (canola‐absent; <2% canola cover within 250 m). Field spatial data from Canada annual crop inventory (Agriculture and Agri‐Food Canada, 2015). Gray linear features indicate the extensive road network
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ece32856-fig-0001: Study area near Calgary, Alberta, Canada, indicating locations of 15 sites adjacent to canola (canola‐present; 20%–95% canola cover within 250 m) and 15 sites not adjacent to canola (canola‐absent; <2% canola cover within 250 m). Field spatial data from Canada annual crop inventory (Agriculture and Agri‐Food Canada, 2015). Gray linear features indicate the extensive road network

Mentions: Canola is a cultivar of oilseed rape (Brassica napus) and is an MFC widely grown throughout the Canadian Prairies and the North‐Central United States. Agricultural activities throughout this area are typically highly intensive, with much of the available land surface under the annual cultivation of either canola or cereal crops (Agriculture and Agri‐Food Canada, 2015). In contrast to many parts of Europe, where studies of wild bees and MFCs have mainly occurred (Warzecha, Diekötter, Wolters, & Jauker, 2016; Westphal et al., 2003), prairie agroecosystems tend to be dominated by large rectangular fields, hedgerows are seldom present, and in many regions, there are few other trees, shrubs, or seminatural land covers (e.g., Figure 1).


Reduced abundance and earlier collection of bumble bee workers under intensive cultivation of a mass ‐ flowering prairie crop
Study area near Calgary, Alberta, Canada, indicating locations of 15 sites adjacent to canola (canola‐present; 20%–95% canola cover within 250 m) and 15 sites not adjacent to canola (canola‐absent; <2% canola cover within 250 m). Field spatial data from Canada annual crop inventory (Agriculture and Agri‐Food Canada, 2015). Gray linear features indicate the extensive road network
© Copyright Policy - creativeCommonsBy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5383479&req=5

ece32856-fig-0001: Study area near Calgary, Alberta, Canada, indicating locations of 15 sites adjacent to canola (canola‐present; 20%–95% canola cover within 250 m) and 15 sites not adjacent to canola (canola‐absent; <2% canola cover within 250 m). Field spatial data from Canada annual crop inventory (Agriculture and Agri‐Food Canada, 2015). Gray linear features indicate the extensive road network
Mentions: Canola is a cultivar of oilseed rape (Brassica napus) and is an MFC widely grown throughout the Canadian Prairies and the North‐Central United States. Agricultural activities throughout this area are typically highly intensive, with much of the available land surface under the annual cultivation of either canola or cereal crops (Agriculture and Agri‐Food Canada, 2015). In contrast to many parts of Europe, where studies of wild bees and MFCs have mainly occurred (Warzecha, Diekötter, Wolters, & Jauker, 2016; Westphal et al., 2003), prairie agroecosystems tend to be dominated by large rectangular fields, hedgerows are seldom present, and in many regions, there are few other trees, shrubs, or seminatural land covers (e.g., Figure 1).

View Article: PubMed Central - PubMed

ABSTRACT

One of the most commonly seeded crops in Canada is canola, a cultivar of oilseed rape (Brassica napus). As a mass&#8208;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 (Bombus sp.) are efficient pollinators of many types of native and crop plants. We measured the influence of this mass&#8208;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&#8208;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.

No MeSH data available.