Bee population declines are linked to the reduction of nutritional resources due to land-use intensification, yet we know little about the specific nutritional needs of many bee species. Pollen provides bees with their primary source of protein and lipids, but nutritional quality varies widely among host-plant species. Therefore, bees might have adapted to assess resource quality and adjust their foraging behavior to balance nutrition from multiple food sources. We tested the ability of two bumble bee species, Bombus terrestris and Bombus impatiens, to regulate protein and lipid intake. We restricted B. terrestris adults to single synthetic diets varying in protein:lipid ratios (P:L). The bees over-ate protein on low-fat diets and over-ate lipid on high-fat diets to reach their targets of lipid and protein, respectively. The bees survived best on a 10:1 P:L diet; the risk of dying increased as a function of dietary lipid when bees ate diets with lipid contents greater than 5:1 P:L. Hypothesizing that the P:L intake target of adult worker bumble bees was between 25:1 and 5:1, we presented workers from both species with unbalanced but complementary paired diets to determine whether they self-select their diet to reach a specific intake target. Bees consumed similar amounts of proteins and lipids in each treatment and averaged a 14:1 P:L for B. terrestris and 12:1 P:L for B. impatiens. These results demonstrate that adult worker bumble bees likely select foods that provide them with a specific ratio of P:L. These P:L intake targets could affect pollen foraging in the field and help explain patterns of host-plant species choice by bumble bees.
The authors declare no competing or financial interests.
A.D.V.: Conceptualization, methodology, validation, formal analysis, investigation, writing – original draft preparation, writing – review and editing, visualization, funding acquisition; D.S.: Conceptualization, methodology, formal analysis, investigation; H.M.P.: Conceptualization, validation; J.F.T.: Conceptualization, validation, resources, writing – review and editing; C.M.G.: Conceptualization, validation, resources, writing – review and editing, funding acquisition; G.A.W.: Conceptualization, methodology, validation, resources, writing – review and editing, funding acquisition.
This work was supported by a Biotechnology and Biological Sciences Research Council (BBSRC) transatlantic partnering award (grant number BB/I025220/1 to G.M.G., A.D.V. and G.A.W.); North American Pollinator Protection Campaign (NAPPC) Bee Health Improvement Project Grant to A.D.V. (2014); U.S. Department of Agriculture–Agriculture and Food Research Initiative–National Institute of Food and Agriculture (USDA–AFRI–NIFA) Predoctoral Fellowships Grant 2014-02219 to A.D.V.; a Natural Environment Research Council (NERC)-funded PhD studentship to D.S.; and generous funding from an anonymous donation to the Pennsylvania State University Center for Pollinator Research.
Supplementary information available online at http://jeb.biologists.org/lookup/doi/10.1242/jeb.140772.supplemental
- Received March 29, 2016.
- Accepted October 6, 2016.
- © 2016. Published by The Company of Biologists Ltd