A. D. Vaudo, H. M. Patch, J. F. Tooker, C. M. Grozinger
Center for Pollinator Research, The Pennsylvania State University
D. Stabler, G. A. Wright
Centre for Behaviour and Evolution, Institute of Neuroscience
Reduction of nutritional resources may be one reason for bee decline. It is well-known that solitary and social insects forage very differently to meet species-specific nutritional intake. The researchers studied the survival rate of two bumble bee species Bombus impatiens and Bombus terrestris and compared the specific Protein: Lipid ratios on synthetic diets.
The results in this study demonstrate that the macronutrient ratios in pollen are a key factor determining bee health. The bees survived best on a 10:1 Proten:Lipid diet; the risk of dying increased as a function of dietary lipid when bees ate diets with lipid contents greater than 5:1. B. terrestris intake diets at ratio 14:1 P:L, and B. impatiens at 12:1 P:L. This research indicates that adult worker bumble bees likely select foods that provide them with a specific ratio. To be effective, pollinator protection activities such as planting pollinator gardens must include plants that provide pollen satisfying the nutritional needs of bees.
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.