Bee populations have been declining for years due to a number of factors, including pesticide use. Poor nutrition was thought to be another cause and scientists have now found supporting evidence. In a new paper published in the Proceedings of the National Academy of Sciences, researchers show that bumble bees are attracted to plant species that better meet their nutritional requirements.
In the past, it was assumed that bees were only attracted to the flower itself. They were thought to make their foraging decisions based on the color, smell, and shape of the flower. This might still be true to an extent but researchers have found another factor that bees take into consideration: pollen quality.
The researchers recorded bumble bees and watched as they foraged in a restricted area containing specific plant species. The pollen from each plant was analyzed for lipid and protein concentrations. They then compared foraging rates to the protein to lipid ratios of the plants visited by the bees. The scientists discovered that the bumble bees were more attracted to plants that had pollen with a high protein to lipid ratio.
In order to confirm these findings, the research team conducted another experiment. They confined the bees to cages and offered them pollen from various plants. There were no flowers or other cues. The bees were still drawn to pollen with higher protein to lipid ratios. The bumble bees always showed this preference, even when the researchers modified existing pollen to contain new protein to lipid ratios.
The authors speculate that a high protein to lipid ratio, as opposed to just high protein concentrations, is nutritionally optimal for bumble bees. Bees may use floral cues, such as color, to remember which plants had quality pollen. Ultimately, the bees care about pollen nutrition.
Bees are major pollinators and important to agriculture. Their current decline is concerning and this research will help conservation efforts. The authors recommend that conservation initiatives incorporate plant species that meet the nutritional needs of bees.
Anthony D. Vaudo, Harland M. Patch, David A. Mortensen, John F. Tooker, and Christina M. Grozinger. Macronutrient ratios in pollen shape bumble bee (Bombus impatiens) foraging strategies and floral preferences. Proceedings of the National Academy of Sciences (2016).