With many bee species facing significant threats, the researchers say they hope these findings can inform conservation efforts from policy changes to individual actions like planting native flowers and reducing pesticide use.
What's on the menu for a healthy bee? A team of researchers has delved into the world of bee nutrition, analyzing pollen to identify the best food sources for these vital pollinators. Their findings could have implications for bee conservation efforts and pollinator-friendly landscaping.
The research, published in Frontiers in Sustainable Food Systems, analyzed the nutritional content of pollen collected from 57 plant species native to North America. The study team, led by Sandra Rehan of York University in Canada, examined levels of essential fatty acids, amino acids and other key nutrients in the pollen samples.
"Despite public interest and a rise in pollinator plantings, little is known about which plant species are best suited for bee health," Rehan said. "This study aimed to better understand the nutritional value of plant species."
When comparing native and introduced plant species, the study found no significant differences in the overall nutritional content of their pollen. This suggests that both native and nonnative plants can potentially provide valuable nutritional resources for bee populations.
Bees rely on two primary food sources: nectar and pollen. While nectar provides bees with carbohydrates and water, pollen is their main source of protein, lipids, vitamins and minerals. Adult bees consume both nectar and pollen, but pollen plays a crucial role in larval development.
When foraging, bees collect pollen using specialized structures on their bodies, such as pollen baskets (known as corbiculae) on their hind legs, or scopal hairs on their abdomen or legs, depending on the species. They then bring this pollen back to the hive or nest.
In social bees like honey bees, worker bees mix the pollen with nectar and their own glandular secretions to create "bee bread," which is used to feed developing larvae. For solitary bees, females provide each brood cell with a mixture of pollen and nectar before laying an egg. This pollen is the sole food source for the developing larva until it emerges as an adult. Therefore, pollen's nutritional quality directly impacts the health, development and survival of bee populations.
Bees require a diet rich in specific nutrients, particularly omega-6 and omega-3 fatty acids. These compounds are essential for the bees' longevity, immune function and ability to handle environmental stress. However, the balance of these fatty acids is crucial. Too much or too little can impair their cognitive abilities. Additionally, bees need essential amino acids for brain health and reproduction. But there's a catch: consuming excessive amounts of these amino acids may increase their susceptibility to certain parasites. Therefore, a well-balanced diet is critical for maintaining bee health and vitality.
The study found that bees require a diverse diet from multiple plant sources to obtain a balanced intake of fatty acids and essential amino acids. No single plant species provided pollen with an optimal nutritional profile.
"There is a potential tradeoff between fatty acid and amino acid content within pollen, suggesting that a diverse floral diet may benefit bees more than a single pollen source," Rehan said. "No one plant species is optimal for generalist wild bee health."
For amino acid content, the study found that almost all plant species contained the ten essential amino acids required by bees in their pollen. However, levels varied considerably between species. Interestingly, pollen from plants in the Asteraceae family (which includes daisies and sunflowers) stood out as particularly rich in essential amino acids. Seven Asteraceae species had essential amino acid levels exceeding 20% of their total pollen content.
The researchers also examined protein-to-lipid ratios and omega-6 to omega-3 fatty acid ratios in the pollen samples, as these are considered important factors in bee nutrition. They found wide variation between species, even within the same plant genus.
"This diversity of pollen nutritional profiles likely enables bees, especially specialist species, to selectively forage on the resources that best meet their unique dietary requirements," the study authors noted.
The study's findings are particularly relevant given the alarming decline in bee populations worldwide. With more than 3,600 species in the U.S. and Canada, bees represent a remarkably diverse group of pollinators. However, many bee species are facing significant threats.
"Approximately 16% of vertebrate pollinators, such as birds and bats, and 40% of invertebrate pollinators, such as bees and butterflies, are at risk of extinction," according to a comprehensive review published in May in CABI Reviews.
Habitat loss and fragmentation; pathogens and disease; pesticides, insecticides such as the neonicotinoids, herbicides and fungicides used in agriculture and landscaping; invasive species; climate change; and competition between honeybees and native bees are some of the reported causes of pollinator declines.
The loss of preferred host plants is a contributing factor to the decline of some bee populations. Additionally, the spread of pests and pathogens poses a serious threat to both wild and managed bee species, with the transportation of managed bee colonies for commercial pollination often exacerbating this problem.
Bee conservation efforts are multifaceted, involving both large-scale policy changes and individual actions. At the policy level, initiatives include protecting key habitats, regulating pesticide use, and supporting research on bee health.
Organizations like the Xerces Society have successfully advocated for federal and state protections for several bee species. They also work with farmers and land managers to implement bee-friendly practices.
Individuals can also play a crucial role in bee conservation. Planting native flowers, reducing pesticide use, and creating nesting habitats are all effective ways to support local bee populations. Even small actions, like converting part of a lawn into a wildflower meadow or leaving bare patches of soil for ground-nesting bees, can make a significant difference.
Rehan and her colleagues say they hope their findings will help inform the selection of plant species for pollinator gardens and habitat restoration efforts. However, they caution that the analysis only looked at 57 plant species out of thousands that exist.
"We hope this work will help inform flowering plant selections for pollinator gardens," Rehan said. "But here we examined only 57 plant species, and there are thousands to examine to understand nutritional profiles. We hope this will inspire future similar research as well as follow-up studies on the preference and survival of bees on different diets."
Banner image of a bee with a sunflower in Tokyo. Image by mrhayata via Flickr (CC BY-SA 2.0).
Liz Kimbrough is a staff writer for Mongabay and holds a Ph.D. in ecology and evolutionary biology from Tulane University, where she studied the microbiomes of trees. View more of her reporting here.
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Stephen, K. W., Chau, K. D., & Rehan, S. M. (2024). Dietary foundations for pollinators: Nutritional profiling of plants for bee health. Frontiers in Sustainable Food Systems, 8, 1411410. doi:10.3389/fsufs.2024.1411410
Brunet, J., & Fragoso, F. P. (2024). What are the main reasons for the worldwide decline in pollinator populations? CABI Reviews, 19(1). doi:10.1079/cabireviews.2024.0016