Some bees value quality over quantity in flower selection

A new study led by Pennsylvania State University has found that when deciding when they will get their next meal, different bee species may be attracted to different flower traits. 

This finding, based on research with two species of solitary bees, highlights the intriguing ways bees select the flowers they visit. 

The study illuminates the importance of floral traits such as number of blooms and nutritional content, expanding our understanding of plant–pollinator interactions.

Bee species with distinct priorities

The research focused on two solitary bee species: the horned-face bee – known for pollinating apples and blueberries – and the alfalfa leafcutting bee, which pollinates alfalfa. 

The scientists discovered that while the horned-face bee gravitated toward plants displaying a large quantity of flowers, the alfalfa leafcutting bee instead preferred blooms with a higher protein-to-lipid ratio in the pollen.

“Information on the foraging strategies of different bee species give insights for understanding how plant-pollinator interactions evolved,” said lead author Jaya Sravanthi Mokkapati, a postdoctoral fellow at Penn State. 

“Our study also highlights the need for more research on seasonal foraging habits among various bee species, which can deepen our understanding of their vital role in pollination and plant reproduction.”

This pronounced difference in focus – quantity for one species and nutritional quality for the other – demonstrates that even closely related insects can exhibit divergent foraging behaviors. 

These variations matter for both ecological balance and practical considerations, such as when and how to restore pollinator habitats or ensure crop pollination.

Co-evolution of plants and pollinators

Pollinators like bees and flowering plants have co-evolved over thousands of years, forming a symbiotic relationship. As bees gather nectar and pollen for sustenance, they assist in plant reproduction, transferring pollen between flowers. 

Crops ranging from fruits to vegetables and nuts depend on this process, which is essential for producing much of the human food supply. However, many pollinator populations are declining, partly due to the loss of the flowering plants they rely on.

“Bees can be attracted to plants based on a number of traits, such as the color, scent, size, number and nutritional content of its flowers,” said  co-author Christina Grozinger, a professor of Entomology at Penn State. 

“However, because these traits are co-evolved in flowers, it can also be very challenging to pinpoint which traits are the ones attracting which bees.”

By analyzing these evolved plant traits, researchers can better grasp how bees make their foraging decisions and, in turn, how best to support pollinator populations in decline.

Choosing flowers for quality

The research team examined two solitary bee species precisely because of their distinct ecological niches. 

The horned-face bee is active during the spring, a season marked by fewer resources and shorter bloom windows. The alfalfa leafcutting bee, on the other hand, emerges in summer, a time abundant in floral options.

“In contrast, the alfalfa leafcutting bee is a summer species that typically has access to more abundant resources,” Mokkapati said. “We hypothesized that these bees can afford to be more selective, choosing flowers based on nutritional quality instead of quantity.”

By observing how these bees visited plants, the scientists were able to pinpoint the different variables each species valued in its foraging. This approach included analyzing pollen content as well as recording the sheer number of flowers on each plant.

Implications for bee conservation

According to the researchers, the results of this study have important implications for restoring and managing habitats for pollinators. 

Landscapes might need to include plant varieties that offer either numerous flowers for bees that seek quantity or high-quality pollen for species focusing on nutritional benefits. 

Ensuring these resources are available throughout the growing season could reinforce bee populations, enhance biodiversity, and bolster pollination services for agriculture.

“By raising awareness of how these gardens can provide essential resources for bees, we can inspire community involvement and commitment to preserving local biodiversity,” Mokkapati said. 

“This collective effort not only benefits the bees but also enhances the beauty and ecological health of our surroundings.”

The researchers note that many pollinator populations require immediate interventions and that these strategies could help sustain not only honey bees (often the focus of public concern) but also lesser-known solitary bees like the horned-face and alfalfa leafcutting bees.

Future research directions

While the study reveals how these two bee species differ in their foraging strategies, the authors suggest deeper investigation is needed to uncover the reasons behind such variations. 

Scientists aim to explore whether differences in sensory perception, genetic factors, or life history strategies inform why one bee species chooses to prioritize floral abundance while another looks for a certain balance of proteins and lipids in pollen.

By diving more deeply into these aspects, future research may shed light on how bees adapt to various environmental conditions. It could also identify potential vulnerabilities if, for example, climate change alters the availability or quality of their preferred flowers.

Ensuring bee health and biodiversity

As pollinators remain fundamental to global food security and ecosystem functioning, understanding these nuanced foraging preferences is critical. 

The study emphasizes that it is not solely honey bees that matter – solitary bees and other pollinators have their own crucial roles. 

Encouraging and facilitating plant diversity, offering both abundant blooms and nutrient-rich pollen sources, may prove key to preserving these vital insects for the benefit of ecosystems and agricultural communities alike.

In the broader context, this work illustrates how the interplay between plant traits and bee behaviors can shape pollinator communities. 

By harnessing this understanding for conservation practices, we can cultivate healthier environments for bees and, in turn, sustain the pollination services that underpin so much of our food supply and natural heritage.

The study is published in the journal PNAS Nexus.

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