Sunflowers are a ‘superfood’ for bumblebees

New research led by scientists at the University of Massachusetts Amherst has revealed that the spiny pollen of plants in the sunflower family can reduce infection of a common bee parasite by up to 94 percent. The study, published in the journal Functional Ecology, has significant implications for pollinator health and the wider ecosystem.

Insect pollinators, including bees, are responsible for fertilizing crops that contribute over $200 billion in annual ecosystem services worldwide. However, many species are in decline due to habitat loss, pesticide use, and other factors. The decline of pollinators poses a significant threat to global food security and biodiversity.

Led by Laura Figueroa, incoming assistant professor of environmental conservation at UMass Amherst, the research team aimed to understand why certain species of flowers, including sunflowers, can help pollinators resist disease infections. In particular, they investigated sunflowers’ effectiveness at combatting the widespread pathogen Crithidia bombi, which lives in a bee’s gut.

“We know that the health benefits from some foods come from the specific chemicals in them. But we also know that some foods are healthy because of their physical structure – think of foods high in fiber,” said Professor Figueroa.

To investigate how sunflowers help bumblebees withstand C. bombi, Figueroa and her team separated the spiny outer shell of the pollen from the chemical metabolites in the pollen’s core. They then mixed the spiny sunflower shell, with the chemistry removed, into the pollen fed to one group of bees. Another group was fed wildflower pollen sprinkled with sunflower metabolites and no sunflower shells.

The researchers discovered that the bees that ate the spiny sunflower pollen shells had the same response as bees feeding on whole sunflower pollen. These bees had a markedly reduced risk of C. bombi infection compared to those fed sunflower metabolites. In fact, they suffered 87% lower infections from C. bombi than the control group.

Additionally, bees fed pollen from ragweed, cocklebur, dandelion, and dog fennel – all members of the sunflower family and with similarly spiny pollen shells – had similarly low rates of C. bombi infection. This raises the possibility that such disease-fighting medicinal effects may be common to plants in the sunflower family.

The findings have significant implications for efforts to protect pollinators, which play a vital role in maintaining healthy and diverse ecosystems. “We depend on them for diverse, healthy, nutritious diets,” said Figueroa. “Understanding how sunflowers protect bees from disease could help us identify other flowers that have similar protective properties.”

Although sunflower pollen is not particularly nutritious due to its low protein content, it has been shown to protect bumblebees from gut pathogens such as C. bombi, which is known to affect the queen bees and their ability to produce offspring.

Study senior author Professor Lynn Adler explained that it is essential to look at the bigger picture of bee health, not just focus on individual factors such as gut pathogens. “It’s no good curing the common cold if you starve the patient. We need to look at the community level, as well as what’s happening in bees’ guts, to know how to help them respond to stressful environments,” said Professor Adler.

To determine the impact of sunflower pollen on colony health, Adler and her team placed commercial colonies of bumblebees on twenty different farms in Western Massachusetts that grew varying amounts of sunflowers. Over several weeks, the team collected samples of pathogens in the bees’ guts, weighed the colonies to determine whether or not they were thriving, and counted the number of daughter queens.

The study found that infection decreased as sunflower abundance increased, and that queen bee production increased by 30 percent for every order of magnitude increase in the availability of sunflower pollen. “It’s really exciting to show that sunflower not only reduces disease but positively affects reproduction,” said Rosemary Malfi, lead author of the study.

Adler and Malfi cautioned that more research needs to be done to fully understand why sunflower pollen benefits queen bees, and that this study only focused on one common species of bumblebee that is not endangered. However, the findings suggest that the sunflower family may play a crucial role in maintaining pollinator health, which ultimately benefits our food systems.

The study provides much-needed food for thought in the ongoing effort to reverse the decline of pollinators worldwide. The results show that the physical structure of pollen can have significant impacts on bee health, which could inform new strategies for supporting pollinator populations.

This research was supported by the US National Science Foundation and Department of Agriculture.

Why bumble populations are declining

Bumblebees, vital pollinators of crops and wildflowers, are experiencing a rapid decline in their populations worldwide. While there are several factors contributing to this decline, the primary reasons are habitat loss, climate change, and pesticide use.

Habitat loss due to urbanization and agricultural intensification is the biggest threat to bumblebees. As natural habitats are converted into farmlands, forests, and urban areas, bumblebees lose their food sources, nesting sites, and breeding grounds. This reduces their population size and genetic diversity, making them more vulnerable to disease and environmental stress.

Climate change is also taking a toll on bumblebees. As temperatures rise, bumblebees are forced to move further north to cooler climates, which can affect their ability to find food and nesting sites. Changes in rainfall patterns can also impact the availability of nectar and pollen, making it difficult for bumblebees to survive.

Pesticide use is another significant threat to bumblebees. Pesticides like neonicotinoids, which are widely used in agriculture, have been linked to declines in bumblebee populations. These chemicals are highly toxic to bees and can impair their navigation, foraging, and immune systems, leading to reduced reproductive success and increased mortality.

The decline of bumblebees is a cause for concern because they play a crucial role in pollinating crops and wildflowers. Without them, we would lose the diversity of fruits, vegetables, and flowers that we rely on for food and aesthetic value. Therefore, it is important to take action to conserve and protect bumblebee populations by reducing pesticide use, restoring natural habitats, and mitigating climate change.

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