Pollen from various plant species protects pollinators from a dangerous pathogen
Biologists and ecologists have been seeking solutions for years to reverse what could become one of the great problems for the future of life on the planet: the increasing mortality of pollinators. Two scientific investigations have come to provide food for thought about this disconcerting reality, by revealing that plants of the sunflower family (Asteraceae) could be the solutionor at least part of it.
The two studies have come to the same conclusion: Sunflower pollen and its ‘relatives’ reduce infection from a common bee parasite between 81% and 94% and significantly increases the production of queen bees.
The conclusions of the research leave no doubt: the abundance of sunflowers reduced the prevalence of a dangerous common intestinal pathogen, crithidia bombiand the intensity of infections, compared to sites with little or no sunflower.
In addition, the abundance of sunflower was also positively associated with a higher queen production in the colonies. But it did not affect the prevalence of other detected pathogens.
“This work demonstrates that a single plant species can drive disease dynamics in the foraging of impatiens bombus (eastern common bumblebee), and that lSunflower plantations can be used as a tool to mitigate a pathogen frequent and, at the same time, increase the reproduction of a species of bee that is important for agriculture”, says one of the reports.
The ‘secret’ is in the exins (hard outer covering of pollen grains), which reduced infection as effectively as whole sunflower pollen, whereas pollen metabolites did not.
The ‘key’ is physics, not chemistry
The investigation revealed that bees fed on pollen from four of the seven other plants in the family Asteraceae had between 62% and 92% fewer infections by Crithidia bombi than those fed with pollen that was not from Asteraceae.
“The importance of bees as pollinators is now widely recognized and we are increasingly aware of the numerous stressors negatively affect their health,” the authors note. These factors include loss of habitatthe pesticide exposure and the parasites.
One of the doubts to clear up was whether the benefits for the health of the bees came from the chemical substances contained in the sunflower or from its physical structure.
To clear up the mystery, the scientists separated the spiny outer layer of the pollen from the chemical metabolites in the nucleus. They then mixed the prickly husk of the sunflower, minus the chemistry, with the pollen that was fed to one batch of bees, while another batch was fed wildflower pollen sprinkled with sunflower metabolites, without the husks.
“We discovered that it’s the prickly outer layer of sunflower pollen, not its chemistry, that reduces infections“says Laura Figueroa, a professor at the University of Massachusetts Amherst and lead author of one of the studies.
“Bees that ate the spiny sunflower pollen husks had the same response as bees that fed on whole sunflower pollen: they suffered 87% fewer infections than those fed on sunflower metabolites,” says Figueroa. So the ‘key’ is in physics, not chemistry.
In addition, they observed that bees fed pollen from ragweed, cockle, dandelion, and fennel—all from the sunflower family—had low infection rates, similar to those fed sunflower.
The “apocalypse” of insects
There is another fundamental aspect to determine the health of a colony: the number of queens it produces. Because the more you produce, the greater the chance that the genes will be passed on to the next generations.
The researchers placed bumblebee colonies on twenty farms, where they grew varying amounts of sunflower. After several weeks, they took samples of the pathogens accumulated in the intestines of the bees, weighed the colonies to determine if they were thriving, and counted the number of daughter queens.
“Infection decreased with increased abundance of sunflower and, perhaps more importantly, queen bee production increased by 30% for every order-of-magnitude increase in sunflower pollen availability,” says Rosemary Malfi, lead author of one of the papers.
The discovery is not trivial, as polarizing insects help fertilize just about everything from blueberries to coffee and contribute to more than 200,000 million euros in annual ecosystem services Worldwide. “We depend on polarizers to have diverse, healthy, and nutritious diets,” Figueroa points out.
There are still unknowns, such as why sunflower pollen benefits queen bee production. “Maybe bumblebees have more energy to reproduce if they’re not fighting disease, or maybe crithidia bombi affects learning and foraging, so reducing infection increases the ability to find food,” the scientists venture.
Lynn Adler, lead author of one of the articles, clarifies that these investigations are not a solution to the “insect apocalypse”, but they are “encouraging” and indicate that the sunflower family may play an important role in maintaining the health of pollinators and, ultimately, that of human food systems.
Reference reports:
https://besjournals.onlinelibrary.wiley.com/doi/epdf/10.1111/1365-2435.14320https://royalsocietypublishing.org/doi/10.1098/rspb.2023.0055
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