Bumblebees and other pollinators face many threats, including exposure to pesticides, climate change, habitat loss from agriculture and development, and pathogens that plague multiple species. But a recent discovery may help lighten their load.
Previous studies have shown that sunflower pollen may work as a medicine for bumblebees afflicted with a parasite called Crithidia bombi, a single-celled organism that settles in the intestine of the bee and harms its health. But scientists couldn’t explain how sunflower pollen won. C. bombi—did it boost the bees’ immune function, or perhaps poison the parasite directly?
New research, published in the Journal of Insect Physiology, shows that the answer is deceptively simple. “Sunflower pollen causes bumblebees to poop a lot,” says lead author Jonathan Giacomini, who eliminates the parasite.
Plant products like nectar and pollen are a treasure trove of potential insect medicines that scientists are just beginning to understand, he adds. “There are natural things that bees interact with that can benefit them,” says Giacomini. And by making changes to the landscape, scientists hope we can help give bees a fighting chance.
Plant power
If you come across a fuzzy, buzzing flying creature in eastern North America, chances are it’s an eastern common bumblebee (An impatient bomb). Striped yellow and black with a rump covered in soft hair, they are social insects that live in colonies and like a good crevice – they build their homes in nest boxes, woodpiles, abandoned burrows and dense grasses.
They are important pollinators, both in the wild and in agriculture, where they are bred and used to pollinate crops, including tomatoes and pumpkins. Like other pollinators, bumblebees face many threats, and C. bombi isn’t even the biggest bumblebee bugaboo. The parasite alone does not have much of an effect on a bumblebee’s health. But when food is scarce, C. bombi can shorten a bee’s lifespan and even reduce the number of young queens a colony can produce.
Lynn Adler is an evolutionary ecologist at the University of Massachusetts Amherst who studies plant-insect interactions. For years, she and her longtime collaborator Rebecca Irwin of North Carolina State University suspected that pollinators might be dosed by flowers, as plants often invest chemically active compounds in their nectar and pollen to help their load. genetics to arrive at their destination.
“Many defensive compounds in plants can be medicinal in certain doses,” says Adler. After all, “most of our human medicine comes from plants.”
Giacomini discovered the effect of sunflower pollen while working in Adler’s lab in 2018. From the first tests, sunflower pollen significantly reduced C. bombi parasite load in eastern common bumblebees, often eliminating infection completely. “We were shocked at how consistent and effective sunflower pollen was,” says Adler.
But they couldn’t figure out how — separate studies over the years have ruled out immune function boosters and couldn’t identify any chemical compounds in sunflower pollen that would be catastrophic for them. C. bombi.
“I started to notice, man, every time we run these experiments, bees fed sunflower pollen are so much dirtier than bees that eat wildflower pollen,” Giacomini recalls. It was then his hypotheses turned towards the scatological.
Bomb a way
In an attempt to understand the mechanism of the medicinal effect of sunflower pollen, Giacomini, then a doctoral student, set up a bumblebee buffet in a laboratory at North Carolina State University.
Giacomini gave sunflower pollen to healthy bumblebees and to bumblebees infected with C. bombi, then compared their excretions to those of other bees that had received only pollen from wildflowers. (Bumblebees don’t separate their solid and liquid wastes like we do, so bumblebee poop is a thin mush that’s often bright yellow from undigested pollen.)
“Bee poop turned out to naturally fluoresce under ultraviolet light,” which made distinguishing between poop and non-poo remarkably easy, Giacomini recalls. “It was very dazzling, it almost looked like a galaxy.”
Regardless of whether they were infected or not, bees that ate sunflower pollen pooped 68% more in volume and 66% more frequently than bees that ate wildflower pollen alone.
The next natural question was Why sunflower pollen had this effect. There are many ways to get the bowels moving – osmotic laxatives soften the stool with extra water, while stimulant laxatives prompt the muscles in the bowel to massage digested food down and out.
But preliminary research from the Adler lab again suggests a surprisingly simple explanation. The outer shell of sunflower pollen is very spiny, which can irritate the lining of the intestine producing a lubricating mucus or somehow dislodge the parasite. According to unpublished data, Adler claims that bees fed only the outer shell experience the same bathroom disturbances and antiparasitic effects as bees fed the kernel of sunflower pollen do.
Robert Paxton, a professor of zoology at Martin Luther University Halle-Wittenberg who studies bee parasites and was not involved in any of the sunflower studies, says the poop-based mechanism would fit with other work on intestinal parasites in bumblebees. Paxton cites a German study that suggests that parasites that plague bees cannot take hold in bumblebees simply because their intestinal transit time – the time it takes food to travel through the entire digestive tract – is so long. shorter.
Paxton adds that he would be eager to see if the bees are infected with C. bombi self-medicate by choosing to eat sunflower pollen more often than healthy bees – a behavior documented in sick bees.
Good for the colony?
Sunflowers are just one plant among countless thousands that likely have medicinal benefits for bees, scientists say. Resin from plants like poplars or apple trees can help bees fight fungal infections, while a compound derived from thyme is used by colony managers to help ward off varroa mites.
And since bees have been around since before the dinosaurs, researchers are also tracking the plants that pollinators use to identify potential candidates for human drugs. After all, they have a 120 million year head start in pollen research.
Peter Graystock, a senior lecturer at Imperial College London who studies bee parasites and was not involved in sunflower research, called the study “elegant”.
The prodigious droppings of sunflower pollen seem decidedly “good for the individual because it reduces its parasite load”, he explains. But since C. bombi is transmitted through feces, having generalized bumblebee diarrhea might not be such a good thing at the community level. “They basically release transmissible spores at a higher rate,” says Graystock. “Does this lead to faster transmission of the parasite in the community? »
There is also the element of nutrition. Sunflower pollen contains less protein than some other flowers and lacks two essential amino acids, so bumblebees cannot feed on sunflower pollen alone. Both Paxton and Graystock worry that the nutritional disadvantages of sunflower pollen may outweigh the benefits of dropping parasites.
But another study from the Adler lab currently under peer review suggests that sunflower pollen is worth the bet. As a postdoctoral student, Rosemary Malfi established healthy bumblebee colonies on 20 New York State farms with varying amounts of sunflower plantings and tracked the colony’s progress over the course of a season. .
“To our delight, the more sunflowers on the farm, the lower the infection in those colonies, both the intensity of the infection” and the proportion of bees affected, Adler says. “And more than that, colonies with more sunflowers actually made more queens,” a key measure of colony health that determines the reproductive success of the next generation.
Not a quick fix
The authors point out that we cannot save bees by flooding our neighborhoods with sunflowers.
The team found mixed results for sunflower pollen on C. bombi in other bee species – modest effects on two species closely related to the common eastern bumblebee and no effect on a third. The researchers plan to go back to basics and look for anatomical differences in bees’ guts that might explain why they react differently to sunflower pollen.
In the meantime, if you’re buzzing with helping the bees, planting “a diversity of flowers is a good idea,” says Irwin. And sunflowers can certainly be part of an assortment of native wildflowers, but be sure to get a variety with pollen – sunflowers bred for cut flowers are usually sterile.
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