MARCH 11, 2020
by Krishna Ramanujan, Cornell University
When it comes to feeding on pollen, honeybees and bumblebees are generalists. They like a buffet of choices—except when it comes to pollen from flowers of the genus Cucurbita, including squash and pumpkin, which they avoid.
A Cornell study, "Pollen Defenses Negatively Impact Foraging and Fitness in a Generalist Bee," published Feb. 20 in the journal Nature Scientific Reports, found that squash and pumpkin pollen have physical, nutritional and chemical defense qualities that are harmful to bumblebees.
"When bumblebees are fed cucurbit pollen, it causes all kinds of problems," said Bryan Danforth, professor of entomology and the paper's senior author. "Adults have damaged and distorted digestive tracts and colonies fed cucurbit pollen failed to rear any offspring."
Bumblebees do visit pumpkin and squash flowers for the nectar, and though they don't collect the pollen, some might inadvertently get on their legs.
"I actually saw them in the field using their legs to groom it off their bodies and then wipe it on a leaf," said first author Kristen Brochu Ph.D. '18, a former Cornell doctoral student in Danforth's lab and a postdoctoral researcher at Pennsylvania State University. "Not only are they not collecting it, they actually hate it."
At the same time, another bee, the squash bee, eats only cucurbit pollen.
"The [cucurbit] system is really interesting because we have specialists and generalist bees feeding on the same resource," Brochu said.
The results suggest that deterring bumblebees from collecting and eating pollen may provide an evolutionary benefit to cucurbit plants.
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