Pollen hitches a ride on bees in all the right spots

Hard-to-groom zones line up with where flower reproductive parts touch the insects

MISSED A SPOT After bees groom pollen off their bodies, there’s still some left over (illuminated here under ultraviolet light). These overlooked areas correspond to places where flowers’ reproductive parts come in contact with the bees, a new study shows.

P. Wester

By Maria Temming

September 6, 2017 at 2:00 pm

Bee bodies may be built just right to help pollen hitch a ride between flowers.

For the first time, scientists have identified where and how much pollen is left behind on bees’ bodies after the insects groom themselves. These residual patches of pollen align with spots on bees’ bodies that touch flowers’ pollen-collecting reproductive parts, researchers report online September 6 in PLOS ONE.

Typically, when honeybees and bumblebees visit flowers for nectar, they brush much of the pollen that powders their bodies into pocketlike structures on their legs to carry home for bee larvae to eat. In fact, bees are so good at stashing pollen that less than 4 percent of a flower’s pollen grains may reach the pollen-receiving parts of a second flower of the same species. Given bees’ pollen-hoarding prowess, researchers wondered how they came to play such a significant role in plant reproduction.

So biologist Petra Wester and colleagues put buff-tailed bumblebees (Bombus terrestris) and European honeybees (Apis mellifera) into jars containing pollen grains. As the bees whizzed around, they stirred up the pollen, evenly coating themselves in just a few minutes. When placed in clean jars, the insects groomed themselves. Even after a half hour of grooming, the insects still had pollen caked on some areas of their bodies, including the tops of their heads, thoraxes and abdomens.

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bee abdomen dusted with pollen, and bee visiting a flower — **ALL THAT GLITTERS** The underside of a honeybee’s abdomen (left), is still dusted with pollen even after grooming. When a bee visits a star-shaped borage flower (right), the underside of its abdomen touches the flower’s pollen receptor, or stigma (red). L. Koch, K. Lunau and P. Wester/*PLOS ONE* 2017

“They cannot reach these spots so easily,” says Wester, of Heinrich Heine University Düsseldorf in Germany, “similar to the fact that people cannot reach their back so easily.”

Wester and colleagues placed other bees in cages with flowers whose pollen-producing anthers and pollen-collecting stigmas had been stained with fluorescent dyes. When the researchers later examined these bees, they found dye smeared on the same ungroomed areas. These findings suggest that these “safe sites” for pollen on bees’ bodies play an important role in pollination.