The relationship between bees and flowers is well understood. Bees visit flowers to gather pollen and nectar for food, and in doing so, they pollinate the flowers and help the plants produce seeds. That's always a win-win situation - or is it?
A colletes bee gathering pollen from a fleabane, a member of the aster family.
Photo: Andreas Müller / Applied Entomology ETH Zürich
Maybe not, at least for some plants in the aster family. Every pollen grain lost to a bee represents one less seed that plant can produce. Pollen production requires a lot of energy from the plant, so it's in the plant's best interest to prevent too much pollen from buzzing off.
Researchers at the Swiss Federal Institute of Technology Zurich discovered an unusual adaptation in asters that limits its number of pollinators. They found that a number of bees belonging to the genus Colletes specialize in the aster family, while other Colletes species went out of their way to avoid the asters. Why would bees steer clear of an abundant family of flowers that provides easy access to its pollen?
The scientists hypothesized that certain aster flowers might produce pollen that contains chemical toxins to deter some bee species. To test their theory, the team fed bee larvae with pollen from the aster family, which was not part of their normal diet. Although the larvae ate the wrong food for up to 30 days, they did not grow. Not one species managed to develop from a larva into a bee – apart from the bees that specialized on this plant family.
Claudio Sedivy, a PhD student in applied entomology, is now collaborating with chemist Rafal Piskorski and student Claude Hüsser to test whether pollen from members of the aster family contains toxins and whether the corresponding bees have adapted their metabolism especially in order to use the pollen.