There is nothing like a bit of candy to satisfy a craving for sweet treats. Humans, along with many other animals, can taste their food and use this sense to detect when food is energy rich, containing carbohydrates like sugar. For a bee, a garden of blooming pollen-laden flowers presents a smorgasbord of potential food sources. However, flower pollen is also highly variable in its chemical composition, suggesting that pollens may have unique tastes for pollinators, yet we know very little about the role that pollen flavour and bee taste play in pollen collection.
Felicity Muth, Jacob Francis and Anne Leonard of the University of Nevada, USA, investigated whether bees used taste to decide which flowers to visit. The researchers used bumblebees (Bombus impatiens), a pollinator species that consumes flower pollen, to answer their research questions. The team created three pollen blends – a sweet blend (including sucrose), a neutral blend (with added cellulose) and a bitter blend (flavoured with quinine) – with similar nutritional value, to test the bees’ preferences. Then, they presented the flavoured pollen blends to bees in fake flowers and assessed the bees’ preferences, their willingness to visit new flowers after their initial pollen experience and the amount of pollen that they collected.
Having observed the frenetic insects’ activities and preferences, the team concluded that bees do have a sweet tooth. The insects spent more time collecting pollen from the flower with sweetened pollen than from the flowers with unflavoured (added cellulose) or bitter pollen. The bees also visited sweet- and neutral-flavoured flowers more often. In addition, the bees that had been provided with the quinine-flavoured pollen collected the smallest amount of pollen: they appear to dislike bitter flavours. And when the scientists presented the bees with additional flower choices, they were more likely to sample a new flower if they had just experienced the bitter pollen.
Muth and colleagues' work shows that bees preferentially collect sweeter, rather than bitter, tasting pollens. This discovery may partially explain the diversity in the chemical composition of pollens. Plants may be ensuring that pollinators remove a little pollen at a time (it tastes good), while ensuring they don't remove it all at once (it can't taste too good). This strategy would also maximize pollen transfer to other plants of the same species to ensure successful pollination and reproduction. This study opens up new avenues for exciting future research that will allow us to understand the basic mechanisms that underlie plant–pollinator interactions.
