The European bee-eater (along with our Pacific Northwest scrub jay and others) might think bees taste pretty good, but here we’ll explore the honey bee’s good ability to taste, rather than its sweet flavor.
WHERE, WHAT and HOW
In an earlier article on this blog (Proboscis, anyone?), I described the honey bee proboscis: the extendable, tube-like mouthparts for drinking honey, nectar, and water. At the end of that article, I promised that I would continue with the story of the bee’s sense of TASTE. This is Part 1 of that two-part story.
And finally, there are also sensors for taste on the bee’s two front feet (tarsi).
Did I say FEET? Yes—it is not at all uncommon among insects! Actually, it is quite practical to be able to sample a potential meal and judge its suitability just by walking on it…..that is, if you are a “bug.”
Taste versus Smell
The distribution of taste and olfactory sensors on the honey bee antennae, mouthparts, and forelegs is closely correlated, and the two senses work together to complete the bee’s perception of its physical and social world.
Both types of sensors are triggered by contact with molecules. The difference between odor and taste is a matter of whether the molecules are sampled from the air (odors) or by direct contact with a liquid source (tastes)—that is, a liquid such as nectar, or a solid dissolved in liquid, such as sugar or a mineral salt, or a solid material that is simply moistened by licking.
What can bees taste?
So far, exactly 10 different taste receptor genes have been identified in honey bees, each of which could code for multiple types of taste receptors. How many distinct types of receptors there are, ultimately, and to what they may each respond is not yet known. The study of the honey bee’s sense of taste is essentially still in its infancy, and there is much more yet to be learned.
We do know that the sensory cells are clustered and housed in hairlike structures called sensillae, which are distributed as described above on antennae, mouthparts, and front feet.
Sensors in each of the three locations respond to particular tastes.
Among the sweet-sensors, one type responds specifically to the sugar fructose. There are two other types of receptors for sweetness that can each detect all the other sugars that bees encounter in foraging, including sucrose, glucose, maltose, melicitose and trehalose.
No receptors for bitter tastes have yet been found in honey bees. However, in laboratory studies, it has been shown that bees do avoid liquids with concentrated bitter taste—which in plants is characteristic of toxins that some species produce naturally to defend themselves.
Without specific bitter-receptors, how can foragers avoid potentially toxic nectar? A possible mechanism was observed in lab experiments: in liquids that contained both bitter and sweet components, the response to the sweet taste was inhibited, rendering the “artificial nectar” less attractive to bees.
Stick Out Your Tongue!
Honey bees spontaneously extend the proboscis when they detect something sweet and potentially palatable. There is a different threshold for this response depending on which of the taste receptors are stimulated: sensors on the antennae require only a 3% sugar concentration to cause the extension, whereas those on the feet need a concentration close to 34% to trigger the same automatic response.
Tiny sweet droplets can be carried in a breeze from floral sources to a bee’s exposed receptors and trigger this flick of the tongue as the forager approaches an open flower. With advanced notice of nectar on offer, the bee can assess whether the source is worth a visit, and if so, it has its collecting gear in ready position for quick, efficient work. You might observe this fascinating behavior if you carefully watch foragers in the field.
Now we’ve seen where the honey bee’s taste receptors are located, how they function, and what kinds of tastes they can discern. In Part 2, learn about the role and importance of taste to the individual bee’s life, and the ways in which good taste is essential to the daily and seasonal activities of the colony.