Honeybees taste things by using sensitive receptor nerve cells contained in hair-like structures known as sensilla. In the honeybees' case, sensilla may be found on the antennae, mouth and the tarsi (end portions of the honeybee's legs). Scientists have known for some time that honeybees taste their food using their tarsi, but how that information is processed and used to distinguish different tastes is not well known.
In order to study the taste mechanism, researchers from the University of Toulouse examined the reactions of hundreds of honeybees when salty, sugary or bitter solutions were exposed to the tarsi. Their results were published recently in the journal Frontiers in Behavioral Neuroscience.
Upon the honeybees exposure to various solutions, the research team monitored the tongues of the bees - retracting the tongue means a honeybee did not like the taste and would not attempt to drink the solution; extending the tongue means a honeybee liked the taste and was preparing to drink the solution. Not surprisingly, the team discovered that just like human children, honeybees are extremely sensitive to sugar and are highly attracted to it. The bees extended their tongues to drink dilute sucrose solutions as well as concentrated ones.
The team also discovered some new insights into specific receptor locations on the tarsi and how the information was processed. Nerve cell activity was measured in different areas of the tarsi to determine more specific areas of sensitivity. For example, the double claw that forms the end of the tarsi was found to be extremely sensitive to sugary solutions, while the segments immediately before the claws (the tarsomeres) had a higher sensitivity to salty solutions. Why the tarsi are so sensitive is not fully understood (since the other sense organs of honeybees contain more sensilla than the tarsi do) but it is likely an adaptive mechanism to help the honeybees distinguish the presence of nectar on the plants they land on.
Since both tarsi are involved in the tasting process, the research team wondered what would occur if each tarsus received contradicting information - for example sugar solution on one side but water on the other? They discovered that it's a literal race. While the honeybee processes the information it receives from both tarsi, it gives added weight to the side that the honeybee tastes first. When sucrose was detected first, the honeybee extended its tongue and ignored the other input, but if the first input was less attractive, the honeybee was less likely to extend its tongue for the sucrose once it detected its presence.
This paper claims to be the first integrative study on the taste mechanism of honeybees using both a behavioral and electrophysiological approach. It seems likely that this technique will be put to greater use in future insect research.