Proboscis extension reflex

When the taste receptors on the antenna or tarsi are stimulated by sugar water, the proboscis automatically sticks out to drink.

The PER paradigm is most commonly used in associative learning experiments in honeybees and bumblebees because it is easy to use for simple Pavlovian conditioning.

For example, the bee is presented with an odor (CS) and an application of the sugar (US) solution to its antennae, upon which she reflexively extends her proboscis.

In some variations, the bee is immediately fed with sugar at this point; this constitutes an operant reinforcement which would tend to establish the odor as a discriminative stimulus.

Then a stream of odorant blown towards the bee's head was immediately followed by touching the antenna with a sugar droplet.