It is dopamine that drives bees to leave the hive to forage.

by Sophie Bécherel

Dopamine is a neurotransmitter involved in the cerebral reward system and the sensation of pleasure in mammals. While in humans dopamine is a key element in the mechanism of drug addiction, in bees this neurotransmitter is responsible for the departure of foragers from the hive, not only to satisfy their individual desire to feed, but also to search for food in order to meet a social need and provide the colony with the nutritional inputs it requires.

Introduction

According to an international team of scientists, foraging bees are prompted to leave the hive by dopamine, a neurotransmitter that sends the brain a signal corresponding to a “desire to eat.” The researchers were able to measure the levels of this substance by tracking the insects’ activity.

The decision to leave the hive in search of food is guided by an increased level of dopamine in the insects’ brains.

In mammals, including humans, desire, wanting, or what one might call “immanent motivation” arises through chemical reactions in the brain. These reactions are triggered by the activation of a neuronal circuit via dopamine. This neurotransmitter effectively conveys a signal from the midbrain to the frontal lobe, the area responsible for the voluntary coordination of movement, language, and decision-making. A Franco-Chinese research team has now demonstrated the presence of this same dopaminergic circuit in the brain of the honey bee, a quintessentially social insect.

Motivated for themselves and for others

Led by Martin Giurfa, professor of neuroscience at the CNRS at the University of Toulouse 3 – Paul Sabatier, these scientists, in collaboration with the Fujian Agriculture and Forestry University in China, studied for four years foraging bees that left their hive to search for food, motivated by the reward of nourishment. Their work, published in Science, shows similarities between the brains of these insects and that of humans.

“We observed that bees leaving in search of food show an overactivation of their dopaminergic system, similar to what is observed in humans. Once they reach the feeding site and begin to eat, dopamine levels decrease,” explains Martin Giurfa. Unlike humans, however, bees do not forage solely to satisfy their individual desire to eat; rather, as the researcher adds, “they search for food to satisfy a social need, to provide the colony with what it requires.” It is indeed from the food brought back that the hive is able to produce honey.

The decision to leave the hive in search of food is therefore guided by the increased level of dopamine in the insects’ brains. In isolated foragers, dopamine levels also rise, but to a lesser extent. This motivational circuit thus operates at two levels: that of the individual and that of the group, when the bee forages to meet the needs of the colony.

A dopamine surge also to inform nestmates

Even more fascinating, according to Martin Giurfa, is that “once back in the hive, dopamine is released again.” It is precisely when the insects begin to dance in order to inform their nestmates of the location of the coveted food that dopamine levels surge. The bee dance—those stereotyped movements discovered by the German ethologist Karl von Frisch—allows the insects to indicate very precise directions in space (100 m to the west, 30 m to the south, etc.). “It is as if there were a reminiscence of what they had experienced that activates this appetitive system at the moment of the dance,” the researcher concludes.

It remains to be determined how the bees that observe the dance in turn activate their dopaminergic system to take over and set out in search of food. The study was not able to determine this.

Observations en temps réel

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It is dopamine that drives bees to leave the hive to forage.

Introduction

Motivated for themselves and for others

A dopamine surge also to inform nestmates