Nectar-borne GABA promotes flower fidelity in bumble bees

To enhance pollinator loyalty, which is vital for plant reproduction, flowers have evolved rewards like nectar or excess pollen. Besides nutrients, nectars contain a plethora of secondary metabolites (SMs). Although the primary function of SMs is to protect plants from herbivores, growing evidence suggests that some of them may have adaptive functions in plant-pollinator interactions. GABA, which is prevalent in the nectar of many plants, interferes with learning and memory in restrained bees. Crucially, it is yet to be tested whether GABA affects pollinator foraging behaviour. The study aims to test whether free-flying bumble bees (Bombus terrestris) show a preference for artificial flowers dispensing GABA and whether GABA impacts bees' learning of visual floral cues and promotes flower fidelity. We used three concentrations of GABA throughout the experiments, including two within the natural range and a third above it, to investigate any dosedependent effects on foraging activity in flight arenas. The results showed that GABA did not affect bumble bee foraging preference at any concentration tested. Bees successfully learned to visit rewarding flowers regardless of the concentration of GABA, and no concentration affected the speed of learning. After learning, they tended to stay loyal to these flowers even when they became unrewarding. However, bumble bees that experienced GABA at the natural doses, but not at the unnatural high dose, remained faithful significantly longer to unrewarding flowers. The study provides insights into the use of SMs by plants to influence pollinator behaviour, with potential applications in agriculture.