Discrimination of unrewarding flowers by bees; Direct detection of rewardsand use of repellent scent marks

Bumblebees and honeybees deposit short-lived scent marks on flowers that th ey visit when foraging. Conspecifics use these marks to distinguish those f lowers that have recently been emptied and, so, avoid them. The aim of this study was to assess how widespread this behavior is. Evidence for direct d etection of reward levels was found in two bee species: Agapostemon nasutus was able to detect directly pollen availability in flowers with exposed an thers, while Apis mellifera appeared to be able to detect nectar levels of tubular flowers. A third species, Trigona fulviventris, avoided flowers tha t had recently been visited by conspecifies, regardless of reward levels, p robably by using scent marks. Three further bee/flower systems were examine d in which there was no detectable discrimination among flowers. We argue t hat bees probably rely on direct detection of rewards where this is allowed by the structure of the flower and on scent marks when feeding on flowers where the rewards are hidden. However, discrimination does not always occur . We suggest that discrimination may not always make economic sense; when v isiting flowers with a low handling time, or flowers that are scarce, it ma y be more efficient to visit every flower that is encountered.