That may not be news (the study in question* was published in 1992), but this is a rather interesting result… Bees are able to detect if flowers have been visited by another bee, and more readily leave those that have recently been. This behaviour is not difficult to explain: you better have to move if there is less to forage (don’t waste your time where reward is probably lower). Direct cues to assess nectar availability can be used by bees (when nectar content of a flower can be seen, or smelled), but this way isn’t always possible with any flower morphology and requires some level of inspection, i.e. there is a time cost. But bees are making the process easier by marking the flowers they visit with a special scent.
The effect of the scent was here experimentally reduced in the study (with artificial flowers) via an air extractor. When on, flower rejection dramatically decreased, flower inspection and visit time were also increased, while the number of visits was unchanged between the two experimental conditions. I find it amazing how far and finely tuned behaviours have evolved in these insects…
But we may also notice that the experimental flowers were still providing a great reward even after they were visited. This means bees in the experiment were stuck into their innate foraging method and losing resources aside. This probably means there is no such thing as a continuously rewarding flower in nature… :-)
M. Giurfa and J.A. Nunez (1992).Honeybees mark with scent and reject recently visited flowers. Oecologia 89: 113-117.