Patrick Guilfoile: Shocking news about the flowers and the bees
Flowers are “sensory billboards” according to a recent article in Science magazine.
Flowers vie for the attention of bees using a variety of strategies to help ensure their pollination. Strong, pleasing odors are one example. Bright colors are another. Flowers also produce floral patterns that are attractive to bees. Some of these patterns are beyond the detection of our eyes, since these winged creatures can detect ultraviolet light, something we cannot see.
The fact that flowers can use scent and color to attract bees would seem to be a full palate of sensory targeting. Yet, there appears to be at least one additional factor that bees can use to judge whether a flower is worth targeting: electrical attraction.
To determine if this might be the case, researchers first measured whether bumblebees were electrically charged. The scientists used a special pail containing sugar water for this experiment. The pail was highly insulated and had a relatively narrow circular opening. When a bee flew inside, any charge it contained was detected as a small, but measurable, change in voltage. With this device, the scientists determined 94 percent of the bees in their sample were positively charged.
Researchers also measured the electrical charge of flowers, and found most of them were negatively charged. Since opposite charges attract, it is clear that bees could be drawn to negatively charged flowers. But were they? The first set of experiments involved testing whether bees could detect an electrical field on a flower. The scientists constructed fake flowers, one set with an electrical charge and nectar, the other identical except with no charge and no nectar. Once trained, the bees homed in on the charged flowers with 80 percent accuracy. The researchers then turned off the electrical current, and the bees lost the ability to differentiate between the two types of “flowers”.
Next, the researchers attempted to determine how refined the bees’ electrical discrimination was. The researchers created “flowers” with unique electrical patterns; one uniform, without a reward, the other a “bull’s eye” pattern, with nectar. With practice, the bees were able to correctly identify the flower with a reward about 70 percent of the time.
These experiments showed that electrical cues can be used by bees to distinguish between different flowers. From the point of view of the both the flowers and the bees, electrical signals are a very useful form of communication. Unlike scent or color, which don’t respond immediately to interaction with a bee, the electrical current in a flower can change almost immediately. So, for example, once a flower is pollinated, the electrical current can be shut off, giving a signal to bees that their services are no longer needed. This research shows that, even with as much as we currently know about the interaction of bees and flowers, there are likely other secrets we have yet to uncover.
More information is available in an article by Dominic Clarke, Heather Whitney, and others “Detection and Learning of Floral Electrical Fields by Bumblebees” Science, Vol. 340 66-69, April 5, 2013.
— Patrick Guilfoilehas a doctorate in bacteriology and is the associate vice president at Bemidji State University.