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Bumblebee on miniature petunia. Photo: <a href="">spike55151</a>, Creative Commons, some rights reserved
Bumblebee on miniature petunia. Photo: spike55151, Creative Commons, some rights reserved

Natural Selections: Bumblebees and "flower power"

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Static electricity plays a role in getting pollen to come loose from the blossom and to stick to the pollinator. According to a recent study using petunias and bumblebees, British researchers observed that the flowers increase their electrical charge in response to the presence of pollinating insects. The charge peaks in intensity just before the potential pollinator begins feeding on nectar, and decreases after they go away. Martha Foley and naturalist Curt Stager discuss this unique example of "flower power."

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Summary of this Natural Selections episode:

In a new study published in the 2013 Journal of Science, British scientists found that bees have a magnetic sense that can detect electrical fields. “If you are a flying insect like a bee, as you are going through the air the little particles, air molecules, and the dust strike the surface of the bee and knock electrons off,” says Dr. Curt Stager. That gives the bee a small net positive charge. Flowers rooted in the ground have a slight negative charge, so the bee and flower attract each other.

The scientists put out nectar to attract bees, and found that 94% of the bees that came in were positively charged. They also measured petunias, and found that all of them carried a slight negative charge.

As a bee approached a petunia, the negative charge of the flower was neutralized. It wasn’t the impact of the bee that changed anything; the change occurred before the bee and flower actually touched. Stager says, “Sometimes (because the pollen in the flower is negative, too), it just sort of leaps off the flower onto the bee just before it hits.” After a bee lands on a flower, it takes awhile for the flower's electric field to regenerate. This may signal to other bees that the flower has already been visited and there is no nectar left.

The scientists theorized that these electrical fields may be one of the ways bees find flowers from a distance. They tested this by applying a colorful dye powder with a positive charge that would stick to flower petals. The powder adhered in a particular pattern, demonstrating that there is a distinctive shape to the flower's electric field—just as there is a distinctive pattern to the colors of the flower.

They then made fake flowers that produced electric fields in the same shapes as those created by natural flowers. Some fake flowers were baited with sweet syrup and some with a less appetizing offering. Bees quickly learned which flowers had the reward. But once the scientists turned off the power supply, removing the electric field, the bees could no longer tell which flowers had the food.

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