A Moment of Science

Odors That Push and Pull Pollinators

Ever notice how a little cologne can be attractive, but too much is totally repellent? That principle is used by cycads, an ancient type of cone-bearing tree.

Cycad Tree in the Light

Photo: dinesh_valke (flickr)

This Cyad tree from Mumbai is a male plant which produces male or microsporangiate cones that bear many scales, each with an abundance of microsporangia scattered over the lower surface.

Ever notice how a little cologne can be attractive, but too much is totally repellent?

That very principle is used by cycads, an ancient type of cone-bearing tree. Cycads depend on tiny insects called thrips to carry pollen from the cones of male trees to the cones of female trees. Researchers at the University of Utah noticed that the male cycad cones often emit a strong sharp odor, similar to turpentine.

They observed that when the odor was strongest, the thrips, which normally live inside the cones, scrambled out in droves and flew away. While the thrips are out looking for new homes, some visit and pollinate female cones, which only emit low levels of the smelly compound.

The researchers also discovered that for a few hours each day cycads increase their metabolic rate, which increases the temperature inside the cones up to fifty degrees above ambient temperature. The heating of the cones results in much higher emissions of the noxious odor.

To test whether it was heat or smell that caused the thrips to flee, the researchers put thrips in Y-shaped tubes with a high concentration of the odor in one arm, and a low concentration in the other. They found that thrips were attracted to low levels of the odor, but repelled by high concentrations.

For a few hours a day, male cycads drive away the thrips with too much perfume, while the female cones attract them in with low levels of the same smell. This push and pull of the tiny pollinators between trees ensures that cycads can reproduce and pass on their genes to the next generation.

Perhaps something to remember next time you’re applying cologne!

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