Ozone Overdose Confuses Pollinators

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Ozone isn't just bad for your lungs, it also gets in the way of insects finding their favorite food, say researchers. Ozone, because it reacts readily with aromatic compounds put out by plants, interferes with the come-hither call of the plants to insects.

“The insects need a threshold amount of gas released by the flower,” said Jose Fuentes of Penn State University. That threshold is pretty low, only about six molecules, for the beetles to detect the plant odor.

He and meteorology undergraduate John Zenker and University of Virginia researcher T'ai H. Roulston tested beetles inside a Y-shapped tube so that the insect could choose which branch to follow the plant scent. Researchers collected the insects from pumpkin and squash plants then tested them using wild buffalo gourd plants.

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When they ramped up the ozone, the ability of the beetles to choose the right branch of the tube dropped. When they lowered the ozone again, the beetles were able to detect the gourd plants again. They published their findings in the journal Environmental Research Letters.

On the face of it, this would seem to be good news for the gourd plant, but not really, Fuentes explained.

“There's a very very important ecological story there,” said Fuentes. “We have a lot of plants releasing scents to pollinators.” If ozone increases in rural areas, it could impinge on pollinators' abilities to find flowers. “The pollination will decrease. It will affect both native plants and some crops.”

And since 70 percent of our food comes from plants pollinated by insects, Fuentes said, too much ozone in rural areas could affect our food supply. Urban areas of the United States are seeing lower ozone levels thanks to the Clean Air Act. But rural areas are seeing more ozone as pollution, because the intense industrialization of Asia blows across the Pacific Ocean, Fuentes said.

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Another potential complication for plants is that some are known to protect themselves with scents. When under attack by a plant-eating insect, some plants will release special odors to attract predatory insects which will eat the herbivores. But if ozone is interfering with this distress signal, the plants lose one of their most powerful defenses.

“I think this study is very important with regards to how human activities can affect ecological systems,” said Paul Shepson, who directs a atmospheric chemistry lab at Purdue University. “It's an area of impact that not a lot of people are looking at.”

On the other hand, Shepson point out, not all ozone is bad. At lower concentrations it's essential for breaking down pollutants, even those produced by swamps and other natural features, that can then be rained out of the atmosphere.

“If there wasn't this mechanism for the atmosphere to clean itself, we'd be dead in months, or would have evolved very differently,” said Shepson.

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