Flowering plants emit gases that perfume the air. The fragrant molecules disperse and create a scented plume. Like a game of hot and cold， pollinators use their antennae to follow the gradient， always looking for where the scent strengthens. A strong scent means they are closing in on a bloom. A weaker scent means they're drifting off course.

Researchers focused on five representative floral scent molecules. One molecule they looked at， for example， is called beta-myrcene （BAY-tuh MER-seen）. A number of blooms emit this chemical into the air. Among them： snapdragons， purple coneflower， parsley， hops and certain citrus plants. Normally， this gas can travel some 800 meters （0.5 miles） from its flower source. But in polluted air， this same molecule could travel only half as far. Changes to beta-myrcene and other scent molecules as they interacted with the pollutants meant that insects would have to spend longer in search of a meal.

About 50 percent of foraging insects can sniff out a particular scented plume in 15 minutes if the air was clean. But the same insects could take an hour， the computer predicts， to find the scented plume when air is moderately polluted with ozone. Ozone is one of the primary irritants in urban smog. And the level of ozone considered here would be typical for a major U.S. city on a hot summer day， notes Fuents， who is a scientist.

These findings give scientists clues about what may be going on in nature， says James Blande. He is a chemical ecologist at the University of Eastern Finland in northern Europe. He wasn't involved with this research. Still， he says， "it's important to test these assumptions in real world experiments before drawing any firm conclusions."

But air pollution might do more than just weaken scented plumes. Chemical reactions between air pollutants and plumes may transform the blooms' fragrances， creating new scents. And these scents may be unrecognizable to pollinators.

That's certainly Fuentes' concern. So， he says his next research project will be to look at how insects deal with any new floral scent. "It is possible that some insects will evolve ways to detect and use these new molecules to find food，" he says.

1. Which of the following does NOT play a role in guiding pollinators to flowering plants？ ____.

A. scented plume

B. fragrant molecules

C. their antennae

D. their legs

2. What is the main reason for pollinators to spend more time finding nectar in fresh flowers？ ____.

A. changes to scent molecules

B. loss of habitat

C. harassment from their predators

D. decline in species of flowering plants

3. The word “gradient” in the first paragraph prabably means ____.

A. the fragrance of flowers

B. the path of the scent

C. the rate at which the scent increases

D. the gases emitted by flowering plants