Diesel Fumes Throw Honey Bees Off the Scent

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Diesel pollution snuffs out floral odors, interfering with honeybees' ability to find and pollinate flowers, new research suggests.

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Honeybees use both visual and olfactory cues to recognize flowers that produce nectar in return for insect pollination. Not all flowers produce nectar, and bees avoid those that don't by learning to recognize the odors of nectar-bearing flowers.

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But these floral odors — which consist of reactive chemicals called volatiles — react with other substances in the atmosphere; in the presence of certain pollutants, these scents can chemically transform into undetectable forms, researchers from the University of Southampton report today (Oct. 3) in the journal Scientific Reports. [On the Hunt: Honeybee Scouts Find Food]

The researchers specifically explored whether nitrogen oxides — a group of highly reactive gases released by diesel combustion — are capable of altering floral odors to an extent that would dampen a bee's ability to recognize desirable flowers.

So the scientists produced a synthetic floral odor from a blend of eight volatiles that closely matched those found in oilseed rape flowers. They released the smell into a series of glass containers, and exposed some but not all of the containers to different concentrations of nitrogen oxide gases, leaving others uncontaminated.

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Over the course of two hours, the researchers measured the concentrations of the eight volatile compounds under the various conditions.

Within a minute, two volatiles that together accounted for more than 70 percent of the floral odor became completely undetectable within contaminated chambers, but remained detectable in uncontaminated chambers, the team reports.

The researchers also conditioned a group of honeybees to recognize the synthetic floral odor by repeatedly exposing them to it in conjunction with a nectar reward. The team then introduced the bee groups into the test chambers to determine how the contamination affected smell recognition, which they gauged based on whether the bees extended their proboscis — the strawlike mouthpart they use to suck up nectar — within 10 seconds of exposure to the odor in the study chambers. If the bee did not extend its proboscis, then it was presumed to have lost the ability to recognize the smell.