Does diesel pollution keep bees from finding flowers?

Air pollution may be giving bees the equivalent of a stuffed-up nose. According to a study in Scientific Reports, diesel exhaust distorts the scents of flowers — and as a result, honeybees could have trouble sniffing out plants to pollinate.

Pollination is crucial for farming: By some estimates, about 35 percent of the world’s food must be pollinated. This service, worth about 208 billion dollars per year, is often performed by honeybees. These bees “have a sensitive sense of smell and an exceptional ability to learn and memorize new odours,” which helps them find flowers, the team writes.

Wondering if air pollution might interfere with this process, the researchers conducted several experiments. First, they created a synthetic odor using eight chemicals found in the natural scent of oilseed rape flowers. Then they put the synthetic mix into glass bottles filled with clean air or diesel exhaust.

In the polluted bottle, two of the scent chemicals “were rendered undetectable” in one minute, the team reports. But in the clean bottle, all the odor’s components could still be detected for two hours. And levels of some chemicals in the diesel exhaust bottle dropped lower than those in the clean bottle.

The team then did a similar experiment using nitric oxide and nitrogen dioxide, which are found in diesel exhaust. When those gases were mixed with the synthetic odor, the levels of two scent chemicals fell by 90 and 97 percent, and one couldn’t be detected at all.

Finally, the team trained honeybees to extend their proboscises when they smelled the synthetic odor. When the researchers removed one of the chemicals from the mix, the bees had a harder time recognizing the scent — even though that chemical had made up only 0.8 percent of the mixture.

While bees can also identify flowers by sight, tracking odors is important when the bee is farther away. “[T]he fact that removal of such a minor constituent can have such a profound effect on the ability of honeybees to recognize a floral odour may have significant ramifications for the ability of honeybees to efficiently forage for floral resources,” the authors warn. Such disruptions, they say, could have “major economic and ecological impacts.” Roberta Kwok | 4 October 2013

Source: Girling, R.D. et al. 2013. Diesel exhaust rapidly degrades floral odours used by honeybees. Scientific Reports doi: 10.1038/srep02779.

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