Traffic fumes render the scent of flowers barely recognizable to honeybees and could have a serious impact on their ability to find food, new research has found.
Scientists discovered that reactive pollutants in diesel destroyed key chemicals in the odor of oilseed flowers, making them smell different to the bees.
“Honeybees have a sensitive sense of smell and an exceptional ability to learn and memorize new odors,” said Tracey Newman, a neuroscientist at the University of Southampton.
The effect of diesel fumes on flower scent “could have serious detrimental effects on the number of honeybee colonies and pollination activity,” Newman said.
Three-quarters of the world’s food crops rely on bees and other natural pollinators, a service valued at ￡135 billion (US$218.3 billion) a year globally.
However, there have been serious declines in natural pollinators in recent decades. A combination of factors is blamed, including the huge loss of the flower-rich habitats that sustain bees, as well as disease, and the impact of agricultural insecticides.
The revelation that traffic fumes could be adding to the problems is significant, said Guy Poppy, a professor and ecologist at Southampton, who also worked on the research.
“Diesel exhaust is not the root of the problem, but clearly, with all the other stressors, adding another one is likely to be detrimental to bee health,” he said.
The study, published in Scientific Reports, tested bees’ ability in the laboratory to recognize the aroma of oilseed rape flowers. Bees were strapped down and taught to associate floral scents with food in the form of sugar solutions. Once the bees learned the connection they began sticking their tongues out in anticipation of food even if it was not offered — an indication that they recognized the smell.
When the scent was presented without pollutants, the bees recognized it 98 to 99 percent of the time, but after the scent was mixed with levels of diesel exhaust matching those found at roadsides, the bees only recognized it 30 percent of the time.
“Honeybees are very, very selective on what they home in on ... they do not go randomly from flower to flower,” Newman said.
The team found it was the highly reactive nitrogen oxides that chemically altered the smell by removing key chemicals within a minute of exposure.
Emissions from gas vehicles contained even higher levels of nitrogen oxide, Newman said.