A team of researchers led by Penn State said the pollution-modified plant odors can confuse bees and, as a result, bees’ foraging time increases and pollination efficiency decreases. This happens because the chemical interactions decrease both the scent molecules’ life spans and the distances they travel.
While foraging for food, insects detect floral scent molecules in the air. Wind currents can carry these molecules up to thousands of feet from their original source to where bees have their hives.
“Many insects have nests that are up to 3,000 feet away from their food source, which means that scents need to travel long distances before insects can detect them,” said Jose D. Fuentes, professor of meteorology and atmospheric science, Penn State. “Each insect has a detection threshold for certain kinds of scents and they find food by moving from areas of low concentrations of scents to areas of high concentrations.”
Plant-emitted hydrocarbons break down through chemical interactions with certain air pollutants such as ozone, resulting in the creation of more air pollutants, including hydroxyl and nitrate radicals, which further increase the breakdown rate of plant odors.
The team reported in the current issue of Atmospheric Environment that, as air pollution increases, hydrocarbons’ lifetime and travel distance decreases. For example, at 60 parts per billion ozone levels, which the U.S. Environmental Protection Agency considers a ‘moderate’ level, the researchers found that enough chemical changes took place to thoroughly confuse bees to locate food.
The scent molecule alpha-pinene, which survives nearly 40 hours in an ozone-free environment, survived fewer than 10 hours when ozone rose to 60 parts per billion and only 1 hour when ozone was at 120 parts per billion.
Another molecule, beta-myrcene, which travels more than 3,000 feet in an ozone-free, windy environment, traveled an average of 1,500 feet when ozone was 60 parts per billion and, when ozone rose to 120 parts per billion, most traveled fewer than 1,000 feet.
When ozone rose to only 20 parts per billion, it took 180 minutes for the same amount of bees to find the scent. The team found similar results for the six different scent molecules they analyzed.
Fuentes said, “It’s similar to being asked to get a cup of coffee at the nearest cafeteria while you are blindfolded. It will be hard to locate the coffee shop without using visual cues. The same could happen to insect pollinators while foraging for food in polluted air masses.”
According to the U.S. Department of Agriculture, managed honeybee populations in the U.S. have declined between 25 and 45 percent per year since 2010, including a 44 percent decline from 2015 to 2016.
“Honeybees and other pollinators are in trouble almost everywhere, and they pay us a lot of services through their pollination,” said Fuentes. “The more we can understand about what factors are affecting their decline in numbers, the more equipped we will be to intervene if needed.”