Pollution Is Stopping Insects from "Smelling the Roses"

Researchers ran an outdoor experiment to see if diesel exhaust and ozone would interfere with pollinators’ search for floral scents.

In a field of winter wheat, researchers at the University of Reading planted an unusual fumigation system: eight octagons surrounding clusters of black mustard plants. Each eight-sided “ring” would pump out either ozone, diesel exhaust, a combination of the two, or nothing. The researchers aimed to test whether these common air pollutants affect the insects attracted to the mustard plants’ flowers.

The researchers did two separate counts. The first one counted the overall number of any pollinator that flew into the rings and landed on at least one flower. Compared to the control ring, the number of visitors declined by 69 percent for diesel alone, 62 percent for ozone alone, and 70 percent for a combination of both. The second metric counted visits by four distinct species—bees, moths, butterflies, and hoverflies—and considered how many flowers each insect landed on. Compared to the control, the number of flower landings decreased by 89 percent for diesel, 83 percent for ozone, and 90 percent for both.

Results suggest that air pollution is another potential stressor adding to pollinators' growing pressures. More bad news for the pollinators, who might not be able to forage effectively amidst air pollution, it’s bad news for plants that depend on insects to propagate. It looks pretty bad for humans, too: If insects can’t pollinate crops, we may lose essential products in the food supply.

Insects, including bees and butterflies, smell using their antennae, which are covered in receptors that detect odor compounds. Their sense of smell is keen—much more sensitive than that of humans. When a flower releases chemical compounds in a plume or a chemical column, insects use that as a map to find it. Suppose one or more of the odor compounds are altered by reacting with diesel or ozone; the ratio and concentration of compounds in the plume change. The map becomes distorted, and the insect no longer associates that plume with the flower.

Disrupting pollination, a “keystone service” for ecosystems and agriculture, with fossil-fuel-related emissions, can affect climate resilience and food security in the future. Studies like this are “particularly critical with a growing global population and essential for a growing urban environment.

The adverse effects of air pollutants on pollinators, even at relatively low levels, add to why we should be transitioning away from fossil fuel consumption as fast as possible.