Pollution is changing the scent of flowers

Sensory pollution arising from human activity is degrading the chemical compounds responsible for floral scents, confusing insects trying to locate flowers.

Pale Evening Primrose

The impact of noise pollution and light pollution are known to disorientate a range of animals, but less is know about sensory pollutants and how they affect ecological communities. Researchers have now found that insects may be finding it harder to locate flowers because the scent molecules released by the flowers smell different after they react with pollutants in the air.

Jeff Riffell of the University of Washington in Seattle has conducted research into the effects of anthropogenic pollutants on plant pollinators. The researchers focused on ozone and nitrate radicals (NO3) – the pollutants created from the interaction of car emissions with gases in the atmosphere. Both pollutants were found to break down the scent compounds of their test subject; the evening-primrose (Oenothera pallida), with the nitrate radicals completely eradicating the scent.

Using a nocturnal flower-moth, the hawk moth species, they found that atmospherically relevant concentrations of NO3 eliminate flower visitation by moths. The primroses that released ‘degraded’ scents were visited 70% less frequently than the flowers releasing natural sent. According to Riffell, this drop in visitation could affect hawk moth health and have a knock-on effect on the wider ecosystem, because the researchers calculated that the decline in moth visitations could result in a 28% reduction in the amount of fruit the plants produce.

Global atmospheric models of floral scent oxidation reveal that pollinators in certain urban areas may have a reduced ability to perceive and navigate to flowers. These results illustrate the impact of anthropogenic pollutants on an animal’s olfactory ability and indicate that such pollutants may be critical regulators of global pollination. The team’s models indicate that the distance at which hawk moths can sense flowers has decreased from about 2 kilometres to just a few hundred metres.

In response to the findings, fellow researcher, Joel Thornton, University of Washington said: “This is just another reason that we should switch to energy sources that do not involve combustion,” said Joel Thornton, University of Washington. “If we can reduce nitrogen oxides emissions, it’ll be a win for air quality as well as ecosystem functioning and agriculture.”