Air Pollution Degrades Floral Odors, Making It Harder for Bees to Find Flowers

A new study has found that air pollution is preventing pollinators finding flowers because it degrades the scent.

A research team comprising the UK Centre for Ecology & Hydrology (UKCEH) and the Universities of Birmingham, Reading, Surrey and Southern Queensland, found that ozone substantially changes the size and scent of floral odor plumes given off by flowers, and that it reduced honeybees' ability to recognize odors by up to 90% from just a few meters away.

Ground-level ozone typically forms when nitrogen oxide emissions from vehicles and industrial processes react with volatile organic compounds emitted from vegetation in the presence of sunlight.

Professor Christian Pfrang from the University of Birmingham who collaborated on the research said: "Our study provides robust evidence that the changes due to ground-level ozone on floral scent cause pollinators to struggle to carry out their crucial role in the natural environment also with implications for food security."

The findings suggest that ozone is likely to be having a negative impact on wildflower abundance and crop yields. International research has already established that ozone has a negative impact on food production because it damages plant growth.

Dr Ben Langford, an atmospheric scientist at UKCEH who led the study said: "Some 75% of our food crops and nearly 90% of wild flowering plants depend, to some extent, upon animal pollination, particularly by insects. Therefore, understanding what adversely affects pollination, and how, is essential to helping us preserve the critical services that we reply upon for production of food, textiles, biofuels and medicines, for example."

The researchers used a 30-m wind tunnel at Surrey University to monitor how the size and shape of odour plumes changed in the presence of ozone. As well as decreasing the size of the odor plume the scientists found that the scent of the plume changed substantially as certain compounds reacted away much faster than others.

Honeybees were trained to recognize the same odor blend and then exposed to the new, ozone-modified odors. Pollinating insects use floral odors to find flowers and learn to associate their unique blend of chemical compounds with the amount of nectar it provides, allowing them to locate the same species in the future.

The research showed that towards the centre of plumes, 52% of honeybees recognized an odor at 6 meters, decreasing to 38% at 12 m. At the edge of plumes, which degraded more quickly, 32% of honeybees recognized a flower from 6 m away and just a tenth of the insects from 12 m away.

The study indicates that ozone could also affect insects' other odor-controlled behaviors such attracting a mate.

The research was funded by the Natural Environment Research Council, part of UK Research and Innovation, and was published in the journal Environmental Pollution.

We know that air pollution has a detrimental effect on human health, biodiversity and the climate, but now we can see how it prevents bees and other pollinating insects from carrying out their key job. This should act as a wake up call to take action on air pollution and help safeguard food production and biodiversity for the future."

Professor Christian Pfrang, University of Birmingham