Air pollution prevents pollinators finding flowers

Air pollution dramatically reduces pollination because it degrades the scent of flowers, affecting bees’ ability to find them, a study has found.

A research team comprising the UK Centre for Ecology & Hydrology (UKCEH) and the Universities of Reading, Surrey, Birmingham and Southern Queensland, found that ozone substantially changes the size and scent of floral odour plumes. It reduced honeybees' ability to recognise odours by up to 90% from just a few metres away.

Ground-level ozone, which aggravates respiratory conditions, typically forms when nitrogen oxide emissions from vehicles and industrial processes react with volatile organic compounds (VOCs) emitted from vegetation in the presence of sunlight.

Dr Ben Langford, an atmospheric scientist at UKCEH led the study, which has been published in the journal Environmental Pollution.

He says the new research suggests that ozone is likely to be having a negative impact on wildflower abundance and crop yields. Several international studies have already established that ozone has a negative impact on food production because it damages plant growth.

“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,” says Dr Langford.

Dr James Ryalls, a University of Reading co-author of the research paper, said: “The study provides clear mechanistic evidence of how ozone pollution, concentrations of which are typically higher in rural areas, can reduce pollinator visitation to flowers.”

The new study was funded by the Natural Environment Research Council, part of UK Research and Innovation. The researchers used a wind tunnel to monitor how the size and shape of odour plumes changed in the presence of ozone. As well as decreasing the size of the odour plume the scientists found that the scent of the plume changed as certain compounds reacted away faster than others.

Honeybees, which were trained to recognise the same odour blend, were then exposed to the new, ozone-modified odours. Pollinating insects use floral odours 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 recognised an odour at 6 metres, decreasing to 38% at 12m. At the edge of

plumes, which degraded more quickly, 32% of honeybees recognised a flower from 6m away and just a tenth of the insects from 12m away.

The researchers say their findings indicate ozone could also affect insects’ other odour-controlled behaviour such as their ability to attract and find a mate. Last year, the same research team published the first study to find common air pollutants, including ozone and diesel exhaust fumes, had a negative impact on pollination in the natural environment

Langford et al. 2023. Mapping the effects of ozone pollution and mixing on floral odour plumes and their impact on plant-pollinator interactions. Environmental Pollution. DOI: 10.1016/j.envpol.2023.122336. Open access.