Common air pollutants may be reducing insect-provided pollination services by preventing bees and butterflies from sniffing out crops and flowers, new research suggests. The study is the first to observe a negative impact of common air pollutants on pollination in the natural environment.

Scientists from the University of Reading, the UK Centre for Ecology & Hydrology (UKCEH) and the University of Birmingham investigated common ground-level air pollutants, including diesel exhaust pollutants and ozone, from both urban and rural environments.

They found there were up to 70% fewer pollinators, up to 90% fewer flower visits and an overall pollination reduction of up to 31% in test plants when the pollutants were present, but still at levels below current air quality standards.

Previous lab studies had shown that diesel exhaust can have negative effects on insect pollinators, but the impacts found in the field were much more dramatic than expected, the researchers say. The results suggest that floral odours are altered by the pollutants or their reactions with the atmosphere, making the flowers harder to find.

The impact this phenomenon has in nature, where insects provide pollination of important food crops and native wildflowers, was less well understood, so the new study aimed to gather evidence on how air pollution affects different pollinating insect species, some of which rely on scent more than others.

The study, funded by the UKRI Natural Environment Research Council, used a purpose-built fumigation facility to regulate levels of nitrogen oxides – present in diesel exhaust fumes – and ozone in an open field environment.

Dr Ben Langford and Dr Neil Mullinger, atmospheric scientists at UKCEH, designed the novel facility that allowed the team to release regulated quantities of the pollutants being studied. The team used pollution concentrations well below maximum average levels - equating to 40-50% of the limits currently defined as safe for the environment.

Scientific experiment in a field

The team built a fumigation system to expose plants to common air pollutants

Scientific equipment in a field

Researchers observed the effects these pollutants had on the pollination of black mustard plants.

Researchers then observed the effects these pollutants had on the pollination of black mustard plants by free-flying, locally-occurring pollinating insects over the course of two summer field seasons.

Observations revealed there were 62-70% fewer pollinator visits to the plants located in polluted air. This reduction was seen in seven pollinator groups, particularly bees, moths, hoverflies and butterflies. There were also 83-90% fewer flower visits by these insects, and ultimately a 14-31% reduction in pollination, based on seed yield and other factors.

Dr Langford said: “Our experiment provides new insights into the impacts of human-induced air pollution on the natural ecosystem services upon which we depend.

“The findings indicate there is an urgent need for research to investigate the wider risk of air pollutants to disrupt the many insect-mediated ecological processes upon which nature and humans rely.”

Dr James Ryalls, a Leverhulme Trust Research Fellow at the University of Reading, who conducted the study, said: “The findings are worrying because these pollutants are commonly found in the air many of us breathe every day. We know that these pollutants are bad for our health, and the significant reductions we saw in pollinator numbers and activity shows that there are also clear implications for the natural ecosystems we depend on.”

The study is published in the journal Environmental Pollution