Air pollutants confuse pollinators and reduce food production

Insects don’t have noses and are not able to “smell” the roses in the familiar sense of the word. Instead, most odor molecules are detected by chemoreceptors that occur on an insect’s antennae. Using these chemical receptors, insects are capable of perceiving and differentiating between thousands of airborne compounds. They use these chemical signals to locate forage plants and mates, as well as to avoid predators.

But now, new research indicates that common air pollutants present in rural and urban environments may be hampering the ability of insects to detect the chemical signals so crucial to their activity as pollinators. 

A team of scientists from the University of Reading has conducted the first study to observe that common air pollutants, including diesel exhaust fumes and ozone, have a negative impact on the success of pollination by insects. 

“We knew from our previous lab studies that diesel exhaust can have negative effects on insect pollinators, but the impacts we found in the field were much more dramatic than we had expected,” said Dr. Robbie Girling, who led the project.

These previous laboratory studies by members of the Reading team showed that chemicals in diesel fumes react with and can change the scents of flowers such that the insects cannot locate the flowers. The research suggested that pollution could contribute to the ongoing declines in pollinating insects, by making it harder for them to locate the pollen and nectar that form their food.

In the new study, the researchers aimed to gather evidence showing how air pollution affects different species of pollinating insects, some of which rely on scent more heavily than others.

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

Although the experiments made use of pollution levels that were way below the maximum acceptable levels considered as safe in the US, the results of the field experiments were dramatic. The researchers observed 62 to 70 percent fewer pollinator visits to the plants located in polluted air. This reduction was seen in seven different groups of pollinators, including bees, moths, hoverflies and butterflies. 

There were also 83 to 90 percent fewer visits to flowers by these insects, and ultimately a 14 to 31 percent reduction in pollination success, based on the measurement of seed yield and other factors.

“The findings are worrying because these pollutants are commonly found in the air many of us breathe every day,” said Dr. James Ryalls. “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.”

Insects are important pollinators of crops upon which we depend for food and so a reduction in pollinating activity could have far-reaching economic and social consequences. Around 70 percent of crop species rely on insects for pollination; these include apples, strawberries and cocoa. 

In addition, pollination supports around eight percent of the total value of agricultural food production, worldwide. The pollinating activity of insects thus generates hundreds of billions of pounds worth of economic value each year. 

Furthermore, far higher levels of air pollutants are found in many areas around the world where people and businesses breach the regulations. For example, a 2019 analysis recorded illegal levels of nitrogen dioxide present in local authorities, in large areas of northern England (including Cheshire and Gateshead), and in southern England (including Wiltshire, Chichester and rural areas such as the New Forest).

“This truly cross-disciplinary work demonstrated very clearly how atmospheric pollutants negatively impact on pollination with direct consequences for food production as well as the resilience of our natural environment,” concluded study co-author Dr. Christian Pfrang.

Their results are published today in the  journal Environmental Pollution.

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By Alison Bosman, Earth.com Staff Writer