Worsening Air Pollution Severely Impairs Pollinators’ Ability to Find Plants

A new field trial found another major driver that led to the plummeting of insect population aside from pesticides and land use changes - road air pollution.

The trial revealed that bees, butterflies and other pollinators exposed to levels of nitrogen oxides and ozone pollution common near roads led to a 70 per cent drop in their numbers. The polluted air caused by diesel cars makes it difficult for them to locate plants to feed on, which could greatly affect both insect populations and crop growth.

There had been previous lab studies that evidenced how air pollutants degrade the floral odour particles released by plants, but the three-year field trial ran by James Ryalls at the University of Reading, UK, and his colleagues aim to understand how those interactions play out in the wider environment.

An "underlooked" factor contributing to insects' decline

(Photo : Photo by Jeff J Mitchell/Getty Images)
ALEXANDRIA, SCOTLAND - JULY 28: Painted Lady butterflies sit on a Buddleja shrub on July 28, 2019 in Alexandria, Scotland. The UK is experiencing a once in a decade wildlife phenomenon this year with a mass influx of Painted Lady butterflies, experts are saying.

Ryalls was surprised to see how steep the falls were and how levels of the pollutants similar with the average concentrations in major UK roads reduced the number of pollinators counted on black mustard plants by up to 70 per cent.

To come up with this result, the team built a system generating nitrogen oxides and ozone pollution in the center of a wheat field, piped it to six octagonal enclosures where the black mustard plants were grown, and filled two more enclosures with ambient air as control.

"We weren't expecting nearly as severe a reduction as we found. It's kind of crazy," Ryalls says. "If the results from this study extend to the landscape scale, air pollution is likely a pretty important but underlooked factor contributing to pollinator decline. It's a bit worrying."

Apparently, "dirty air is confusing pollinators hunting for plants' odours." however, according to Ryalls, "some pollinator groups may be more able to compensate with visual cues than others."

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On the bright side

If you look into it, curbing air pollution is much more feasible than suppressing pesticide use. Dave Goulson at the University of Sussex in the UK, not involved in the study, says while the trial has relatively low replication of its tests, it "does show potentially major impacts of air pollution on both pollinators and wildflowers".

"This calls into question the advisability of encouraging planting of wildflowers on the verges of busy roads, at least while internal combustion engines predominate. We have to transition away from fossil fuels anyway, and we are. We should be doing it faster. It's not as hard as some things to control," says Ryalls.

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