Air pollution reduces ability for butterflies and bees to pollinate flowers and crops, study finds

2022-01-20

A study looking at the impacts of common air pollutants has found that flower pollination is significantly lower where pollution is present.

Key points:

• Visits to flowers by pollinators was more than 80 per cent lower where pollutants were present

• Researchers think the pollution interferes with the insects’ ability to sniff out flowers

• There could be significant impacts on crops and ecosystems where pollution is high

In a controlled field trial, the abundance of bees, flies, moths and butterflies and how often they visited flowers was far lower in the presence of nitrogen oxides (NOx) and ozone (03), compared to plots where those pollutants were absent.

Nitrogen oxides mostly come from agricultural emissions but are also produced when fossil fuels are burnt. Combined with sunlight and volatile organic compounds, they can form ground-level ozone (O3).

According to the researchers, whose paper was published today in the journal Environmental Pollution, the pollinators that appeared to be most affected were those species that rely on smell to detect flowers.

And it appears that vital pollinators are impacted the most.

“We found that those groups of pollinators that are most important [like] solitary bees, bumblebees, honey bees, were most affected in general,” Dr James Ryalls and Dr Robbie Girling from the University of Reading told the ABC.

“But some species within those groups may be less affected than other species, depending on how heavily they rely on odour cues.”

The presence of air pollution, even at levels lower than US national guidelines, appeared to be interfering with the insects’ ability to sniff out flowers and could reduce rates of pollination in areas where air pollution is high, they said.

“The decreases in flower visitation due to air pollution were almost certainly associated with the disruption of floral odour cues.”

“Air pollution levels often exceed these guidelines in agricultural settings, especially if they are near major roadways.

“If this problem is demonstrated more widely and grows in severity, it is certainly likely to have negative consequences for the yields of many insect-pollinated crops.”

Impact on insects worse than expected

While the researchers said they anticipated their field trial to concur with previous laboratory studies, they weren’t expecting such strong results.

“We were surprised by how severe the decline in pollinator abundance and flower visitation was under air pollution.

“Especially considering the relatively moderate levels of air pollution that were used.”

To get their findings, the scientists used generators to pump low levels of ozone, nitrogen oxide, and a combination of the two into plots in a field. They also had “control” plots without any pollutants pumped in.

The plots were filled with black mustard plants (Brassica nigra) and observers tallied the number and species of insect visitations to flowers across each plot.

The yield of developed and undeveloped flowers was also calculated at the end of the trial, and efforts were made to control for variables, including rotating the plots and measuring insect abundance in the absence of flowers.

Beetles, some bugs and wasps not affected

The presence of air pollution reduced the overall abundance of seven pollinator groups, but not for three groups — beetles, true bugs and parasitic wasps.

But even with the continued abundance of those three groups, overall pollinator numbers were reduced by 62 per cent and flower visitation by 83 per cent where pollutants were present.

Ken Walker, senior curator of entomology at the Museum of Victoria, says some insects are what’s known as oligolectic — they rely on a single species for food.

Interfering with their capacity to find pollen could be very damaging to both the insect and the plants they pollinate, he said.

“The nose of insects is on their antennae,” Dr Walker said.

“Anything that disrupts these chemoreceptors on the insects’ noses will certainly make it harder to find food.”

Are insect populations declining globally?

Dr Walker says there’s quite a bit of evidence to suggest there’s been a global decline in insects, but more research is needed.

“I hesitate to say it’s been globally assured that it’s happening. It probably is, but we just don’t have the data,” he said.

“There have been several studies — none in Australia — but there was a study done by amateurs collecting insects in nature reserves in Germany near agricultural areas.

“They found something like a 76 per cent reduction in insect biomass over 25 years.”

While pesticides and the conversion of wilderness to agricultural land have been implicated in the decline, Dr Walker says we’re now becoming more aware of the impact of pollutants, including light pollution.

“There’s been a lot of work done on polluters for human health, but very little has been done on insect health,” he said.

“[But] we’re now beginning to realise the effects on insects and pollinator health might be quite significant as well.”

It’s estimated that roughly one in three spoonfuls of food we eat has involved pollination in its production, Dr Walker said.

abc.net.au, 20 January 2022
; https://www.abc.net.au