Dirty air makes it difficult for bees, butterflies, moths and other pollinating insects to find flowers. This is the conclusion reached by researchers from the University of Reading, who analyzed 22 experimental studies on the influence of ozone and nitrogen oxides on pollination. The study was published in the journal Frontiers in Ecology and the Environment.
The two pollutants change or break down the aromatic substances released by flowers. This makes it more difficult for insects to recognize the chemical signals that direct them to nectar and pollen.
Elevated levels of ozone reduce the efficiency of pollinating insects by an average of 42 percent, and nitrogen oxides - by 46 percent. When the two pollutants occur together, the average drop reaches 68 percent, the summary data shows.
The researchers point out that the combined effect cannot be calculated simply by adding the two averages. Only a small number of the included studies examined ozone and nitrogen oxides together. In these cases, the additional damage was less, because the gases react with each other in the air and partially neutralize each other.
Specialized pollinators are most vulnerable
The risk is not the same for all insects. Species that rely on the scent of a particular plant to find food are more vulnerable. Among them are some moths. More generalist species, including many bees, can use a wider range of cues and plants.
Diurnal pollinators such as bees and butterflies face higher levels of ozone, while nocturnal insects, including many moths, are exposed to more nitrogen oxides.
Period of risk could last decades
Diesel vehicles are a major source of nitrogen oxides. According to the study's lead author, James Ryall, ozone levels are expected to continue to rise until around 2050, even as nitrogen oxide emissions begin to decline as fossil fuels are phased out.
„This will create a difficult time for pollinators over the next two to three decades. Once cleaner fuels are fully deployed, ozone levels should fall, allowing insects to recover, he said.He added that faster reductions in nitrogen oxide emissions, especially from diesel vehicles, could shorten that period. “Most of the food we grow depends on healthy pollinating insects, so protecting them from pollution cannot wait until 2050,” he said.
Most of the data in the analysis came from Europe. This leaves a gap in knowledge about the impact of pollution on pollinators in more heavily polluted areas, including parts of Asia.