As we spend summer after summer swatting them away, it is not easy to imagine they could one day be gone for good.
But flies’ sex lives have been wrecked by air pollution as many species suffer from ‘dysfunctional’ mating signals, a study has warned.
Disturbing new research has revealed that flies struggle to feel attracted to mating partners in the midst of ozone pollutants that ‘drastically corrupt’ their reproductive behaviour.
The results come at a time when shrinking insect populations are a global concern, with flies integral to assisting the pollination of 80 per cent of the world’s crops.
Ozone-exposed flies exhibited ‘unusual courting behaviour’ with males more attracted to their male counterparts and seemingly unable to distinguish between sexes.
Flies were found to exhibit an ‘unusual courting behaviour’ in the face of ozone exposure
‘We knew that elevated ozone levels could affect insect mating systems because the breakdown of carbon double bonds, and thus pheromones, by oxidation is not rocket science in chemistry,’ researchers Nanji Jiang and Markus Knaden from the Max Planck Institute for Chemical Ecology said.
‘Nevertheless, we were shocked that even slightly elevated ozone concentrations had such strong effects on fly behavior.’
Ozone gas is harmful to human health and can cause asthma attacks in addition to inflammation of the eyes, nose, respiratory tract and throat.
While it was present in the lower atmosphere during preindustrial times, experts said values were as low as 10 parts per billion (ppb) compared to today’s values at 40ppb.
Recently, ozone also spiked to 210 ppb in Mexico, according to a separate JGR Atmospheres study, thanks to a blend of climate change and the continued emission of nitrogen oxides.
As part of the study, flies were put in an ‘ozone exposure system’ that mimicked levels of air pollution felt in cities during the summer.
When exposed to 100ppb of the pollutant for just two hours, scientists saw levels of chemical attractants drop significantly among the flies.
Ozone-affected males were also observed to line up in ‘long courtship chains’ that were said to be quite puzzling.
Other species of fly which rely on visual clues for mating rather than pheromones did not change their behaviour.
Dr Jiang and Dr Knaden added: ‘We could explain that males started courting each other after a short ozone exposure, because they obviously could not distinguish ozonated males from females.
The Max Planck Institute study put flies in an ‘ozone exposure system’ that mimicked levels of air pollution felt in cities during the summer. Pictured: Courtship-chain formation of male fly species at 100 ppb for 20 minutes
Scientists felt that flies ‘could not distinguish’ between females and males in the experiment
‘However, we had not thought about this before.
‘Therefore, we were quite puzzled by the behavior of the ozone-exposed males, which lined up in long courtship chains.’
Worryingly, Bill Hansson, co-founder of the Max Planck Center next Generation Insect Chemical Ecology, deemed it ‘unlikely’ that the flies would be able to adapt in the face of rapidly increasing air pollution.
He said: ‘Insects and their pheromones have evolved over millions of years. In contrast, the concentration of air pollutants has only increased dramatically since industrialization.
Pictured: Another male species of fly (D. melanogaster) tested in ozone-enriched air
‘It is unlikely that the communication systems of insects, which have evolved over the course of evolution, will be able to adapt to new conditions within a short period of time if pheromones are suddenly no longer there. The only solution to this dilemma is to immediately reduce pollutants in the atmosphere.’
Now, scientists are looking to broaden their research with a focus on other insects including moths that usually follow pheromone plumes over long distances.
Dr Knaden added: ‘We would like to find out, whether high levels of ozone lead to increased hybridization rates when closely related fly species share their habitat. Finally, chemical communication in insects is not restricted to mating behavior.
‘All social insects like bees, ants, and wasps, use chemical cues to identify members of their colony. We also study whether the social structure within ant colonies is affected, when ants return from their foraging trips during which they became exposed to increased levels of pollutants.
‘You don’t even want to envision what happens if social structures in ant colonies or beehives suddenly collapse because pheromone communication no longer works.’
The Ozone layer sits in the stratosphere 25 miles above the Earth’s surface and acts like a natural sunscreen
Ozone is a molecule comprised of three oxygen atoms that occurs naturally in small amounts.
In the stratosphere, roughly seven to 25 miles above Earth’s surface, the ozone layer acts like sunscreen, shielding the planet from potentially harmful ultraviolet radiation that can cause skin cancer and cataracts, suppress immune systems and also damage plants.
It is produced in tropical latitudes and distributed around the globe.
Closer to the ground, ozone can also be created by photochemical reactions between the sun and pollution from vehicle emissions and other sources, forming harmful smog.
Although warmer-than-average stratospheric weather conditions have reduced ozone depletion during the past two years, the current ozone hole area is still large compared to the 1980s, when the depletion of the ozone layer above Antarctica was first detected.
In the stratosphere, roughly seven to 25 miles above Earth’s surface, the ozone layer acts like sunscreen, shielding the planet from potentially harmful ultraviolet radiation
This is because levels of ozone-depleting substances like chlorine and bromine remain high enough to produce significant ozone loss.
In the 1970s, it was recognised that chemicals called CFCs, used for example in refrigeration and aerosols, were destroying ozone in the stratosphere.
In 1987, the Montreal Protocol was agreed, which led to the phase-out of CFCs and, recently, the first signs of recovery of the Antarctic ozone layer.
The upper stratosphere at lower latitudes is also showing clear signs of recovery, proving the Montreal Protocol is working well.
But the new study, published in Atmospheric Chemistry and Physics, found it is likely not recovering at latitudes between 60°N and 60°S (London is at 51°N).
The cause is not certain but the researchers believe it is possible climate change is altering the pattern of atmospheric circulation – causing more ozone to be carried away from the tropics.
They say another possibility is that very short-lived substances (VSLSs), which contain chlorine and bromine, could be destroying ozone in the lower stratosphere.
VSLSs include chemicals used as solvents, paint strippers, and as degreasing agents.
One is even used in the production of an ozone-friendly replacement for CFCs.