Disturbed mating behavior: Airborne ozone pollution can destroy insect sex pheromones and thus possibly contribute to insect mortality, a study on fruit flies suggests. The reactive oxygen molecule therefore breaks bonds in the fragrances and thus destroys their signaling function. This leads to behaviors that affect the reproductive success of the flies. The scientists say that many insect species could possibly be affected by this effect.
Instead of two oxygen atoms, it has three, which makes ozone a problem: It develops "aggressive" effects in the air near the ground and can thus impair human health. Its formation is favored by air pollutants such as nitrogen oxides from combustion processes and other man-made substances. As a result, the ozone levels in many regions shaped by humans have risen well above the natural levels, studies show. Of course, we are not the only ones affected by this: other living beings also suffer from the increased ozone pollution in the air.
Broken pheromones
A research team at the Max Planck Institute for Chemical Ecology in Jena has now investigated the possible consequences for insects. “We already knew that environmental pollutants like ozone and nitrous oxide degrade flower odors, making flowers less attractive to their pollinators. Since compounds with carbon double bonds are particularly sensitive to degradation and almost all insect sex pheromones carry such double bonds, we wondered whether air pollution also had an impact on how well insect females and males can find and identify each other for mating,” says Co-author Markus Knaden.
The researchers conducted their studies on the science's model insect: the fruit fly, Drosophila melanogaster. An important role in their mating behavior is known to be played by pheromones, which males release to entice females and keep rivals away. For the experiments, some male flies were exposed to an increased ozone concentration, which can often occur in cities in summer today. It was then measured whether the flies were still releasing the pheromone. It turned out that if the insects were only exposed to ozone for two hours, the measured pheromone values were surprisingly reduced compared to a control group. Apparently the carbon-carbon double bonds of the substance were severely broken.
factor in insect mortality?
The scientists observed that the loss of the “insect perfume” was accompanied by significant changes in behavior: the increased ozone concentration made males less attractive to females. But not only that: the less “male” smelling individuals suddenly became interesting for their same-sex conspecifics and were courted by them. Apparently, they could no longer distinguish the ozonated males from females, the researchers explain. The team was also able to observe these effects of increased ozone levels on the mating behavior of other Drosophila species.
Since communication in many insect species is based heavily on chemical attractants, the researchers believe the results may have far-reaching significance. This is because most insect pheromones contain ozone-sensitive carbon-carbon double bonds. In addition to the use of insecticides and the destruction of habitats, the increased ozone effect could also contribute to insect populations declining worldwide. “Insects and their pheromones have evolved over millions of years. The concentration of pollutants in the air, on the other hand, has only increased drastically since industrialization. It is unlikely that the insects' evolutionary communication system would be able to adapt to new conditions in a short period of time if pheromones were suddenly gone," says co-author Bill Hansson.
In further studies, the Max Planck researchers now want to examine the effects of ozone on other insect species as well. "In insects, chemical communication is not just limited to mating behavior," emphasizes Knaden. “Social insects such as bees, ants and wasps use chemical signals to identify members of their colony. We are currently investigating whether the social structure within ant colonies is affected when the ants return from foraging trips where they were exposed to increased concentrations of pollutants," says the scientist.
Source: Max Planck Institute for Chemical Ecology, Article: Nature Communications, doi: 10.1038/s41467-023-36534-9