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A research team at the Max Planck Institute for Chemical Ecology in Jena, Germany, demonstrates that increased levels of ozone resulting from anthropogenic air pollution can degrade insect sex pheromones, which are crucial mating signals, and thus prevent successful reproduction. The oxidizing effect of ozone causes the carbon-carbon double bonds found in the molecules of many insect pheromones to break down. Therefore, the specific chemical mating signal is rendered dysfunctional. Most remarkably, the disrupted sexual communication also led to male flies exhibiting unusual mating behavior towards ozonated males of their own species.
Insect sexual communication relies to a significant extent on pheromones, chemical attractants that specifically allow males and females of a species to mate. Sex pheromones are distinctive to males and females of a species. Even the smallest differences, such as those observed in the formation of new species, ensure that mating no longer takes place, because males and females only find each other through the unmistakable odor of their conspecifics.
Most insect pheromones are odor molecules containing carbon-carbon double bonds. Such double bonds are known to be easily destroyed by ozone. "We already knew that environmental pollutants such as ozone and nitric oxide degrade floral scents, making flowers less attractive to their pollinators. Since compounds with carbon double bonds are particularly sensitive to ozone degradation, and almost all insect sex pheromones carry such double bonds, we wondered whether air pollution also affects how well insect females and males find and identify each other during mating", says Markus Knaden, who heads the Odor-guided Behavior Group in the Department of Evolutionary Neuroethology and is a lead author of the study (Air pollution renders flower odors unattractive to moths).
To study the effects of ozone on the mating behavior of the model fly Drosophila melanogaster, the scientists first developed an ozone exposure system for flies that could mimic ozone levels in the air as they are nowadays often measured in the cities in the summer. To do this, the researchers had to create a continuous airstream with precisely defined ozone levels, which is complicated by the fact that ozone is not a stable chemical compound and decomposes easily. At the same time, flies often carry very small amounts of pheromones even under normal conditions. "We therefore needed a technique that would allow us to measure even tiny amounts of pheromones on individual flies that had either been exposed to ozone or not prior to the measurements. To do this, we used what is known as a thermal desorption unit coupled to a gas chromatograph/mass spectrometer, which allowed us to measure tiny amounts of odors emitted by individual flies," said first author Nanji Jiang, describing the technical challenges.
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Insect sexual communication relies to a significant extent on pheromones, chemical attractants that specifically allow males and females of a species to mate. Sex pheromones are distinctive to males and females of a species. Even the smallest differences, such as those observed in the formation of new species, ensure that mating no longer takes place, because males and females only find each other through the unmistakable odor of their conspecifics.
Most insect pheromones are odor molecules containing carbon-carbon double bonds. Such double bonds are known to be easily destroyed by ozone. "We already knew that environmental pollutants such as ozone and nitric oxide degrade floral scents, making flowers less attractive to their pollinators. Since compounds with carbon double bonds are particularly sensitive to ozone degradation, and almost all insect sex pheromones carry such double bonds, we wondered whether air pollution also affects how well insect females and males find and identify each other during mating", says Markus Knaden, who heads the Odor-guided Behavior Group in the Department of Evolutionary Neuroethology and is a lead author of the study (Air pollution renders flower odors unattractive to moths).
To study the effects of ozone on the mating behavior of the model fly Drosophila melanogaster, the scientists first developed an ozone exposure system for flies that could mimic ozone levels in the air as they are nowadays often measured in the cities in the summer. To do this, the researchers had to create a continuous airstream with precisely defined ozone levels, which is complicated by the fact that ozone is not a stable chemical compound and decomposes easily. At the same time, flies often carry very small amounts of pheromones even under normal conditions. "We therefore needed a technique that would allow us to measure even tiny amounts of pheromones on individual flies that had either been exposed to ozone or not prior to the measurements. To do this, we used what is known as a thermal desorption unit coupled to a gas chromatograph/mass spectrometer, which allowed us to measure tiny amounts of odors emitted by individual flies," said first author Nanji Jiang, describing the technical challenges.
Air pollution impairs successful mating of flies
High levels of ozone destroy the chemical mating signal of the insects and may thus contribute to global insect decline
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