As the concentration of ozone increases, the likelihood of hybrid offspring among fruit flies also rises. Insect pheromones are odor molecules used by insects in a population to communicate chemically, among which sex pheromones play a crucial role in insect mating behavior. These unique odors not only attract males and females of the same species but, more importantly, they help maintain physiological isolation between different species.

Previous studies by researchers in evolutionary neuroethology have shown that ozone can severely disrupt the chemical communication within flies. Ozone primarily destroys the carbon-carbon double bonds in insect pheromones, leading to male flies being unable to identify female flies, thus male flies may exhibit mating behavior toward both sexes.

Recent research has further explored whether the destructive effect of ozone on sex pheromones would break down the mating isolation between different species. The study found that even a slight increase in ozone levels could increase the frequency of hybridization between closely related species. Such hybridization often leads to sterile offspring, which could, in turn, lead to a reduction in insect population sizes.

Researchers selected four species from the genus Drosophila for their experiments, including the globally distributed Drosophila melanogaster (D.melanogaster) and Drosophila simulans (D.simulans), as well as the Seychelles fruit fly (D.sechellia) and the Mauritius fruit fly (D.mauritiana) found on specific islands. These flies release similar pheromones, but each has a specific way of mixing them. The key lies in how these pheromone mixtures change in ozone and how this affects the flies' selection and mating behavior.

By simulating ozone levels during urban heatwaves, fruit flies were placed in this environment for two hours. Female flies then made a choice to mate between males of the same species and those of different species. Hours later, the females were separated from the males and laid eggs. To determine which males the females mated with, researchers analyzed the morphology of the male offspring's sexual organs, a method that can distinguish between different species and their hybrids.

The latest experimental study found that an increase in ozone concentration significantly raised the instances of interspecies hybridization among fruit flies. In regular ambient air, fruit fly hybridization is rarely observed. These organisms rely not only on chemical signals to find a mate but also produce a unique song by vibrating their wings to attract a partner. Additionally, they use visual signals as a means to attract mates. However, the study showed that despite these auxiliary mating signals, the increased level of ozone still made it difficult for female fruit flies to distinguish between males of the same species and those of another.

Director of Evolutionary Neuroethology Hansson explains: "We previously thought that ozone interference in pheromone communication might slightly increase the number of fruit fly hybridizations. However, the results were surprising; even with the assistance of sound and visual cues, some female fruit flies were still unable to effectively distinguish between males of the same species and different species." The hybrid offspring of male fruit flies are often infertile or have extremely low fertility, making such hybridization events a useless investment for the fruit flies, which can sometimes even lead to the extinction of a population.

Unlike male hybrid fruit flies, female hybrid fruit flies usually can reproduce normally and are sometimes even more favored by males. This phenomenon has also been observed in research. Among the more than 1500 species in the fruit fly genus, it is known that about a hundred species have the possibility of hybridization. This means that hybridization induced by pollutants may facilitate the creation of new hybrid species among some closely related species.

Insects rely not only on scent during mating. In addition to sex pheromones, insects also utilize aggregation pheromones to attract conspecifics, or release alarm pheromones when encountering threats. Especially social insects like ants, depend on pheromone trails for navigation or use the colony's unique scent to recognize mates in the nest. Ozone, due to its ability to destroy odor molecules that contain carbon-carbon double bonds, could disrupt chemical communication in these areas. Researchers have expressed their concerns and plan to conduct more in-depth studies on organisms like ants.

In addition to ozone, other oxidizing pollutants outside the lab, such as nitrogen oxides, despite having regulatory limits, may enhance the effects of ozone. Considering that even at trace levels, these pollutants could have significant effects on chemical communication amongst insects, the current restrictions on these substances should be re-evaluated, Knaden points out. Given the rapid decline in insect populations in terms of total biomass and biodiversity, we should pay more attention and try to mitigate all potential factors contributing to this decline.