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Pigeontail on the approach to a purple flower

Photo: imageBROKER / alimdi / Arterra / Philippe Clément / IMAGO

Because of all the exhaust fumes, insects probably have difficulty finding their way to flowers. Pollutants in the air, with their influence on fragrances, may be limiting pollination worldwide. A research team reports this in the journal “Science”.

Not only noise and artificial light influence the behavior of animals that pollinate, but also substances released by humans. Studies have already shown that high concentrations of diesel exhaust or ground-level ozone affect how well insects can detect smells. The team led by Joel Thornton and Jeffrey Riffell from the University of Washington wanted to know how the oxidants ozone (O₃) and nitrate radical (NO₃ radical) affect the nocturnal pollination of evening primrose by moths. Both substances are, among other things, the result of car traffic.

The researchers observed 300 flowers of so-called evening primroses over 200 hours. Evening primroses exude a strong floral scent. In addition, individual components of the scent and their respective effects on the moths were examined.

The team's observations and experiments showed that NO₃ radicals quickly break down certain fragrances. Individual so-called monoterpenes, i.e. chemical compounds that are found in eucalyptus oil, for example, are particularly affected. They are actually particularly attractive to butterflies. But due to air pollution, the flowers are hardly or no longer noticeable to the nocturnal butterflies. The number of flower visits by moths has fallen by around 70 percent. As a result, evening primrose fruit production is reduced by around 30 percent.

Using a global model, Thornton and Riffell's team also showed that O₃ and NO₃ radical pollution in the atmosphere in many urban and peri-urban areas is sufficient to significantly reduce the distances over which pollinators can perceive flowers. In certain populated regions around the world, scent detection distances have decreased by 75 percent or more since pre-industrial times, the team concludes from modeled comparisons. The scientists suspect that air pollutants could have a decisive influence on pollination and yields.

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