Air pollution inhibits moths’ ability to smell flowers

Air pollution inhibits moths’ ability to smell flowers

One of life’s many pleasures is to stop to smell the roses, but flowers don’t just create their sweet scents for human pleasure. Scents are biological signals that transmit a plant’s location to potential pollinators. The pleasant (or occasionally terrible) smells that flow from the breeze enable plants to attract insects and other animals to stop and spread some pollen. Unfortunately, air pollution is getting in the way, according to a study published Feb. 8 in the journal science.

The researchers behind the new paper assessed the effects of ozone (O3) and a nitrate radical (NO3) on the ability of some moths to detect and pollinate evening primrose flowers at night. They found that these pollutants, common byproducts of car exhaust and fossil fuel burning, react with and deactivate the main attractive chemicals in the scent of flowers. In the presence of nitrate radicals, far fewer moths visit primrose flowers. The plants rely on moths and other nocturnal pollinators to produce fruit, and the scientists’ results suggest that — amid air pollution — evening primrose flowers are less able to propagate the next generation. It’s a troubling set of findings that carry implications far beyond an insect’s diet or a flower’s seed production.

“Pollinators play a major role in community ecology; they are critical to plant fitness. If you affect that, then you have impacts on the entire ecosystem,” says Jeff Riffell, co-author of the study and professor of biology at the University of Washington. “Pollinators are also critical to our food system and food security,” he adds—mess with the wrong insects and people can end up paying the tax, too.

Pollution isn’t always as simple as a deadly chemical spilled into a lake. less direct, sensory pollution can harm animals in a surprising variety of ways. It’s the city lights that attract migrating birds to crash against building windows and the loud boats that can deafen the squid. The way humans alter animals’ olfactory environments can also be harmful. This latest study builds on previous research that also found air pollution can disrupt pollinators’ ability to smell.

Image of Manduca sexta moth visiting Oenothera scented paper flowers.  CREDIT Image by Charles Hedgcock.
Image of Manduca sexta moth visiting Oenothera scented paper flowers. CREDIT: Image courtesy of Charles Hedgcock.

However, the new research adds to the scientific record in several notable ways. It was one of the first to explore this particular system of moths and flowers in such high detail. And the study links to the exact chemical compounds at play, demonstrating a precise explanation for the problem, says Jeremy Chan, the study’s lead author and a postdoctoral researcher at the University of Naples Federico II. By understanding the precise mechanisms and feedbacks at play, Chan and his co-researchers were able to expand their analysis from a single ecological partnership to the impacts that nitrate radical and ozone pollution can have on plants and pollinators worldwide. the world. “We can extrapolate with more confidence where this is going to be a significant problem, how long it’s been a problem, and what we can actually do about it,” says Joel Thornton, co-author of the study and a professor of in atmospheric sciences at the University of Washington.

Ultimately, the researchers found that in many parts of the globe, radical ozone and nitrate pollution can hinder the ability of pollinators to detect their host plants. In much of the Northern Hemisphere, these pollutants can reduce the distances at which insects are able to locate flowers by 75% or more—from more than five kilometers in the pre-industrial era to less than 400 meters in the present.

Achieving this global conclusion required many previous steps and discoveries. Chan, Riffell, Thornton and their colleagues began their investigation back in 2017 by first observing pale primrose plants (Oenothera pallida) and their insect visitors. The scientists recorded a variety of pollinators stopping by the flowers during the day and at night, but they noted that two species of hawks were particularly frequent visitors at night: the white-lined sphinx moth (Hyles lineata) and moths in the genus Manduca, which includes tobacco hornworms. In their first field experiment, the researchers excluded pollinators at different times of the day and demonstrated that nighttime pollination played a greater role than daytime pollination in whether or not primrose flowers produced viable fruit.

Next, they analyzed the heady scent of primrose. Through gas chromatography and mass spectrometry, they identified each of the floral odor compounds. The researchers used tiny disembodied insect antennae from moths and bees – attached to electrodes – to determine which of these many chemicals the insects were most likely to respond to. They found that a chemical class called monoterpenes were uniquely attractive to pollinators.

From there, scientists took a turn as perfumers by composing a synthetic fragrance to match the attractive ones. When they exposed their fake floral scent to nitrate radicals and ozone, they found the main monoterpenes degraded and disappeared over time.

In wind tunnel experiments, Chan and company tested how well the mushrooms found different scent sources, including their fake flower scent, a real flower, and their primrose perfume mixed with nitrate radicals and ozone at concentrations similar to what might be expected in an urban environment. In a natural and unpolluted environment, clams can fly 80 kilometers in one night and be able to take refuge in flowers from kilometers away. But the results of the study showed that, in the presence of nitrate radicals, white-lined sphinx moths could not find a primrose flower at all – just two meters away – and tobacco hornworms were about 50% less successful at finding their food source. They replicated the same results in field trials, where they found no difference in insect visitation between their synthetic scent and real flowers, but did observe a 70% reduction in visitation by molluscs to scent lures exposed to pollution.

Combining their data on primrose pollination rates and the effects of air pollution, the researchers postulate that nitrogen trioxide levels present in many populated areas can make primrose plants 28% less successful at producing of seeds, simply based on the loss of primrose pollination alone. . The real impacts on plants may be much greater, as diurnal pollinators are also known to suffer from reduced olfactory capacity around certain pollutant sources, such as oil emissions.

All these findings together allowed the researchers to run their global model of NO3 and O3 pollution and present a theory of how insects around the world may be losing their ability to detect flowers from afar.

However, there are some important limitations to note. First, because they only studied one plant and two moth species—it’s possible that other insects and flowers have different chemical systems that aren’t as affected by the same pollutants, Chan says. In addition, he adds that nitrate radicals are more common at night because they degrade rapidly in sunlight, so the study is more relevant for nocturnal pollinators. However, other compounds (such as the hydroxyl radical) may play similar roles in the daytime atmosphere, Thornton says. More research is needed to determine the impacts of air pollution on different plant and pollinator systems and on daylight pollination, both Thornton and Riffell say.

However, the study provides a complete and disturbing insight into another way in which humans are destroying ecological systems. “The beauty of this research is that it is truly multidisciplinary, combining laboratory and field experiments,” says Mark Elgar, professor of evolutionary biology at the University of Melbourne. Elgar has previously studied the effects of particulate pollution on pollinator odor, but was not involved in the February study. The new research, he says, shows that insects face multiple stressors from air pollution. “We’d be crazy not to continue to investigate this.” adds Elgar.

Hiding among the ominous news is a small silver lining: since the 1980s, environmental protections in many countries, such as mandatory standards for car emissions, have significantly reduced radical ozone and nitrate pollution, says Chan – which means that it is possible that we can make further reductions. “It’s just more motivation,” says Thornton, “to shift our transportation and energy needs away from burning fossil fuels and toward other energy sources.” Greener transport and fewer emissions will mean we can all breathe (and smell) a little easier – including moths.

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