Insects lose their sense of smell because of air pollution, humans go to pollinate plants themselves

Air pollution is preventing pollinators like bees and butterflies from smelling the nectar. That doesn't just affect insects and plants in particular.

Because many of our food sources depend on insect pollination, scientists predict future yields of some crops could be reduced because of air pollution.

And that even affects food security as the world gets more crowded. Many foods such as vegetables, apples, cherries and cocoa will have a decrease in yield or we will have to artificially pollinate them on a large scale.

Insects are losing their sense of smell due to air pollution.

Ambush of pollinators

The field of canola flowers at the Sonning farm of the University of Reading, UK these days suddenly appear giant circles assembled into octagonal blocks. But it wasn't an art installation contest or an alien trail. In fact, the scientists are installing there a huge fumigation system.

Fumigants are nozzles that spray chemicals into the air to kill insects, the same way you spray insecticides with an industrial sprayer. But here, scientists don't want to destroy any insects, they are just simulating an air polluted environment with common impurities.

These octagonal eight-sided fumigation nozzles emit ozone and diesel exhaust. The goal was to test whether these common pollutants affect insects and how they pollinate flowers.

To be able to get accurate numbers, scientists at the University of Reading had to make two ambushes. They were trained to stand as still as possible, like a mannequin in a mustard garden, eyes wide open just to count the number of insects that entered the octagon.

• The first ambush is when the fumigation device is not turned on.
• A second ambush later for comparison when the machine was spewing diesel and ozone emissions.

Giant circles form an octagonal block.

The results showed that, compared with the first ambush, the scientists in the second ambush counted significantly lower numbers of pollinating insects. When the fumigator sprayed diesel, the number of insects that flew to and landed on at least one flower was reduced by 69%.

The figure is 62% for ozone and 70% for a combination of both pollutants.

When they counted each separate insect species, including bees, moths, butterflies and flies - and factored in the number of flowers each insect perched on, the scientists found that their visits were reduced. 89% for the fumigator released diesel, 83% for ozone and 90% for both pollutants.

"Our results suggest that air pollution is a potential contributor to additional pressure on pollinators," said James Ryalls, lead author of the study. diseases, habitat loss and pesticides.

Air pollution causes insects to lose their sense of smell

The researchers suggest that the reason insects are less likely to pollinate canola flowers is because pollutants interfere with the flower's scent. Some commentators say it's because the fumigation machines or the smell of chemicals scare away bees and butterflies. But Ryalls took that possibility into account and found that when they placed a pan trap (a type of insect trap) within the octagon, they did not see a decrease in the number of insects in the trap.

That means insects are not afraid of the fumigation machine or the smell of chemicals, they still tend to fly inside, but the number of landing on flowers is reduced because they are confused not to smell the pollen in the air. where.

The sense of smell of pollinators is inherently very sensitive.

Insects, including bees and butterflies, smell using their antennae. These antennae are covered with olfactory receptors, which detect odor compounds.

The sense of smell of pollinators is inherently very sensitive - much more sensitive than the sense of smell of humans. When a flower releases a cluster of chemical compounds that give it a scent, insects use it as a map to navigate, looking for places where they can suck nectar.

If one or more odorant compounds are changed by reaction with diesel oil or ozone, the proportion and concentration of compounds in the aroma beam will change. It makes the insect's locating map distorted, from which it can no longer find the flower's location.

If in our atmosphere there are "good ozone" molecules, which are doing the job of shielding the planet from ultraviolet rays from space, then below ground, we have "bad ozone" being born. emitted from automobile fumes, power plants, and oil refineries.

Ozone near the ground can cause serious effects on human health such as cardiovascular and respiratory problems. Now, it has also been found to interrupt insect pollination.

A 2020 US Environmental Agency report cites an experiment that showed that in the presence of elevated ozone, wasps' ability to navigate by scent was impaired.

The study concluded: "A range of evidence supports a 'possibly causal relationship' between ozone exposure and insect-plant signaling changes." 

Safe concentrations of nitrogen dioxide (NO2) are less than 53 ppb.

Currently, safe concentrations of ozone in the air are determined to be below 70 ppb (parts per billion). Safe concentrations of nitrogen dioxide (NO2) are less than 53 ppb. During Ryalls' rounds of experiments, the ozone concentration he used was approximately 35 ppb, and the concentration of nitrogen dioxide, a component of diesel engine exhaust, was about 21 ppb.

These figures, according to Ryalls, are equivalent to only half the concentration of ozone and diesel emissions next to a busy London road. Thus, "only moderate levels of common air pollutants can reduce the percentage of free-living insects that find and pollinate flowers," he said.

What are the consequences of that?

This is not only bad news for pollinators, whose insects may not be able to find food amid air pollution, but also bad news for plants that depend on insects for reproduction. alike.

The outlook is pretty dire for humans, too: If insects can't pollinate crops, we could lose essential products in the everyday food supply chain.

Although some crops are wind-pollinated, others depend entirely on insects. "If we lose all pollinators tomorrow, we won't be able to produce cocoa beans, Brazil nuts and some fruits, which pollination is necessary for reproduction," says Ryalls. property".

It also means that humanity will no longer have apples, cranberries, melons and vegetables like cruciferous vegetables. Crops such as blueberries, cherries and almonds are also disappearing as they depend almost entirely on honey bees for pollination.

A scientist is in ambush in a cabbage garden.

But Ryalls said the consequences don't stop there. The fact that insects' sense of smell is affected by polluted air also makes them unable to smell their own pheromones.

Pheromones are compounds produced by insects to attract mates of the same species. "If communication with pheromones is disrupted in the same way, it could lead to insects struggling to find mates. This could affect biodiversity within the insect species." ", Ryalls forecast.

"No matter what kind of pollution -- whether it's light, noise or chemical pollution -- in one way or another," said Jaret Daniels, an associate professor of insect conservation at the Florida Museum of Natural History. other affect pollinators".

And that will have a great impact on natural ecosystems as well as human agricultural activities. Increased fossil fuel-related emissions not only affect the planet's climate, but also affect our own and our children's food security.

Studies like these are therefore "especially important, given the growing global population, especially in developing urban environments where pollution is particularly severe." , Daniels said.