Photo: Pixabay/rostichep

The number of insects has been dropping dramatically across the planet and this poses grave threats to biodiversity and food security alike. Scientists have identified a variety of causes for the vanishing of creepy crawlies from climate change to intensive agriculture.

Now we can add chronic air pollution to that list.

An international team of researchers from the University of Melbourne, Beijing Forestry University and the University of California Davis has found that polluted air reduced insects’ ability to find food and mates. The reason for this is that their sensitive antennae become contaminated by particulate matter emitted by factories, vehicles and other sources of air pollution.

“While we know that particulate matter exposure can affect the health of organisms, including insects, our research shows that it also reduces insects’ crucial ability to detect odours for finding food and mates,” says Prof. Mark Elgar, a researcher at the University of Melbourne who was an author of a  paper published in Nature Communications.

“This could result in declining populations, including after bushfires and in habitats far from the pollution source,” Elgar notes. “As well as being fascinating creatures, many insects play a critical role in pollinating plants, including almost all the crops we rely on for food, and breaking down decaying material and recycling nutrients.”

The scientists subjected flies to a variety of experiments to see how the insects were affected by airborne pollutants. In one, they used a scanning electron microscope on houseflies and found that as air pollution increased, more particulate material collected on their antennae.

In another, they exposed houseflies to varying levels of air pollution in Beijing for 12 hours and then placed the flies in a Y-shaped tube maze. “Uncontaminated flies typically chose the arm of the Y-maze leading to a smell of food or sex pheromones, while contaminated flies selected an arm at random, with 50:50 probability,” they report.

“Neural tests confirmed that antenna contamination significantly reduced the strength of odour-related electrical signals sent to the flies’ brains, which compromised their capacity to detect odours,” they add.

Not only is it only flies that are affected. In bushfire-prone areas in rural Victoria in Australia the antennae of diverse insects, including bees, wasps and moths, are found to have been contaminated by smoke particles, even at considerable distances away from the fires themselves.

“Insect antennae have olfactory receptors that detect odour molecules emanating from a food source, a potential mate, or a good place to lay eggs,” the scientists say. “If an insect’s antennae are covered in particulate matter, a physical barrier is created that prevents contact between the smell receptors and air-borne odour molecules.”

“When their antennae become clogged with pollution particles, insects struggle to smell food, a mate, or a place to lay their eggs, and it follows that their populations will decline,” Elgar explains.

“About 40% of Earth’s landmass is exposed to particle air pollution concentrations above the World Health Organisation’s recommended annual average,” the scientist adds.

“Surprisingly, this includes many remote and comparatively pristine habitats and areas of ecological significance because particulate material can be carried thousands of kilometres by air currents.”

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