Research Clarifies Air Pollution’s Role in Insect Decline

When people talk about the decline in insect populations, the focus is generally on pesticide use, and habitat destruction. There’s no question that these are major factors, but there’s another that has apparently been under-estimated: air pollution. I talk about air pollution a lot on this blog, and while that’s mostly focused on how it affects humans, I did post last November about how air pollution made it harder for fig wasps to find their aphid prey. The researchers speculated that the presence of diesel fumes and ozone masked the scent of their prey, but that prey feeding on cabbages and other brassicas were smelly enough to cut through the pollution. Now a new study has come out, which demonstrates that air pollution particles can collect on an insect’s sensory organs, affecting their sense of smell in general:

The research team conducted several related experiments:

  • Using a scanning electron microscope, they found that as air pollution increases, more particulate material collects on the sensitive antennae of houseflies. This material comprises solid particles or liquid droplets suspended in air and can include toxic heavy metals and organic substances from coal, oil, petrol, or woodfires.
  • They exposed houseflies for just 12 hours to varying levels of air pollution in Beijing 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.
  • Neural tests confirmed that antenna contamination significantly reduced the strength of odour-related electrical signals sent to the flies’ brains – it compromised their capacity to detect odours.

In addition, continuing research in bushfire-affected areas in rural Victoria has shown that the antennae of diverse insects, including bees, wasps, moths, and species of flies, are contaminated by smoke particles, even at considerable distances from the fire front.

Insect antennae have olfactory receptors that detect odour molecules emanating from a food source, a potential mate, or a good place to lay eggs. 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,” Professor Elgar said.

“About 40 per cent of Earth’s landmass is exposed to particle air pollution concentrations above the World Health Organisation’s recommended annual average.

“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,” Professor Elgar said.

I’ll be honest: If you had asked me how air pollution was contributing to the decline in insect populations, I would have guessed ill health through inhaling, drinking, or eating air pollution, but I wouldn’t have gone with “it messes with their sense of smell”. Given the fig wasp thing I mentioned above, I guess it should have been higher on my list, but I apparently didn’t give it enough thought. I think it’s partly that being a visual creature that gets food from stores, I sometimes forget the importance of smell to other animals. Repetition aids memory, though, so now I’m more likely to remember it. I suppose the next question here will be how big this olfactory problem is, but while we wait for a number, we can add this to the already-huge pile of reasons why it’s good to reduce air pollution.


  1. StevoR says

    Yes. Another twist and extra unforeseen threat in the “insect apocalypse” *that doesn’t get enough attention even with articles like this one :

    The collapse of insects

    The most diverse group of organisms on the planet are in trouble, with recent research suggesting insect populations are declining at an unprecedented rate. … (snip)… As human activities rapidly transform the planet, the global insect population is declining at an unprecedented rate of up to 2% per year. Amid deforestation, pesticide use, artificial light pollution and climate change, these critters are struggling — along with the crops, flowers and other animals that rely on them to survive.

    “Insects are the food that make all the birds and make all the fish,” said Wagner, who works at the University of Connecticut. “They’re the fabric tethering together every freshwater and terrestrial ecosystem across the planet.”

    Source :

    Plus this one :

    Insect decline in the Anthropocene: Death by a thousand cuts

    … (snip).. The 11 papers in this collection examine insect decline from geographic, ecological, sociological, and taxonomic perspectives; evaluate principal threats; delve into how the general public perceives news of insect declines; and offer opinions on actions that can be taken to protect insects. Insect declines have been the focus of a range of popular media, with widely varying levels of accuracy. Consequently, a core intention of this special issue is to provide a scientifically grounded assessment of insect population trends; contributors were urged to provide critical evaluations of raw data, published studies, and reviews, given that a few of the more highly publicized reports of insect decline suffered from unjustified assumptions, analytic issues, or overextrapolation.

    Source :

    As well as this one :

    Extreme land use combined with warming temperatures are pushing insect ecosystems toward collapse in some parts of the world, scientists reported Wednesday. The study, published in the journal Nature, identified for the first time a clear and alarming link between the climate crisis and high-intensity agriculture and showed that, in places where those impacts are particularly high, insect abundance has already dropped by nearly 50%, while the number of species has been slashed by 27%.

    Source :

    And more .. but certainly not mor eenough or getting attention enough in my view.

    Sorry if this is too depressing folks.

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