Air pollution kills insects, influences their ability to smell flowers: Study

Insects — the most important pollinators on earth — are under threat due to land-use change, habitat loss and chemicals-based farming. Scientists now have evidence to prove that air pollution is also one of the factors that is causing rapid decline in the population of bugs.

Insects help humans and our natural surroundings in a number of ways. They keep pests (that attack our crops) under control, pollinate crops, and finish up our waste so that the world doesn’t turn into a heap of garbage. The productivity of about three fourth of global crop species depends on efficient functioning of insects. Thus it would be safe to conclude that for a country like India, food security is largely dependent on the well-being of the insect world.

Robbie Girling and James Ryalls from the University of Reading in the United Kingdom recently published a study which found that insects exposed to ozone and nitrogen oxides (NOx), released via fumes from diesel vehicles, resulted in 70 per cent drop in the number of pollinator insects and 90 per cent fewer flower visits. The insects whose numbers dropped include honey bees, bumblebees, solitary bees, parasitic wasps, moths, butterflies, hoverflies, beetles etc.

The research concluded that the impact of air pollution on biodiversity and food production is much greater that perceived so far.

Importantly, the pollution levels, during the study, were kept much below the limits defined by US law as safe for the environment. In a country like India, where most big cities have bad or even alarming levels of air quality all through the year, the impact on insects and their populations could be phenomenal.

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Shannon Olsson, an American ecologist based at Bengaluru’s National Centre for Biological Sciences (NCBS), told Down To Earth that a study conducted in Bengaluru in 2020 found a drastic reduction in honeybee health.

Olsson’s team found suspended particulate matter (PM 2.5) had bearing on Giant Asian honey bees, which produce more than 80 per cent of the honey in India and pollinate more than 687 plant species. Over 80 per cent of bees died within 24 hours after being collected from moderately polluted sites. Olsson believes the statistics are alarming and need urgent attention of the authorities in India where nine of its cities rank in the top 10 most polluted cities across the globe.

So, how does pollution hurt insects?

While air pollution is known to cause lung cancer, asthma, heart diseases and obesity among several ailments in humans, in honey bees it was found to affect heart rates, stress and blood cells counts.

Olsson said air pollution can also affect the insects’ ability to sniff flowers, thus lowering pollination services.

Flowers release odour as chemicals called volatile organic compounds, which help insects locate flowers. Pollutants could react with and change the scents of flowers, making them harder to find.

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Bad air quality could also affect insects’ social bonds. For instance, insects use airborne odours to attract opposite sexes. If pheromone communication is disrupted similarly, it could result in insects struggling to find mates, which could have ramifications for insect biodiversity, the study found.

Scientists, however, found air pollutants impacted different insects in different ways. For example, beetles and parasitic wasps appeared resilient to pollutants. They said this could be because beetles and wasps relied on visual cues rather than odour to reach flowers.

In conclusion, researchers said more study needs to be done to understand how different air pollutants impact the insect world.