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Air Pollution Has Devastating Consequences for Pollinators

Air Pollution Has Devastating Consequences for Pollinators content piece image
Pseudocolorized, non-coated scanning electron micrographs of two foraging Giant Asian honeybee (Apis dorsata) wing regions, one (top) collected from a low polluted site in Bangalore, India (average respiratory suspended particulate matter, RSPM10 particles < 10 μM at 33.7 μg/m3) and one (bottom) collected from a highly polluted site 7.7 km away (average RSPM10 at 98.6 μg/m3). Note the presence of pollen (top) and RSPM (bottom) in the images. Credit: Micrograph obtained by Geetha Thimmegowda with a Zeiss merlin compact VP microscope at 1 kV EHT and 460X magnification.
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Our air is the one thing that surrounds all of us. According to the World Health Organization (WHO), 9 of the world’s 10 most polluted cities are now in India. Yet, we have almost no idea how air pollution is affecting other organisms who breathe the same air as we do. In some of the first research in the world to try to address the physiological and molecular impacts of air pollution on our wild plants and animals, scientists from the Bangalore Life Science Cluster show that air pollution could be devastating for organisms we rely on most for our own survival – like the honey bee.

For several years, members of Shannon Olsson’s lab at the National Centre for Biological Sciences (NCBS) in Bangalore had observed fewer pollinators in urban centres of the city. Was it pesticide use that caused this? Lack of water or shade? Determined to find out, Geetha G Thimmegowda traveled to different locations of this megacity to observe and collect the Giant Asian honey bee.

Apis dorsata, or the Giant Asian Honey Bee, is not only a common resident of Indian cities, but it is an important contributor to India’s food security and ecosystems. This bee produces over 80% of the country’s honey, and pollinates over 687 plants in Karnataka alone. 75% of our crop species rely to some extent on animals, and mostly insects, for their production. India is the largest fruit and second largest vegetable producer in the world. Without insect pollinators like our honey bees, the yearly mango export would lose over Rs. 65,000 Lacs. The importance of bees and other pollinators to India’s plant biodiversity and agroeconomy cannot be overstated.

With this in mind, Geetha examined collected bees under high-powered electron microscopy. First, Geetha examined a bee from the BLiSC campus on the northern and relatively low-polluted edge of the city:

As hoped, this foraging honey bee was carrying copious amounts of pollen on her body, ready to pollinate new flowers. Then they looked at the body of a bee from Peenya, an industrial area of the city:

This bee was covered in small particles that they later found to contain lead, tungsten, arsenic, and a host of other toxic metals. These tiny debris, less than 10 microns in size, are known as Respirable Suspended Particulate Matter, or RSPM, a major component of air pollution.

“I couldn’t believe what I was seeing. I remember turning to Geetha with tears in my eyes and saying - We have to work on this and find out what this pollution is doing to our wild animals. People need to hear about this, and more importantly, people have to care,” Olsson remarks.

This painful discovery prompted a four-year study of over 1800 wild bees published this week in Proceedings of the National Academy of Sciences, USA on the effects of air pollution on the behaviour, physiology, and molecular aspects of the Giant Asian Honey Bee in one of India’s fastest growing megacities. Through a series of experiments along with honeybee expert Dr. Axel Brockmann of NCBS, and cardiovascular researcher Dr. Dhandapany Perunderai of the Institute for Stem Cell Science and Regenerative Medicine (inStem) and The Knight Cardiovascular Institute, the scientists found that bees from more polluted areas of the city exhibited lower flower visitation rates than in less polluted areas. Bees from more polluted areas likewise showed significant differences in heart rhythmicity, blood cell count, and the expression of genes coding for stress, immunity, and metabolism. Repeating these experiments with lab-reared Drosophila found similar effects, suggesting that the impact of air pollution is not species-specific, nor likely the result of other environmental factors.

Dr. Hema Somanathan, who studies bee behaviour and pollination ecology at the Behavioural and Evolutionary Ecology (BEE) Laboratory, Indian Institute of Science Education and Research, Thiruvananthapuram, notes:

“There are extreme gaps in our knowledge on the status of our wild pollinators in India. This study by Dr Olsson and colleagues is a very important step in addressing this pressing concern. Bees are important pollinators in our landscapes, and this study clearly shows how pollution adversely affects the health of bees.  The study was done with wild bees naturally visiting flowers in Bangalore city and not in lab assays on reared honey bees kept in hive boxes that may already be stressed or immuno-compromised. Thus, in my opinion this study provides us with hard evidence that all is not well with our wild bees. Given the scale of landscape alteration and urbanisation in India, it is expected that these effects are widespread and likely to worsen with time.”

Perhaps most strikingly, they found over 80% of the bees collected from the moderate and highly polluted sites died within 24 hours. These RSPM levels were similar to the “Interim Target II” guidelines proposed by the WHO. To this end, Arunabha Ghosh, founder and CEO of the Council on Energy, Environment and Water notes:

“So far, much of the air quality studies in India have either considered sources of pollution or impact on human health, and to an extent on economic productivity. This study covers important new ground, by examining the impact of air pollution on pollinators, which would have serious implications for agricultural output in India. From a policy perspective, we need, first, more dense air quality monitoring networks in agricultural areas (rural areas suffer from data blindspots). Secondly, impact studies for different agro-ecological zones should be initiated, so that we have a better sense of how air quality is likely to impact pollinators and plants in various regions. Thirdly, there is a need for clearer communication of the results of such studies to communities, so that they become more aware of the livelihood consequences of the poor air they are breathing. Finally, such findings further underscore the need to raise India's ambient air quality standards.”

Finally, Shloka Nath, Executive Director at the India Climate Collaborative and the Head of Sustainability and Special Projects at Tata Trusts, comments:

“Better application of research and evidence in development policy making can save lives, reduce poverty, and improve quality of life. In the case of this study, the research speaks for itself: we now have concrete proof that by polluting our air, we are not only endangering our own health, we are also affecting the wild animals and plants who depend on it for sustenance. This has far reaching implications for the complex ecosystems we are part of, as these changes affect the quality of habitat and food sources we all depend on.”

Thimmegowda, G, et al. A field-based quantitative analysis of sublethal effects of air pollution on pollinators. PNAS, August 10, 2020 https://doi.org/10.1073/pnas.2009074117

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