Anxiety, fatigue, asthma, lung cancer, and heart diseases are just some of the consequences of air pollution observed in humans. In light of the current levels of air pollution, which are well beyond the WHO’s permissible limits, such particulars have become common knowledge. It also doesn’t help that with 9 out of 10 of the most polluted cities in the world, India is the 3rd most polluted country.
But how does air pollution affect wildlife?
In a recent study, Dr. Geetha Thimmegowda and Dr. Shannon Olsson from NCBS (Bangalore), along with their colleagues, studied the effect of different levels of pollution on the Giant Asian honey bee (Apis dorsata) - an important and widely prevalent pollinator of India. The study threw up some shocking results!
Selected study sites with varying levels of pollutions
To understand the effect of minute pollutant particles (also called RSPM or Respirable Suspended Particulate Matter in technical terms) on honeybees, researchers first selected four locations with different levels of pollution (low, moderate, high and rural) in and around Bangalore. Over the next 3 years, bees visiting flowers in these areas were observed and counted by following a well-defined protocol. Several bees from each area (1820 in total) were brought back to the laboratory for in-depth molecular and physiological analysis. The bees were even monitored closely to understand how long they would survive for, given adequate food.
Data collection and observation
Observation data suggested that fewer bees visited flowers in highly polluted areas. In addition, they were 80% less likely to survive as compared to bees in non-polluted areas! On close inspection, RSPM particles were found deposited on the bees’ bodies, containing atoms of toxic metals such as lead and tungsten!
Analysis of physiological data interestingly put forward that while humans breathe at a slower rate due to air pollution, there was no difference in the rate of breathing of the honeybees. However, bees from higher polluted areas showed arrhythmic heartbeats and had fewer blood cells (hemocytes), which impacts their circulatory system. Moreover, the molecular analysis indicated that bees from polluted areas had increased stress levels, lowered immunity, and lipid metabolism!
Heart beats of bees at less and high polluted sites. Can you spot the difference?
However, the question arose - what if these differences were observed because of the differences in the diet of bees in different locations, or just because they belong to different colonies? To ensure that the results obtained were a direct result of air pollution, fruit flies (Drosophila melanogaster) were bred in laboratories (and hence were previously unexposed to pollution) and were introduced to the same locations from where the honey bees were collected.
Similar observations and experiments showed that just like the Giant Asian honeybees, flies from polluted sites visited fewer flowers, survived less, had depositions of RSPM on their bodies, had arrhythmic heartbeats, fewer hemocytes, increased stress levels, and lowered immunity and lipid metabolism!
This suggests that the effects observed on honeybees were a result of air pollution and not because of other factors like diet and colony. This experiment also suggests that it is not just the honeybees that are adversely affected by air pollution, but other insects and pollinators are likely to be affected in a similar manner.
Then again, what effect could reduced survival and flower visitation of bees have on us? Bees are key pollinators of a variety of crop plants. A decline in their numbers, competency, and efficiency might mean a decline in food production!
This serves as a warning from researchers -- We must act soon, as, after the pandemic, we certainly do not want a food crisis!
Source: Thimmegowda, Geetha G., Susan Mullen, Katie Sottilare, Ankit Sharma, Saptashi Soham Mohanta, Axel Brockmann, Perundurai S. Dhandapany, and Shannon B. Olsson. "A field-based quantitative analysis of sublethal effects of air pollution on pollinators." Proceedings of the National Academy of Sciences 117, no. 34 (2020): 20653-20661.
Link to original article: https://www.pnas.org/content/pnas/117/34/20653.full.pdf
Article written by: Bhaavya Malpani, edited by Devica Ranade