Not only humans, air pollution also a threat for honeybees: Study

Forget humans, Bengaluru’s polluted air has deleterious effects even on the honeybees that survive much less in such contaminated air and have a crippled life in which they can not visit the flowers as frequently as they should if the air was cleaner.

In what may be the world’s first systematic study on the impact of air pollution on honeybees, scientists at the National Centre for Biological Sciences, Bengaluru on Monday reported that bees collected at sites with comparatively higher levels of air pollution showed lower survival rates as well as alterations in flower visitation, heart rate, and blood cell counts.

Furthermore, detailed analysis of bees’ antennae and heart tissue showed that air pollution is associated with an increase in the expression of genes involved in stress, lipid metabolism, and immunity. More strikingly, over 80% of the bees collected from the moderate and highly polluted sites died within 24 hours.

"We were astonished to see how strong the impact of air pollution was. More than 80% of bees were dead within 24 hours of collection,” Shannon Olsson, a scientist at NCBS and one of the members of the study told DH. The research has appeared in the Proceedings of the National Academy of Sciences.

While the majority of air pollution studies focus on humans, Bengaluru biologists turn their attention on a non-human species to check how such contaminated air impacts the insects.

For the study, the scientists picked up Apis dorsata or the Giant Asian honeybee, which is not only a common resident of Indian cities but 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.

Between January 2017 and April 2019, the researchers examined the impacts of pollutants like particulate matter, ozone, nitrogen dioxide, sulphur dioxide and volatile organic compounds on 1,820 Giant Asian honeybees across four sites in Bengaluru.

The sites were chosen to reduce the effects of other potential variables such as pesticide use, immediate floral abundance within 100 m of the collection site, traffic, shade, presence of human-made structures.

Subsequently, they collaborated with researchers at the Institute for Stem Cell Science and Regenerative Medicine, Bengaluru and the Knight Cardiovascular Institute, Portland, USA to study the behavioural, physiological and genetic aspects of the bees collected from polluting sites and compared them with the bees picked up from not so polluted areas in and around the southern metropolis.

The revelations were startling. The honeybees from more polluted areas exhibited lower flower visitation rates than those in less polluted areas. They showed significant differences in heart rhythmicity, blood cell count, and the expression of genes coding for stress, immunity, and metabolism too.

Repeating these experiments with laboratory-reared Drosophila (fruit fly) found similar effects, suggesting that the impact of air pollution is not species-specific nor likely the result of other environmental factors.

“The study was done with wild bees naturally visiting flowers in Bangalore city and not in lab assays on reared honeybees. It 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,” commented Hema Somanathan, who studies bee behaviour and pollination ecology at the Indian Institute of Science Education and Research, Thiruvananthapuram and not associated with the study.