Air pollution killing giant Asian honey bees: Study

The giant Asian honey bee or apis dorsata, which produces more than 80% of India’s honey, is falling prey to air pollution, according to a first-of-its-kind quantitative analysis on the impacts of air pollution on insects by the National Centre for Biological Sciences (NCBS), Bengaluru. The study indicates a decline in India’s insect population. NCBS is a centre of the Tata Institute of Fundamental Research.

Through a four-year study of over 1,800 apis dorsata, an eight-member team led by NCBS found that more than 80% of the bees collected from moderate and highly-polluted sites died within 24 hours in Bengaluru as compared to less polluted areas where the number of dead bees was less by 20%.

Between January 2017 and April 2019, average respiratory suspended particulate matter – also called PM10, which is fine particulate matter of diameter 10 microns or less – was around 28.32 micrograms per cubic metre (ug/m3) at a rural site; and 33.73ug/m3, 45.95ug/m3 and 98.59ug/3 at low, moderate and highly-polluted sites respectively. The main sources of air pollution include transport emissions, industries, integrated land-use developments and open burning.

Results also revealed that the rate at which giant Asian honey bees visited flowers was lower in more polluted areas. Additionally, bees from more polluted areas showed irregular heartbeats, lower blood cell count, and the expression of genes coding for stress, immunity, and metabolism. Bee debris also contained several toxic elements. For instance, metals found on the bee cuticle comprised lead, tungsten, chromium, arsenic, aluminium and cobalt.

While the study sites chosen were specific to Bengaluru, Shannon B Olsson, lead author and associate professor at NCBS’s naturalist-inspired chemical ecology laboratory, said she would imagine severe impacts on the heath of the wild bees in more polluted cities such as Delhi and Mumbai.

“In a city like Delhi, which is among the top 10 polluted cities in the world, there are likely to be more severe effects on bees than in Bengaluru, but there may not be the same exact impacts since the sources and components of air pollution are different in the two cities,” said Olsson.

Globally, studies have recorded declines in insect populations with one in six species of bees reported locally extinct in various regions and attributed reductions in habitat quality which include pollution as a factor.

“The present study on the native pollinator is one of the few studies worldwide to address physiological and molecular impacts of air pollution on wild plants and animals with field experiments,” said Olsson.

Titled “A field-based quantitative analysis of sublethal effects of air pollution on pollinators”, the study was published in the Proceedings of the National Academy of Sciences, United States of America, on Tuesday.

With India being the world’s largest fruit producer, second-largest vegetable producer as well as the second-most populous country, scientists said the findings are important because this wild pollinator is not only a common resident of Indian cities, but also an important contributor to India’s food security and ecosystems. For instance, it pollinates more than 687 plants in Karnataka alone.

“India also is home to nine of the world’s 10 most polluted cities, but we have no idea of the impact of air pollution on plant and animal systems. We measure pollution using air quality index which is based on human health. The importance of bees and other pollinators to India’s plant biodiversity and agro-economy cannot be overstated,” said Olsson.

For the study, four different sites were chosen based on multiple parameters, such as pollution levels, proximity to traffic, and lack of pesticide application. With India facing rapid and increased urbanisation within and among its agricultural lands, Geetha Thimmegowda, another lead author and post-doctoral researcher, NCBS, said, “There is an urgency for more studies on wild plant and animal systems to better inform Indian and international air quality guidelines. Such studies are imperative to reveal the full impact of air pollution not only on the health of humans and environmental ecosystem, but also economic loss to pollinator-dependent crops and food security in highly polluted and vulnerable regions such as India.”

Researchers said more than 80% of all flowering plants rely on animal pollination, and that India’s annual mango export could stand to lose over Rs 65,000 lakhs because 53% mangoes would disappear without insect pollinators like honey bees.

India’s crop species are mostly dependent on insects for their production and one reason of studying the giant Asian honey bee is because they are present in both urban and rural settings. Studies have shown this species, in addition to be often found nesting in cities, also migrates its colonies repeatedly over many kilometres throughout the year among urban, rural, and forest habitats.

“As a consequence, any long-term physiological or behavioural impacts of urban air pollution will also impact the pollination services these insects provide to agricultural and forest areas where they migrate,” stated the study.

Arunabha Ghosh, founder and CEO of the Council on Energy, Environment and Water, said 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. Such findings further underscore the need to raise India’s ambient air quality standards,” he said.

The impact of poor air quality did not just take its toll on apis dorsata. Experiments undertaken with drosophila melanogaster (fruit fly) reared in the laboratory displayed similar effects when exposed to air pollution. Researchers said this suggests the impact is not species-specific nor likely the result of other environmental factors.

“This study provides us with hard evidence that all is not well with our wild bees since it was done with wild bees naturally visiting flowers in Bengaluru city and not in lab assays on reared honey bees kept in hive boxes that may already be stressed or immuno-compromised,” said Hema Somanathan, who studies bee behaviour and pollination ecology at the Behavioural and Evolutionary Ecology (BEE) laboratory at the Indian Institute of Science Education and Research, Thiruvananthapuram, and who was not involved in the study. “Given the scale of landscape alteration and urbanisation in India, it is expected that these effects are widespread and likely to worsen with time,” said Somanathan.

In addition to NCBS, collaborators include Massachusetts Institute of Technology, Cambridge, Institute for Stem Cell Science and Regenerative Medicine (inStem), Bengaluru, Knight Cardiovascular Institute, and the department of medicine and molecular and medical genetics at the Oregon Health and Science University, Portland.