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Pollinator Numbers Are Falling Around the World – But for Different Reasons

Pollinator Numbers Are Falling Around the World – But for Different Reasons

A honey bee pollinating a plum tree in Sombrerete, Mexico, March 2020. Photo: Tmasjeg/Wikimedia Commons, CC BY-SA 4.0

  • At least $235 billion’s worth of the world’s yearly crop output may be at risk due to pollinator decline.
  • A new study has found that what we know about the causes of pollinator decline from the West isn’t likely to be useful to deal with the problem in South Asia.
  • One problem going ahead is that there are few studies focused on how pollinators, land-management and climate change are related to each other.

Hyderabad: Populations of pollinators, like bees, butterflies and moths, seem to be on the decline around the world. But although there is robust data from the global north about the potential causes of this decline, we know little about what could be holding them back in other parts of the world, which pollinators warrant more, and how this disturbing trend could affect human activities.

A new study led by Lynn Dicks, an agro-ecologist at the University of Cambridge, has shed some light on these questions. The research team comprised 20 pollination scientists and people of Indigenous communities. Of them, Parthib Basu, a professor at the department of zoology, University of Calcutta, and Thingreipi Lungharwo, of the Naga Women’s Union, Manipur, were from India.

One of their most important conclusions is that what we know about the causes of pollinator decline from the West isn’t likely to be useful to deal with the problem in South Asia and Africa.

Why should we worry?

In 2019, the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES) released the ‘Global Assessment of Biodiversity and Ecosystem Services’ report. It said, “More than 75% of global food crop types, including fruits and vegetables and some of the most important cash crops, such as coffee, cocoa and almonds, rely on animal pollination.”

Further, $235-577 billion’s worth of the world’s yearly crop output may be at risk due to pollinator decline.

The role of pollinators extends beyond finances. Pollinators enable sexual reproduction among plants – so if their numbers decline, entire ecosystems will be threatened. According to a 2016 report from IPBES, pollinators also help maintain the diversity of plants and other animals in different ecosystems, and bear aesthetic and cultural significance for various native and Indigenous communities.

However, proving that the population of pollinators has been declining around the world is a contentious process. One reason is the lack of large-scale studies that have tracked pollinator diversity and population over long periods.

According to a 2013 paper by ecologist Adam J. Vanbergen (also a member of the Dicks et al. study) and the Insect Pollinators Initiative, the lack of large-scale data has forced researchers to make do with sparse data about particular species or about the environmental impact of specific pollinator loss.

But some data does exist from the global north showing clear signs of pollinator decline. Vanbergen’s paper quoted a few such studies (such as this and this) showing wild bee and hoverfly species diversity has been declining throughout Europe. Similarly, butterfly and bumblebee populations have been shrinking or are on the brink of extinction across the world’s north. And in both Europe and North America, populations of wild, feral and managed honey bees have been falling.

The current study

The study led by Dicks began in September-October 2017, according to Parthib Basu. “After the IPBES 2016 assessment, we realised that most of the data about pollinator decline is from North America and Europe, and that we still have a couple of things to understand from other global regions,” he told The Wire Science.

He also said that the IPBES 2016 report “identified different drivers of pollinator decline” but it didn’t say anything about their relative importance. Dicks, Basu and others wanted to fill this gap.

To this end, their study used an “expert elicitation paradigm”. First, team members segmented the data into eight major drivers and 10 major perceived risks to people, based on the 2016 IPBES report and discussions among themselves.

Next, they scored the relative importance of each of these drivers and risks  through three rounds. Each expert’s score depended on the scientific evidence available as well as their own experience.

In addition, the group also designed a matrix of drivers and risks. Based on the level of agreement between experts, the nature of evidence available and the level of certainty, the matrix categorised the drivers and risks into four qualitative categories: ‘well-established’, ‘established but incomplete’, ‘inconclusive’ and ‘unresolved’.

Scores based largely on experience also increased uncertainty. Basu said that while a risk was sometimes scored based on experience, it was important to have the agreement of the other experts as well.

Through this exercise, they found that the relative importance of drivers of decline varied between different biogeographical regions. For example, land cover and topography (a.k.a. configuration), land management and pesticide use were found to be the most important drivers globally – but land management seemed to matter much less in Africa.

The group faced similar conundrums vis-à-vis the risks of pollinator decline to human beings. While crop pollinator deficits and loss of wild pollinator diversity were seen as the biggest risks globally, Latin America was perceived to have the greatest risk to human beings due to pollinator decline – while Europe was perceived to have the least.

On a different note, while the researchers believed climate change to be an important driver worldwide, their paper reported a “unanimous lack of confidence over its importance relative to other drivers” due to lack of long-term evidence.

Behavioural and evolutionary ecologist Hema Somanathan, at the Indian Institute of Science Education and Research, Thiruvananthapuram, called this variation an important finding.

“This is probably the first time a study has provided solid support for differences between the global north and the global south on the need to attend to issues of pollinator decline differently in these regions,” she told The Wire Science.

“This is because land-use and -management practices in the global north are very different from those in the global south; therefore, threats to pollinators are also very different.”

Palatty Allesh Sinu, an ecologist and assistant professor at the Central University of Kerala, said pollinator biology is more complex than we think. For example, the risk posed by pesticides to pollinators depends “on when the pesticide is sprayed, if it is sprayed on flowers – since that is when pollinators visit the plants – and for how long the pesticide remains on the plant,” he said.

The study didn’t assess the relative importance of indirect drivers – for example, an increase in land conversion as a result of lower crop yield – or interactions between drivers.

Lack of evidence

For their efforts, however, the study team concluded that lack of evidence forced most of their findings into the ‘established but incomplete’ category of the confidence matrix. Their paper asked for more research on “the ecology and status of all but the most common pollinator species, and the relationships between pollinators, human economies and cultures.”

In India in particular, Basu said it’s about time studies focused on how pollinators, land-management and climate change are related to each other. “Otherwise, we may be too late.”

Somanathan agreed, and said the absence of such studies could be the result of a general apathy among agriculture-research institutions towards pollinator research. “For most wild plants and even crop plants, we have no idea who the actual effective pollinators are, how much these plants depend on the pollinators and, for that matter, what is happening to our pollinators,” she said.

Reversing the decline

In 2016, the Government of India launched a ‘sweet revolution’, encouraging farmers to shift to apiculture1 to bolster their incomes and improve crop yield by supporting pollination.

However, Sinu, of the Central University of Kerala, said introducing honey bees as pollinators in an area could be a futile exercise. By way of example, he described his team’s work in large cardamom plantations of the eastern Himalaya, where managed beekeeping to better pollinate cardamom flowers is a well-known exercise.

When Sinu and his team disallowed the pollinators other than honey bees to visit the flowers, they found that the efficiency of large-cardamom pollination by honey bees was effectively 0%. “Large cardamom seems to be majorly pollinated by large bumblebees,” Sinu said. “In such cases, it is important to preserve native populations of these wild pollinators.”

Basu also said that more than not helping with pollination, introducing managed honey bees could harm native bees. “India has around 800-odd varieties of solitary wild bees, which don’t produce honey, along with various varieties of honeybees,” Sinu said. The managed bees compete with the native ones and further endanger the latter’s prospects.

The Indian Pollinator Initiative

In 2020, some Indian scientists came together to form the Indian Pollinator Initiative (IPI). Basu, Somanathan and Sinu are among its seven founding members. “After three ‘bee meetings’ in 2018, 2019 and 2020, which were attended by beekeepers, NGOs and academicians, we realised the need for pollinator researchers to break free of their isolation and organise themselves to share ideas and data,” Somanathan said.

The initiative has arranged for talks from members of similar pro-pollinator initiatives around the world. They’re also encouraging younger researchers to present their work at these talks, and to network with other researchers.

“Our goal is to come up with a simple, wide-scale framework for a pollinator study that can tell us about the pollinators available in India,” according to Somanathan. The IPI also has plans to include citizen science initiatives.

“It is crucial that we now pay focused attention to … our pollinators and to whether they are doing okay.”

Sayantan Datta (they/them) are a queer-trans science writer, communicator and journalist. They currently work with the feminist multimedia science collective, and tweet at @queersprings.

  1. Rearing honey bees

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