Off the coast of Tuscany is a tiny island in the shape of a crescent moon. An hour from mainland Italy, Giannutri has just two beaches for boats to dock. In summer, hundreds of tourists flock there, hiking to the red and white lighthouse on its southern tip before diving into the clear waters. In winter, its population dwindles to 10. The island’s rocky ridges are coated with thickets of rosemary and juniper, and in warmer months the air is sweetened by flowers and the gentle hum of bees.
“Residents are people who like fishing, or being alone, or who have retired. Everyone has their story,” says Leonardo Dapporto, associate professor at the University of Florence.
Giannutri island’s remote location made it a perfect open-air laboratory for the bee experiments. Photographs: Giuseppe Nucci
It was Giannutri’s isolation that drew scientists here. They were seeking a unique open-air laboratory to answer a question that has long intrigued ecologists: could honeybees be causing their wild bee cousins to decline?
To answer this, they carried out a radical experiment. While Giannutri is too far from the mainland for honeybees to fly to it, 18 hives were set up on the island in 2018: a relatively contained, recently established population. Researchers got permission to shut the hives down, effectively removing most honeybees from the island.
Punta San Francesco, a popular spot with hikers on the island. Photograph: Alessandro Cini
When the study began, the island’s human population temporarily doubled in size, as teams of scientists fanned out across the scrubland tracking bees. Then came the ban: they closed hives on selected days during the peak foraging period, keeping the honeybees in their hives for 11 hours a day. Local people were sceptical. “For them, we were doing silly and useless things,” says Dapporto. But the results were compelling.
“‘Wow,’ was my first response,” says the lead researcher, Lorenzo Pasquali, from the University of Florence. When the data came together, “all the results were pointing in the same direction”.
A wide variety of plant species thrive on Giannutri. Photograph: Giuseppe Nucci
The findings, published in Current Biology earlier this year, found that over the four years after the honeybees were introduced, populations of two vital wild pollinators – bumblebees and anthophora – fell by “an alarming” 80%. When the honeybees were locked up, there was 30% more pollen for other pollinators, and the wild bee species were sighted more frequently. Scientists observed that the wild species appeared to take their time pollinating flowers during the lockups, displaying different foraging behaviour. “The effect is visible,” says Dapporto.
Global bee battle
In terms of sheer abundance, the western honeybee (Apis mellifera) is the world’s most important single species of pollinator in wild ecosystems.
Originally native to Africa, the Middle East and southern Europe, honeybees have been shipped around the planet by humans to every continent except Antarctica. The battles playing out on this small Italian island are likely to be echoed in ecosystems everywhere.
While the number of honeybees is increasing (driven by commercial beekeeping) native pollinators are declining globally due to habitat loss, climate breakdown and use of chemicals in farming. But we are only beginning to understand how the great honeybee boom could also take a toll on wild pollinators.
Honeybees compete with wild pollinators for limited food sources in ecosystems around the world. Photograph: Giuseppe Nucci
In southern Spain, where honeybee numbers have more than tripled since the 1960s, research shows managed honeybees spilling into flower-rich woodlands after the orange crop has bloomed. The result: increased competition with wild pollinators.
During California’s annual almond bloom, about 90% of the US’s managed honeybees are recruited in to pollinate, with beekeepers trucking hives across the country to meet demand. “For this approximately month-long period, the impact of honeybees on native pollinators is likely huge,” says Dillon Travis from the University of California San Diego. During the off season – when honeybees are less in demand – beekeepers often keep them in wild ecosystems. “Native pollinators need to compete with millions of honeybees for limited food sources.”
Most of the US’s managed honeybees are recruited in to pollinate during California’s almond bloom. Photograph: John Schreiber/Alamy
If conditions are right, honeybees go feral and set up colonies in the wild. A 2018 study looking at the presence of honeybees in natural ecosystems found them in 89% of sites.
In California, feral honeybees are increasingly turning up in vast numbers in natural ecosystems hundreds of miles away from the almond fields.
Honeybee takeovers
Each spring, after the winter rains, San Diego’s coastal scrub landscape bursts into life. Sagebrush, white sage and buckwheat unfurl their leaves, throwing sweet aromas into the hot air. These sights and smells greeted graduate student Keng-Lou James Hung when he started studying this area of southern California in 2011, aged 22, after a well-regarded biologist told him it was one of the richest bee habitats on Earth.
Keng-Lou James Hung in southern California, where he discovered that feral honeybees removed about 80% of pollen during the first day a flower opened. Photograph: Jena Donnell
The landscape has all the hallmarks of a pristine ecosystem: no tractor has tilled the land, no cattle grazed it; few humans tread here. “You can equate it to primary growth Amazonian rainforest in terms of how intact and undisturbed the ecosystem is,” says Hung.
When Hung began his research, however, what he discovered flummoxed him. “I got to my field sites and all I was seeing were honeybees,” he remembers. “Imagine as an avid birder: you get to a pristine forest and all you are seeing are feral pigeons. That’s what was going on with me when I set foot in this habitat. It came as a shock.” Honeybees were everywhere – nesting in utility boxes, ground squirrel burrows and rock crevices.
The coastal scrub landscape of southern California, where feral honeybees thrive. Photograph: Keng-Lou James Hung
In July, Hung – now an assistant professor at the University of Oklahoma – published a paper finding 98% of all bee biomass (ie, the weight of all bees) in that area were feral honeybees. They removed about 80% of pollen during the first day a flower opened, according to the paper, published in the journal Insect Conservation and Diversity.
Such high rates of pollen extraction leave little for the more than 700 species of native bees in the region, which need pollen to raise their offspring. Some of those species have not been seen for decades.
Hung believes honeybees’ social structure gives them the edge. Using the “hive mind”, they communicate the locations of plants and remove most of the pollen early in the morning before native bees begin searching for food. Most other bees operate as single agents, making decisions in isolation.
“It’s like a local grocery store trying to compete against Walmart,” says Hung. “Once they’ve escaped and established themselves there’s very little we can do to really stop honeybees. They’re very powerful and resilient creatures.”
Cactus bees collect pollen from the prickly pear cactus. Photograph: Keng-Lou James Hung
In 1956, some experimental “Africanised” honeybees were accidentally released from a research apiary in São Paulo, Brazil, spreading out across south and Central America and into California. Their expansion has been described as one of the “most spectacular biological invasions of all time”.
Wider ecological effects
Habitat fragmentation, chemical use in farming and rising temperatures are key drivers of pollinator declines, but in areas such as in San Diego it is likely honeybees are also a significant contributing factor. “It is very difficult to imagine a scenario where a single species can remove four-fifths of all the pollen … without having too much of an impact on that ecosystem,” says Hung.
Not only is it bad for native wild bees, it can have effects throughout the ecosystem.
Studies have confirmed that plants in San Diego county are less healthy when pollinated by non-native honeybees. Potential impacts include fewer seeds germinating, and those that do may be smaller and produce fewer flowers. “This may create an ‘extinction vortex’,” says Travis, where less-healthy plants breed over generations until they can no longer survive. “I am unaware of any studies that determined that honeybees are beneficial where they are not native, excluding agricultural areas,” he says.
In some parts of Australia and America – where honeybees are not native – they can reach densities of up to 100 colonies per square kilometre. In regions such as Europe, where they are native, the picture is different.
Wild European honeybees in Monmouthshire, Wales. About a fifth of the UK’s honeybee population is estimated to be wild. Photograph: Nature Picture Library/Alamy
There are about 75,000 free-living honeybee colonies across the UK, according to research last year, which was the first to quantify the density of these colonies. Based on these estimates, more than 20% of the UK’s honeybee population could be wild-living. “In Europe, the honeybee is a native species and low densities of wild-living colonies are natural components of many ecosystems,” says researcher Oliver Visick from the University of Sussex.
Visick has found densities of up to four wild-living colonies per square kilometre in historic deer parks in Sussex and Kent. “At these densities, wild-living colonies are unlikely to have a negative impact on other wild pollinators,” he says.
In ecosystems where honeybees are introduced, scientists say there should be more guidance on where large-scale beekeepers keep their hives after crops have bloomed to reduce their impact on native species. In other areas, such as islands, relocation or removal may be feasible.
The honeybee-free island
On Giannutri, when researchers told national park authorities their results they banned bee-keeping on the island.
The island, which is part of the Tuscan Archipelago national park, has been honeybee-free for more than a year and may now serve as a cautionary tale to other protected areas planning to introduce honeybees. Since the hives were removed, at least one of the species scientists have been monitoring appears to have slightly increased.
When the honeybees were locked up, there was 30% more pollen on Giannutri for other pollinators. Photograph: Giuseppe Nucci
The story unfolding on this little Italian island and the scrublands of San Diego shows that honeybees may not be the universal environmental stewards we paint them to be, and challenges the popular view that they are the best way to save nosediving pollinator numbers. Unchecked, they can cast a long shadow over fragile ecosystems that some might believe they help preserve.
When the scientists returned to Giannutri, “It was a bit weird to go back to the island this year without the honeybees around. We were used to seeing them everywhere all over the island,” says Pasquali. “I was happy to observe the island in this new condition.”
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