A landscape photograph of the Tibetan Plateau

The Tibetan Plateau is the world's highest and largest plateau, standing at an average elevation of 4,500m above sea level and expanding over 2,500,000km² © Jan Reurick/flickr 

The quest for one of the world's oldest bumblebees

Mountains around Tibet are the greatest global hotspots of bumblebee diversity, including one of the oldest living bumblebee species, Bombus superbus.

There are about 260 known species of bumblebees worldwide. Most notably, the mountains around the Tibetan plateau, the world's highest and largest highland, are home to many of those species, including one of the world's oldest and least known bumblebee species, Bombus superbus.

'Bombus superbus may be one of the few truly endemic bumblebee species of the extreme habitats of the high Tibetan plateau,' says Dr Paul Williams, an entomologist at the Museum. 'We are using gene sequencing to discriminate species and to help identify them and reconstruct their ancestral relationships and distributions.'

Despite the region's importance, the animals that live there are still not fully understood for several reasons. These include the vast size and height of the location, political and cultural constraints, as well as sparse vegetation towards the north and the west, making it difficult to find bumblebees.

'The Tibetan Plateau has become familiar from television as a land of extremes - a place where it is possible to get sunburnt and frostbitten on the same day,' says Paul. 'Together with its encircling mountains, it has been a major cradle of diversification for bumblebees and the focus of recent research into the unique conservation challenges now faced in the region.'

Paul and his team have accurately identified Bombus superbus using modern DNA techniques and producing identification tools. They have also mapped the distribution of the species, are moving towards a preliminary bumblebee atlas and are assessing threat levels for conservation.

Despite public interest in the insects over the last two centuries, bees are generally difficult to distinguish. Different species often look similar, and even bees of the same species vary in appearance across their distribution ranges.

A worker of the B. superbus © Paul Williams
 

Finding the bees

Working in collaboration with two students from the Chinese Academy of Agricultural Sciences (CAAS), the Museum directed an expedition to a location where the suitable habitat was expected to occur.

The first B. superbus specimen, collected by a Russian explorer in the late nineteenth century, was labelled as having been found in Mongolia. But during a Chinese expedition undertaken a century after the initial finding, four B. superbus were found in the northern Tibetan plateau, raising questions about where the species really lives. It was probably found in northern Tibet, and the Mongolia label was added later as a mistake.

Thanks to technology such as GPS navigation, DNA sequencing, computer databasing and GIS mapping, it is now possible to locate the region.

There have since been sightings of thousands of bumblebee specimens in the Tibetan plateau. However, B. superbus was not one of them, leaving the distribution of the species an unsolved mystery.

Zhengying Miao, a scientist at CAAS, was collecting in a likely area of the Tanggula Mountains, near the centre of the plateau. At an elevation of more than 5,200 metres, it had a small stream, a patch of green and only a few flowers. There, feeding on the nectar of white flowers, were individuals of B. superbus. These were the first bees of their kind to be documented in situ.

Genitalia of a male B. superbus. Bumblebees are often identified through their genitalia. © Paul Williams.
 

The next steps

Although China has nearly half of the world's bumblebee species, they had not been systematically surveyed or mapped until recently.

China's interest in bumblebee species is driven mainly by the needs of commercial breeding for crop pollination. Bumblebees are no doubt one of the most important groups of pollinating insects in the world and therefore a valuable natural resource. China, like Europe, has already started breeding bumblebees and using them on fruit crops on local farms.

'There's a huge commercial concern for rearing colonies for artificial pollination of crops like tomatoes,' says Paul. 'It's working up to a point but in an effort to move bumblebees around the globe, there is a worry that other native bee populations may collapse.

'For example, we think that pathogens from European bumblebees may have been introduced into North America and hit the population of several species there quite hard, although this hasn't been confirmed. Similarly, the Bombus terrestris introduced to South America is pushing back the native species.'

While the answer may be to commercially rear native bees in each country, it is much more expensive and difficult to do so.

Intensive grazing in and around the mountains severely reduces the height and abundance of vegetation, which in turn affects the diversity of bees - an issue which has been overlooked by conservation © Carsten.nebel/wiki
 

Another aim of the investigation is to understand the evolution of bees in changing mountain ranges and climates.

Genetic analysis suggests that B. superbus is one of the oldest bumblebee species to have persisted in Asia. About nine million years ago, the connecting mountain ranges were uplifted and the climate cooled, providing corridors for early bumblebees to spread through the mountain ranges to new areas of Europe and diversify.

'Analyses of their current distributions and the evolution of their climate preferences support the idea that these bumblebees dispersed outwards along corridors of mountain meadows through the high Eurasian mountain chains,' says Paul.

'What's more, its habitat in Tibet must have been stable for a long period of time, more than ten million years, for it to have survived there. The plateau has relics of these very early groups of bumblebees, so understanding B. superbus will help us understand the old world high alpine ecosystems.'

However, there are growing concerns about climate warming in the alpine zone. The Tibetan Plateau is warming three times faster than elsewhere, leading to the loss of high glaciers and streams which feed the small islands of flowers that support the bees. Alpine bees could be listed as near threatened as their source of food is eradicated.

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