US bumblebees in 'alarming' decline

Grim outlook for 'important pollinators'

US researchers have announced that numbers of four species of Stateside bumblebees have declined to the point of extinction, and have fingered a pathogen genus thought to be responsible for a similar collapse in honeybee populations worldwide as a contributory cause.

A team led by Sydney Cameron of the University of Illinois conducted a three-year survey of eight species at 382 sites across 40 states, comparing the resulting data with 73,000 historical records.

The sobering conclusion is that "the relative abundances of four species have declined by up to 96 per cent and that their surveyed geographic ranges have contracted by 23–87 per cent, some within the last 20 years".

Speaking to Reuters, Cameron described bumblebees as "the most important pollinators of native plants", which also play an crucial role in pollinating blueberries, cranberries and tomatoes.

Significantly, the team found "declining populations have significantly higher infection levels of the microsporidian pathogen Nosema bombi". The related Nosema ceranae has been associated with Colony Collapse Disorder, which has seriously affected honeybee numbers worldwide.

In 2007, Professor Dave Goulson of the UK's Bumblebee Conservation Trust warned that Britain had already lost three of its 50 bumblee species in the last 50 years, and 10 were "severely threatened", while two were "teetering on the edge of extinction and could be gone in five to 10 years quite easily".

While Goulson attributed this to "pesticides and agricultural intensification", the US research now suggests a possible link with Nosema fungi.

Whatever the ultimate cause of the bumblebee's woes, Cameron concluded: "This is a wake-up call that bumblebee species are declining not only in Europe, not only in Asia, but also in North America."

Cameron's findings are published in the Proceedings of the National Academy of Sciences (abstract here). ®

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