What causes bumblebee populations to plummet all over the world?

Question of the Week, 27.1.2011

Bumblebees comprise a genus of some 250 species. Weakened by inbreeding and disease, they have died off at an astonishing rate over the past 20 years with US populationsdiving more than 90 per cent. Bumblebees are major pollinators of flora, and if they continue to disappear many traditional native plants will suffer, reproduce less, and cause a ripple effect of sweeping changes to the countryside. Some types of clovers, vetches and many rare plants have already started to disappear from traditional areas. In addition to the adverse effect on the environment, the demise of the bumblebee could have a serious impact on trade. Many crops depend on bumblebees for pollination and some, such as broad, field and runner beans and raspberries, are heavily dependent on them. Without the insects there would be little or no crop to harvest.

The problem of bumblebee decline was first recognized in Britain in the 1950s. Since then, numerous studies have documented long-term deteriorations in species ranges, with habitat loss being the generally accepted cause. However, recent reports confirmed dwindling genetic diversity and a worrisome accelaration of bumblebee decline. It is often associated with the bee pathogen Nosema bombi, a type of fungus with which an increasing percentage of bumblebees is infected. Still, various explanations remain possible, as high parasite prevalence may simply indicate that the declining species naturally support high populations of the parasite.

Read more:

Mark J. F. Brown, Conservation: The trouble with bumblebees

Nature 469, 169–170


Thomas Jagau