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Cause of decline in wild bumblebee populations identified (Feb.)



Hindu, Delhi, Thursday 20th February 2014

Is there a connection between the declining population of honeybees (which is tackled by active management by beekeepers) and bumblebees, which are wild pollinators?

A study published today (February 20) in Nature has found not only a global decline of bumblebees but also evidence to prove that the pathogens that infect honeybees have started infecting the wild pollinators.

M.A. Fürst, the lead author of the study from the Royal Holloway University of London, and others used a combination of field data and laboratory experiments to clearly demonstrate that emerging infectious diseases (EID) affecting honeybees are indeed affecting wild bumblebees as well.

They found the prevalence of deformed wing virus and Nosema ceranae in honeybees and bumblebees were indeed “linked.” “[Honeybees] is the likely source of at least one major EID in wild pollinators [bumblebees],” they note. Deformed wing virus (DWV) and N. ceranae are the major culprits in causing a decline in honeybee populations

The ability of the pathogens to jump from one pollinator species to another is a major concern as these insects play a vital role in agriculture. The ability to jump interspecies is simple as both pollinators “share diverse foraging sites.” The same is the reason for pathogens to move laterally from commercial bumblebees to wild bumblebees.

Analysis of genetic variation in the virus showed that bees collected at the same site shared more closely related virus strains than bees from different sites, indicating on-going disease transmission.

The transfer of emerging infectious diseases from honeybees to bumblebees is a “major cause of mortality” of bumblebees wherever managed bees are maintained, they note.

In controlled inoculation experiments carried out by the researchers, they found of the two pathogens (DWV and N. ceranae), the DWV was infective in just 21 days compared with controls. Also, the deformed wing virus, as the name suggests, causes the typical problems in bumblebees as they do in honeybees.

The overtly infected bumblebees produce non-viable offspring and suffer from reduced longevity. Both these factors combined result in rapid decline in their population.

That field estimates showed conservative prevalence should not be surprising considering that insects with deformed wings would not be able to fly and hence not captured.

Controlling the spread is a big challenge as there is a global trade of both honeybees and commercial bumblebees. Though monitroring and controlling EIDs is another big challenge, the need to do it is imperative.