Killer Insect Virus Helping to Decimate World's Bee Population

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Common Dreams

Killer Insect Virus Helping to Decimate World's Bee Population

Weakened by habitat loss and chemical pesticides, bloodsucking parasite wreaking havoc on vital pollinators

by
Common Dreams staff

Varroa destructor is a bloodsucking parasite that feeds on honeybees and has spread globally, destroying colonies worldwide. (Photograph: Alamy)

A new study published in the journal Science has revealed that, in addition to the destruction of natural habitats and the widespread use of industrial chemical pesticides, the global bee die-off witnessed in recent years is also caused by a deadly virus carried by bloodsucking parasitic mites.

The report in Science is available to subscribers only, but according to The Guardian's Damian Carrington, the researchers who conducted the study warn that the virus, called Varroa destructor and carried by the varroa mite, is now one of the "most widely distributed and contagious insect viruses on the planet." Equally troubling, the new dominance of the killer virus poses an ongoing threat to colonies even after beekeepers have eradicated the mites from hives.

The research team, led by Stephen Martin of Britain's University of Sheffield studied the impact of Varroa in Hawaii, which the mites have only recently invaded.

"This data provides clear evidence that, of all the suggested mechanisms of honey bee loss, virus infection brought in by mite infestation is a major player in the decline," he told Reuters in a telephone interview.

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Reuters: Bee-killing virus gets supercharged by mites

Bee populations have been falling rapidly in many countries, fuelled by a phenomenon known as colony collapse disorder. Its cause is unclear but the Varroa mite is a prime suspect, since it spreads viruses while feeding on hemolymph, or bee's "blood".

To clarify the link between mites and viruses, a team led by Stephen Martin of Britain's University of Sheffield studied the impact of Varroa in Hawaii, which the mites have only recently invaded.

They found the arrival of Varroa increased the prevalence of a single type of virus, deformed wing virus (DWV), in honey bees from around 10 percent to 100 percent.

At the same time the amount of DWV virus in the bees' bodies rocketed by a millionfold and there was a huge reduction in virus diversity, with a single strain of DWV crowding out others.

"It is that strain that is now dominant around the world and seems to be killing bees," Martin said in a telephone interview. "My money would be on this virus as being key."

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The Guardian: Honeybee decline linked to killer virus

Martin noted that the weakening of colonies through lack of food or the presence of damaging pesticides would make them more vulnerable to infestation.

The varroa mite's role means the virus is now one of the "most widely distributed and contagious insect viruses on the planet", the researchers warned. Furthermore, the new dominance of the killer virus poses an ongoing threat to colonies even after beekeepers have eradicated the mites from hives.

Varroa destructor has spread from Asia across the entire world over the past 50 years. It arrived in the UK in 1990 and has been implicated in the halving of bee numbers since then, alongside other factors including the destruction of flowery habitats in which bees feed and the widespread use of pesticides on crops. Bees and other pollinators are vital in the production in up to a third of all the food we eat, but the role the mites played was unclear, as bacteria and fungi are also found in colonies along with the viruses.

But the mite's arrival in Hawaii in 2007 gave scientists a unique opportunity to track its deadly spread. "We were able to watch the emergence of the disease for the first time ever," said Stephen Martin, at the University of Sheffield, who led the new research published in the journal Science. Within a year of varroa arrival, 274 of 419 colonies on Oahu island (65%) were wiped out, with the mites going on to wreak destruction across Big Island the following year.

A particular virus, called deformed wing virus (DWV), was present in low and apparently harmless levels in colonies before the mites arrived, the scientists found. Even when the mites first invaded hives, the virus levels remained low. "But the following year the virus levels had gone through the roof." said Martin. "It was a millionfold increase – it was staggering."

The other key finding was that one DWV strain had gone from making up 10% of the virus population to making up 100%. "The viral landscape had changed and to one that happened to be deadly to bees," Martin said, noting the DWV strain was the same one found around the world. "There is a very strong correlation between where you get this DWV strain and where you get huge amounts of colony losses. We are almost certain this study seals the link between the two." [...]

Martin noted that the weakening of colonies through lack of food or the presence of damaging pesticides would make them more vulnerable to infestation.

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