The Amazon Pink Dolphin’s Voice: Honeybee decline linked to killer virus

Honeybee decline linked to killer virus

Parasitic mites wiping out bee colonies by transmitting deadly virus directly into the bloodstream of the bees, research reveals.

Varroa mite blood-sucking parasite at honey bee

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

The deadly link between the worldwide collapse of honeybee colonies and a bloodsucking parasite has been revealed by scientists. They have discovered that the mite has massively and permanently increased the global prevalence of a fatal bee virus.

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 thewidespread 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.”

Even if a colony is cleared of varroa mite infestation, the deadly DWV strain remains dominant. “That means the colonies will collapse very fast, so beekeepers must keep the varroa levels down: it’s even more critical than we knew before,” said Martin. Other research by members of the team, conducted in Devon, showed that even when the varroa mites are kept under control, the presence of the fatal DWV strain kills about 10% of colonies each year.

The varroa mite magnifies the impact of DWV for three reasons. First, it transmits the virus directly into the bee’s bloodstream as the parasite feeds. This means it bypasses all the bee’s natural immune defences which are deployed when the virus is transmitted via food or sexual contact. Second, the virus can massively multiply in the mite. And third, the DWV strain best suited to transmission via the mite rapidly comes to dominate and is a strain that is particularly harmful to bees.

“This work provides clear evidence that, of all the suggested mechanisms of honeybee loss, virus infection brought in by mite infestation is a major player in the decline,” said Ian Jones, at the University of Reading, who was not involved in the work. But Martin noted that the weakening of colonies through lack of food or the presence of damaging pesticides would make them more vulnerable to infestation.

Hawaii is a particularly significant bee-keeping location as almost all the queen bees used in the US are bred on the islands. The islands also have a significant macadamia nut industry, which is entirely dependent on bees for pollination. “The bees are dropping like flies in Hawaii: macadamia nuts may be about to get very expensive,” Martin said.

Source: The Guardian



Honey bees greatly benefit the human economy, as they pollinate crops and provide us with honey and other hive products. But in recent decades, the spread of appropriately named Varroa destructor mites has caused millions of honey bee colonies to perish, and many researchers have tried to determine ways to slow, or stop, the speedy destruction.

After the parasitic Varroa mite found its way into Hawaiian honey bee colonies in 2007, scientists from several organizations began a long survey of the islands’ bee populations. By following the mite invasion from the beginning, and finding exactly how the mites aided in colony destruction, they figured it would be possible to determine ways to aid bees in the future.

The researchers were particularly interested in the evidence of Varroa increasing prevalence of certain viruses. One of the five viruses the team watched for — deformed wing virus — greatly increased in areas the mite had populated. On Hawaii, deformed wing virus was detected in 6 to 13 percent of Varroa-free colonies, but prevalence of the virus increased to 75 to 100 percent of bees in colonies affected by the mite.

The Hawaiian bees were introduced to the archipelago back in 1857. The European honey bees came from California and were mostly managed, but feral colonies popped up on every island.Varroa was first discovered on Oahu Island in August 2007. A team surveyed the island bees in 2007-2008, and found 274 out of 419 untreated beekeeper colonies had collapsed. Feral colonies on the island also perished. Though quarantine measures were enacted, the mite was found on the Big Island in January 2009. People again tried to stop the spread, but eradication efforts failed.

“Just 2,000 mites can cause a colony containing 30,000 bees to die,” said Dr. Stephen Martin, of the University of Sheffield’s Department of Animal and Plant Sciences. “The mite is the biggest problem worldwide for bee keepers; it’s responsible for millions of colonies being killed.”

Deformed wing virus can be transmitted from bee to bee through feeding and sex, but the mites were able to change the virus to become more deadly, with exponentially greater viral loads and one virulent strain. Hawaiian colonies showed a progressive decrease in strain diversity. On Oahu — the island infected longest — there was only one strain detected in 2009. On Big Island, nine different strains were present in 2009, but only four strains were found one year later.

The research was conducted by scientists from the University of Sheffield, the Marine Biological Association, the Food and Environment Research Agency and the University of Hawaii, and was recently published in Science.


Bee-killing virus gets supercharged by mites

(Reuters) – Parasitic mites have turbo-charged the spread of a virus responsible for a rise in honey bee deaths around the world, scientists said on Thursday.

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”.

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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.”

Other factors – including fungi, pesticides and decreased plant diversity – are thought to play a role in colony collapse, but Ian Jones of the University of Reading said the latest findings pointed to the virus and mite combination as being the main culprit.

“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 said.

Jones, who was not involved the research, said the findings published in the journal Science reinforced the need for beekeepers to control Varroa infestation in colonies.

The threat to bee populations extends across much of Europe and the United States to Asia, South America and the Middle East, experts say.

Bees are important pollinators of flowering plants, including many fruit and vegetable crops. A 2011 United Nations report estimated that bees and other pollinators such as butterflies, beetles or birds do work worth 153 billion euros ($191 billion) a year for the human economy.

Source: Reuters

SELVA Vida Sin Fronteras acknowledges Kevin Schafer’s important contribution towards protecting the highly endangered Amazon pink fresh water dolphin. Title photographs of our “The Amazon Pink Dolphin’s Voice” were taken by Mr. Schafer. 

Editorial: SELVA-Vida Sin Fronteras


~ by FSVSF Admin on 11 June, 2012.

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