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.
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