Mite Helps a Bee-killing Virus Spread

(The following brought to us by the American Bee Journal.) June 4, 2012

The spread of a parasitic mite across Hawaiian honeybee colonies has enabled a virus to thrive within colonies of these valuable insects, researchers report. In other parts of the world, the appearance of both the mite and the virus has coincided with major colony deaths, though this has only occurred on Hawaii where the mites have been established for at least two years. The mite's arrival there, where it has only spread on certain islands, is relatively recent. Stephen Martin and colleagues took advantage of this unusual opportunity to monitor Hawaiian honeybees during the invasion and learn how the virus was spreading and evolving. Deformed wing virus (DWV) can infect bees by itself, but the Varroa mite helps things along by acting as a host and incubator.

The mites' feeding behavior also allows the virus to be transmitted directly into the bees' circulation system. The authors report that the introduction of the Varroa mite has increased the prevalence of  DWV from about 10 percent to 100 percent within honeybee colonies. The amount of virus in the bees' bodies also skyrocketed, while the diversity of the viral strains did the opposite. In fact, just one DWV strain is now dominant in Varroa-infected colonies. The authors conclude that the global spread of Varroa has selected DWV variants that have emerged to allow DWV to become one of the most widely distributed and contagious insect viruses on the planet.

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