A major investigation into a deadly threat to the honeybee has identified two common infections working together as the cause
Colony Collapse Disorder [CCD], that sees seemingly healthy honeybee colonies that go into sudden, steep decline, has been one of the prime causes of concern for beekeepers and farmers of the huge range of crops that depend on bees for pollination since it was identified in 2006. Now a group of biologists have completed a study that claims to have found the cause: a combination of two common infections - one fungal, one viral - working together to create a condition far more serious than either would in isolation.
The researchers used mass spectrometry techniques to identify proteins in the remains of bees from collapsed and failing hives from a wide geographical area , separated by thousands of miles, as well as control colonies from Australia, which has no CCD, and isolated hives in Montana that have no contact with other honeybees and have also not reported any CCD.
Of 900 different species of invertebrate-associated microbes found, 121 were suspected of infecting bees and insects. Twenty-nine of those were specific to bees and they became the focus of the analysis, particularly viruses, fungi and microsporidia (a kind of single-celled fungus) called Nosema.
A review of suggested causes including the varroa mite, insecticides, Israeli acute paralysis virus and other diseases were eliminated when they were found not to occur in all of the CCD colonies.
One group of diseases, the invertebrate iridescent viruses [IIV], were found to be present in 100 per cent of cases, but also in some strong colonies. A high correlation was found between Nosema and IIV in collapsed colonies, but finding Nosema alone was not found reliably to predict collapse.
To test the correlation, newly born bees were caged and fed a common type of Nosema (Nosema Ceranae, originally found in the Asian honeybee but now also seen in the European bees found in domestic and commercial beehives around the world), or a dose of IIV, or both, or none. The rate of deaths increased in those fed a combination of the two pathogens, but those fed only one or the other survived for the same length of time as the control group, who remained free of either infection.
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