Varroa Research

Two recent pieces of research throw more light on the question of the long term co-existence of Apis mellifera and Varroa destructor.

Dr Stephen Martin of Sheffield University spoke at the BIBBA meeting at Stoneleigh in April on the topic of Varroa tolerance and resistance.

It is now commonly accepted that it is the viruses for which Varroa is a vector which kill colonies. Viruses can exist in bees without causing problems—a condition named “inapparent infection”. If they were ingested, it would take about 100,000,000,000 virus particles to kill a bee. When transferred directly into the bee’s haemolymph by a Varroa mite, only 100 particles are required to cause disease. Infected bees often die away from the hive, leaving it empty, apart from the queen and a tiny number of attendants. Dr Martin then went on to speak of mite resistance to pyrethroids. There are three ways in which resistance could have developed:

1. by growing a thicker cuticle.

2. by producing a detoxifying enzyme in the blood to counteract the pyrethroid.

3. by making changes to the sodium channel in the cell walls, so that the pesticide cannot enter the cells.

Recent research suggests the third method is the route by which resistance has occurred, and that this happened in Sicily in just one mite, and all resistant mites are descended from this single mite. This logically means that Beekeepers are not responsible for the spread of resistant mites because of their misuse of chemicals, but because of their misuse of bees! Resistant mites have been spread around by beekeepers importing bees, in the same way as Varroa first reached these shores. All Varroa mites are virtually clones of one-another, since brother-sister mating means that they are genetically identical to one another. Thus, once having developed resistance by the sodium channel route, Varroa will never lose it. Bayvarol and Apistan will never work again, once resistance becomes established in an area.

Thanks to Jim Ryan of the “Irish Beekeeper” for that report—via BEES.

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