Secrets of Resistant Varroa Revealed

New research by Rothamsted has revealed the different gene mutations that have enabled varroa mites to become resistant to acaricides, including pyrethroids (such as the active ingredients of Apistan and Bayvarol). The findings have also helped explain Vita’s earlier observations about differing patterns of resistance across the world.

Tau-fluvalinate is a pyrethroid that can kill vulnerable mites by overstimulating their nervous systems. It interferes with sodium channel proteins that are involved in generating electrical signals in nerve cells.

Earlier research showed that resistance to tau-fluvalinate in central and southern England evolved through a mutation of a single base in the varroa’s DNA. This latest research has shown that a different mutation evolved in resistant varroa mites in the USA.

Dr Max Watkins, Technical Director of Vita (Europe) Ltd, explained: “In our ongoing studies of resistance to pyrethroids, we noticed that the pattern of resistance in the USA was different to that of the UK which was different again to that of continental Europe. We have long suspected that different mutations are responsible for these variations.

“In continental Europe, the graphs plotting the amount of tau-fluvalinate required to kill the mites over time were a very different shape to those in Britain. Investigations in the USA suggested a third pattern, that is, a third mutation, distinct from the first two. This new research has precisely identified the difference between the UK and USA evolutionary resistance paths.”

The practical implication for beekeepers is that resistance evolves only when mites are exposed to a single treatment type over many years. Therefore, by alternating treatments and using Integrated Pest Management techniques, as recommended by Vita, the evolution of resistance can be delayed or even prevented, enabling the first generation varroa-control products like Apistan using tau-fluvalinate to continue to be effective.

Watkins continued: “The Rothamsted researchers say they can now develop diagnostic screening tests to analyse individual mites for the presence or absence of the mutations. That would be extremely useful, although I suspect that these will have to be laboratory, rather than hive-side, tests. This is excellent work and we look forward to hearing more results from this study. Meantime, Vita plans to continue its monitoring of acaricide resistance in Europe.”

The Rothamsted research was carried out in collaboration with scientists working in Spain, the USA and Germany). The study is published in the journal PLOS ONE.