BBSRC-funded scientists at Rothamsted Research have made a discovery which could help in the fight against the parasitic Varroa mite, which is devastating to bee colonies. They have developed a test for the detection and management of resistance to an insecticide used to treat Varroa-infected honey bee hives.

There has been a significant decline in European honey bee colony numbers over recent years and hive infestations of the mite, Varroa destructor, are an important factor in contributing to this decline. One of the most effective treatments for removing the mites from a hive is the use of selective pyrethroid insecticides that are highly toxic to the mites, but safe for use with bees.

The intensive use of these compounds over the years has led to widespread resistance in Varroa populations, greatly reducing their effectiveness. Rothamsted Research scientists, who are strategically funded by BBSRC, have now identified the genetic change that causes this resistance in UK mite populations. They have also developed a diagnostic test that allows rapid monitoring of the frequency of resistant mites within individual infected bee hives. The test provides an accurate measure of resistance within Varroa-infected hives before treatment and hence it enables informed decisions of the likely effectiveness of the available treatments. The study is published today in the journal PLOS ONE.

The diagnostic test that Dr González-Cabrera and his colleagues have developed enables individual mites to be analysed quickly and accurately for the presence or absence of the mutation. The test is robust and can be applied to live or dead individual mites making it easy to assess the frequency of the mutation in infected hives by taking the debris from the hive and simply separating out the mites. Initial results using the test have shown that the mutation is only present at high frequency within hives that have a recent history of pyrethroid treatment. This indicates that the resistance mechanism is less frequent and widespread within Varroa infected hives than is generally thought. Therefore, by carefully monitoring the distribution and frequency of the mutation in local Varroa populations using the diagnostic test, it should be possible to develop a pro-active resistance management programme. Such programme could involve rotation of different products (including pyrethroids) aimed at maintaining a more effective control of this highly damaging pest.

Professor Lin Field, Head of Biological Chemistry and Crop Protection at Rothamsted Research, said: "Given that honeybees are an essential component of the nation's biodiversity and contribute to food security by pollinating some crops, it is vital that we identify the best possible management strategies of the Varroa mite. Our work contributes new tools in order to effectively manage the health and abundance of bee colonies."