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A female worker bee removes a Varroa infested male drone pupa from a cell
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PHOTO GALLERY: Breeding bees resistant to the varroa mite

Louis Rummer-Downing

22nd October, 2010

British honeybee populations have been decimated by the varroa mite, but hidden inside hives in deepest Cornwall, something very special is happening...

Beekeeper Rodger Dewhurst is not just in it for the money, or the honey; he has taken it upon himself to save our honeybees from the clutches of the varroa mite, by breeding varroa-tolerant native bees, Apis mellifera mellifera.

Varroa mites (Varroa destructor) have spread throughout mainland UK since their appearance in 1992. They are just 2mm wide and feed off developing bees in brood cells and on adults by attaching themselves to their fleshy tissue. They weaken the bee's immune system and are vectors for other viruses and disease such as Deformed Wing Virus. Just 2,500 mites in a colony of more than 30,000 bees can prove fatal.

Native bees

I met Rodger at the Royal Duchy College near Camborne, where he has an apiary of more than 15 hives, and teaches beekeeping. 'When we got varroa in 1992 I recognised that we would lose our native bee species. We needed people like the bee-breeders group I belong to, Cornwall Bee Improvement and Breeders Group, to keep those bees alive. The belief within our breeding group is that native bees have adapted to our environment and have learned to live with the extremes of temperature, climate and foraging opportunities, making them the best bees to survive in this country.'

Within their hives, native bees are known to store two weeks' worth of pollen, the protein-rich food that is vital for their development. Thus, they can carry on replenishing the colony's population, especially important in the spring and summer when worker bees will only live up to six weeks. The breeders group has even reported native bees flying at temperatures of 6C, 3C lower than it was believed possible for them to do so. Now, with more than 30 of these native-bee-breeders groups across the UK, their popularity is on the rise.

The understanding that honeybees have the capacity to defend themselves against varroa inspired Rodger to start his research.

'I had been beekeeping since the age of 12, and had always wanted to research more into bees, so when the opportunity presented itself to change career I took it, and expanded our honey and bee products business, Gwenen Apiaries.'

In fact, his honey business has become very respected, winning a prize in the Great Taste Awards and supplying Stein's Deli in Padstow. 'But,' Rodger says, 'while it's my livelihood I need resilient bees, so I research how they interact with varroa and breed from the best.'

Biting back

Rodger has been tirelessly breeding these ‘remarkable qualities' into his bees for 18 years in an attempt to allow them to manage varroa mites more effectively. These behaviours, called ‘grooming', ‘biting' and ‘hygienic cleaning' have been developed by the bees throughout their 10-million-year history, but are now being adapted again to fight off varroa mites.

'If a bee is infested with varroa it will sense the mite on its body and groom it off. If a bee manages to grasp that mite, it will use its strong mandibles to crush it, break the legs or cut the mite's mouth off.' This behaviour is the ‘grooming' and ‘biting' working together. In one colony, Rodger even found 70 per cent of the dead mites damaged by biting bees.

'I've seen infested bees pounced on by guard bees as they attempt to enter the hive. The guard bees mount them and shake the infested bee vigorously to dislodge any mites on their bodies, then they chase them away,' Rodger adds. This ‘grooming' behaviour is very important to the health of a colony and the first defence against varroa attack. 'I've noticed bees display this grooming behaviour only for other bees to become very interested and then initiate social grooming "parties".'

What this could mean is that this behaviour is not only passed down through genetics, but through learned behaviour, from one bee to another.

Rodger's bees also display ‘hygienic behaviour': if a developing larva becomes infested with varroa, a hygienic colony pulls that larva out of the hive, thus disposing of it. This breaks the breeding cycle of the mite and reduces any infection that the varroa may have spread.

To identify which bees out of his 80 colonies are the best at controlling varroa, Rodger can spend many hours recording what he finds on the floor of every hive he inspects. 'When a mite is removed by a bee, or a bee removes an infected bee larva or pupa, some of the remains will be found on the floor. It is my job to interpret the debris left on the floor, recording whether the mite has been bitten or brushed off.'

Through a well-managed and incremental process, Rodger has reduced the amount of varroa treatment he uses in some of his remotely placed hives. 'To gain knowledge I must take risks,' he says. Though there is the potential to increase varroa count, a bee-breeder must be able to see how his or her bees perform naturally, always on guard in case treatment is needed. Rodger has not had to treat some colonies for nearly two years.

‘It has to be done. It's a no-brainer'

'Over 50 to 70 years we could develop a near varroa-tolerant bee population,' Rodger says. He accepts that with so many variable factors such as imports of foreign bees, new disease and climate change, we will always be aiding the bee in its fight for survival, but should give the bees the best opportunities to help themselves. He was awarded the Josef Stark Scholarship Foundation Award for his conservation work in 2008.

Rodger is searching for PhD funding to carry out research on varroa tolerance, and hopes that his work will prove how important ‘grooming behaviour' is. He also hopes to inspire other beekeepers to look for this amazing behaviour within their colonies. With work from people like Rodger and his bee-breeding group it is becoming more likely that we are securing a future for our honeybees.

Louis Rummer-Downing is a freelance journalist. A video on the varroa mite can be see here

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