Drones and Varroa

At the last meeting of South Cheshire Beekeepers Association, Bob Parsonage read out the letter from Roger Patterson published in the August edition of BBKA news. Roger was alarmed at the high incidence of poor queen-bees in recent years, and thought that this had to be related to varroa infestation. Most of us had not yet received our copies of the newsletter, but there was a general concern among the membership which coincided with what Roger Patterson was writing. There was not, however, a lot of knowledge about the facts of the effect varroa might have on the mating ability of drones and queen bees. I therefore undertook to do some research on the internet and report here my findings.

It quickly became clear that Roger’s concerns have long been shared by beekeepers in countries which had varroa before us – chiefly North America and Mainland Europe – and there has been a considerable body of research which confirms the fears. There is some disagreement between findings, probably due to the inevitably less-than-100% reliability of any research project. In an article published in the American Bee Journal in 2001, Collins and Pettis reported that varroa infestation did not affect the semen of drones, but it did reduce, almost to nil, their chance of living to mating age. These findings are contradicted by most other researchers: In particular a study by the Tübingen and Sao Paolo Universities in 2002 (Duay, de Jong, Engels – www.funpecrp.com) studied the ability of drones to fly the necessary long distances for a mating flight, and their sperm count. Using a small windtunnel (!) they found that most drones which had been infested by one adult female mite (I take this to mean during the larval stage before capping) were able to fly as long as unaffected drones. Those which had been infested by two adult mites were on average only able to fly a third as far. They then took a sperm count from the same drones and found that those infested by one mite had a quarter less sperm, those infested by two mites had only half the normal sperm-count.

This simply confirms what one might always have assumed: that varroa affects queen-bee mating. If varroa infestation is severe in an area, few drones would reach a DCA and even fewer would be able to mate successfully. This may cause queens’ mating flights to fail. The fact that many of us are cutting out drone brood in order to reduce infestation would seem likely to reduce the number of effective drones still further. However, this is not to say that the practice is wrong.

The article by Karl Showler in the same edition of BBKA News adds a further dimension to this. If, as he says, drones can fly several miles to DCAs (up to 15 kilometres, it is said) and are accepted readily into colonies to which they do not belong, then, as the favoured host of varroa mites, they are clearly the main means by which varroa spreads – to infect, or reinfect our hives.

In terms of practical beekeeping, I do not think this gives cause for panic, but rather re-inforces the need for all the measures we are taking at the moment. If drones not only attract varroa mites, but also spread them, we are right to cut out and destroy as much drone brood as we can. On the other hand, a beekeeper who wants to produce good mated queens must ensure that his/her colonies are as free from varroa as possible at the right time, and produce as many healthy drones as possible. We are still relatively lucky in Northern England to be able to use Bayvarol and Apistan effectively. I can find no indication, by the way, in any of the research I have come across, that the anti-varroa treatments themselves can affect drones’ mating ability. In American and European research, however, these two varroacides are largely ignored, presumably because resistance in those parts of the world is so widespread as to render them totally useless.

I have been impressed by the amount of information on the internet, and, indeed by the amount of research going on in the world into varroa and its various effects. It is disappointing, however, that British universities and research institutions are never mentioned as taking part in the research, or even attending conferences on the subject. I know we are just a tiny off-shore island, but this has not sheltered us from Varroa, and it is a shame that our information about the pest seems to be so parochial.

Peter Sutcliffe

CHESHIRE BEEKEEPERS' ASSOCIATION

Apes curamus et nos curant (We look after bees and they look after us)

Founded 1899

Registered Charity No. 227494

Drones and Varroa

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