Posted 04 Sept 04
Silent spring in northern Europe ... part 2
|Reproduced with kind permission from|
|Bees for Development Journal 72 (Sept 2004)|
©Bees for Development www.beesfordevelopment.org
We received considerable correspondence from readers following Börje Svensson’s Silent Spring in Northern Europe in BfDJ 71.
Further letters to The Editor are welcome.
We had similar experiences here. I lost six out of ten hives, a friend six out of six and another 17 out of 25. In most cases I am sure it was due to virus damage, and the inability of the bees to keep up with the queen's egg laying. As a result colonies became weak, dwindled and all that was usually left were combs of dying emerging bees. No problem with Varroa control itself: the thymol-based Apiguard worked well.
I have received similar stories from many other countries and I am waiting to hear from Brenda Ball about how long viruses can remain inactive or dormant in hive parts ready to re-infect bees. This I am sure must be a problem.
John Phipps, Greece"
Brenda Ball, virus expert working at Rothamsted Research, UK, replies
I've heard of increased bee losses in Germany and France in the past year but I'm not aware that anyone has identified any particular virus infection as being responsible. Do you have any specific information about this? The viruses of bees do not persist for long outside the body of the bee. Even larvae killed by sacbrood virus fail to cause infection after a few weeks when fed to other larvae. There is absolutely no need to sterilise any equipment. The viruses live in the bees the whole time - as latent or unapparent infections and only occasionally multiply sufficiently to cause any problem - that is until Varroa destructorcame along. The mite just acts as a hypodermic syringe transmitting virus from severely infected to healthy individuals when it feeds. As viruses do not respond to antibiotics etc, the only way to reduce their prevalence is by knowledge of their epidemiology in association with the mite and disrupting the transmission at the right time of year. When you intervene depends on the virus.
I was very interested in the article by Börje Svensson, regarding the high loss of his bees during the winter 2002/2003. Not knowing the weather conditions during the previous summer and autumn, I cannot offer an explanation for the losses except to cite similar examples that have occurred during the time that I have kept bees, since 1946. I have recently completed a history of beekeeping in Norfolk, eastern England, covering the last 80 years since Norfolk Beekeepers' Association was reformed in 1923 after the First World War. The annual reports have usually included comments on the previous season and, together with my own observations of weather and honey crops, these have shown that, without exception, an unusually cool, wet summer and autumn have been followed by very high losses starting at the turn of the following year. These colonies have perished surrounded by plenty of stores and often, if the losses have occurred after mid-January, with patches of brood - much of it sealed. The losses of colonies have always been greater with colonies that had over-yeared queens. The conclusion I have reached, based on my own observations, is that queens under these weather conditions, cease laying towards the end of July and the colonies go into winter with only old bees that reach the end of their lives before they can be replaced by young bees reared after the turn of the year, although, in some cases, they have made late attempts to do so. The dead colonies have usually had only a handful of worker bees together with a queen, as cited by Börje.
To give examples from recent years; my losses during the winter 1985/86 were 50%; going into winter with 126 colonies and losing half of them, of the remainder only 40 gave any crop that year. Nationwide, it appears that the losses increased in severity going further north and west. Being a member of Bee Farmers' Association I heard details of losses over these islands including a commercial beekeeper in Scotland who lost all but five of his 400 colonies. More recently, in 1999, I lost 27 out of 42 colonies that went down to winter, and another bee farmer in the North of England told me his losses were even greater. In both these cases, and in local beekeeping history, high losses have always followed the summer and autumn conditions already stated. I think the losses due to the use of insecticides, of which I have had experience, are more immediate; in this respect I think that the use of such chemicals is far more widespread in this part of England than occurs in the Sala District of Sweden.
I do not know the weather conditions in the summer and autumn of 2002/2003 in Sweden, and can only cite similar conditions in Norfolk and the conclusions I have drawn. In the meantime, my commiserations to Börje and a hope that this occurrence is one-off.