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Severe Bee Losses in Germany:
Somewhat Expected and Not at All Mysterious
Last year's news about severe bee losses in the USA not only scared beekeepers but the public too. In spring 2007, beekeepers' associations and bee institutes could still give an all-clear signal, because everything was ok in Germany after overwintering. But this spring things look different!
Already in early summer of 2007, the bee institutes warned against possible danger and asked the beekeepers to treat their bee colonies in time against Varroa infestation. Because of the relatively warm winter in 2006/2007, Varroa mite populations had started to grow earlier than usual. Actual data confirmed these concerns. According to conservative estimates by the Working Group of the Bee Research Institutions, around 30% of the colonies in Germany could have died. Things don't look better in Austria, Italy and Switzerland. Five years ago, some beekeepers lost everything; however, others lost nothing. Similar to prior losses, southern regions seem to be mainly affected.
Many Varroa Mites Found and Viruses Too
The results of nationwide monitoring to investigate the initial causes of colony losses and the analysis of case histories of some affected colonies are not yet available. However, actual evaluations and examinations give a first impression. The National Reference Laboratory (NRL) at CVUA Institute of Animal Health in Freiburg examined bees of collapsed colonies of nearly 80 apiaries and 350 colonies from all over Germany. In more than 90% of empty hives, masses of Varroa mites (>100% infestation) could be found on the remaining bees and brood. To a similar large extent, Deformed Wing Virus infected the bees. Quite surprising was the presence of Acute Paralysis Virus in half of the affected apiaries. Twenty years ago, this virus was first associated to colony collapses in Germany. However, such a massive presence of this virus has not been observed for a long time. The Israeli type of this virus found with some cases of the Colony Collapse Disorder (CCD) in the USA seems to be not involved. Until now less than 25% of the cases with diarrhoea was associated with Nosema microsporidia. Therefore, Nosema ceranae, the recently imported and already spread type of this pathogen, can be excluded as a causal agent. Even if it cannot be definitely concluded whether the pathogenic agents found are the initial cause or the result of the collapse, they are closely connected to the sequence of events leading to colony death.
Treatment Often Applied Too Late
The affected beekeepers gave us a description of their Varroa control methods. Many of them kept to the recommendations of the experts, but very often treatments were applied too late. Late treatments, which in earlier years did not cause any problems, were fatal for many colonies this year. In many cases by mid-August, mite infestations reached a level that damaged the bees’ health. Furthermore, viruses transferred by the mites were spread throughout the colony. Therefore killing mites late in the season showed only a minimal success for colony survivorship. Apart from the important factor of colony management, the timing of colony deaths depended on location. Here the environmental conditions like climate, food availability and last but not least bee density played an important role. The distance from bee colonies to others in the neighbourhood can be an essential factor for the spreading of the Varroa populations. Damaged bees fly to neighbouring colonies bringing along mites and viruses. Furthermore bees from healthy colonies are robbing dying colonies and can quickly acquire a large population of immigrant Varroa mites.. In this way, a healthy colony can quickly turn into an ill one. In areas where many colonies are collapsing within a small area, the problem can initiate a kind of domino effect because of the ease of mite transfer between colonies. In addition, the more colonies and apiaries that are affected, the faster the problem develops.
Complicated Interactions
On the phenomenon called "Colony Collapse Disorder" (CCD) in the USA, empty beehives, or those left with only a handful of bees and in most cases large amount of brood and stored food, surprised beekeepers. Even strong colonies can apparently collapse within a few weeks. The collapse seems to be mysterious and provokes ambiguous attempts of explanations that can even reach the public. Without any doubt, stressors like the persisting environmental pollution and reduced food diversity, in addition to management and breeding problems, have important influences on the susceptibility of an organism. The more the stressors increase the more disastrous are the effects of infestations by mites, viruses, and bacteria.
Until end of May other diseases like Nosema induced diarrhoea could cause more damage. Therefore, things could even turn worse for already damaged colonies. Of course, this is most annoying, sad and frustrating for the individual beekeeper. But beekeeping has always been closer to nature than other animal keeping and therefore has been confronted to a larger extent by such ups and downs and setbacks. Beekeepers are well aware of that. To work in close touch with nature keeps their profession so thrilling and eventful. Every setback is followed by redevelopment. And as this is supported by a large multiplication rate, there are good pre-conditions to care for enough bees and honey also in future!
Dr. Wolfgang Ritter
President of Apimondia Standing Commission for Bee health
International and National Reference Laboratory for Bee Diseases (NRL)
at CVUA Institute of Animal Health in Freiburg/Germany
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