Effects of honey bee virus prevalence, Varroa destructor load and queen condition on honey bee colony survival over the winter in Belgium

Since 1999, European beekeepers have reported increased mortality in overwintering honey bee, Apis mellifera L. colonies. Viral infections are often cited as the potential cause for increased mortality. Many honey bee viruses commonly occur within bee populations and in many cases infected colonies appear asymptomatic. There is increasing evidence that the global spread of Varroa destructor has resulted in a significant change in the prevalence, distribution and / or virulence of viruses causing mortality in honey bee colonies. We report here the first survey of the prevalence of five RNA bee viruses and their effect on overwintering survival of Belgian honey bee colonies. In the autumn of 2006, samples of adult bees were removed from 36 apiaries. Adult bee samples were analyzed by using RT-PCR for virus identification. Varroa mite prevalence in these samples was also quantified. A follow up visit of colonies in the spring permitted us to assess colony survivorship which permitted the effect, if any, of autumn varroa loads, virus presence and queen condition on colony survivorship to be ascertained. Although acute bee paralysis virus was the least prevalent of the detected honey bee viruses, it was strongly linked with increased colony mortality. Co-infection with more than two viruses also had an appreciable negative effect on colony survivorship.