Honey bee pathogens and parasites in Swedish apiaries: a baseline study

This nation-wide survey including 382 Swedish apiaries is the first to document base-line information of the prevalence and distribution of the ectoparasitic mite Varroa destructor, the mite-associated viruses Deformed wing virus and Acute bee paralysis virus, and the bacterial honey bee pathogens Paenibacillus larvae and Melissococcus plutonius in the country. Varroa and associated viruses were not detected in the northern regions of the country. The bacterium P. larvae was detected in 6% of the investigated apiaries and it was absent in more than half of the counties, M. plutonius was detected in two apiaries in one county. Other results from our study include questionnaire responses, in which beekeepers reported total winter colony losses of 6.4%. Fifty-three percent of the beekeepers reported to have purchased queens the year preceding this study, and 40.1% moved colonies to the apiary. Queens were imported from European countries and the USA. The movements of bees were one of the factors strongly associated with the prevalence of the disease-causing organisms surveyed and colony losses. The majority of the participating beekeepers were not aware of any disease related signs in their apiaries despite positive laboratory findings. This highlights the importance of further outreach efforts to increase the beekeepers' awareness of diseases and disease management. The results provide a disease baseline for improvements of the surveillance system.