Reports of honey bee population decline has spurred many national efforts to understand the extent of the problem and to identify causative or associated factors. However, our collective understanding of the factors has been hampered by a lack of joined up trans-national effort. Moreover, the impacts of beekeeper knowledge and beekeeping management practices have often been overlooked, despite honey bees being a managed pollinator. Here, we established a standardised active monitoring network for 5 798 apiaries over two consecutive years to quantify honey bee colony mortality across 17 European countries. Our data demonstrate that overwinter losses ranged between 2% and 32%, and that high summer losses were likely to follow high winter losses. Multivariate Poisson regression models revealed that hobbyist beekeepers with small apiaries and little experience in beekeeping had double the winter mortality rate when compared to professional beekeepers. Furthermore, honey bees kept by professional beekeepers never showed signs of disease, unlike apiaries from hobbyist beekeepers that had symptoms of bacterial infection and heavy Varroa infestation. Our data highlight beekeeper background and apicultural practices as major drivers of honey bee colony losses. The benefits of conducting trans-national monitoring schemes and improving beekeeper training are discussed.

-The first pan-European harmonized active epidemiological surveillance program on honeybee colony mortality (EPILOBEE) was set up across 17 European Member States to estimate honeybee colony mortality over winter and during the beekeeping season. In nine Member States, overwinter losses were higher and statistically different from the empirical level of 10 % under which the level of overwinter mortality was considered as acceptable with usual beekeeping conditions. In four other countries, these losses were lower. Using multivariable Poisson regression models, it was showed that the size of the operation and apiary and the clinically detected varroosis, American foulbrood (AFB), and nosemosis before winter significantly affected 2012-2013 overwinter losses. Clinically detected diseases, the size of the operation and apiary, and the non-participation to a common veterinary treatment significantly affected 2013 summer losses. EPILOBEE was a prerequisite to implement future projects studying risk factors affecting colony health such as multiple and co-exposure to pesticides.honeybee health / EPILOBEE / epidemiological survey / winter mortality / seasonal mortality INTRODUCTIONNumerous hazards threaten honeybee populations (Apis mellifera ) worldwide. Many publications that looked into colony losses from any part of the world reported that several biological and environmental factors acting alone or in combination have the potential to cause premature colony mortality (Genersch et al. 2010;Potts et al. 2010; Spleen et al. 2013). In the USA and Canada, alarming losses of honeybee colonies were recently reported (Steinhauer et al. 2014). In Europe, the decrease in honeybee colonies was estimated at Corresponding author: M. Chauzat, marie-

Seventeen Member States of the European Union were brought together to set up the first EU-wide active epidemiological surveillance program on honeybee colony mortality (EPILOBEE) based on representative beekeeper populations of randomly selected apiaries and colonies from 2012 to 2014. Visits were performed to estimate the mortality of bee colonies over the winter and during the season. Beekeeping practices and clinical signs of the main honeybee diseases were recorded through a questionnaire. Winter and seasonal mortalities widely varied according to the Member States and when comparing both years. The highest winter mortality was recorded in Belgium in 2012-2013 (31.73%) and the lowest in Lithuania (2.16%) in 2013-2014. In the multivariate Poisson regression models combining both years, the country was studied as a random effect. Using a hierarchical clustering of observations, the highest winter mortality rate (14.04%) was affected to a cluster including hobbyist beekeepers over 65 years of age with small size apiaries, with a production including queens and a small experience in beekeeping. The lowest winter mortality rate (8.11%) was affected to a cluster with professional beekeepers between 30 and 45 years of age, with large migrating apiaries. The management promoted the increase of the livestock. These professional beekeepers had attended a beekeeping training during the past three years, used an apiarist book, had a qualification in beekeeping, were members of a beekeeping organisation, and had an experience in beekeeping superior to five years. These apiaries did not suffer from any disease. Variables with a statistically significant effect on honeybee colony mortality during the beekeeping season were colonies clinically affected by the varroosis, the absence of beekeeping training during the past three years of the beekeeper's activity, the non-use of an apiarist book and the nonparticipation to a cooperative veterinary treatment. Being a pilot project, EPILOBEE was rich in lessons leading to the formulation of recommendations for future epidemiological surveys. © ANSES, 2016Key words: honeybee health, colony mortality, honeybee diseases, epidemiology. Disclaimer: The present document has been produced and adopted by the bodies identified above as authors. This task has been carried out exclusively by the authors in the context of a contract between the European Food Safety Authority and the authors, awarded following a tender procedure. The present document is published complying with the transparency principle to which the Authority is subject. It may not be considered as an output adopted by the Authority. The European Food Safety Authority reserves its rights, view and position as regards the issues addressed and the conclusions reached in the present document, without prejudice to the rights of the authors.Acknowledgements: EPILOBEE has been co-funded by the European Commission together with each Member State taking part in EPILOBEE and ANSES through the EURL for honeybee health. This ...

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