A large-scale epidemiological study on the prevalence and risk factors of losses of honey bee colonies during winter seasons in Poland.

We conducted a citizen science survey on winter honey bee colony losses in Poland. A total of 2169 beekeepers, possessing 77 867 colonies, reported valid loss rates from all regions of the country between 2017 and 2022. We identified five beekeeping management-related factors and three types of apiaries (small-scale apiaries, medium-scale apiaries, and large-scale apiaries) and analysed their impact on winter bee colony losses. In large-scale apiaries, migration, replacement of queens, and replacement of brood combs were practiced more often than in others. Monitoring and treatment of varroosis were practiced with equal frequency in all apiary types. In total, beekeepers reported 9466 lost colonies, accounting for 12.2 % of the overall winter bee colony loss rate (95 % confidence interval (CI 95 %): 11.4 %-12.8 %). The highest overall winter bee colony losses were reported from the small-scale apiaries (14.8 %, CI 95 %: 13.2 %-16.7 %), followed by large-scale apiaries (11.6 %, CI 95 %: 10.4 %-12.8 %) and medium-scale apiaries (11.4 %, CI 95 %: 10.4 %-12.5 %). The primary category of losses was characterised by the presence of "dead colonies", with symptoms that could be linked to either colony depopulation syndrome or starvation. All management-related factors contributed to the lower winter bee colony loss rates, but the relationships were mainly mild, complex, and highly dependent on the type of apiary.