Abstract
We conducted a citizen science survey on overwinter honey bee colony losses in Austria. A total of 1534 beekeepers with 33,651 colonies reported valid loss rates. The total winter loss rate for Austria was 15.2% (95% confidence interval: 14.4–16.1%). Young queens showed a positive effect on colony survival and queen-related losses. Observed queen problems during the season increased the probability of losing colonies to unsolvable queen problems. A notable number of bees with crippled wings during the foraging season resulted in high losses and could serve as an alarm signal for beekeepers. Migratory beekeepers and large operations had lower loss rates than smaller ones. Additionally, we investigated the impact of several hive management practices. Most of them had no significant effect on winter mortality, but purchasing wax from outside the own operation was associated with higher loss rates. Colonies that reported foraging on maize and late catch crop fields or collecting melezitose exhibited higher loss rates. The most common Varroa destructor control methods were a combination of long-term formic acid treatment in summer and oxalic acid trickling in winter. Biotechnical methods in summer had a favourable effect on colony survival.
Highlights
Apis mellifera, the western honey bee, is an important pollinator for wild flowers and crucial for the pollination of the world agricultural production
Questions on hive management practices are part of the COLOSS international survey and were used unmodified. These questions concerned topics like the number of the wintered colonies that had a new queen, observed queen problems in colonies during foraging season compared to previous seasons, certified organic beekeeping, queens bred from varroa tolerant/resistant stock, hives fabricated from synthetic materials, insulated hives, screened bottom boards, purchase of wax from outside of the own operation, natural comb without foundation, small brood cell size, migratory beekeeping, replacement of brood frames, notice of bees with crippled/deformed wings, and foraging crops perceived by the beekeeper
The winter 2018/2019 represented an average year in terms of overwinter honey bee colony losses in Austria
Summary
The western honey bee, is an important pollinator for wild flowers and crucial for the pollination of the world agricultural production. The threats for honey bees are increasingly well studied and understood and range from abiotic stressors, such as pesticides, to biotic stressors [2,3,4] The latter include parasites, pathogens, and pests, like the parasitic mite Varroa destructor or monoculture plantings that influence the quality and richness of forage sources [5]. Synergistic effects of single factors may add up to a threat that is greater than the sum of its individual factors. Beekeepers try their best to support their colonies by optimizing their hive management to help them cope with the environmental conditions they are facing. Efficient treatments of colonies against varroa mite are necessary, as this parasite is known to reduce winter survival [10,11,12]
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