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SummaryFor the past six years in which overwintering mortality of honey bee colonies has been surveyed in the USA, estimates of colony loss have fluctuated around one-third of the national population. Here we report on the losses for the 2012–2013 seasons. We collected data from 6,482 US beekeepers (6,114 backyard, 233 sideline, and 135 commercial beekeepers) to document overwintering mortality rates of honey bee colonies for the USA. Responding beekeepers reported a total 30.6% (95% CI: 30.16–31.13%) loss of US colonies over the winter, with each beekeeper losing on average 44.8% (95% CI: 43.88–45.66%) of their colonies. Total winter losses varied across states (range: 11.0% to 54.7%). The self-reported level of acceptable winter loss was 14.6%, and 73.2% of the respondents had mortality rates greater than this level. The leading self-identified causes of overwintering mortality were different according to the operation type; backyard beekeepers generally self-identified “manageable” factors (e.g., starvation, weak colony in the fall), while commercial beekeepers generally identified non-manageable factors (e.g., queen failure, pesticides) as the main cause of losses. For the first time in this series of surveys, we estimated mortality during the summer (total loss = 25.3% (95% CI: 24.80–25.74%), average loss = 12.5% (95% CI: 11.92–13.06%)). The entire 12-months period between April 2012 and April 2013 yielded a total loss of 45.2% (95% CI: 44.58–45.75%), and an average loss of 49.4% (95% CI: 48.46–50.43%). While we found that commercial beekeepers lost fewer colonies than backyard beekeepers in the winter (30.2% (95% CI: 26.54–33.93% vs 45.4% (44.46–46.32%) respectively), the situation was reversed in the summer where commercial beekeepers reported higher average losses than backyard beekeepers (21.6% (95% CI: 18.4–24.79%) vs 12.1% (11.46–12.65%)). These findings demonstrate the ongoing difficulties of US beekeepers in maintaining overall colony heath and survival.

SummaryEstimates of winter loss for managed honey bee (Apis mellifera) colonies are an important measure of honey bee health and productivity. We used data from 5,500 US beekeepers (5,244 backyard, 189 sideline and 67 commercial beekeepers) who responded to the April 2012 Bee Informed Partnership Winter Colony Loss Survey and calculated loss as the difference in the number of colonies between October 1, 2011 and April 1, 2012, adjusting for increases and decreases over that period. In the US, the total colony loss was 22.5% for the 2011–12 winter; 45.1% (n = 2,482) of respondents reported no colony loss. Total loss during 2011–12 was substantially lower than loss during 2010–11 (29.9%). Of the 4,484 respondents who kept bees in 2010–11 and 2011–12, 72.0% reported that the loss during 2011–12 was smaller or similar to the loss during 2010–11. There was substantial variation in total loss by state (range 6.2% to 47.7%). The average loss per beekeeping operation was 25.4%, but the average loss was not significantly different by operation type (backyard, sideline, commercial). The average self-reported acceptable loss per respondent was 13.7%; 46.8% (n = 2,259) of respondents experienced winter colony losses in excess of the average acceptable loss. Of beekeepers who reported losing at least one colony during 2011–12, the leading self-identified causes of mortality were weak condition in the fall and queen failure. Respondents who indicated poor wintering conditions, CCD, or pesticides as a leading cause of mortality suffered a higher average loss when compared to beekeepers who did not list these as potential causes.