US bee-keepers lost 40 per cent of their honey bee colonies between April 2014 and April 2015. Winter losses improved over previous years, but summer losses made up for the reduction.
Commercial bee-keepers were badly hit, with summer losses higher than winter losses for the first time in five years.
‘We traditionally thought of winter losses as a more important indicator of health, because surviving the cold winter months is a crucial test for any bee colony,’ says Dennis van Engelsdorp, an assistant professor of entomology at the University of Maryland and project director for the Bee Informed Partnership.
‘But we now know that summer loss rates are significant too. This is especially so for commercial bee-keepers, who are now losing more colonies in the summertime compared to the winter. Years ago, this was unheard of,’ he adds.
The 6,000 bee-keepers who took the survey – now in its ninth year – reported 42.1 per cent of colonies were lost over the year. Winter losses fell from 23.7 per cent to 23 per cent, while summer loss rates increased from 19.8 per cent to 27.4 per cent.
The survey covered nearly 15 per cent of the country’s 2.74 million managed bee colonies.
For amateur bee-keepers – defined as those managing less than 50 colonies – the varroa mite is thought to be to a major factor, but the cause in most cases is unclear.
‘Backyard bee-keepers were more prone to heavy mite infestations, but we believe that is because a majority of them are not taking appropriate steps to control mites,’ says van Engelsdorp. ‘Commercial keepers were particularly prone to summer losses. But they typically take more aggressive action against varroa mites, so there must be other factors at play.’
The survey is part of a wider study into why honey bee colonies are in poor health. Valuable crops, such as almonds, depend on honey bees for pollination. Honey bee pollination contributes between $10billion and $15billion to the US agricultural economy annually.
‘The winter loss numbers are more hopeful especially combined with the fact that we have not seen much sign of Colony Collapse Disorder (CCD) for several years, but such high colony losses in the summer and year-round remain very troubling,’ says Jeffery Pettis, a senior entomologist at U.S. Department of Agriculture and a co-coordinator of the survey. ‘If bee-keepers are going to meet the growing demand for pollination services, researchers need to find better answers to the host of stresses that lead to both winter and summer colony losses.’