A US government-funded study has revealed that beekeepers lost almost half their colonies over the past year.

Between April 2015 and April 2016, beekeepers in the USA lost 44 percent of their honeybee colonies, according to a survey funded by the U.S. Department of Agriculture (USDA). The results of the survey, which was completed by both commercial and small-scale beekeepers, showed both summer and winter losses worsened considerably, marking the second consecutive survey year in which summer loss rates rivalled winter losses.

"We're now in the second year of high rates of summer loss, which is cause for serious concern," said Dennis vanEngelsdorp, an assistant professor of entomology at the University of Maryland and project director for the Bee Informed Partnership which conducted the survey. "Some winter losses are normal and expected. But the fact that beekeepers are losing bees in the summer, when bees should be at their healthiest, is quite alarming."

Almost 6,000 beekeepers responded to the survey, which is now in its tenth year, representing about 15 percent of domestically kept bees in the US. Beekeepers’ losses of 44.1 percent of colonies marks an increase of 3.5 percent over the previous study year (2014-15), when loss rates were 40.6 percent. Winter loss rates increased from 22.3 percent in the previous winter to 28.1 percent this past winter, while summer loss rates increased from 25.3 percent to 28.1 percent.

According to researchers, pests and disease are amongst a number of factors behind the losses. They said one clear culprit is the varroa mite, a lethal parasite that can easily spread between colonies, but added that pesticides and malnutrition caused by changing land use patterns are also likely taking a toll, especially among commercial beekeepers.

A study from last month that looked at commercial and backyard beekeeping operations in the US found that the varroa mite is far more abundant than previous estimates indicate and is closely linked to several damaging viruses. Nathalie Steinhauer, who also worked on the survey said, "Many backyard beekeepers don't have any varroa control strategies in place. We think this results in colonies collapsing and spreading mites to neighboring colonies that are otherwise well-managed for mites. We are seeing more evidence to suggest that good beekeepers who take the right steps to control mites are losing colonies in this way, through no fault of their own."

Commenting on the findings, Jeffery Pettis, a senior entomologist at the USDA and a co-coordinator of the survey said, ”The high rate of loss over the entire year means that beekeepers are working overtime to constantly replace their losses. These losses cost the beekeeper time and money. More importantly, the industry needs these bees to meet the growing demand for pollination services. We urgently need solutions to slow the rate of both winter and summer colony losses."