US beekeepers lost almost four in ten of their honeybee colonies over the past year, raising fresh concerns over the crucial pollinators.

There have been intense efforts to bolster and rebuild devastated bee colonies after the Colony Collapse Disorder appeared around 2006.  

"It's disconcerting that we’re still seeing elevated losses after over a decade of survey and quite intense work to try to understand and reduce colony loss," said Geoffrey Williams, assistant professor of entomology at Auburn University.  "We don’t seem to be making particularly great progress to reduce overall losses."

Colony Collapse Disorder saw workers bees simply abandoning their hives and dying off, usually attributed to the widespread use of insecticide in agriculture.  But the beekeepers' troubles have been compounded over the last year by bad weather, disease, and the loss of bee-friendly habitats to mono-culture farming.

The latest nationwide survey of agricultural bee health showed 37 percent of honeybee colonies were lost to beekeepers.  Overall, 40% of colonies died off over the entire year to April, which is above the 38% average since the survey began