The report, produced with industry group the Bee Informed Partnership, showed that the death rate for October 2013 to April of this year was better than the 30.5% losses for 2012 to 2013, but worse than the 21.9% in 2011 to 2012.

Prior surveys found colony losses averaged 29.6% over the last eight-year span.

Bee populations have been dying at a rate which the US government says is economically unsustainable. Honey bees pollinate plants that produce about a quarter of US consumer foods.

Scientists, consumer groups, and bee keepers say the devastating rate of bee deaths is due at least in part to the growing use of pesticides sold by agri-chemical companies to boost yields of staple crops such as corn.

They pointed to a study issued on May 9 by Harvard School of Public Health that found two widely used neonicotinoids — a class of insecticide — may significantly harm honey bee colonies over the winter.

“With the damning evidence mounting, pesticide companies can no longer spin their way out of this crisis,” said Michele Simon, a public health lawyer who specialises in food issues.

Monsanto, DuPont, Syngenta, Bayer, and other agrichemical companies say the bees are being killed by other factors, such as mites.