Honeybee numbers are in decline
Almost a fifth of the UK's honeybees died last winter, the British Beekeepers' Association has said.
Combined with an average 30% loss the year before, it means beekeepers are struggling to keep colonies going.
Honeybees are worth £200m a year to UK agriculture because of their work pollinating crops.
Bees are suffering from viruses, a parasitic mite and changes in the weather. Experts are calling for more money to be put into research.
A survey by the British Beekeepers' Association (BBKA) suggested an average of 19.2% of colonies died over winter, which is "double" the acceptable level.
The highest losses were recorded in the north of England, where 32.1% perished, and the lowest in eastern England, where 12.8% did not survive.
The survey showed an improvement on the previous year, which the BBKA put down to the period of really cold weather in the winter which encouraged the bees to "cluster" together, helping them to survive.
It also said the good weather in early spring enabled them to forage for nectar and pollen.
'Onslaught of threats'
But there was still a "worrying and continuing high level of colony loss", said the BBKA's president Tim Lovett.
"It underlines the need for research into the causes and remedies for disease in order to ensure that our principal economic pollinator, the honeybee, can survive the onslaught of the threats it currently faces," he said.
"These ongoing losses in the pollination army of honeybees cannot continue if we are to secure food supplies."
Nearly all the UK's 250 species of bee are in decline. In the last two years, honeybee numbers have fallen by 10-15%.
The conservation watchdog Natural England recently called on people living in urban areas to consider keeping bees.
Its chief scientist Tom Tew told the BBC: "We want urban people to engage with wildlife and get joy and pleasure from it. The more hives you have the more resilient the whole population is to the outbreak of disease."
The BBC presenter Martha Kearney is an amateur beekeeper and has seen for herself the decline in numbers.
She told Breakfast on BBC One: "They've died out on me before and it was really distressing.
"You put the bees away for the winter and you hope they're going to be OK.
"And when you open up the colony in the spring and see lots of dead bees in there, it's unpleasant.
"Beekeeping is a fascinating hobby and I love it. But they are dying. This year is slightly better than last year though."
A report by the Parliamentary Accounts Committee last month warned the government was giving "little priority" to the health of the nation's bees despite their importance to the agricultural economy.
Experts say sustaining bee populations is essential to ensuring the survival of Britain's plants and crops.