Ruderatus - an all-black bumblebee - pollinating a broad bean plant
Wild bee populations around the UK are experiencing "catastrophic declines", the Bumblebee Conservation Trust has warned.
Mary Celeste Syndrome - where a honey bee hive is found almost completely deserted - has appeared in Scotland.
The Stirling-based trust's Dr Ben Darvill described bumblebees as an "insurance policy", given the problems facing colonies of honey bees.
Bees are important pollinators of flowers and crops.
Dr Darvill said: "The whole suite of pollinators are declining simultaneously."
The UK has 18 true bumblebee species and many are seriously threatened due to habitat loss.
The great yellow - the rarest bee in the UK - clings to survival in the Highlands and Islands.
Dr Darvill said the insects' demise has serious implications for food supply and the price of goods.
He said: "When a bee visits a flower, it picks up pollen on its fur, and transports it to another flower, pollinating it in the process.
"Without pollination, flowering crops like beans, peas, strawberries and raspberries won't produce anything to harvest, and wildflowers won't produce any seeds.
"The loss of the nation's pollinators is likely to affect your dinner plate, and will change the wider countryside beyond recognition."
Mr Darvill said the "catastrophic declines" could be eased with help from farmers and the general public.
Government-backed agri-environment schemes offer payments to farmers to help them maintain flower-rich areas for bees and other wildlife.
Gardeners have also been encouraged to plant wild flower varieties.
Tony Riome, vice president of Ayr and District Beekeepers Association, said it had been estimated every third mouthful of food consumed could be linked to pollination by bees.
He said: "If there are no bees there will be no steak.
"A lot of pollination is wind blown, but bees play a very large part in pollinating the plants that animals eat."
Bumblebees along with wild and managed honey bees are suffering following a poor summer last year.
Honey bees have also fallen prey to varroa mite.
The parasites leave bee larvae deformed and can spread a condition called Israeli Paralysis Virus.
These attacks in turn have been suspected as the cause of Mary Celeste Syndrome, named after a ship discovered deserted in 1872.
Mr Riome said it had appeared in Scotland and only outer islands had escaped varroa mite.
He said: "With Mary Celeste Syndrome a healthy colony of bees is found to have disappeared, or only 100 are found with the queen.
"Because the bees die while out foraging it cannot be established how they died."
The beekeeper said the US government was spending about £8.1m on research into Mary Celeste Syndrome, called Colony Collapse Disorder in the US.
But he said: "The British government is supporting beekeepers with £200,000.
"Due to a lack of funds the only research laboratory, which was based in the Home Counties, was closed and one of the leading experts in this country on bee diseases was made redundant."