Pesticides developed to replace banned bee-killing insecticides have been found to reduce colonies by half.
It was hoped that sulfoxaflor would provide an alternative to neonicotinoids, which have been shown to drastically reduce bee numbers, and is currently under review for licencing in Britain.
But researchers at Royal Holloway, University of London found exposure to the new pesticide reduced both the size of bumblebee colonies and the number of offspring produced by 54 per cent.
Doctoral student Harry Siviter said: “Neonicotinoids are the most commonly used insecticide in the world, but the evolution of resistance by pests, as well as bans and restrictions on their usage has resulted in a demand for alternative pesticides.
“Sulfoximine-based insecticides are a likely successor and are being registered for use globally.
“Our results show that sulfoxaflor can have a negative impact on the reproductive output of bumblebee colonies under certain conditions.”
Researchers say they do not know if the pesticide would be as harmful in the wild as they do not know how much bees would be exposed to.
However, they say the study shows that sulfoxaflor pesticides do have the potential to harm wild bumblebee populations.
Professor Mark Brown said: “We need to know much more about what levels of emerging insecticides wild bees will be exposed to in the field – only with realistic and publicly available exposure data for a range of crops can we determine the true risk of these insecticides to wild bees and other important pollinators.”
In April EU member states, including the UK, voted in favour of an almost complete ban on the use of neonicotinoids, which will be in place by the end of the year, despite opposition from farmers. They can now only be used in closed greenhouses.
But charities said the Government needed to make sure the pesticides were not replaced with another harmful chemical.
Commenting on the study Sandra Bell, pesticides campaigner for Friends of the Earth said: “The upcoming ban on neonicotinoids is great news for our bees – but the Government must ensure that alternative pesticides don’t harm these crucial pollinators too.
“This study shows that replacing one harmful pesticide with another is not the solution to protecting our crops. Sulfoxaflor should not be approved in the UK at this time due to concerns about its safety for bees.
“The Government must use the opportunity provided by its post-Brexit farming policy to help farmers get off the chemical treadmill and support them to use non-chemical alternatives wherever possible.”