A newly developed pesticide that could soon be introduced in the UK poses a serious threat to bumblebees, research suggests.
Scientists found that sulfoxaflor reduced the size of bumblebee colonies and male drone populations.
Exposed colonies experienced a 54% drop in reproductive offspring, consisting almost entirely of drones.
The pesticide is currently licensed in 47 countries around the world and under review for potential introduction in the UK.
It and similar “sulfoximine” agents are seen as likely replacements for neonicotinoids, which are now being banned for outdoor use in Europe because of the alleged harm they cause bees.
Lead researcher Harry Siviter, a PhD student at Royal Holloway, University of London, 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.”
For the study, 25 bumblebee colonies were exposed to sulfoxaflor and compared with 26 untreated colonies.
Differences between the colony populations began to emerge two to three weeks after first exposure and continued until the end of the colony life cycle.
As well as their drone numbers being greatly reduced, none of the treated colonies produced new queens.
Drones do not collect pollen and nectar but are vital to a colony’s future. Their job is to mate with the queen and secure the next generation of bees, including the all-important workers that are female but sterile.
Dr Elli Leadbeater, another member of the Royal Holloway team, said: “Our study highlights that stressors that do not directly kill bees can still have damaging effects further down the line, because the health of the colony depends on the health of its workforce.”
The findings are published in the latest issue of the journal Nature.
In April European Union member states voted in favour of an almost complete ban on neonicotinoids, which had already been severely restricted since 2013.
After a phase-out period of some months, the pesticides will in future only be allowed in greenhouses and other enclosed spaces.
Sandra Bell, pesticides campaigner at the environmental group 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.”