A group of chemical insecticides known as neonicotinoids that have been banned in Europe due to fears about potential harm to bees have been found in new research to have very differential risks for bumblebees.
Scientists who conducted the research said their findings showed that at least one neonicotinoid in the banned group - clothianidin – may have been unfairly named as among the offenders.
This insecticide did not show the same detrimental effects on bee colonies as the others, imidacloprid and thiamethoxam, the researchers found. All three neonicotinoids have been subject to an EU-wide moratorium on their use.
"(From our findings) we can clearly see that the banned neonicotinoids are not the same, so they should be considered independently when considering risk and legislation," Chris Connolly, a specialist in bee research at Dundee University's neuroscience department, told reporters at a briefing.
He said the results suggested it would be premature to place a permanent ban on the use of clothianidin. "That said, a moratorium on its use should continue until the knowledge gaps are filled on its wider impact on other species," he added.
Often with yellow and black stripes and bigger than honeybees, bumblebees live in small nests of up to 200 and do not make honeycombs. Europe has around 68 species of bumblebee, and some are commercially bred to pollinate tomatoes and other crops in greenhouses.
The European Union limited the use of neonicotinoid chemicals - made and sold by various companies including Bayer CropScience and Syngenta - two years ago, after research pointed to risks for bees, which are crucial for pollinating crops.
Crop chemical makers say the research blaming neonicotinoid pesticides is not backed up by field evidence. They argue that a global plunge in bee numbers in recent years is a complex phenomenon due to multiple factors.
To try and find out more, and to test the effects of each of the three neonicotinoids separately, Connolly's group worked with colleagues from St Andrews University on a study involving 75 bee colonies at five separate locations in Scotland.
They found that while imidacloprid and thiamethoxam had the negative effects seen in previous research, clothianidin did not pose the same threat for bumblebees.
"What we have found is that imidacloprid and thiamethoxam, but not clothianidin, exhibit toxicity to bumblebee colonies when exposed at field-relevant levels," Connolly said.
Given these results, he said, specialists should examine in more detail the effect of each chemical on each species.
"Small changes in the pesticide structure or its target site in insects are likely to be critical to risk assessment," he said. "Each pesticide/insect combination needs to be considered independently."
(Editing by Robin Pomeroy)
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