Bumblebees are not badly affected by all insecticides – of the three most commonly used neonicotinoids, clothianidin was found to be much less detrimental compared to thiamethoxam and imidacloprid, even though the European Union has imposed a moratorium on all three, said a team of scientists from the University of Dundee and the University of St. Andrews, both in Scotland.
Dr. Chris Connolly, a Research Associate at the Centre for Environmental change and Human Resilience (CECHR) and Reader in the Division of Neuroscience at Dundee’s School of Medicine, and colleagues wrote in the journal Scientific Reports (citation below) that at least one known neonicotinoid – clothianidin – may have been unfairly named when it comes to risks to bumblebees.
Several studies have identified neonicotinoids – a relatively new type of insecticide used in the past two decades to control a variety of pests – as presenting a serious risk to bee populations, leading to several bans across the world on their use.
The scientists suggest that perhaps it was unjustified for the EU to ban the neonicotinoid insecticide clothianidin, which they found was not a threat to bumblebee populations, unlike thiamethoxam and imidacloprid. (Image: adapted from wildlifetrusts.org)
EU clothianidin ban unjustified?
There is currently an EU-wide moratorium on the use of three types of neonicotinoids – thiamethoxam, imidacloprid and clothianidin. It appears that banning clothianidin may have been unwarranted, the authors explained.
Dr. Connolly is one of the world’s leading authorities on the effects of neonicotinoids on insects, especially bees. He led this latest study which showed that each of the different neonicotinoids presented very different risks for bumblebees.
Regarding the risk to bees from neonicotinoid insecticides, Dr. Connolly said:
“There has been growing concern over the risk to bee populations from neonicotinoid insecticides and their long-term consequences to essential ecosystem services and food security.”
Most scientific knowledge regarding the risk of neonicotinoids to bees has been based on studies of thiamethoxam and imidacloprid. The findings from those two insecticides have generally been extrapolated to clothianidin, i.e. they did not extensively study clothianidin on its own.
A 2015 study found that British bumblebees are increasingly opting for flowers on the road-facing side of hedgerows, because the field-facing side has fewer pickings, due to pesticides and fertilizers. (Image: Bumblebee Conservation Trust)
In this latest study, the scientists gathered and analyzed data on all three neonicotinoids in parallel.
No evidence of clothiandin toxicity to bumblebee colonies
While they found that imidacloprid and thiamethoxam exhibited toxicity to bumblebee colonies when exposed at field-relevant levels, this was not the case with clothiandin.
Dr. Connolly said:
“There was also further variation in the effects on bees between the three insecticides. So we can clearly see that the banned neonicotinoids are not the same, so they should be considered independently when considering risk and legislation.”
“From our findings, we consider that it is 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.”
Dr. Connolly and colleagues tested seventy-five bee colonies at five different locations across Scotland.
Their study once again confirmed the threat to bumblebees from the use of thiamethoxam and imidacloprid.
Dr. Connolly explained:
“We have seen further evidence to indicate the risk from these insecticides, including deficits in colony strength.”
“Given these findings, small changes in the pesticide structure or its target site in insects are likely to be critical to risk assessment and each pesticide/insect combination needs to be considered independently – evidence should not be extrapolated to similar chemicals or insects. Real risk must be determined empirically.”
In an Abstract in the journal, the authors wrote:
“Both imidacloprid and thiamethoxam caused deficits in colony strength, while no detrimental effects of clothianidin were observed. Given these findings, neonicotinoid risk needs to be considered independently for each compound and target species.”
Neonicotinoid pesticides trigger cravings in bees
Neonicotinoid pesticides work on the brains of bees in the same way nicotine from cigarettes does on the human brain, triggering cravings and making them addicted, said a team of British and Irish scientists in 2015.
If they become addicted, bees are likely to gorge themselves and dangerously raise concentrations of toxins within their bodies.
Just like nicotine does with the human brain, Neonicotinoids act on certain kinds of Bees’ brain receptors – they act on brain cells so that the insects desire more.
Study leader, Prof. Geraldine Wright, from Newcastle University in England, said:
“Bees can’t taste neonicotinoids in their food and therefore do not avoid these pesticides. This is putting them at risk of poisoning when they eat contaminated nectar.”
“Even worse, we now have evidence that bees prefer to eat pesticide-contaminated food. Neonicotinoids target the same mechanisms in the bee brain that are affected by nicotine in the human brain.”
“The fact that bees show a preference for food containing neonicotinoids is concerning as it suggests that like nicotine, neonicotinoids may act like a drug to make foods containing these substances more rewarding.”
“If foraging bees prefer to collect nectar containing neonicotinoids, this could have a knock-on negative impact on whole colonies and on bee populations.”
Citation: “Neonicotinoids target distinct nicotinic acetylcholine receptors and neurons, leading to differential risks to bumblebees,” Christopher Moffat, Stephen T. Buckland, Andrew J. Samson, Robin McArthur, Victor Chamosa Pino, Karen A. Bollan, Jeffrey T.-J. Huang & Christopher N. Connolly. Scientific Reports 6, Article number: 24764. 28 April, 2016. DOI: 10.1038/srep24764.
Video – Neunicotinoids: The New DDT?
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