Pesticides 'give bees a buzz'
Published 22/04/2015 | 18:06
Bees get a "buzz" from nicotine-like pesticides in much the same way as smokers are stimulated by tobacco, startling new research suggests.
In a series of experiments, bumblebees and honeybees actively preferred sugar solutions laced with the neonicotinoid chemicals.
This was despite evidence that the bees could not taste the pesticides.
Rather than enjoying the taste, they seemed to be reacting to a pleasurable "high" as the chemicals activated reward centres in their tiny brains, the scientists believe.
Just like smokers reaching for another cigarette, the bees returned to food tubes containing the "spiked" sugar again and again, choosing them over solutions free of pesticide.
The research is important because it suggests bees may be exposed to harmful doses of "neonics" as a result of being so attracted to the chemicals.
Lead scientist Professor Geraldine Wright, from the Institute of Neuroscience at the University of Newcastle, 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."
Previous research indicating that exposure to neonicotinoid residues might be decimating bee colonies led to a two-year European ban on the use of three of the pesticides on flowering crops that began in 2013.
But the move remains highly controversial, with some critics insisting it is not backed by sufficient evidence. While having to enforce the moratorium, the British Government has publicly stated it does not support it.
The new research is one of two new investigations reported in the journal Nature that sound further warnings over the use of neonicotinoids to control insect pests.
The other study, led by Dr Maj Rundlof from Lund University in Sweden, found the pesticides had harmful effects on bee populations in replicated agricultural environments, not just laboratory settings.
Oilseed rape sown from seeds coated in neonicotinoids reduced wild bee density, solitary bee nesting, and bumblebee colony growth and reproduction.
However, neonicotinoid exposure did not have a significant impact on honeybee colonies. As a result, tests on "domesticated" honeybees could not readily be extrapolated to wild bees, said the authors.
Neonicotinoid pesticides are chemically similar to nicotine for a good reason. Nicotine is a potently toxic compound used by some plants, notably tobacco, to defend themselves against herbivorous insects.
Prof Wright pointed out that although highly toxic, in very small doses nicotine - and presumably its neonicotinoid cousin - act as stimulants rather than poisons.
She said: "It's complicated. A little bit's medicine and a lot's toxin. If you have a high enough dose of the stuff it will kill you. At very low doses, though, like the ones found in cigarettes, it's got a pharmacological effect that affects the reward pathway in the human brain. I think what's happening here is something very analogous.
"I don't think they (the bees) can taste it at all. They're learning the location of the food that contains it. And during the time that they're eating it they're getting a stronger feeling of reward.
"It must be very fast acting. As soon as it gets into their blood they're getting a little buzz, as it were, and they're responding to that."
Prof Wright added: "We don't have any evidence that it's addictive, but it could be."
The team recorded electrical activity from the bees' mouth parts to show that the insects' "taste" neurons were not reacting to neonicotinoids. This was strong evidence that the bees could not taste the pesticides.
Sandra Bell, from the environmental group Friends of the Earth, which has campaigned against neonicotinoids, said: " The scientific evidence that neonicotinoid insecticides harm our under-threat bees keeps stacking up.
"These dangerous chemicals should have no place on our farms and gardens. Bees are essential to us - it is vital that action is taken to reduce all the threats they face.
"The next UK Government faces a key green test. It must support a complete and permanent European ban on these bee harming chemicals, and help UK farmers find safer alternatives."
Biologist Professor David Goulson, from the University of Sussex, said: "At this point in time it is no longer credible to argue that agricultural use of neonicotinoids does not harm wild bees."
But Professor Lin Field, head of biological chemistry and crop protection at the Rothamsted Research agricultural institute in Harpenden, maintained the two studies did not go far enough to put an end to the neonicotinoid debate.
She said: "We simply need more data before we can really say what the risks are. We also have to consider the reason why we use these compounds: can we afford not to control pest insects? Is it acceptable that yields would be reduced as a result? Are the alternative insecticides any safer to bees? These are questions that a two-year moratorium on neonics is unable to answer."