Two interesting new papers came out last week on the dangers that neonicotinoid insecticides may pose to bees, both of them in the influential journal Nature.
Because one showed (again) some clear and negative impacts on bees that forage in crops grown from neonic-treated seed, in this case canola, it got the lion’s share of the headline space.
But the more interesting research, I think, demonstrates that these nicotine-like insecticides may actually be drawing bees into harm’s way.
Researchers at Newcastle University and two other UK schools set up a lab experiment of piercingly simple design: a “two-choice feeding assay” that offered bees a pair of sugar solutions, one pure and the other treated with insecticide.
The treated solutions were laced with one of the three neonics that have been mostly widely used in British agriculture (although at the moment all three are temporarily banned, under a moratorium adopted by the European Union over British objections).
With one of the neonics, clothianidin, the bees fed on treated and untreated solutions without showing a preference. But with the other two, imidacloprid and thiamethoxam, both honeybees and bumblebees showed a strong preference for the treated option — they chose it more often and consumed it in larger amounts, even after beginning to experience some toxic effects.
The reason for this preference is not known, but clearly it resides in the brain, not the palate. Neurological examination demonstrated that they couldn’t taste the compounds at all.
Instead, they seemed to experience a pharmacological effect inevitably likened to the smoker’s “buzz.”
Challenge to makers’ claims
These findings present a sharp counter to assertions by neonics’ manufacturers and promoters that real-world bees could never ingest these substances at the doses shown to harm bees in laboratory tests.
In the first place, they’ve said, sweet-seeking bees will be repelled by the bitterness of the nicotine-like compounds. And besides, the crops themselves — with corn the leading example — are comparatively poor sources of nectar and pollen, thus unappealing to the foraging bee.
As Nature noted in an accompanying commentary headlined, “Tasteless pesticides affect bees in the field”:
Studies that have reported adverse effects of neonicotinoids on bees have been criticized for several reasons: that exposure tests are carried out under laboratory or semi-field settings rather than in the field and use pesticide-treated foods containing unrealistically high dosages; and that bees can detect chemical residues on treated crops and avoid foraging on them….
When hungry worker bees could choose to collect from feeders containing either a solution of neonicotinoid-treated sugar water or an untreated solution, neither species avoided the treated food, which contained neonicotinoid concentrations comparable to those found in the nectar and pollen of treated crops. Surprisingly, the bees in fact preferred the treated solution in the imidacloprid and thiamethoxam tests, which the authors suggest arises from the pharmacological action of these insecticides on receptors in the bees’ brains. The authors corroborated their behavioural results with neurophysiological measurements showing that bees are unable to taste neonicotinoids in sugar water….
It is hard to say whether the preferences … for nectar containing imidacloprid and thiamethoxam residues would occur in a more complex field setting, where many variables could interfere with foraging decisions. However, their study does imply that foraging bees are unlikely to avoid seed-treated crops in the field, and supports previous reports of honeybees and bumblebees bringing back nectar and pollen from treated fields. If the preference for treated food does apply in the field, these findings suggest that we could be underestimating the exposure risk to bees from treated crops.
No sign of addiction — yet
It has been widely though erroneously reported that the study also demonstrated addiction behavior in bees that fed on neonics. Not so. That was beyond its scope.
But one of its authors, Geraldine Wright, told interviewers that the team hopes to look at that possibility next.
Nicotine is of course highly addictive in mammals, thanks to its ability to create a wide range of both stimulating and relaxing effects, and in a mere instant. Or, actually, in seven seconds in the case of a human smoker.
I found that statistic for lung-to-brain transit in a quick Wikipedia summary of nicotine’s pharmacological functions.
It triggers release of glucose from the liver and epinephrine from the adrenals. In the brain, it ramps up such potent neurotransmitters as serotonin, acetylcholine, norepinephrine and every addict’s favorite, dopamine, not to mention beta-endorphins.
I had forgotten this: The skilled smoker can select nicotine’s primary effect by taking short puffs for stimulation, long drags for relaxation. Because it reliably enhances mental performance on such tasks as, oh, writing, it is second in popularity only to caffeine among drugs used to improve focus and concentration.
All of this made me want a cigarette, but glad that I quit a long time ago. Also, that the nearest convenience store is many miles from my door these days.
Effects at sublethal doses
In bees, of course, neonicotinoids have been linked to colony collapse disorder, although the nature of that linkage has become less clear over time as the picture of all the variables afflicting bees grows more complex.
Various studies have suggested that sublethal exposure to neonics can cause multiple neurological problems in bees, including memory impairment, motor-nerve disruption, and reduced capabilities for navigation, flower identification and various forms of learning.
The Nature paper does not attempt to characterize the “buzz” its honeybees and bumblebees were deriving from the treated sugar solution.
But in a statement issued by Newcastle’s press office, the clear sense is that it’s a pleasant or otherwise positive one:
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.
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Links to this Nature paper (and the other, on bee impacts of neonic-treated canola) can be found here, but you’ll have to pay for access.
