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randy oliver <[log in to unmask]>
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Informed Discussion of Beekeeping Issues and Bee Biology <[log in to unmask]>
Date:
Thu, 29 May 2014 21:22:59 -0700
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>A few studies showing neurotoxicity of neonics at "sublethal" levels:
Oliveira, Regiane Alves, et al. "Side-effects of thiamethoxam on the brain
and midgut of the africanized honeybee Apis mellifera (Hymenopptera:
Apidae)." Environmental toxicology (2013)

Christina, I'm surprised that you cited this study as evidence.  In the
first place, the tests were performed solely on newly-emerged, protein
starved bees that even in the control group lived for an average of only 8
days, suggesting that those bees were highly stressed.

Furthermore, the researchers themselves point out "that newly emerged
honeybees are more
susceptible to environmental pollutants due to the biochemical
mechanisms of adaptation and compensation. The main
hypothesis for this difference is that the enzymes glutathione
S-transferase (GTS) and mixed-function oxidase,
which are largely responsible for the metabolism of neonicotinoids
in animals (Casida, 2011), have lower activity in
newly emerged honeybees."

So they tested the effect of thiamethoxam on a group of highly-stressed
bees that were too young to possess the ability to metabolize the active
ingredient, and too protein-starved to develop that ability.

Then there's the matter of dosage, which they fed to the bees as a daily
ration.  Their 1/10th LD50 was 428 ppb; their 1/100th LD50 was 43 ppb.
Virtually any other researcher would consider such doses to be at the edge
of lethality.

And then there are the mixed effects, with a lower dosage sometimes
appearing to cause more damage than the higher dose.  Furthermore, again
and again they found that after a couple of days, the apparent damaging
effect appeared to disappear.

I was, however, impressed by the concluding sentence of the paper:
"Furthermore, the present results show that intoxication with sublethal
doses (1/100 of LC50) [43 ppb] of thiamethoxam does not affect the survival
of bees but that it can be harmful as high doses that cause the immediate
death of the insect."

Hey, it's awful quiet out there.  Are Christina and I the only ones reading
these papers?  They are open access.

-- 
Randy Oliver
Grass Valley, CA
www.ScientificBeekeeping.com

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