Chris Slade wrote:
> Is this proven fact or supposition?
>   
I have seen so many references to it that at the time of posting I 
thought it was fact. However, I think the French beekeepers managed to 
get the chemical banned for use with sunflowers and the BBKA article 
(snippet below) by Graham White indicates that imidacloprid does have an 
effect in the right concentrations.

“Klaus Wallner confirmed in his study of Imidacloprid prepared Phacelia 
with a burden of 50 g/hectare, that the bee’s honey-sac average 
contamination was 5ppb and the pollen taken from the 'pollen baskets' of 
the bees contained 7ppb. The centrifuged honey contamination level could 
not (yet) be ascertained. The level was less than the 3ppb trace ability 
level for honey.

* Clarification in ** France**: *
In a report issued by the French Agriculture Ministry it was stated: 
According to the sunflower variety the residues in the flower on the 
65th day (at start of blossom period) varied between 2.5ppb (Pharon) and 
8.7ppb (Natil). These values could possibly be higher at point of 
harvest. The sunflower pollen is contaminated at an average level of 
3ppb (up to 11 ppb max.). In untreated plantings (sunflower, rape and 
corn), which were planted in Imidacloprid-contaminated-soil, up to 
7.4ppb was detected in the flowers.

“The Bayer study produced a mortality rate due to Imidacloprid for bees 
as follows: The LD 50 (the lethal dose which kills 50% of test organisms 
within 48 hours) lay between 3.7 and 40.9 Nanogrammes of Imidacloprid 
per bee. Long term injury was investigated by Bonmatin. He achieved an 
LD 50 after 8 days by feeding individual bees an Imidacloprid/ sugar 
solution of 0.1 ppb. The substance showed itself to be highly toxic when 
delivered over time.”

The complete article can be found here :

www.bbka.org.uk/articles/imidacloprid.php

It also includes some useful references.

All the best

Steve Rose

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