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From:
Christina Wahl <[log in to unmask]>
Reply To:
Informed Discussion of Beekeeping Issues and Bee Biology <[log in to unmask]>
Date:
Thu, 22 May 2014 16:01:16 +0000
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What are the levels since "sublethal" can be anything less that LD100?


Bill Truesdell
Bath, Maine

?

Actually, "sublethal" is anything less than LD50.  Doses over LD50 are considered toxic and not recommended.  This is arbitrary, of course, but that is what the authorities call "sublethal".


Rossi et al:

" Bees were exposed to imidacloprid

concentrations of LD50/10, LD50/100 , and LD50/50?"


Hatjina et al:

"Imidacloprid was administered in the food:

2 ?g/kg in the sugar solution and 3 ?g/kg in the pollen pastry"


Oliveira et al:

"...lethal concentration 50 (LC50) of thiamethoxam was

4.28 ng a.i./lL of diet. To determine the lethal time 50 (LT50), a survival assay was conducted using diets containing sublethal doses of thiamethoxam equal to 1/10 and 1/100 of the LC50.?"


van der Sluijs et al:

 "Acute toxicity is expressed as the lethal dose (LD) at

which 50% of the exposed honeybees die within 48 hours:

abbreviated to 'LD50 (48 hours)'. Neonicotinoids are

highly toxic (in the range of ng/bee) to honeybees [98 ],

both when administered orally and by contact. They also

have high acute toxicity to all other bee species so far

tested, including various Bombus  species, Osmia lignaria

 and Megachile rotundata  [99-102 ]. O. lignaria  is more

sensitive to both clothianidin and imidacloprid than is

B. impatiens , with M. rotundata  more sensitive still [100 ].

In an acute toxicity test under semi field conditions on the

Indian honeybee Apis cerana indica , clothianidin showed

the highest toxicity, followed by imidacloprid and thiamethoxam

[103 ].

 In contrast to acute lethal effects, there are no standardised protocols for measuring chronic lethal effects. Therefore, in

traditional risk assessment of pesticides they are usually

expressed in three ways: LD50: the dose at which 50% of

the exposed honeybees die (often, but not always, within

10 days); NOEC (No Observed Effect Concentration):

the highest concentration of imidacloprid producing no

observed effect; and LOEC (Lowest Observed Effect

Concentration): the lowest concentration of imidacloprid

producing an observed effect. However, for neonicotinoids

and its neurotoxic metabolites, lethal toxicity can

increase up to 100,000 times compared to acute toxicity

when the exposure is extended in time [10 ]. There has

been some controversy on the findings of that study,

which is discussed in detail by Maxim and Van der Sluijs

[40,42 ]. However, the key finding that exposure time

amplifies the toxicity of neonicotinoids is consistent with

later findings...

 Sublethal doses of neonicotinoids impair the olfactory

memory and learning capacity of honeybees [127,128,

129,130 ] and the orientation and foraging activity

[131 ]. The impact of sublethal exposure on the flying

behaviour and navigation capacity has been shown

through homing flight tests [82,126,132,133 ]. Exposed

to a very low concentration (0.05 m g kg1 ) imidacloprid

honeybees show an initial slight increase in travel distance.

However, with increasing concentration, starting at

0.5 m g kg1  imidacloprid decreases distance travelled and

interaction time between bees, while time in the food

zone increases with concentration [134 ]. Imidacloprid

disrupts honeybee waggle dancing and sucrose responsiveness

at doses of 0.21 and 2.16 ng bee1  [135 ].?"


Christina



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