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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