The low residue levels in honey bees probably are best
explained from the fast imidacloprid metabolism by the
honey bee A. mellifera. After exposure to sugar water dosed
at 20, 50 or 100 lg 14C-imidacloprid kg-1 honey bee, halflives
were 4–5 h (Suchail et al. 2004a, b). The major
metabolites are 4- and 5-hydroxy-imidacloprid and olefin.
Olefin peaked after about 4 h, while the hydroxy metabolite(
s) appeared either immediately after termination of
exposure and then decreased in concentration (Suchail
et al. 2004b) or showed a peak after about 4 h (Suchail
et al. 2004a). The total amount of imidacloprid and
metabolites in honey bees decreased with a half-life of 25 h
(Suchail et al. 2004a). Imidacloprid was the main compound
in the abdomen (38% of accumulated 14C) directly
after treatment. In the head, four metabolites were detected
with imidacloprid levels always being B5% of the ingested
dose, and olefin and 4- and 5-hydroxy-imidacloprid being
the main metabolites after 24 and 30 h, respectively. Imidacloprid
and its metabolites were also detected in other
body parts of the honey bee (hemolymph, midgut, rectum)
with highest amounts in the thorax (Suchail et al. 2004a). It
should be noted that dosages applied in these metabolism
studies are much higher than the levels found in the field
and might even be in the toxic range. The relevance of
these data for the metabolism at field-realistic concentrations
therefore remains uncertain.
Acetamiprid was also rapidly metabolized in bees, with
a half-life of 25 min after oral administration with sugar
water (100 lg kg-1) and producing four metabolites. The
major metabolite had a peak corresponding to approximately
48% of the dose after 8 h, and the other three
metabolites reached maximum levels of 22–25%. After
72 h, the bees contained only metabolites. The metabolism
of 14C-acetamiprid seems to be tissue specific and showed
a similar distribution pattern in the honey bee as imidacloprid
(Brunet et al. 2005).
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