Insect Control: Biological and Synthetic Agents - Index of

Figure 14 Systemicity of neonicotinoids. Relationship between
the translocation of neonicotinoids to barley shoots following
uptake by the roots (expressed as the transpiration
stream concentration factor), and the octan-1-ol/water partition
coefficients (as log Kow). (Diagram and experimental data taken
from Briggs, G., Bromilow, R.H., Evans, A.A., 1982. Relationships
between lipophilicity and root uptake and translocation of
non-ionized chemicals by barley. Pestic. Sci. 13, 495–504). Because
of the higher lipophilicity, thiacloprid and clothianidin
show the best uptake by the roots from solution, whereas nitenpyram
and ( )-dinotefuran are more xylem mobile than the
other neonicotinoids.
stem or granular treatments and seed treatment.
Because of imidacloprid’s systemic properties it is
evenly distributed in young, growing plants (Elbert
et al., 1991, 1998).
3.3.4.1.2. Thiacloprid It is stable towards
hydrolysis even under conditions of heavy rain.
Once applied to leaves, thiacloprid shows good
rainfastness and photostability, and remains in or
on leaves for a considerable time, thus allowing a
continous penetration of the active ingredient into
the leaf. Its half-life in water at pH 5, 7, and 9 is over
500 h. Photolysis in water (buffered at pH 7) shows
a half-life of >100 days. On soil surfaces thiacloprid
is also stable under sunlight irradiation (Jeschke
et al., 2001). The penetration and translocation
behavior of thiacloprid in cabbage was comparable
to those reported for imidacloprid (Buchholz and
Nauen, 2002). The amounts of thiacloprid stripped
off from cabbage application sites were 23% and
17% at 1 day and 7 days after treatment, respectively.
Levels in the true leaf increased from 63% to
77% as measured 1 day and 7 days after application,
respectively. These results demonstrate that
thiacloprid is readily taken up by cabbage leaves,
thus providing good systemic control of leaf-sucking
pests. The visualization of the translocation pattern
3: Neonicotinoid Insecticides 77
Figure 15 (a) Translocation of [ 14 C]-thiacloprid in cabbage
plants 1 day after application of 2 5 ml droplets onto the first
true leaf. Radioactivity on the surface of the cuticle (residue)
was removed by cellulose-acetate stripping; (b) translocation
pattern of thiacloprid sprayed to a cucumber leaf.
of [ 14 C]thiacloprid-equivalents by phosphor-imaging
technology revealed xylem mobility, i.e., translocation
of the active ingredient in the upwards direction,
even 1 day after application to cabbage leaves
(Figure 15a). This xylem mobility is further highlighted
in Figure 15b, showing excellent distribution
of thiacloprid in cucumber leaves after spray
application.
3.3.4.1.3. Thiamethoxam It is a crystalline,
odorless compound with a melting point of
139.1 C. This neonicotinoid has a relatively high
water solubility of 4.1 g l 1 at 25 C and a low
partition coefficient (log POW ¼ 0.13 at pH 6.8).
In the range of pH 2 to 12 no dissociation is
observed (Maienfisch et al., 2001a). These properties
favor a rapid and efficient uptake in plants and
xylem transport (Widmer et al., 1999) (Table 3).
Through this systemic activity, all plant parts
situated acropetally from the application can be